Which is the best engine to go with ITB?

Exactly, the baseline may not be 150BHP as per the book. A true 50BHP gain is pushing the boundaries IMO

ITBs are fantastic- don't get me wrong here.

I personally think they are better suited to higher revving high comp bottom ends with very hot cams given the purchase and mapping costs

A k jet setup with ms still gives great figures as has been said. It's all in the mapping

 

It does not liberate 50bhp, the baseline for stock motor and SEM is Gurds at 173bhp 163lbft, this is up 20BHP and 20+lbft from kjet all on stock ABF. Add ITB's ported head and mild cams you can get 190+bhp from stock compression no extra rpm, torque stays around 160+lbft.

But its all about the mapping and the inlet track.

 

In addition to your bike itbs, inlet manifold and possibly a 1.8T with suitabler injectors, you a MS in alpha-N config and an ABF engine.
As per this discussion and to extend the abilty for the engine to breath you would need cams with an adjustable gear plus some map tweaking. You can also port and polish the head to increase flow and cylinder filling for more torque in certain conditions.
To increase torque and revs further you will need to increase the compression.
This would require and engine rebuild with new pistons and rods.
As you already now from your Miata/MX-5/Eunos there are improvments to be seen at WOT with the above steps but you do want to map whichever engine combo for max response to WOT to less to suit your driving stlye and what you are doing with the vehicle.

Hope this answers your question.

 

It all about keeping the torque high. This is where you get your headline figures.

Stock MK3 16v cars tend to be around 147-154bhp with 130-135lbft on the tough love dyno always peaking at ~6100rpm for power and 4500rpm for torque. The power profiles are dictated by the factory ECU and the way it is calibrated for some power, cat operation, fuel economy and user friendliness ( A/C /Traction control EDL/ABS/PAS).

On Kjet with its "I will run lean fuel as I am mechnically dictated" after 6000rpm around 140lbft@5400rpm and up to 160bhp@6600rpm. WUR mod tend to fudge the fuel window. You can also adjust the valves in the metering head and achieve the same effect or do both for more resulotion. Kjet cars do not run a cat and void of most MK3 comforts and MOT limits.

But things change when you understand what you are doing and can dictate to an engine controller how much fuel you KNOW the engine requires and when to start burning it.

Torque then can be as high as 160+lbft on non cat vehicles.
On a std engine, because of its limitations, it does not hold on to torque in excess of 150lbft@7000rpm = 200bhp, this is where careful well thoughout modifications can work on this torque gradient to make it less negative. It may be, to achieve that "magic" number, you may have to buy brand name items to achieve this or make your own. You still have to think about what is going on to avoid throwing parts at the engine just to chase a number and making the engine run like a PieceOS everywhere else. Focus on the engine's breathing then buy the right bits once.

I agree, when this airflow exiting from this component then interacts with high compresssion, head works, cams, lighten reciprocating mass and tuning, the effect can be much greater than if bolted to a stock engine that is not built to spin to 8200rpm. However with mapping a stock engine with such a component can be made to fairly aggressive from sub WOT conditions. The straight-ish path the air has to take works fine increasing engine fury when at 6000-7200. This is no problem on a factory bottom end.

It is indeedy as was proven elsewhere in this forum.

 

There is a lot of choice out their for ITB's, there are quite a few of the shelf items that are very good at what they do, Jenveys DTH would be my choice if I was looking to build from fresh, they seem expensive but if you do start modifying bike ITB's the costs soon add up, if you can fabricate, have lots of spare time and are willing to develop your own homebrew ITB's then go this route as it will be cheaper, but if you are paying for the fabrication etc it would not work out cost effective.

The other option is what danster has surgested and to use webbers or the like this would be cheaper but you would only be using MS for ignition and not the fueling, and IMO would be less effective, i would go EFI plenum over webbers any day of the week.

have a look here for Jenvey ITB's - thread is long and there were lots of issues that were not issues as first thought.

have a look here for building your own ITB's.

and here for building your own Carbs.

and here for just MS'ing your stock ABF with plenum.

 

And to throw some more in the mix, I came across a black mk1 at GTi festival earlier this year clocking early 13's on the 1/4. Speaking to the driver, he said his best was 12.9ish. Looking under the bonnet, he had a fully built abf 16v (read high comp, flowed head, cams) but was still on a factory plenum albeit worked. He mentioned figures of over 215bhp all built by racepower motorsport.

Gurds

 

Interestingly the Super 1600 NA rally cars can make about 220bhp with a 34mm intake restrictor fitted with a single plenum.
That is about half the size of a std ABF tb and also, way smaller than what you would fit on one of the 4 single itbs!

EDIT. This is incorrect size, 34mm is for the WRC turbo cars. 60mm TB for Super 1600.

 

And probaly span much less torque to 9000rpm.

 

I've seen this MK1 Run a few times and yes 12.8 sec 1/4 at pod, excellent power and with a ABF inlet plenum

There are many routes to 16v power most tried by many of us and the good thing is all the information is shared on this Forum by everyone.

Well Done Fellow Members

 

There has been a lot of 'std' engine development tales in the paddock at the golf championship meetings.. Wher of course we are limited to the factory fuelling and ignition...

