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I agree that the engine you have there with those ingredients should be easily capable of 450hp bye 20psi so just make sure your not leaking exhaust gas out the wastegate and make sure your not leaking intake pressure somewhere? Then if those are holding and check out it’s up to your tune to get the air fuel right along with ignition map to take advantage it’s ok to be safe on the first few dyno tunes but you should pull back fuel and ignition until you get to a happy smooth place with numbers they don’t lie on the graph. Good wise band and knock sensors make sure of this! Good luck and keep us posted
If the power doesn’t increase with further boost, there are two main possibilities. First, exhaust back pressure is causing the exhaust valves to bounce off the seat and the engine needs more seated load on the exhaust valves. Second, the exhaust back pressure grows really fast with more boost with a high multiplier.
If the power doesn’t increase with further boost, there are two main possibilities. First, exhaust back pressure is causing the exhaust valves to bounce off the seat and the engine needs more seated load on the exhaust valves. Second, the exhaust back pressure grows really fast with more boost with a high multiplier.
Back pressure with a GT35 0.82 housing will not be a problem on this set up and this boost level.
The whole set up is comparable to a configuration I used to run on my 8V engine, and I think the camshaft used here has too much overlap causing a leak in dynamic compression ratio relative to the low static compression ratio. I suggest using a stock 9R camshaft.
Back pressure with a GT35 0.82 housing will not be a problem on this set up and this boost level.
The whole set up is comparable to a configuration I used to run on my 8V engine, and I think the camshaft used here has too much overlap causing a leak in dynamic compression ratio relative to the low static compression ratio. I suggest using a stock 9R camshaft.
Oh, that's super interesting Thom. Thanks for that tip. I will have to do a lot of reading in this area to understand it better.
I have adjustable cam timing gear, is this something that could be dialed out, or even just proven, by changing cam timing? Or is the overlap static and dynamic compression won't be impacted by the relation to crank timing?
Ah, yep. The 944.105.155.9R has an LSA of 110 degrees versus my cams which have 112 degrees. Reading around, this will improve top end and effective compression. Not sure how much two degrees will make but it probably is the better cam for a modern turbo.
Didn't have the most luck at the dyno. This is a mustang heart breaker but this looks less than expected compared to similar builds. He says in 4th gear it makes 346hp 383tq. Maybe that's closer to 380hp on an inertia style dyno like a dynojet? Anyway, the issue seems to be intake temperatures which are rising 40+ degrees. The FMIC seems to be the limiting factor. He says it's an ebay / chinese core with fins that aren't nearly as dense as a garrett core.
Motor doesn't seem to be responsive to boost. He's tried higher boost pressures but it just raises intake temps with very little gain. Looks like turbo is able to hold pressure in the rev range, but HP drops off in the higher revs. Maybe just 8v head not breathing?
I have seen many china cores that heatsoak, rising IAT to 40+++ C.
I have adjustable cam timing gear, is this something that could be dialed out, or even just proven, by changing cam timing? Or is the overlap static and dynamic compression won't be impacted by the relation to crank timing?
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Ah, yep. The 944.105.155.9R has an LSA of 110 degrees versus my cams which have 112 degrees. Reading around, this will improve top end and effective compression. Not sure how much two degrees will make but it probably is the better cam for a modern turbo.
You can play with the cam timing to see how it affects the torque curve. I spent much time doing this and it was fun to learn how it affected engine behaviour but it did not cover up for the excessive overlap of the camshaft I was using at the time. You might find a satisfying setting, but you just might. It's fun trying though, but mind exhaust temps and knock at upper rpm when advancing the cam timing "too much".
From what I can see the "Webcam 274" has a symetrical inlet/outlet profile with durations of 234° at @0.050" of lift.
Anyway, with an LSA of 112° and @0.050" of lift the "Webcam 274" has 10° of overlap against a max of 0° for the 9R camshaft (which has an actual LSA of 114°, not 110°). On paper and in my opinion the "Webcam 274" has too much overlap for a static compression of 8.75:1. I guess this is where your set up "bleeds" dynamic compression. The narrow LSA causes the high overlap and the "Webcam 274" certainly works very well on a 944 NA.
Great info, thank you much Thom. Will keep my eyes open for a 9R camshaft and will throw it in to try on the next timing belt. Is there anyone who reproduces these cams new? Or is it all about the luck on ebay/rennlist ebay?
I think I have a extra late NA 9R camshaft if your interested For $150 shipped it’s nice and clean In bag on shelf still in oiled cam housing with lifters! I put one in my last build 5 years ago it was a mild ported all fresh engine and turbo k26/8 turbo S with A tune, 3” exhaust and 3bar fpr it was ca smog legal made 285hp and with exhaust all wrapped it made 16psi bye 3000 rpm and pulled hard tearing 265 series tires up all the way to 5800
here is some good info on turbo cams and the effects the lobe separation and durations do to low compression turbo motors vs High comp NA
and some real world users granted most of these are V8 cars and V6 cars but the ideas are similar to ours for LS and Duration when you want lift overlap compared to piston movement in a pressure in intake and back pressure in exhaust scenario
Thanks for the offer, I just pulled the trigger on another one earlier today. If it's messed up I'll give you a shout though. Yeah thanks for the links, I've been doing a lot of reading on this and reaching out to builders and tuners.
I wish I had more info on the 9R cam. A couple sources call this different from the 09 cam including a company that regrinds them so there must be something to it.
https://members.rennlist.com/951_racerx/CamProfiles.pdf mentions the 110 lobe separation on the 9R, tighter than the 09 at 114. Tighter would be better here as it would increase the effective compression. The webcam is 112 so moving to a 114 LSA cam would actually be a downgrade in that aspect. If it really is 110 that would be a clear win.
The 09 cam is a win for overlap. Don't want overlap for the turbo so 0 is fine on the 09. If the 9R *is* a different cam, I can't find an overlap value for it. It could potentially be worse than the 10 degrees on the webcam274.
If the 9R cam is 110LSA with 0 overlap, its a huge win over the webcam. Well, if win = biggest horse power number. It's not so much 'better' as different. Better for a road race car which is what I have.
If the 9R is the same as the 09, then it's a slightly wider LSA which is a disadvantage, but 0 overlap which is an advantage. I don't know which one makes more of a difference nor how much better this would be than the webcam.
Elgens calls the 9R an 09 cam with more 'area under the curve'. I suspect the cam profile PDF is wrong above, and it's a 114 LSA 0 overlap cam with slightly better characteristics than the 09 cam.
Porsche made 3 camshafts only for the 8 valve cars
1983-1986 05
1986-1988 non turbos 09
1989 2.7 10
these numbers and letters refer to the casting part numbers on the actual camshaft. The R letter is stamped in some but not all of them just after number on end that Elgin site is just taking a 09 cam and slightly modifying it for there performance grind
then for more extreme race cam they have to use new billets I believe. Here is a pic of the factory spec book on the cams. It doesn’t tell the whole story you have to get cam doctor to run the printout of it but basically the 09 in a turbo motor gets you a bump in compression down low where you need it and these motors don’t make anything after 5800 anyway so having the exhaust open for longer helps move that hot air through turbo quicker, on modded cars this is a plus for sure. I think I have a cam sheet on either the 09 or 10 I will dig it out tomorrow!
01-26-2020, 03:28 AM
