What about the builds that have used a factory intake mated to a 16v flange and head? Would that resolve the thought that the 951 intake is inadequate?

I'm in the middle of building such an engine right now, and I'm seriously hoping the intake is not a choke point (using a larger tb of course).

 

From what I read, Thom isn't suggesting that the stock intake is useless. More, that physics alone would dictate that by reducing and modifying the runners (and plenum) has to have some effect on the resultant curve. Sure, the discussion of who favours what type of powerband is subjective. Some would argue that when running a big-ish turbo would favour reaching 'Over the wall' and into the low to mid 7krpms as to fall back into the meat of the turbo's efficiency on upshifts. Understood that there are other factors involved with regards to that.

 

What camshaft were you running on that 3.0.L and is this a 16v or 8v, aside Back pressure has nothing to do with intake , the stock intake will do 450- 500 whp on a 2.5 i would increase the tank volume on a 3L...



That car was built with the intent of running it at lemans also and the first 16V turbo was ran at lemans in 82 as a 2.5L..

How did you verify this and please quantify "up top" and power targets ..

 

The 968 turbo was primarily for the ADAC series. There was a Lemans version - but what the hell was Porsche thinking of when they did that? Pretty low power output, they could have done a lot better!!

BTW, the 82 entry was technically a 924....
I would love to get a hold of the valve covers from one of those...

 

You nailed it.
With shorter runners your [peak TQ ; peak HP] rpm band may be narrower and be shifted higher, but the engine should accelerate quite a bit faster between these two RPM points, as shifting the RAM effect to the right will give the room beyond 6k to stay longer in the efficiency range of the (large) compressor and get you back not too far away from peak torque rpm after each upshift.

 

You should get into variable length programming on the dyno, alot of those misconceptions would disappear fast .

 

It was entered as a 924 GTP to hide it's roots to the upcoming 944 .....

 

Ok, here is where I am getting confused. You want to run the engine in a RPM range that requires a drysump (unless you only run the engine on a dyno) with custom intake and exhaust manifolds, A large turbo, a custom cam and head work.....but the 16v head is out of the question?

The 16v head way outflows the 8v and the valve train is much lighter and can service high RPMs - on the other hand the 8v head is very good at midrange torque...so I still don't get trying to spin up an 8v engine....Am I missing something?

Now that I think of it, it sounds like you want to run a NASCAR motor at F1 speeds....

 

...with restrictor plates and carburetors!

 

The point you are missing is that I am not going to keep discussing the pros and cons of the stock intake with anyone who has not done back to back testing of different intakes on a 3.0 8V yet reckons the stock intake is good enough because of that "wide area under the curve" drivel.

Again, try the stock intake on biltz's engine and let's see how the curves look like.

 

OK, ship his car over to me and put down a deposit for the dyno time and I'll do it.

If you consider 'area under the curve' as drivel then you have absolutely no clue as to what real performance is and I am clearly wasting my time try to pass on some useful knowledge.

I will toss out one more thing that you may or may not thought of in your attempt to rev the **** out of an 8v - you will need to change the gearing on your transaxle to benefit from running at higher revs....not too many aftermarket 951 gear sets out there.

 

Hi Thom, I am the owner of the car and I think what Chris is trying to tell you is that no matter what your goal is the intake isnt a major factor for an 8V.
I spoke to Jon miledge about my 2.5 build, before in knew Chris, and remember asking him about the intake. He cuts the stock plenum and widens it but its not a game changer for performance. He suggested strongly the SFR headers... nothing about the intake, as Chris is suggesting, time and money should be used in other places.
Maybe another way of looking at this by comparing other cars Chris and others have done with the SFR intake like mine but with other components that are different since back to back testing doesnt seem to be available. While the dyno numbers may be similar the curve is not. I think my power/torque curve is better than many others who have a similar build because of the head work, the cam, headers and the turbo. This combination works well and those who have driven the car notice its not like other street 3 liters. The car does not seem to be working hard, pulls great off boost, has power all around and doesnt seem to have any weak points. Others with the SFR intake may not be able to say this and may not have the area under the curve I have and the reason is not because of the intake its the other parts that make the difference.
My head was D ported which to some makes no sense because its typically done on v8's because of the angle head/intake, my intake valves are larger by 2mm and the intakes are 1mm more approx. the head guy did not feel more was needed. I trusted him and let him do what he felt would work because he has lots of experience. The head,headers with the JME cam, which was supposed to be for the 2.5L, and the HTA gt3582R just rounded things out to really make the difference. Also have to consider Chris tuning the stand alone which accounts for alot. This is where I focused. I bought the SFR intake for turbo clearance only not for any performance but the other parts I really researched.
My question is I wonder what would happen if I went with the Jme cam thats rated for my HP but I then I possibly would loose response and also going with the bigger hotside but the car works so well I will wait a while.
By the way, it would be hard to test the car with the stock intake because the SFR intake has been port matched so not really possible.
Hope this helps.

 

If you are trying to convince me that the stock intake will be good enough then yes you are definitely wasting your time, as I have trodden this path and noticed for myself that the engine was still trying to pull an invisible parachute past 6k rpm when I was running the stock intake. That is with a GTX3076R 0.82 A/R turbine housing showing no more than 1.1 backpressure/boost ratio, which tells me that it's not the exhaust that was causing that invisible but clearly palpable wall.

You are missing again the point, which Patrick made above. It's not about revving the **** out of an 8V, it's about getting enough RPM room beyond 6k rpm to push the engine far enough for getting back as close as possible to peak torque RPM after each upshift.
As for the gearing, thank you but I have a special 6 speed gearbox in the works with tall gearing that will be good for 210mph at 6k rpm. I drove an original M44/60 engine with a turbo RS KKK recently using the same gearbox, and while the torque felt just sufficient for the gearing, I'm confident that my "upper rpm" engine will get up there in a far shorter time, if I can keep the car on the ground at those speeds.

 

Thanks for chiming in. I'm not questioning in any way the work that Chris did on this engine - the curves speak for themselves.
While I agree that there are many areas that will need being looked at before looking at the intake, I think we are several who have been able to notice, on our own particular set ups, that it becomes an issue after most of those other areas have been checked. I'm sure your car is a hoot to drive and wish you a lot of troublefree miles with it - keep us posted.

 

Nice build for sure. What cam was used for the posted dyno?