JMR Development blog

Discussion in 'JMRacing' started by mr hillclimber, Sep 27, 2011.

  1. Mike_H Forum Addict

    Joined:
    Oct 16, 2004
    Likes Received:
    17
    Location:
    iQuit
    Hopefully before Curby ;) Come and see it... and bring a car!

    I didn't get a chance to digest those messages yet.

    EDIT - will take a pic of the manifold-injector boss fit.
     
  2. mitlom

    mitlom Forum Member

    Joined:
    Jun 20, 2006
    Likes Received:
    93
    Location:
    Ripley, Derbyshire
    I would come along but we are on holiday that weekend down in the SW, plan to drop in on Jason and see how he's getting along with my build while I'm down there......

    Cheers Mike, I have been chatting to ratfink about the flanges and I have created a CAD drawing of a one piece flange....just need to check that it has correct clearancing to allow access to the sparkplug for cyls 2 & 3 before I send the file off to get it cut, I will also be getting some DCOE type flanges cut to mount the ITBs on ;)
     
  3. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    8v exhaust flow

    I've been meaning to do an exhaust flow article for ages as I've never been able to understand the "big exhaust valve" phenomena on the 8v's when no other 8v I can think of prioritizes the exhaust over the inlet...normally for good reason.

    Exhaust flow only needs to be in proportion to the inlet flow. Making the exhaust flow more than is needed "sometimes" helps further reduce pumping looses in theory, but in practice it's not always the case, and certainly not what I've found in testing to date.

    For an engine to make power it needs to be fed as much air as possible...the more the better. Fueling is easy as we can get as much in as needed via correctly set up carbs or fuel injection...then we need to light it up to make it go bang...so a nice strong ignition system is needed...again easy enough.

    The most pressure possible helping to get air in is atmospheric pressure...forgetting turbo & supercharging for the moment.

    To help get the exhaust gasses out there is a pressure build up after combustion of anywhere between 80 & well over 100 psi ready to burst out of the cylinder. So as the exhaust valve opens the actual gas velocity can exceed the speed of sound for an instant...reducing as the valve opens further but still expelling fairly rapidly....it certainly doesnt get that much help being forced into the cylinder!

    When a performance cam is thrown into the mix (as many will run with a ported head) which opens the exhaust valve earlier, to a higher lift, and closes it later, the exhaust flow, or I should say exhaust blowdown time, of the cylinder has even more of a helping hand.

    It was said may years ago that the exhaust flow needed to be at least 75% of the inlet flow for best power. On a good 40mm inlet valve ported head that makes around 86-88cfm, that would need around 65-66cfm from the exhaust port...which from a std 33mm ex valve is asking a bit much. Latterly though, through many more years of testing it has been determined that in fact 65-70% will do the job well enough...in fact some race engines make do very well on 60-65% exhaust flow...though the more radical the engine spec, in particular the higher the compression ratio, the less measured exhaust flow is needed...but thats another story for another day.

    So in our case, with a std 40mm GTi inlet valve making 86-88cfm when ported, the 65-70% ratio sees us needing around 55-60 cfm on the exhaust side...which is perfectly possible from the std size 33mm exhaust valve when ported correctly. When a 40.5mm inlet is used the std exhaust valve capacity is being stretched a bit @ 65% but can get close. So how much power do you think your really loosing by having an exhaust port that flows a couple of cfm less than maybe ideal?

    I can answer that...not a lot. I've run race spec engines (100hp per litre) with between mid 50cfm exhaust flow (60% of the 94cfm inlet flow) to almost 70cfm exhaust flow (70% of 97cfm inlet flow) with no real world power difference in 185-190hp power band 1800's. In fact tony b's original head I re-ported had between 65-70% exhaust flow from it's 94cfm inlet flow to make over 200hp from his 2ltr 8v and win the Welsh hillclimb championship outright...so not really lacking much.

    So...anyone think their road engine "really" needs a bigger exhaust valve with a std inlet valve to make 140hp now?...make inlet flow a priority every time.

