The Limit of AGG Rods? / Where to get Steel rods from?

I already have a Big Valve Head. The parts i have in the garage for this engine it had better be bloody quick.

A quick list off the top of my head, starting at the bottom working up,

lightened and balanced, flywheel, pulley, intermeadiate shaft.
Knife edged diesel crank.
all new bearing and bolts.
Big valve head.
I have a 270 degree cam altho im looking for a 285+ cam.
4 branch manifold.
40mm dual throttle, throttle bodies from a R6, im trying to work out how to use the second set of throttles.
Megasquirt ecu.

feck! dont start adding that up!

 

.. never add up what you spend...

Do you have big inlets ?

Kent do a 285 degree cam, GS3H (yours is hydraulic is'nt it ?), looks like a good profile. I've seen a similar cam used in 2ltrs before (in fact I'm just about to use one again) with very good results (155hp and still on a plenum).

Speak to Kent cams on 01303 248666 or take a look here... http://www.kentcams.com/

 

no i decided that i wasnt going to that far...... well that was february, im now thinking i should have. but im sure that the difference isn't as obvious bigger exhaust valves.

I was looking at the gs3, but was sure whether to get phillip walker to get me a 288 schrick profile.

yes its still hyd which is a limiting factor, so im told.

 

Hydraulics are a limiting factor to a point, but not in the way many think, it's the speed that the valve opens that can cause the real issues.. to high an initial valve acceleration on hydraulic lifters causes the oil to be squeezed from the follower (lifter) with obvious serious problems there after !

Long-ish overall duration can still be used, but for a regular road application, a 285-ish duration will work well overall in a 2-2.1ltr engine.

Big inlet valves are more important than big exhausts, it's a lot easier for an engine to force out exhaust gases than it is to inhale.. larger exhaust valves work to a point, but bigger inlets are more benificial, its getting air "into" an engine that makes more power. Getting air out faster (bigger valves) helps exhale burnt gases which is certainly good news (though longer duration and more valve lift on a performance cam do the same thing) but getting more air in to mix with more fuel to create a bigger bang is "much" better news... even more so to take advantage of filling bigger cylinders.

And a much better way to spend the money you would on funkey rods..

A basic formula sites the exhaust valve size as only really needing to be 0.8x or 80% of the inlet valve, thus a 40mm inlet would have a 32mm exhaust (33mm standard).

As an example, a 2lt Ford pinto ( ) uses a 44mm inlet valve in fast road guise, a fast road 8v Vauxhall a 43mm inlet... and most still only run a 40mm inlet in out beloved 8v VW's..

 

hmm maybe a call to the man in the shed, wonder what it will cost? the head hasnt been used yet so wont any work other than the valves.

 

Valves are about 15 quid each, inserts similar I think, plus the work to open out the throat area to suit, and maybe the ports, depending on the size he did them to originally.

 

how big will they go? i have heard on 40.5mm being used on the pack d heads which come from the shed. I seem to remember reading about someone having 41mm inlets but ithink that they used 34mm exh valves.

 

40.5mm inlets will go on a standard seat (maybe thats why they only fit that size ?), any bigger will need the inserts changing.

I have 41.91 inlets and 35.5 exhausts (1.65 & 1.4, hence the odd metric size) so they certainly fit together, and I was looking at a 42/35 head last week when talking valve & port sizes with an engine builder friend, so it's certainly possible to go that far at least.

I've heard that inlets bigger than 40.5 dont produce anymore power, which means my 193hp 1800 is down on power...... and also the ports an throats cant be opened out big enough to take advantage of the bigger valve... well, the examples above have rather large ports without any break-through into water jacket problems, yet on the 8v head in my project thread, I broke through into a water jacket without even going too big in one of the bowls, it all depends on the casting, some are fine, some arnt. It's an easy solution tho, just weld up the hole and grind it back again.

I've seen 44mm inlets listed, I'd like to see those fitted in a head.. though a smaller exhaust would be needed, which believe it or not, would be fine on a very high output (race) engine... horses for courses again.

 

if limited on valve size, can't you just lift more and have a longer duration?

 

Thats certainly true to a point, but obviously care has to taken in matching the cam to its application and usable compression ratio for a road application (and competition to a point) at least. A bigger curtain area (more room for the air to get in to the cylinder) is possible sooner in the valve lift curve with more valve area whilst keeping the cam sensible.

 

193bhp 1800, sounds interesting! whats the spec? is it on carbs

 

I have heard that too, something to do with the shrounding of the seat causing the air to slow down.

 

So the experts say, but it does'nt seem to be a problem in mine.. I doubt it would make more power on smaller valves. And yes bud, mines on carbs (48's).

 

The view I've heard from someone 'in the trade' is that 42mm inlets are only worth thinking about on a full competition engine. On a road / clubman engine, the shrouding lower down will balance out the top end gains, so the extra money to re-insert the inlet side of the head is better spent elsewhere.

 

mike, im open to any suggestions i want to do it right first time, or at least almost right.

 

what does it rev to?

 

If it was mine, and mainly a road car, I'd stick with 40.5 as a maximum. You've already been to the shed, so shouldn't you just fit the head you've got? Ring him up and ask advice, if you're not sure, but above all, get it built and drive it, rather than changing your mind all the time (it's expensive!)

and Mr H is right (above) that 40.5 is the biggest valve that goes on a standard insert, so avoids the 100 ish for inserts.

 

So it's a competition engine running HHEEEEEUUUUGGGEEEE carbs - ideally suited to 42mm inlets I'd think. How's the power below 3000 rpm?

 

It revs to 9k, but peak power comes in at 7,5 and starts dropping off at 7,9 (if you call a 1hp drop tailing off ), I normally use 8,4-ish as it will always drop into the peak torque band from there.

 

Not as bad as you'd think Mike, I can pull away in 5th from 1,800 rpm on about a 1/4 throttle, which I dont think's too bad with a 318 degree cam, 4-1 manifold and 39mm chokes.

It'll drive like any road engine up to 3k using up to 3/4 throttle, full throttle does'nt go well with race cams under 3k.. , but theres no need anyway when it pulls so well with less throttle, but it's certainly not the valve size causing a problem.

The "very" same engine when we de-tuned it for grass-track use by fitting a 276 cam (before I bought the "bits" from the blow-up!.. which was nothing to do with us by the way... broken crank tail via animal driver) with the 42mm inlets and still with a "big" bore 4-1 & 48's with 39mm chokes, gave 36hp at the wheels @ 2k and 67 @ 3k... and that still an 1800, not 2ltr.

A totally standard 1800 has 31hp @ 2k, 54 @ 3k... a Standard 2ltr 8v has 37hp @ 2k, 60 @ 3k... as you can see, big valves "dont" cause a lack of low end power in a correctly set up engine, "big" cams are a different matter.