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Do you have any dyno sheet supporting the bold claim that the stock 944 turbo intake is good for 500hp, or is it part of your theory?
You won't ever find me arguing that the stock intake can't be improved upon for specific desires.
The rest of that comment was actually referring to you specifically, Thom:
in the 951 world the stock intake manifold is very good for 99% of street cars, past 500hp. however the subset who really want that extra rush of power 5500+ rpm have got large plenum short runner intakes (a few options on market, plus custom ones).
these intakes have runner lengths (including the head port) way too short to have any meaningful resonance tuning (8.25" should work in the 9-10000rpm range for 3rd harmonic)
to your question...
Shawn/refresh951 did it...note I said hp not whp.
Going off the typically-cited 15% factor this run is just past 500 crank hp.
Mods:
Hybrid Stoker 3.12L,
Garrett GT3582R ,
Rogue M-Tune,
Rogue Tuner/Logger,
4 Bar FPR,
MBC ,
3" Exhaust, 3" DP, WG Dump,
5x 80 lb Injectors,
Tial 38mm WG with 1.1 bar spring,
Modified Stock IC + Custom IC Pipes,
Ford 65mm Throttle Body.
Following the recent discussion on FB I sort of thought you were refering to my set up, whence my reaction.
From what I have seen over the years comparing dyno results between what we usually see in Europe and the numbers "measured" stateside, I have come to believe that US rwhp = Euro crank hp. In this context the results posted above tell me the car in question made about 440 euro crank hp. The peak torque on this engine sits at about 460 ft.lbs, a figure often observed with the stock intake on a 3L 8V, but again measured at the crank this side of the ocean.
If we now stop nit-picking regarding figure interpretation and the fact we are not exactly close to 500 actual "horse power", the shape of the torque curve shows a remarkable torque loss of nearly 100 ft.lbs betwen peak torque rpm at 4200 rpm and peak power at ~6000 rpm. This tells me the magic figure of 430 "hp" quoted is reached through the beauty of Maths that simply tells that power = torque times rpm and that the power display of this set up may be taken with a grain of salt and that it may not really "feel" like a "500 hp" car. The problem probably lies in the fact that most folks will rate an engine's performance from its peak power figure, which is rather misleading and does not necessarily express how an engine behaves, and, more to the point, how exploitable that power will actually be.
From another point of view, and just for the sake of returning a dyno graph to compare with the one you posted, here are the results from another 3L 8V 944. Not only does it reach the magical 500 crank hp (500 us rwhp) up top, but peak torque is slightly higher, the torque curve is flatter and wider, and at last but not least, the torque loss between peak torque rpm and peak power rpm is a limited 63 N.m which is 46 ft.lbs, which is roughly half the loss observed on the dyno you posted above.
Guess what intake this engine is running? The Lindsey intake, which is a short runner, large plenum intake, very much unlike the stock intake.
While dumping the stock 944 turbo intake may not feel quite obvious for any new owner willing to get deep into engine mods, and even for most confirmed 951 folks I talk with, using a proper turbo and a proper tune along with a proper intake should bring consistent results and the stock intake down the garbage bin.
Apologies to ptuomov for slightly hijacking his thread.
I don't think there's any obvious reason that for a street car a short runner intake and a smaller turbine is better than a long runner intake and a larger turbine. It's going to be a case by case situation.
Straight runners would always be preferable to curvy runners, for a given runner length.
Thom,
First I want to clarify I am not arguing anything here - just answering questions related to my "theory". I do value your experience and input provided on intake design over the years and am incorporating your thoughts into the design of my own forthcoming custom manifold.
I have seen references to the US/ROW dyno discrepancies before and don't understand why things seem to be so different in EU/Oz vs USA. Maybe optimistic dynos, cheating operators, maybe different types of dynos used? Don't really know.
I think what happened using that very nice dyno graph you just posted relates to my other point from that other post - that using the short-runner/big-plenum intakes like the LR, Shawn's later custom one, and yours, move the "tuned length" of the runners outside of any usable tuning region.
At that point the intake is merely serving as ducting for the pressurized air to get from intercooler to intake valves.
Those intakes flow so well and have so much volume to breathe from that they undoubtedly make more power at the high end, and the loss of any resonance tuning flattens the torque line (eliminates the "tuned peaks").
Food for thought on that - here is a dyno graph from a stock Chevy LT-1 engine from 1992-1997. 5.7L V8, mild cam, EFI. Total runner length from plenum to intake valve is about 8.3", like the 944 intakes under discussion.
No possible resonance tuning with that length, but look at the shape of the torque line! (wheel numbers, but they stopped the run about 1000rpm too early)
Spencer, I would not compare the results of a 90° crankshaft V8 with that of a (flat plane) 4 cylinder engine. I spent quite some time comparing pulse wave tuning with different runner lengths on known well-prepped 951 engines only to reach similar results as yours, which was that the runners were never long enough to make sense to me. However, a differential approach showed me that a runner length close to the Lindsey's were a pretty good compromise as confirmed from driving 3 different 3L 8V cars using it with different turbos and tunes and returning consistent engine behaviours.
I don't think there's any obvious reason that for a street car a short runner intake and a smaller turbine is better than a long runner intake and a larger turbine. It's going to be a case by case situation.
Well, in my case I observed the opposite, which was that long runners and a "large" (GT35) turbo made a very unhappy pairing, but that shorter runners were doing fine with small turbine (GT30) and doing much better with a large turbine (GT35).
