terry gt

Like warp drive?

GregBBRD

If you are going to use my name as a reference, I'd prefer that you also tell them that I had you regrind them to a completely different specification.

As you've worded this, people might be under the illusion that I approve of your cam grinds.

Where the actual truth is that I still have no stinking idea of what you were trying to accomplish by moving the lobe centers to 114 degrees.

terry gt

I am not a cam expert . But I can say my car idles much the same as with the stock GT cams . Gets better fuel economy , power comes on at a lower rpm 3500 ,stock was 3800 , runs smother at highway speeds , and has more than 350 hp at the rear wheels

Strosek Ultra

114 degrees of lobe centers - wow that is much, not much overlap. Suppose he is looking for good idle, low emissions, smooth uneven pull from idle and up, minimum trade off from low end torque but is that what we are seeking when installing hot cams?

Åke

danglerb

I googled a few bits of the description and part number and came up with some old posts from PhilT showing the cams as 928 developments.

mark kibort

How did you get 350rwhp with a set of GT cams . other mods?? just the ones on your signature?? MSDS headers, some special cams?, and thats it??? seems pretty stout for only a set of headers. Ive got a lot of little mods to the 5 liter engine and it only got up to 335rwhp , which was a lot for a 5 liter GT cam'ed S4 engine.

BC

Because he pays attention to the details and probably actually took some advice and tuned his car.

Mark Anderson

Lizard928

MK,

These are substantially bigger than GT cams.

Terry has MSDS headers and a true dual mandrel bent exhaust.
The car has been tuned, and there is still a little on the table we will be extracting this year.

To answer the question about the LSA. I went with 114 LSA for a number of reasons, good idle, broader power band instead of a peaky power band. Additionally, the wider the LSA the less prone to detonation your engine is, with how prone the S4 and GTS is to knock, I wanted to get away for that as much as possible.

The Z06 with the LS7 runs a very similar profile but with a 120 LSA.
Running a more narrow LSA with massive overlap also can drastically reduce MPG in town driving. I did not want to put out a product which have good power, but killed fuel economy, MPG, idled poorly and had trouble passing emissions. As it stands you can bolt these cams in and still pass Cali emissions, improve your MPG with a little tuning, and have little to no effect on idle quality yet still get good power increases.

It should also be noted that I can change the grind for those that wish and with that I can decrease the LSA to 110 should anyone decide.

SMTCapeCod

Thanks for the info above wrt the actual design intentions of 'tri-flow', and also for the measured exchange on specs/LSA etc. This could be a good thread...

I caught the pricing in 2011 dollars on another forum....any MLK Day sales?

j/k...

Actually, has the cam profile performance under S4 vs S3 intake manifolds already been covered somewhere, or could you offer some views on that (Colin, Gregg)?

Regards

Lizard928

Åke,
Most people who will be going with larger cams still need the car to idle and be able to pass emissions.
Can you tell me on a stock S4/GT/GTS intake manifolded car with headers, and a full exhaust how much of a power increase you could obtain from going from 114 LSA to a 110 LSA with .437" lift and 230 duration @.050" intake, .437" lift and 228 duration @.050" exhaust?
This will be for the most part my main group of purchasers.
When I researched this I found that the difference in peak numbers was very minimal <5rwhp/ft lbs. I didn't feel the trade off would be worth it for the majority of people. But as I said before, I'm more than happy to change the grinds to give people what they want.

Lizard928

There have been a few who have changed for an S3 manifold to the S4. I have not, so I cannot do a comparison. However PorKen has been able to get more bhp from the 85/86 cars than the S4 at this time. I believe this has more to do with the S3 camshafts, and the better port velocity that would be seen on the S3 head design.
But I seem to be a lone wolf on the preference to the S3 head design vs the S4.

terry gt

MK The car is a 91GT ,so the stock cams were GT cams ,now collecting dust . 290 hp stock . 350+ with Colins cams ,and exhaust . Just like it says below . I am running high flow cats so it passes emission tests and two mufflers so it is nice and quiet , and need to change injectors . so there is still more HP left on the Table . I wanted the car to have a conservative tune .

jcorenman

Cam design is tricky stuff, something I know almost nothing about. What matters is how the engine is going to be used, and personal preferences. And the numbers are Bistromathics, they do not follow the rules of anything else in the universe-- reality and unreality collide on such a fundamental level that each becomes the other and anything is possible, within certain parameters.