    Once you get into the bigger inlet valve territory...41-42mm inlets...then yes, the 33mm std size exhaust valve is being stretched, so a 34-35mm exhaust valve starts to become a help in keeping the balance.

    I have however seen some 35mm exhaust valve heads lacking in potential....fitting a bigger valve and just blending the seats in...exhaust "or" inlet for that matter...wont automatically improve flow...the port and throat area needs increasing to make it worth the effort & expense...a correctly ported 33mm exhaust port can outflow a below par 35mm port...and cost less money in the process.

    For the record...a std 40mm GTi inlet port makes around 72-73cfm, a std 33mm exhaust port makes 44-45cfm....that's 62-63%...are VW really that stupid or was it the luck of the draw...err...no...I doubt it very much.
     
  4. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    Blog update time...

    We've been busy with a number of projects of late but one in particular took the "late" bit to the limit!

    Nick Penfold runs one of our engines in his MK1 Golf which was originally built to the old Slick 50 regs many moons ago. That meant the good old archaic K-jet injection system coupled to a lumpy cam...not the best recipy for a smooth idle but with some juggling it works to a point.

    The first round of the VAG Trophy was cancelled due to snow earlier in the year and was re scheduled to join the British GT championship on the new Snetterton 300 track. After Nick's first outing of the year at Cadwell Park it was obvious the game had moved on a bit from last year. Nick had fitted new suspension for this season which had mostly transformed the previous "drunk camel on roller blades" handling (more on that later) but the hills of Cadwell highlighted the class B cars Nick runs with had a clear power advantage under the new power to weight regs.

    With Snetterton only a month after Cadwell and Nick away on business and a holiday between the two rounds it didn't leave a great deal of time to execute a plan...some bright spark said "your not going to Snetterton to run at the back of the field...get the car down down here before your trip's, whip the K-crap off and we'll sort the power issue...oh and take the head off while yr at it!!...

    Said clever cloggs went on the hunt for an ebay special manifold only to draw a blank...hmm...I dont give in that easy. A call to fellow MK1 racer Tony Barber (tonyb) to ask if he may have a DCOE type inlet manifold in his parts collection revealed an even better option..."may have!....in fact there's a pair of 45 Dellorto's here too!"...RESULT!!

    I already had some Weber's lined up for a short term loan, but Tony's set up had a better starting point in terms of jets and chokes so that would help a treat, along with his "yeah no problem" reply to my next question...."do you mind if I make the holes in the manifold bigger!"

    Not wanting to make life too easy for myself by just swapping the K jet for carbs, I wanted to go inside the head too whilst we were at it as I knew the power gain we needed wasn't going to come just from the carbs alone. Upon Nick removing the head we discovered a bit of a bonus...Nick's old Slick 50 head had 41mm inlet valves fitted when it was originally modified 15+ years ago, so I knew from previous versions of this head what the starting flow point would be (86-88cfm) and where I could take it. Sure enough the flowbench revieled the std flow for these heads in this form (87.3cfm in fact) which is a good bit below the potential on the valve size fitted.

    As the inlet ports in the manifold needed opening to suit the required airflow and blending into the port, it was easy enough (relatively!) to continue the size increase into the ports so as to open them to my preferred size ratio to balance airflow with air speed...I wanted this engine to punch above it's weight in the mid range coming off corners as well as the long straights at Snetterton, so biggest wasn't going to be best here, plus there was a time element to consider...digging a valve seat at this stage wasn't an option! So the throats were left as they came for this phase with further improvements possible, all I needed this time was a flow increase to around 93-94cfm and we'd be on the money....so when the flowbench flashed up 96.7cfm I was a happy bunny indeed!