At this point I believe that long runners are only any good when running at low load to maximise fuel efficiency and torque at low & medium load, as per usual OEM requirements. In my experience, as soon as we add boost they do nothing but interfere with the results we would expect, at least on a I4 engine.
At this point I believe that long runners are only any good when running at low load to maximise fuel efficiency and torque at low & medium load, as per usual OEM requirements. In my experience, as soon as we add boost they do nothing but interfere with the results we would expect, at least on a I4 engine.
it'd be an interesting experiment to strap a 951 to a dyno with the throttle held open at say 20%, and compare the stock intake vs a LR or similar, to measure "low load" torque output.
it'd be an interesting experiment to strap a 951 to a dyno with the throttle held open at say 20%, and compare the stock intake vs a LR or similar, to measure "low load" torque output.
In such low load situations I'm 99% sure the stock intake will return superior results, regardless of engine size.
In real life situations though, and on a 3l engine at least, the subsequent amount of low load torque can be cumbersome when and where the engine needs to be slow enough such as in town driving, on slow roads, etc.
In my opinion, there are three steady state WOT modes in a pump gas turbo motor:
1. The engine not yet producing enough exhaust energy to run the compressor to hit the knock limit of the engine.
2. The engine at the knock limit. This mode is entirely about the trapped charge temperature.
3. The engine at the compressor mass flow limit, and not able to reach the knock limit.
Tuned intake runners only give any benefit in the first mode. Therefore, you either tune the runners to increase VE at the rpms when turbo can’t reach the knock limit or you forget about tuning altogether and just go with short and unrestricted intake runners. If you however get the intake tuned to the rpms where turbo is about to spool, you either get earlier spool rpm or you can run a bigger turbine at the same spool rpm.
Running a tuned long runner intake that tunes to an rpm at which the turbo has already spooled to the knock limit is in my opinion a fools errand. When one is at the knock limit, one should mostly worry about temperatures and intake-exhaust port pressure ratios to the extent cylinder evacuation is a problem.
I agree for the most of the above post, except with the thought that long runners should always provide enough ram effect to load a "large" turbine, but then it depends what "large" means. As I said the stock 951 intake didn't work well with my GTX3576R 0.82, regardless how much I would play with the PID numbers in the closed loop boost control. Perhaps that's an I4 thing that's not going to happen on a 5L+ V8 though. Exhaust pressure interference between adjacent cylinders is a real problem on single scroll I4 engines.
I agree for the most of the above post, except with the thought that long runners should always provide enough ram effect to load a "large" turbine, but then it depends what "large" means. As I said the stock 951 intake didn't work well with my GTX3576R 0.82, regardless how much I would play with the PID numbers in the closed loop boost control. Perhaps that's an I4 thing that's not going to happen on a 5L+ V8 though. Exhaust pressure interference between adjacent cylinders is a real problem on single scroll I4 engines.
You think it’s hard with I4 and turbo on the intake side? Please. Crossplane V8 with exhaust manifolds has problems beyond the imagination compared to that. I’ve got 90 and 180 degree exhaust blowdown interference to deal with, and no distance to force separation. In catastrophe theory, the scientific nomenclature for the situation is formally called “totally fvucked”.
in any case, the tuned intake only works if it’s tuned exactly to the “about to spool” rpm. It’s not a license to increase turbo size without a limit.
Quite a long shot but how about swapping inlet sides with exhaust sides, à la latest BMW M5?
if you locate both turbos in between the V you might be able to build a suitable exhaust manifold and separate, short runner intake manifolds. I'm not aware what this involves exactly on a 90° V8 crankshaft though. You might as well build a flat plane crank.
Quite a long shot but how about swapping inlet sides with exhaust sides, à la latest BMW M5?
if you locate both turbos in between the V you might be able to build a suitable exhaust manifold and separate, short runner intake manifolds. I'm not aware what this involves exactly on a 90° V8 crankshaft though. You might as well build a flat plane crank.
Too involved, as the current setup will get me to the traction limit easily on street tires at most street relevant rpms. John and I aren’t a car factory! We’ll likely lean on some JDS magic later to deal was th the blowdown interference fall down, though.
In my opinion you have pushed the boundaries further than the factory would ever have. A flat plane crank and the subsequent mods may not amount to much more work than what you have already provided, considering how focused/**** Mr Kuhn seems to be. Anyone who will fork out the budget for a 928TT conversion should not wince for say an additional $5k due to a flat plane crank. I know I would if I was not convinced the 944 turbo was not a better mod platform
In my opinion you have pushed the boundaries further than the factory would ever have. A flat plane crank and the subsequent mods may not amount to much more work than what you have already provided, considering how **** Mr Kuhn seems to be. Anyone who will fork out the budget for a 928TT conversion should not wince for say an additional $5k due to a flat plane crank. I know I would if I was not convinced the 944 turbo was not a better mod platform 😁
Let's see. You'd need a new crankshaft, new cams, and new intake manifold (actually two four cylinder ones). And then likely a new block because the 928 block wasn't designed for the vibrations from a flat crank. If you do a new block and a crank, then you'll almost certainly need new pistons and new pistons will need new rods. So one could maybe reuse the head castings? ;-) I think changing that much would take another decade and violate the spirit of making minimum necessary modifications to meet the goals.
01-05-2018, 11:49 AM