The important thing about cams is not the duration and LSA (lobe separation angle), but when the various valve events take place in the combustion cycle-- intake opening and closing, exhaust opening and closing. (Same thing, just-- for me-- a more helpful way of looking at it).

Start from TDC, you've lit the air/fuel mixture on fire and created a bunch of pressure which is pushing the piston down to make power. Before it gets to the bottom you want to open the exhaust valve and release the pressure ("blowdown"), to start evacuating the combustion chamber and send a pressure wave down the exhaust-- which makes a nice sound and also helps evacuate the cylinder ("scavenging") in its wake. Open too early and you waste pressure, too late and you don't get the advantage of scavenging.

Exhaust continues until the piston is approaching TDC to begin the intake cycle, when you open the intake valve. For a moment both valves are open ("overlap"), and the hopefully-low pressure on the exhaust side helps to start the intake air moving. But pretty quickly you need to close the exhaust valve, and continue pulling in air/fuel from the intake. This gas keeps flowing via momentum until we begin compressing, at which point we need to close the intake valve before it all leaves. Close too early and we haven't packed as much air as we can, too late and the intake flow reverses. Four independent events, each optimized for max efficiency at some particular RPM. Overlap helps power but at low RPM's allows the gases to reverse their flow (reversion) which creates idle (and emission) problems.

This all gets distilled into a few numbers: intake and exhaust duration, the separation between the center of those (LSA), and valve lift. For cams with modest duration, optimizing the opening and closing with minimal overlap (for good idle) leads to a smaller LSA, e.g. S4 cams-- 106 LSA and relatively small duration.

GT cams have bigger duration but a larger LSA, so overlap is still modest-- but exhaust opens earlier, intake closes later, and they "breathe" better at higher RPM's. Devek B1 cams have significantly larger duration but a smaller LSA (more overlap), and they do struggle at idle and low RPMs-- but once RPMs are up "on the cam" they have good power and torque for mid/high RPMs. S3 cams have the same duration as GT (IIRC) but a larger LSA (114), and less overlap.

Colin, for his Stage-2 cams, wanted big duration but also minimal overlap for a good idle, which means a larger LSA (114) but also means that the exhaust opens earlier, and intake closes later. And moving that direction favors higher RPM's (Bistromath again).

What I found when I started modeling things (with Dynomation V) was that big duration with less overlap (e.g. larger LSA) did indeed produce good top-end power, but at the expense of the lower and mid-range RPMs. And this is where personal preference comes in: We wanted good performance across a broad range of RPM, and if we came out of a corner without downshifting then we wanted the car to pull hard, and continue pulling all the way up. GT cams do a good job of that, but you can get more without much compromise.

So what I did was spec out a bigger-than-GT cam with more lift and the same LSA of 110, which means the exhaust opens a bit earlier, a bit more overlap, and intake closes a bit later. And they fit "inside" Colins S2 cams, i.e. could be ground from S2 cams, and he did that for us. If the model is correct they have less power at 6000+ RPM but more everywhere else. They dyno at a little over 340 rwhp (SAE), about 330 tq, and over 250 tq from 2300 and up (stock GT, Devek L2 headers, Sharktuned). That's completely consistent with Terry's 350+ at the top end, but I suspect we have more low-to-mid-range power which suits us perfectly. Like I said, it is all about personal preference and we're completely happy.

And the quality of Colin's cams was excellent, we've got a little over 30K miles on them and "peeked" recently, and they look like new.

Cheers, Jim

Hilton

Terry, what size injectors do you have currently? 24lb?