I wish that were true but the difference between the two cams is that S3 centerline is 8º retarded from the GT centerline. Each sprocket on the intake cam is going to advance or retard the cam timing by 19º, so it's too big a jump. As you know the S3 & GT exhaust cams are identical.

So intake centerlines are (deg ATDC):

GT: 112.5
S3: 120.5
S3-1t: 101.6

Lobe separation angles:

GT: 110.0
S3: 114.0
S3-1t: 104.5

The S3-1tooth LSA is pretty close to the 968 when the Variocam is in intake advance mode. You'd probably have to run race gas unless you can get some cc out of the combustion chamber. I'd be curious to see how this runs but this setup presents more problems than the GTS.

-Dennis

 

Thanx Errka :-)

 

I'm stuck with low end torque then.

 

Interesting conversation. I have nothing to add, just wanted to say it's very interesting.

 

Appreciate the input Louie. As mentioned I'm going back in to revert to stock timing if only to ensure even consistant compression. Once satisfied I'll go back to playing with Kens most excellent tool.

 

Is there any possibilty of 'slotting' the cam gears giving a multitude of adjustment?

Back in the m/cycle racing days we'd have bolt on sprockets where the cams were threaded and the sprockets slotted to allow variable cam timing.

 

I have a set of gts cams and gt cams. What set or combination of theses cams would work best in my murph stage 3 gts engine?

 

I believe Adam B is still running the GTS/S4 cam combo on his 88S4. Don't remember the exact results but it seems loss of power at bottom end but better breather/power at the top end.?...Adam..correct me if I'm wrong..


Later,
Tom
89GT
82 Track car in progress

 

Dennis,
Check with Adam Birnbaum on the exact effects of using GTS cams in his S4, then swapping in the S4 exhaust cams and leaving the GTS intake cams. AFAIK, that is the setup he's still running. I believe that swapping the GTS cams for the S4 cams in his S4 gave the usual good low end torque curve the GTS is noted for , but like the GTS it pretty much died above 4500. Swapping back to the S4 exhaust cam may have lowered the low end torque a bit, but still better than stock S4 troque, and it was also better than stock S4 power on the top end. Adam has the dyno graphs and they are probably posted somewhere too. My only first hand experience is to install GT cams in a GTS and along with X pipe exhaust mod get almost 50 hp increase with more low end than the stock GTS and way better top end. Above 4500 it drove like it was was coming alive. Here is a dyno graph of the difference. I can't remember if this dyno run was after we found the mouse nest (packed full of fiberglass insulation) in the intake tubes or before. There was no mouse nest with the stock GTS runs. The stock GTS power curve is about normal for a GTS.

https://rennlist.com/forums/attachme...1&d=1200421088
garthGTSdynograph.pdf

 

Wow, good information here. However, Dennis, we are talking about advancing the intake cams 20 degrees (40 crank degrees ) if you are skipping one tooth on the chain.

mk

 

You meant cam sprocket in both paragraphs. In theory, it could be done, most likely with a split sprocket that would be bolted together as well as to the cam. My CBXs have two piece cams with a one-piece sprocket bolted over the end of one cam half, with the cam halves joined by Oldham joints.

 

ah yes Bill; I got my Laverda's mixed with my Ducati's.

IIRC the CBX crank had a chain to the intake cam with an additional hy-vo chain (sp) between the intake and exhaust. I also recall the split cams for both intake and exhaust; essentially 4 cams. I rebuilt 2 CBX engines in my time and still have the nightmares.

 

I did this years ago on a '78 Honda 750 and the performance gains were significant. It was all a part of retiming the engine to get the cams to true top dead center. The theory was that when the engines were built they estimated TDC. Amazed at what a couple of degrees could do.

I have 2 or 3 sets of 85-86 cams on the shelf in my shop for those that might be interested.

 

Yep, they are a bit of a nightmare. I had one of mine apart because several of the long studs pulled out of the aluminum engine case, requiring 16 Time-Serts. That was fun - NOT!

 

Guys I have tried many different engine and cam combos, and comments as follows:

1. GTS cams in a 5 litre 32 valve worked well, when sharktuned, and gave improved mod range acceleration. Top end about the same+/-5bhp. This engine I then supercharged and works well.

2. Advance inlet 1 tooth or advance within cam timing slot - moved the power band and seemed to show some increases at certain rpm, but at the expense of flat spots and losses elsewhere. I never dynoed/performance tested it as it didn't seem there was much to gain overall;

3. GT cams into a GTS I have done several times - the power increase on their own was more in the 10-15bhp range. Sound like most of the gains Louie saw were from the exhaust/headers or the combination with.

4. I haven't tried it yet but I think that keeping the GTS inlets in a GTS and just changing the exhaust cams to GT may well be the best combo for that engine overall and after sharktuning. Haven't had chance to try that yet, but if anyone has, I would be interested in the results on the 5.4l

5. I've rebuilt many 32 valve engines to WSM spec and never noticed any appreciable difference between banks when hot or cold?

Adrian