Custom Cams

[Group3J]

Is he the sort of guy who would be willing to be emailed or does he prefer to be left alone? I'm interested to know what he thinks/knows of venturi porting and why it works, amongst a help of other things.

Also, your honesty is greatly appreciated. It's nice to come across people who are willing to admit when they're getting out of their depth - it's hard when you're trying to learn and you end up with half truths. The vast majority of people I talk to about all this generally make it up as they go, so again, thanks for the honesty.

[P10DET]

Originally posted by Group3J
Is he the sort of guy who would be willing to be emailed or does he prefer to be left alone? I'm interested to know what he thinks/knows of venturi porting and why it works, amongst a help of other things.

Also, your honesty is greatly appreciated. It's nice to come across people who are willing to admit when they're getting out of their depth - it's hard when you're trying to learn and you end up with half truths. The vast majority of people I talk to about all this generally make it up as they go, so again, thanks for the honesty.

It's my pleasure. I have no secrets to keep. Besides, most of my knowledge is coming from various friends who are more closely involved with this stuff. I built a serious NA engine a couple of years ago (somehow it ended up with steel shot throughout and totally wrote off the engine). During that time I got to know Mike pretty well and now we're pretty close friends.

I'll send you a private message with his e-mail address. I'm sure he'd be willing to tell you what he knows. I know he is interested in the GTi-R head and manifold. He figures the GTi-R manifold is good for around 15 bhp through computer modeling.

[Group3J]

Thanks very much....now I've just got to work out how to find the pm's.....

I'm also very keen to chat to him about injector placement. I've already got Throttle Bodies of sorts.
I hand made a manifold to adapt some stipped down and sealed Dellorto carbies (DHLA 40's which are a bit small, but I had them lying around so they cost me nothing. (see the pic below and in the next post). Being I'm running aftermarket MoTec injection, there's no need for an AFM.
I've got the choice of either modding the carbies and fitting the injectors in them or mounting the injectors at the trumpets. A good friend of mine (with a rally car....not running an SR) did some dyno work testing injector placement and found a gain in mounting them at the trumpets. I'm keen to do the same but want to understand WHY it works, rather than just playing the sheep.

[Group3J]

And here they are mounted on the head.....

[P10DET]

Originally posted by Group3J
Thanks very much....now I've just got to work out how to find the pm's.....

I'm also very keen to chat to him about injector placement. I've already got Throttle Bodies of sorts.
I hand made a manifold to adapt some stipped down and sealed Dellorto carbies (DHLA 40's which are a bit small, but I had them lying around so they cost me nothing. (see the pic below and in the next post). Being I'm running aftermarket MoTec injection, there's no need for an AFM.
I've got the choice of either modding the carbies and fitting the injectors in them or mounting the injectors at the trumpets. A good friend of mine (with a rally car....not running an SR) did some dyno work testing injector placement and found a gain in mounting them at the trumpets. I'm keen to do the same but want to understand WHY it works, rather than just playing the sheep.

Wow! Very cool fab work. They should be good from some nice top end hp. I wish I could help you with injector placement, but I cannot. It does strike me as odd that adding the injectors at the trumpets would produce the best power. I would have thought differently. I'd guess it has to do with fuel atomization and dispersion.

[Group3J]

Thanks, it took a while but should offer a good improvement along with the porting and cams.

Yeah, it's not something I have a very strong grasp on. I suspect it is indeed to do with the fact that the fuel has more time to homogenise with the air in the runners, forming a more complete mixture. Strangely enough, though, it was worth literally 2-3hp if he moved them ~20mm from the trumpet, as opposed to sitting just at the tip. As I mentioned, I want to understand why this all works, not just copy it. It doesn't work as well at low rpm (as I suspect the injector is mainly wetting the butterfly).
Incidentally, I have noticed that a number of race cars use this setup. Most use 2 injectors per runner (I believe to get past the low rpm issues), but there are a couple I've seen with only 1 injector.......it's all very interesting!

[P10DET]

Originally posted by Group3J
.......it's all very interesting!

Quite!

[T4 Primera]

Originally posted by P10DET


I wish I could help you with injector placement, but I cannot. It does strike me as odd that adding the injectors at the trumpets would produce the best power. I would have thought differently. I'd guess it has to do with fuel atomization and dispersion.

As alternative why speculations:

Since fuel vaporisation (endothermic) has a cooling effect on the intake charge:

a) IF a fuel/air mixture is more dense than air alone, then placement of the injector upstream may increase the length, hence mass, hence inertia of the intake charge. The increased inertia might aid cylinder filling - especially with a cam that closes the intake valve later after BDC. It depends on whether air or a fuel/air mixture is more dense.

If that speculation is crap, then try this one:

b) IF the density of air alone is different from a fuel/air mixture, then placement of the fuel injector may affect the resonance of the intake column - which also affects cylinder filling.

Both of these speculations could probably be tested mathematically - howz ya physics