Once you go full custom I don't see why to keep the TB at the back, other than for a rear cowl base intake, but from memory that is low pressure.

 

Because the oil filler neck is in the way at the front, and there is a engine crossbar in the way at the front, and the hood is lowest at the front.

In addition, I would like to leave open the possibility that a customer may be able to use our after-market manifold with the stock LH engine management, which means I need to leave room for a MAF sensor and they are kind of big.
That kind of room is only available at the back of the motor.

Anyway, those are my reasons for leaving the throttle body pointing toward the firewall. Cowl-induction was not a consideration.

 

Well done! Great numbers, but yet again they confirm how restrictive the stock intake is... We got to pretty much the same absolute power/torque (510hp/600Nm) levels out of 5.4ltrs, high compression engine on ITBs. We make the power and torque a bit higher up - maybe 300rpm - but in general if I gave you my dyno graph you would not be able to tell the difference. Adrian Clark in the UK got 570hp/670Nm out of his 6.4ltr stroker on ITBs. I am sure he would have gotten more if he followed my advise on trumpet length. So, Carl - time to figure out how to package these ITBs neatly in the engine bay.

 

I'm on it

We are examining two designs - how much HP can we get and still fit under the hood, and if our flow software tells us that the height of the space envelope is the problem (which I already suspect); how much more HP we could get if we were a little taller. We'll see.

 

I know the market for 928 performance parts is kind of limited, but I have sold 6 sets of ITB adapters, and I am sure more would be bought if we could figure how to package the ITBs and their airboxes neatly in the engine bay. On a race car, it is not that much of a problem, but I would love to have a breathed on engine in my daily '89 5spd with LSD, which also looks like a factory job and not a home built exercise. I am sure others would be supportive. So the market could turn out to be bigger than we think.

 

There is a thread here on RL by Hans SerVaas about his CNC machined intake manifold flanges, and they are very good. And he still has them, years later, with no sales.

I also developed a set of printed intake manifold flanges several years ago, and have sold only one set. https://928motorsports.com/parts/intake_runners.php

Both of these could be used by an owner to make ITB's or a sheet metal manifold. But nobody did.

This tells me that the solution needs to be more plug-n-play. A bolt-on swap or very close to it. That's where I am going this time. Adam's motor is going to get the first one.

 

I think there is no doubt that when displacing larger volumes the ITB setup is essential to optimise the potential of bigger motors. What still seems to be vague is what [if any] the stock manifold is costing the stock motor. Carl's interesting work in this thread shows that his latest mods kick in above 4k rpm but below that one presumes there is not much difference in the two sets of curves, albeit there is some difference.

On a stock motor in terms of air displaced, that rpm point increases to 5200 rpm all things being equal so the potential rev band of the benefit will be noticeably reduced. All I can say is that my intincts have told me for years that my S4 motor is struggling to breath above 5k rpm and by 6k rpm it is dying. As with all things performance wise all gains are welcome but some are not cost effective but it would interesting indeed to see what difference a set of exhaust headers mated with improved inlet breathing might achieve with a stock manifold.

Not sure if anyone has put ITB's on an otherwise stock 5L motor- that is also another interesting potential performance indicator. 64 bhp per litre is a very modest output. 80 bhp per litre [400 bhp] would be a nice add on. This motor is currently at 77.5 bhp/litre.

Real nice to see this particular car coming back to life- well done chaps.

 

And now the answer we have all been waiting for...

Stock internals GTS engine, GT cams, totally stock intake, 928 international headers, custom 2.5" dual exhaust - 308rwhp

The same engine, but with E39 M5 ITBs and custom dual airbox - 385rwhp

So on average, the stock intake costs you at least 75bhp

The results were done this weekend...

 

BRAVO Cheburator, I've always wondered about this!

 

That engine is the one in this thread?

https://rennlist.com/forums/928-foru...age-a-gts.html

 

Well done!

So that begs the question as to how much of that differential could be recovered from improvements to the stock system along the lines Carl put into his build- 50% of that quantum?

Rgds

Fred

 

Which is why I funded the development of a decent intake once and for all, something that could be resold and be repeatable as opposed to one off designs. On my motor, we are at 503hp with all those mods, including a massaged stock design intake. With the bone stock intake we are substantially less.

Basically the 928's intake is like a giant restrictor.

 

Not correct. Hans sold several sets.

 

Reminds me of the results from this project:

https://rennlist.com/forums/928-foru...rari-chat.html

 

Interesting, hadn't seen that. I am not letting this product die a death though. My motor won't be done without it so Carl will get weekly pestering emails and phone calls until it is done