    A thorough clean and assemble later revealed the first stumbling block...a broken inner valve spring! A quick rumage through the JMR spares boxes found the original valve springs that ran with the cam we use in this engine (Nick kept his original springs during last years re-build), so a quick clean up and in they went...but it wasn't going to be that easy! The previous head these springs were fitted to must have had the spring seats lowered...as I discovered when the cam locked up turning it over to check the valve clearances! Enter stage left the next hero of the hour...Tim Moll (mitlom)..."how you getting on with Nick's head...running yet"?...."not with a broken valve spring and another set that wont work"!!....."dont forget my two sets of springs sat on your bench"!

    Oddly enough Tim's text came through just as I was eyeing up his Supertech boxes!.....cheers Tim! A quick measure up of both the free & fitted length reveled they would be perfect for the job! As it was rocking past midnight the sensible thing to do was call it a night...Nick had joined me in the workshop for a couple of days to get some small jobs done on the car and re-fit the head. With other pressing JMR duties looming and time not on our side I stripped the head again, fitted the Supertech's and re ground a couple of shims to get the valve clearances just right...after dropping spanners at 1.45am I figured trying to time the cam up was best done after some sleep!

    By the time I returned in the morning Nick had the smaller (std) front roll bar fitted as suggested to improve the turn in, so it was straight on with torquing the head & putting a base cam timing setting in to kick us off later on the rollers. Whilst Nick fitted & wired up the fuel pump I gave the Dellorto's a clean up and base re-jet to save time later. A juggle with some linkage parts and we were all ready to make some DHLA type noise. After a bit of diesel battery boost from my trusty Passat and a bit of twiddling we had a race engine with an idle much better than it ever gave on K-jet with a 296 degree cam.

    Nick had to get back home to Bristol for the next day but time was getting short to get on the rollers for the time I wanted to spend on the car...so Nick was dispatched homeward bound to let myself and my dyno wizard Alvin Powell at AP Motorsport drag the required power from the engine.

    In K-jet form we extracted 124 at the wheels from it last year giving us 135hp per tonne, so with the power to weight target of 152hp per tonne at the wheels as the class maximum we needed to hit around 140hp at the wheels with the current 916KG weight. I was less worried about peak numbers on this as I wanted it to pull strong off the corners to get a head start on the turbo brigade as well as improve the top end breathing, so response was the key here...dyno numbers are useless without an engine that responds, which is something numbers don't tell the full story on.

    After the best part of the day with my dyno man turning the wheels while I changed jets to get the fuel slope balance right, timing the cam for the best power spread and edging up the ignition until there was no more to give we hit our final power run....137hp at the wheels was resonable for the spec and only 3hp off the target, which I expected as the current exhaust manifold is too small now. The best bit though was the 10-12ibft torque increase in the mid range to make just on 140ibft total, which isn't at all bad for an 1800 8v, and not far off what I get from the full race/hillclimb engines making 30hp more at peak and a lot more revs. This engine is still on a largely std bottom end...std crank and rods, ARP rod bolts but with cast pistons, so we kept the revs down to a max of 7,500, where power was only dropping off 5hp from the 7000rpm peak.

    Fast forward 3 days to Saturday morning practise...I awoke to Nicks first text of the day....brakes "awefull" (another story!)...engine AMAZING!

    I had told Nick to expect much better performance than the numbers had shown, with strong punch off the corners and much better throttle response than the K-jet would ever give, but what I must admit I wasn't quite expecting was for him to be able to not only pull clear of the turbo cars off the turns, but also to hold them side by side in a straight drag under full power!

    Whilst the turbo cars run to the same power to weight regs, they have a much better torque spread per tonne, so on paper their mid range grunt of almost a clear 30ibft per tonne advantage should give us a bit of a work out....but as is often the case, numbers dont tell the full story....turbo or not, our 1800 8v can more than hold its own right through the rev range now with a much better power spread than before...oh and there was another bonus...loosing the K-jet system has helped drop the weight by a few kilo's...we're now slap bang on the 152hp per tonne class limit!....every cloud....

    After practice Nick worked his way up through the field in the dry start of race one, but with one eye on caution with an alarmingly long brake pedal and the other eye on the looming black cloud above, plus with another grid to line up for the next day he took the mid field finish in the eventual downpour with open arms.