Having replaced everything with new parts.. (injectors, wur, metering head, pump, lift pump, accumulator, filter, lines, etc etc). the car reacts to the changes better than any 20yr old system ever would.. (Yes I know I could probably be runnning Pectel or Motec for the money i've spent on Bosch K-jet!)

Fuelling isn't the issue with K-jet. If you know enough about what your doing with it, and have enough time to play with EVERYTHING, you can make it do pretty much whatever you want.

Ignition control being the limiting factor. Linear and not particularly aggressive.

Cam timing being another intersting variable about getting the best out of what we have to play with..

 

Was that you out in the J-Tech car on Saturday?

Gurds

 

True...
But I'd argue with 'no extra RPM' as most mild cams will make peak power at least 500, if not nearer 1000 RPM above ABF cams, so you do need o run them higher.

Still on stock internals, CR, valve sizes etc and running VAG hydraulic lifters, I'd say 7300-7500 is perfectly safe for both the top end and bottom end...and you should hit the figures you list.

I'd be amazed if I see any more than 10 BHP of a gain, going to ITBs over my current ported ABF manifold on straight back to bac teating.

The gain comes from removing the Digi 3.2 ECU 'issue' and allowing slightly wilder cam set-ups to be run...268/268, 276/268 etc...
But by then you aren't comparing apples with apples.

 

Let me now try to make up for past post error.
Search for "Super 1600 intake restrictor specs" and get sent to turbo WRC restrictor.

Anyway,
Something to consider if going ITBs with management, is that some engines come with an oem trigger wheel and crank sensor that could be utilised. eg ABF.

Discuss potential trigger wheel failure only if we must.

 

No, that was Jamie Packham (Number 37)

I run the sister car to that (Number 38)

 

OK my piper 264's peaked at 6778rpm and max torque was 5236rpm, they are rated from 2500-6500 so i do not expect them to put out anymore by me reving harder. This is why i stated without increase in rpm, at 6500rpm my torque is 146lbft dropping fast, so i really only rev to 7k which to me is no increase in the rev range.

But this was only a quick, tune after many hardware and some software niggles, so when I go back it will be interresting to see if that torque holds for longer.

EDIT just looking at my old engine with the same cams, that engine peaked at 7200rpm

 

The problem with any of us quoting or comparing figures is that different dynos give different readings.

Unless we are all singing from the same hymn sheet then DD, dynopack, maha, sun ram et al will produce different figures.

I have personally seen a 25bhp difference between different RRs for the same car with identical engine spec. Book power of 187. Maha said 216, DD gave 188

 

Hi Gurd's car both kjet and MS, my car with the ITB'ed ABF and the baseline MK3 ABF's Eddie has talked about were all tested on the same dyno, so what i have been referring to is all off the same hymn sheet so to speak.

Your car on standard compression would be in the ball park of what i would gestimate, maybe bigger cams than mine making it slightly peakier and less torque? But yours was a different dyno so no real comparison, but both dynos are DD so going to be fairly close.

Were you expectin more from the ITB's? as the limiting facture i beleive is the compression and cams, put bigger cams on with stock compression = loose.

High comp and some tasty cams and your then as you said you will be pushing the right side of 200bhp but at what cost? are high comp bottem ends worth the money? I am keeping the standard bottem end (ABF) and will try and squeeze as much out of it NA, why? not for the power it produces as mentioned earlier i would go forced induction. But it is fun optimising and playing around with setups for reasonable money and MK2 ITB valvers go well and sound great.

I am very interested in what Gurd's has achieved and will be keeping a close eye on his developments, if I was the OP i would also stroll over and have a look at what can be acheive on the plenum add head work and cams ???bhp but will the compression hold it back? Gurd's get some cams and head work done, who needs a roll cage?

 

on many DTH cars I have supplied bodies to, the gains reported back from just changing from kjet to DTH bodies and DTA ecu (or their own mappable ecu of choice), and these gains have varied from 22bhp-37bhp depending on their engine specs.

 

^with the same 7,200rpm limit?

I bit the torque gains acroos the board were more impressive, and noticable in the seat!?

 

I know most of the talk on this thread is aimed at 16v engines, and it is interesting to see all the various options and opinions. (like Eastenders for petrolheads).

A lot of the performance increases discussed are based on factory ecu settings which are far from being optimised for power or torque. The Megasquirt conversion of VWsingh with help from Toyotec being a fine example among others, of what a standard engine could do if mapped in a different way.

This is interesting as the NA 20v ADR large inlet port engine is supplied with a meagre 125bhp as standard, and looking at it's intake manifold system which appears quite restrictive, I was wondering what this engine could potentially produce if mapped in a similar way to optimise for performance rather than emissions and everyday driving. Probably with ITBs as there is a very simple and cheap option to carry out this conversion.
The std inlet manifold splits about 100mm back from the head into perfectly formed stubs for installing GSXR ITBs (leaving the std injectors and fuel rail in place). These match perfectly using the oem rubbers on the inlet manifold and are 42mm at the butterfly but taper out to 50mm, and then have their own rampipes. The ITBs use 9 x 8mm spacers to open the bore centres from 80 to 88mm to match the 20v head. (same as 16v out of interest)
These ITBs can be got 100 off ebay, leaving just the ecu and wiring to sort out. Pretty cheap setup and not much in the way of manufacturing bespoke parts either.