tomboyea123

Im in the process of putting a gts 5 speed drivetrain in my 89 gt.The car will also have a Tim murphy intercooled kit on it and I plan on having 8 to 10 lbs of boost .I will drive the car in colorado at around 9000 ft. My question is wheather I should stick with the gts cams or put in my 89 gt cams sinse I already have them.I am also interested in lift and duration numbers for both sets as well as there centerlines and overlap.It is my understanding that the tighter the centerline( the smaller the number)will be less user friendly for the blower and will also have a choppier lope.I have also heard that a moderate amount of lift is a good thing with blowers.I would also be interested in reliability over the long run between the two camsets. My quess is that the gt cams would really wake up the gts motor and would be superior in this application.Thanks in advance to all!

Imo000

Get the car running and drive it for few miles, then perhaps change the cams. This way you run less of a chance of something going wrong with the engine swap. As a rule of thumb, I always change one thing at a time, this way I can see what it does. If you do a bunch and run into a problem, it will be hell trying to figure out what is causing the problem.

As for the cams, sorry don't have experience with that.

Rick Carter

Lag has talked about this before. You may want to consider keeping the GTS intake cams and perhaps use the GT exhaust cams since you have them.

Dynamic CR revisited

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In Feb 2004 Lagavulin had posted on this with some interesting thoughts, especially regararding boost. I found this site where you plug in the values and see the projected effective CR.


http://www.wallaceracing.com/dynamic-cr.php

For a 5 liter the bore is 100mm/3.927", stroke is 78.9mm/3.1063", I don't remember the rod length but it is close to 5.9". S4 static CR is about 10:1 and 85/86 static CR is about 9.55:1.
Cam specs, intake closes ABDC in crank degrees:

36 degrees ABDC – S4
42 degrees ABDC - GT
50 degrees ABDC – 85-86
61 degrees ABDC – GTS

Using my 85 as an example at 0' the dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 7 PSI is 8.35 :1.
An S4 with the same boost level would be at 9.35:1 and a GT with 10:1 static CR at the same boost level would be at 9.11:1 dynamic CR.

I didn't plug in GTS values because I don't remember the stroke and rod lengths off the top of my head. Lag had commented before that GTS intake and 85/86 exhaust cams should be a good combo for boosted engines.

What these calculations don't address are the effects of boost regarding heat and detonation. I would like to have a formula to calculate charge temps effect on detonation.
__________________
Rick
85 32v modified - 366 RWHP/352 RWTQ

It costs a lot to repent and follow Jesus, it costs a lot more not to do so.

ZEUS+

http://www.928developments.com/stree...t_packages.htm

mark kibort

yes, the GT cams are better (and so are the 85 cams) best lift and best duration. Do a search ,and the GTS vs GT cam spec can be found

MK

Imo000

Does this apply for a boosted engine too?

Rick Carter

Lag had commented before that GTS intake and 85/86 exhaust cams should be a good combo for boosted engines.

Ispeed

Duuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuude................... What the hell happened to your '89 GT engine???? I don't know the story, was it boost related, or leanness that killed it?
edit: saw the cracked head thread. Sorry to hear it.

sweanders

Do you have hearsay or facts to back it up?

Rick Carter

http://www.wallaceracing.com/dynamic-cr.php

Of the variables, the most important is cam timing which has a dramatic effect on your "dynamic" as opposed to your static compression ratio. The more "overlap" your cam has, the lower your "actual" as opposed to your static compression ratio will be. This is one area you can easily change.

This is for intake, on exhaust it is more hearsay as I am quoting Lag.

tomboyea123

Thanks all! No, the 89 gt motors death was not boost related, I let the engine get hot and didnt watch my gadges.What a waste!Does anyone know the actual lift and duration #s of the gts cams.I cant find them .Is it a big job to switch cam sets if a waterpump tb job is being done? Thanks again.

drnick

i have posted with the numbers for my GTS cams before after they were indexed here in the uk. the GT cams produce more power n/a and you would expect this to translate to boosted as well, no?

Rick Carter

Yes for the same boost level. In theory, since no one AFAIK has done it, you should be able to run higher boost safely with GTS intake cams; see link to Wallace Racing in above post.

the flyin' scotsman

This do:

SwayBar

Since the engine will have a blower on a 10.4:1 engine, by all means keep the GTS camshafts!

This is correct.
Yes and no.

YES in that as one will get better numbers NA (..normally aspirated), and likewise, one will get proportionally better numbers with the supercharger installed.

But NO, I would not recommend them in this situation because the GTS engine has a higher static compression ratio of 10.4:1. And as Rick has pointed out, combining that high static compression ratio with the GT cams will produce a much higher dynamic compression ratio than with the stock GTS cams, and the difference is truly enormous as far as the engine is concerned.

The GTS intake is held open much longer after-bottom-dead-center than any of the other 32v cams. What that means is that cylinder pressure is 'bled off' through the still-open intake valves as the piston rises in the bore on the compression stroke, lessening the available mechanical compression as it does so, and giving one greater headroom when it comes to avoiding detonation.

Comparitively, the GT intake closes much sooner, allowing mechanical compression to commence much sooner, thus generating greater cylinder pressure. On an engine with a static compression ratio of 10.4:1 with a blower on it, the margin of safety is small to say the least.

Again, as Rick has pointed out, it's not about static compression ratio, it's all about the engine's dynamic compression ratio, something which the GT camshafts raises MUCH higher than the blower-friendly GTS camshafts, and ESPECIALLY on a engine whose static compression ratio is 10.4:1.

There is no doubt, as noted above, that the GTS camshafts will be much more reliable, period.

Try to keep in mind that your car is going to be STUPID FAST with either camshaft installed, and I'd wager you wouldn't be able to tell the difference one way or the other since it will have so much power. So set the car up so that it will be as reliable as humanly possible which means keeping the GTS camshafts in it, and you'll be MUCH happier in the long run.

If you were going to keep the motor normally aspirated, then without a doubt, pop in the GT camshafts.