    The first race finish put Nick right in the middle of the pack for the second round on Sunday. I advised Nick to be careful not to accelerate into the back of slower starting cars off the line...something which he was a little doubting of until he lept off the line and started out dragging VW Cup cars who where invited to race with the VAG Trophy boys!

    A race long battle with various VR6 and turbo powered cars is showing the MK1 is now on the pace...being able to run within the pack and hold off ex Leon cup cars on a fast track like Snetterton has shown what a great championship John Hillon and the team have put together to enable old & new tech to mix.

    Take a look at the in-car action from Rob Allum's Ibiza... http://www.youtube.com/watch?v=giCYzwhfk3E ...watching a brick shape MK1 Golf with carburettors and bob weights run up next to a turbo fed multi valve engine made me chuckle at the amount of times I've heard 8v's lack breathing.

    Nick now has plenty of time to sort the lack of brakes before Brands Hatch at the end of August, along with some fine tuning of the suspension...replacing the front roll bar with a std GTi unit in-place of the previous bigger version has much improved turn-in as I expected, so if he can get the MK1 to stop as well as it now goes we can challenge for a solid class podium finish...Nick ran as high as 2nd in class at Snetterton but the long pedal didn't inspire the late braking lunges that the opposition were able to achieve, so the need to back off early saw him swamped too many times to be able to hold position....lets see how the next round goes...I'll be shouting from the Brands banking myself so hopefully my day pass from Devon will be worth the trip!

    http://www.karlbowdreyphotography.co.uk/-/galleries/motorsport/2013/msvr-vag-trophy/cadwell-park
     
  5. Ben S

    Ben S Forum Junkie

    Joined:
    Aug 1, 2005
    Likes Received:
    345
    Location:
    Essex
    Wow Jason, that was a good read, are your fingers OK after all that typing? Cheers -Ben
     
  6. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    Not half as sore as they get working on the dam thing!!! lol

    Yr welcome Ben....that was a bleary eye'd couple hours worth of typing over the last couple nights....more blog update to follow...
     
  7. vw_singh Events Team Paid Member

    Joined:
    Oct 29, 2003
    Likes Received:
    781
    Location:
    United Kingdom
    Thanks Jason, that really is worth a read. Long and daunting but reads like a good book!

    Good result too! Love it when a mk1 mixes it up with newer machinery. Reminds me of when the Carvells used to run circles around newer cars in the VW Cup.

    Gurds
     
    Last edited: Jun 26, 2013
  8. Admin Guest

    Excellent result for 8v's. Great read always love hearing stories like this, keep them comming!
     
  9. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

    Joined:
    Jul 26, 2006
    Likes Received:
    3,086
    Location:
    Creating Pfredstarke
    Thanks for posting Jason.
    Good read on 8v development, keep them coming!
     
  10. samfish

    samfish Forum Member

    Joined:
    Jul 30, 2009
    Likes Received:
    40
    Great read Jason, thanks! Sounds like it is going very well!
    Oooh, I can feel this is going to get competitive! ......I just compared Nicks lap times to when I was last there :) My weekend fastest was faster, but race laps a bit slower despite the fact I had no traffic.

    I am going to be at Brands as my first outing of the year. I seem to only manage Brands each year at the moment, although hopefully I can make Snett too.
    I'm still overweight/underpowered though - excuses already lol

    Those Mk4's are so tricky to overtake because of their grunt mid-corner means they can get to the right side of the track onto the straights to defend the next corner.
     
  11. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    Thanks alot chaps....

    There will be more MK1 shape action up at the sharp end next year...no need to guess how many valves either Gurds...;)

    Cheers Tom...considering an upgrade to 8v power now then...lol

    Thanks Eddie...more 8v development coming...:thumbup:

    Ah great stuff Sam...I'll be cheering you on too then at Brands!...competitive is good...pedal harder! Getting the weight out is fairly cheap and easy...getting the power is just a carbide burr & a pair of 45's away Sam...;)

    Nick's not having any mid corner grunt issues anymore against the turbo cars...the other option is to qualify higher...both of you...you can do it! :thumbup:
     
  12. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    About time I did the write up for this one too...

