Well, it looks like the long duration GTS cams decompress the 5 liter motor too much to yield any net benefit despite the higher lift (and longer duration). I've attached my dyno from yesterday showing a pull of 250.6hp/248ft.lbs. I attached my previous dynosheet from the same dyno which shows a pull of 275.66hp/292.07ft lbs with the stock cams. These numbers are not corrected.

GTS CAMS


S4 CAMS


I believe Lag posted some extrapolations showing an S4 with GTS cams would have a static C/R of about 8.3:1. (If someone can post the link to the thread I'm referring to, it would be much appreciated, I can't find it). I was thinking that even with the miller cycle effect of the long duration on the exhaust cam, the extra lift would more than compensate for it. Aparently not. So what next? I think the GTS exhaust cam is the true culprit here. I'm going to run the S4 exhaust cam with the GTS intake and see where I wind up. Louie ran some sims of this set up on one of his dyno programs and it looks to be a healthy combo. We'll see.


-Adam

 

Adam,

I am interested in your results of this combo, as I plan on doing the same thing with my blown SC rebuild......

 

How do 85/86 32V cams compare with the GTS cams in lift and duration? What about GTS intake, and 8532V Exhaust - or does this get us back the problem in the dyno above?

 

Try to get the corrected charts, or better yet, the dyno data files for both runs if you can. The dyno computer usually keeps the data files all stored on it's hard drive.

 

z,

I do have the data file for the S4 cams. The GTS is still on their dyno computer, which is a dinosaur. Tom M. was able to transfer the files from our prior dyno days onto a 3.5" floppy. I actually tried to get him to explain to me how he did it while I was there, unfortunately, I don't speak DOS. Next time Tom is in town, we'll make the run and download the info. I would really like to be able to put the graph on the RunViewer program. It's odd to me that at first glance, the power curve doesn't really look that different, it looks like I just lost 20hp across the board. It would be a little easier to see if I could get them both on the same graph.

 

If for some reason you can't get the data files from the dyno computer, at least get a printout of the GTS cam run that uses the corrected numbers. With that, the two charts can be sized so that the scales are the same and overlayed with a graphics program. It's not as convienient to compare them that way, but it's still better than trying to put one on top of the other, holding them up to a light, and trying to line them up that way. BTDT

 

Ar ethe gts cams timed correctly....should have power peak at lower rpm than stock s4 cams
Marc

 

good question marc, watching this thread with interest.

 

Another interesting fact...if you look closely at the graphs...notice the second torque peak....very much like a GT..higher second peak...occurred in both graphs...with S4 cams and the GTS cams....
At first we thought it was the GT brain that Adam was running..but when that went south..and he got a rebuilt one..(stock S4)...it still showed the same...

so..interesting...wonder what his engine really is?? ;-)

Keep in mind....replacement block with no stamped engine block numbers..

Later,
Tom

 

Why not advance the GTS intake and fit a GT exhaust in its standard position? THis will give you overlap and close the intake sooner to build pressure in the chamber. The S4 and GTS exhaust really suck compared to the GT. I think that would be a really interesting experiment.

 

By advancing I mean by one tooth on the GTS cam.

 

Do you mean advancing the GTS intake cam one tooth on the chain? That's a whole lot of advance...........

Dave

 

Marc wrote:

I did my best to run the cams straight up. I was really tempted to advance them a bit, but wanted to get the baseline reading with no advance or retard. I had mentioned in another thread that I would be re-measuring the timing before dropping in the S4 exhaust cams just to make sure they "stayed" at straight up. If they aren't, I'll re-time and re-dyno.

Greg Gray wrote:
I agree with Dave that advancing the cam on the chain is a lot of adjustment. I really wonder what dialing in some overlap would do to one of these motors. I don't think it would be a good thing, seems like it would have the potential to tweak out the engine management system. Definitely could make passing emissions difficult. I really like the cut of the GTS cams, if only we could individually dial in each stick. It's unfortunate that an adjustable cam chain gear hasn't been successfully devised, that would probably be one of the most beneficial mods to our motors. You would only need it on one stick to make it work. Any takers? I'd be happy to run the GT exhaust cam if anyone wants to donate/lend one to the cause. I am very curious to see what the S4 exhaust cam does, it looked really good on the sims with the stroker motor.

Tom wrote:
Not true any more Tom. Last time both our cars were at the shop, I did a little swap. Now you don't have any engine block numbers..... and a taller first torque peak....

 

what happened to stirlings variocam system? did he abandon this?

 

ok, i see that stirling went to custom billet cams eventualy although it seems there may not have been anything wrong with the welded 968 type sprocket he trialed first. apart from the sprocket there dosent seem that much to it mechanicaly - 968 valve covers, an extra mounting point on the head and an electronic control unit. the whole thing would rest on the integrity of re-engineering the camshaft sprocket.