GregBBRD

Web cams? Not today, thanks.

RyanPerrella

yeah i dont think the seller has even tried them yet..... not sure i would wanna pay for that development

docmirror

The LH map is also different on the GT as the fuel profile fits the cam and C/R. You can get 85/86 cams, and have the left exhaust modified to fit the head. Once you have that, a bit of surfacing on the head will bump your C/R to suit the cam and the LH/EZK.

I have the rods out of my GT engine, and they do not look like forged units, although it could be. the S4 rods look exactly like the GT ones, so either I have a set of forged, or the GT ones are cast. By the porosity, and the flash work, I would say that all S4/GT rods are cast(or they could all be forged too).

RyanPerrella

sinter forged is it?

I dont think they are your typical forged from billet either, but they are a stronger rod then the ones found in the S4, although the S4 may have gotten the same rods in 91.... who knows

blown 87

I wish some one had a definitive answer to which, if any, of the 928 rods were forged.

Mrmerlin

89 and newer heads also have the longer bolts needed due to the heads having thicker bosses at the head bolts

blown 87

I think the 89 S4 heads have the thicker bolt bosses that take the longer bolts also.

ptuomov

Based on the heads that I have seen, all heads with casting revision .2R or later have the taller bolt bosses, whether they are on a GT or S4 engine.

Casting revision .5R (i.e., GTS) heads also have the extra cooling passages on the exhaust side.

I have not been able to find any difference between .2R and .4R heads that I now own. If someone knows what the difference is, please let me know.

Vilhuer

These were also used in both '91 GT and S4.

Have you measured port size at intake side? IIRR early GT heads had hand modified ports after casting for better match up with larger intake. Later on heads might have been directly cast with larger ports.

blown 87

My 87 has the 1R heads and the 89 has the 2R heads.
If I have to do another set of heads it will be the 2R heads that go on my car.

I have also heard you can do a cooling mod to the 2R heads that make them close to the GTS heads.

docmirror

Well, all I can tell you is that the rods I got from Sterling to replace mine were inspected carefully by me and the machinist. They are identical in material and machining. I wouldn't have used them in my engine if they were different. I had my recip masses balanced carefully, and we ground on the old rod a bit as well to see if the metal looked the same, and it did. Not scientific, but I'm comfy with the results.

I'd be much more worried about the top end of the engine matching GT specs.

AO

I know the GT's received tolerance group 1 pistons (not sure if all S4's did or not). Also, I talking with the mad scietist up in Green Bay, he said the rings in the GT are different than the S4 rings - although there is no different part number. He said they're more like a 951 ring which is more pliable vs. brittle. I can't confirm 100%, but he know's his stuff.

Also, I believe the intake uses a slighly different casting vs. the S4. But the key is the cams.

namasgt

Michael
I think grinding cams to GT specs will cost alot. one of my friends payed around 3000 $ to get the 86 cams to GT specs.
I know you sayed buying a GT engine is not an option but $5500 is not bad for a 89 GT engine (are these the blue printed ones?). Instead of spending money and time to get the S4 engine to GT specs buying the GT engine might be better and then you can sell the S4 engine. It might cost the same going both ways.

Vilhuer

All GT engine do not have tolerance 1 pistons. Neither do S4 engines. There are 0 and 2 engines also. They are rarer than group 1 engines like always but they do exist.

Easiest option for GT like performance is modified S3 cams with 0.5mm reduction in base lobe diameter. Those should give more than 330 DIN hp out of any healthy othervise stock S4 engine. Add X-over and 350+ should be easy.

RicerSchnitzzle

Why stop at GT specs? Just reducing the base circle on S4 cams at $100 a stick can yield nice results. Seems like if something is not overly complicated and expensive it just can't work on our cars. Then someone goes and does something simple, gets results and then is chastised for not getting enough of a result, or the max possible benefit. We often forget the return on investment argument. $400 for cam grinds will yield a nice improvement. Is it worth the extra $3500 for that extra 1 to 2%? Not in my book.

As an example, I put JME cams in my Euro S hybrid. Got a nice increase for $1300. Just got my spare Euro S cams back from Delta. Just a base circle reduction and yet for $200 I have more intake lift (.513 vs .503) and about the same duration as the $1300 cams? As good? Maybe not. But good enough and better than stock S cams? Hell Yeah! $900 difference buys a lot of Taco Bell and Gas.