    Toward the end of last year I was approached by Tim Hughes (timo16v) whose 8v MK2 was lacking a fit of fiz. Tim had done the rounds on the rollers with varying degree's of head scratching and solutions to his lack of power. During one trip to the original engine builders a cam change was needed after a worn cam was discovered and hydraulic lifters found on the verge of breaking up.

    With lifters changed and the cam upgraded at the same time the top end noise was cured but resulted in no extra power from either the fact an unworn cam was now fitted or in fact said cam had more lift and duration...a bit of an odd case.

    Thinking cap on, it was obvious to me where a possible initial problem may be...in the exhaust system. I've seen this a few times in the past and it's quite simple...no matter what power potential your engine has with whatever cam or head you have fitted, if you cant get the dead stuff out the engine will struggle to breathe. Cries of "it's got XYZ exhaust" largely fall on deaf ears as I'm sorry to say many manufactures make systems based on the latest trend or style...it's seems that they employ people in either the design team or manufacture stage that basically couldn't care less or cant grasp the concept of how a "performance" exhaust should be designed.

    The first test is really simple...go around to your exhaust and feel how much pressure is coming out...be careful not to burn your hands!...use some discretion! If you can feel a good slug of exhaust gas either pulsing in your hand or with a little help from a blip on the throttle then your exhaust flow is reasonable at least...if it feels like coughing in yr hand then either the silencers are breaking up and blocking the system or your fancy shiny exhaust is just pants!

    As Tim was bringing the car down for some transmission work he asked me to cast an eye over the power output and see what I thought. Well the above test confirmed what I suspected during our conversations...there was very little pressure coming from the exhaust! As it was fitted with a twin outlet tailbox with a so called "sting" in it's tail I was prepared to bet on the outcome I'd find if Tim let me cut open the rear silencer...

    As pictures speak louder than words I found exactly what I expected after I'd removed the tailbox and established there was plenty of pressure emitting from the remaining system...

    [​IMG]

    As can be seen, the inlet pipe into the silencer hits a total brick wall in terms of flow, with a token gesture of the gas pressure being able to escape out of the perforations into the small chamber before eventually finding it's way up the two smaller pipes out into atmosphere....top design!!!

    A swift call to our friends at Jetex saw a universal silencer land at JMR towers along with some simple pipework to make a single outlet. I cut off the over axle pipe from the old silencer and had it welded onto the new Jetex box, then cut, slotted and clamped on a simple tailpipe outlet. With the engine cracked into life we now had some proper exhaust flow coming out of the rear of the car rather being held up with the old cork in the bottle.

    I had my dyno man Alvin at AP motorsport run the car up before I attacked the exhaust to see what we had as a starting point...103hp at the wheels was the answer which is way short of what a 2ltr 8v should make with a ported head and 276 cam. With no extra noise coming from the now freer breathing exhaust Alvin turned the rollers yet again for me where we recorded a solid 110hp at the wheels between 5,500-6k....but that's not the best bit. In addition to the peak power gain we had a really strong mid range increase to go with our extra 7hp peak...how does 13hp extra at the wheels sound at 4500rpm!....and +8hp at 2,500, +9hp at 3-3,500, +8hp at 4K, +7hp at 5-5,500, +9hp at 6k and +7hp at 6,500...not bad for just a tailbox change!

    Whilst we had it on the rollers I did some cam timing checks but just moved the power band around within a couple of hp, so all credit to Tim's cam timing with a little guidance...

    With some fuel pressure adjustments I balanced the mixture out better than it was when it came in, no real power gains here but a better mixture compromise across the range. I still feel there is unlocked potential in this engine and I think I know where it's likely to be....it's currently making less low end power and not much more top end than my 1800's with them having 8 degrees less cam duration, tho in true 2ltr style it's very strong in the mid range... stay tuned for an update later in the year.

    Tim reported it's the best it's been during his drive home whilst bating Audi Quattro's off of wet roundabouts with his new found grunt and Quaife diff we fitted while in our care. Further proof of the new found power was his recent 4th in class finish from 13 cars in the Gurston Down hillclimb championship which now places him 2nd in the class championship overall....not bad for another 8v charge against multi valve opposition with them having a much larger paper hp advantage...oh and the Golf is on road tyres v's their list 1B sticky rubber...once we have the key issues sorted I can feel some more carbs being dusted off eh Tim!
     
    timo16v likes this.
  13. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    405
    Location:
    United Kingdom
    Good stuff. No substitute for 'straight through'....
     
  14. TonyB Paid Member Paid Member

    Joined:
    Jan 6, 2010
    Likes Received:
    168
    Location:
    Ammanford, Wales
    Good to see you've woken up and posted some updates (says me!!) lol

    I'm hoping to see my carbs on the podium soon, all sound like it's going to plan :thumbup:

    That exhaust is shocking, who thought that might be a good idea for a peformance exhaust. I understand when OEM have what look like strange designs but they have all sorts of hoops to jump through and ultimate performance is not on top of the list however, as I said, the one above is shocking.
     
  15. Ben S

    Ben S Forum Junkie

    Joined:
    Aug 1, 2005
    Likes Received:
    345
    Location:
    Essex
    I do enjoy these blog posts you do Jason! Good investigation & output increase :clap:

    On the Jetex exhausts I thought I would share my experiences with their 2.5" system for Mk2 Golf 16v.

    While they do provide increased output over the OEM systems, some bits just don't look right.

    For starters the rear box appears to not be straight through. The rear 1/4 of the box has changed colour due the chamber being exposed to exhaust gas.
    This on it's own may not be bad at all as it is right at the back of the system & may just be for noise / sound.

    It's the next bit that I wasn't too happy with. The 1st/mid box (in the non-resonated system it is the first box) is significantly smaller internally than the diameter of the 2.5" pipe.
    This suggests to me that it is the mid box from the smaller diameter 8v system. I replaced this for a universal item that is 2.5" all the way through.

    [​IMG]

    Would be interested in your thoughts on this one :thumbup:
     
  16. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    Thanks Ben...

    A good point...I must admit I've seen something similar on a MK1 only last week...the rear box looks good and is certainly 2.5" but the front silencer is certainly smaller...I've not measured but it's not 2.5...looks closer to 2"...someone else mentioned the same thing re another manufacture recently too.

    I've seen the above system make a clear 160+hp at the wheels so it's not as bad as you'd first think...at least it's not hitting a brick wall... and that engine made a solid 186hp on the engine dyno with a bigger dyno system. However I'm looking into exhaust's fairly soon with another exhaust partner...I've had one manifold and system done for an in-house project and it's a great job...mild steel...see how that pans out in the next couple of months once the engine is finished.

    The Jetex universal silencer's certainly work tho...however I'll look into the systems and find out the score.
     
    Ben S likes this.
  17. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    Cheers Jon...certainly not in this case.

    I've told Nick to hold back a little as I don't want him to add to much value to old carbs Tony!!! lol...but I'm sure it wont be long before we see carbs on the podium. The hole's in the manifold were too small as suspected all those years ago, tho I think we can say your current system works ok!...so no need for a return to old tech in your case ;)

    Yes the exhaust in question is pityfull to say the least...tho I've seen the same on old Magnex tailbox's on Mk2's...tho my old MK1 Magnex was fine...bizzare thinking from both manufactures. I can't be said either it's a noise issue...when I ran up Tim's with just the front & mid silencer it was still quite quiet, so there was no need at all to make such a hash of the tailbox design.

    The same can be said of manifolds...I've got one in the workshop now that looks the part until you find the outlet pipe has been pushed in too far so there's a bit overhang lip for the exhaust gas to trip over on the way out...that's an old Magnex 16v manifold.
     
  18. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    There's a bit of an 8v theme at the mo!

    I had a visit from Tim Moll (mitlom) last month armed with his budget track day toy. Tim was visiting his race car shell being prepped near by...well Gloucestershire isn't that far!...so Tim asked if I'd be game for giving the red rocket a last hoorah on the rollers pre sale.

    This was another car that had done the rounds at various rolling roads, none of which really got the best from the 1900 8v, so much so Tim had a valiant go at playing with the fueling himself, with positive improvements in feel and fuel consumption but no figures to back up the seat of the pants.

    After driving the car myself at Castle Coombe last year whilst testing Nick Penfold's racer in it's now old spec K jet form, Tim's car felt pretty quick and was a close match to Nick's when I was was driving!...sorry Tim couldn't resist!!...so on that bases I figured the power shouldn't be a million miles different and possibly better than Tim's last rolling road figure of 111hp at the wheels.

    As Tim was brave enough to head Southwest bound we darkened the doorstep of AP Motorsport again. Now in all honesty neither Alvin at AP or myself are big fan's of K-jet with very lumpy cams...we spent 3 days on Nick's last year swapping metering heads and adjusting fuel pressures to get the best compromise as that is all you'll get on this system with big overlap cams, so as Tim's had a wilder cam than even Nick's we looked forward to making very little improvement over what Tim already had achieved!

    We should learn to be a little less harsh on ourselves as after a couple hours of juggling fuel pressure and ignition timing we got a better fuel curve than we started with which helped Tim use an awefull lot less fuel going home than what was consumed coming down to us! The above combined with a bit of cam swinging netted a better idle and virtually identical power curve up to 5-5,500 where a couple of hp extra was gained. From there on in we had a positive increase at 6000 from 106hp to 112, 6500 came up from 108 to 114, with peak climbing from 109 to 117 @ 7k. Power was still hanging on well enough to push a little more to 7,500 where we saw a touch under 112hp up from the previous 106....pretty peaky on K-jet.

    The odd thing was I expected to knock the cam timing back from it's heavily advanced position to find more low to mid range power, but retarding the cam...though actually giving it "less" advance as we had a lot to start with...knocked power off everywhere. To get the power increase I had to give the cam even more advance which gave the top end improvement without affecting the low end.

    The trend I see is this...K-jet cars on tame cams like very little advance...i.e not much more lift at TDC on the inlet than the exhaust. When a big cam is added...sub high 290 to just over 300 degree's...they make the best overall power with a lot of advance. Cue open induction...the same cam, as in the case of Nick's Golf earlier back in the thread, likes a lot less advance for best spread & peak, the wilder the cam the closer to split timing makes the best power on open induction...I've seen that with other engines too.

    This was yet another engine that went up the road very well considering the numbers, even tho the low end was down a fair bit over our road spec 1800's, and not coming alive until 6000 when the road engines are dying away. The moral is...don't over cam for road use...enjoy the low end grunt, don't fit big cams with K -jet unless regulations dictate so...even then, I believe as much or close to the same top end power is possible with a lot less cam but better head flow for a better overall power spread...if in doubt get the carbs out!...this engine would have no doubt benefited from open induction had Tim been keeping it...the next car / engine certainly wont have a breathing issue eh Tim...


    I'll try and get all the above power curve's on a graph next week if time permits.
     
    drunkenalan and mitlom like this.
  19. timo16v

    timo16v Paid Member Paid Member

    Joined:
    Nov 18, 2006
    Likes Received:
    13
    Thanks Jason ...........from a terrace in cyprus with cold beer in hand!

    I feel a head swap coming on end of season..............JMR are the only 3 letter tuning for me from now on
     
  20. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    135
    Location:
    Southwest
    Your a true gent Tim...thank you very much!

    Core head is in stock ready to go...;)

    I'm in a hot workshop with the sun shining through the door with a luke warm Tango in my hand....not sure who's got the best deal really....lol
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice