DeWolf

Hi All,
Doing an intake refresh and have the valve covers off as well for powder coating and looking at the cams and thinking it might be a good time to pull the cams and get them reground. I am going to Porkenize the motor and X pipe, FPR etc and would like the car to sound nice and lumpy. Anybody recommend a grind for decent top end power and a nice lumpy idle. Something like this at idle


Cheers
Scott

FredR

Scott,

Re-grinding a set of S3 cams is not a small undertaking and for sure it is not a cheap upgrade option- maybe John Gill or Hilton can offer you good advice in that regard down under.

Whether or not a re-grind will change your exhaust note to your delectation remains to be seen- I doubt it but..? In my experience exhaust sounds are very subjective and more often than not you do not really know how they are going to turn out until after the fact. Even listening to recordings does not replicate the real thing in my opinion- just gives you some idea.

As I am aware exhaust note is more a function of system acoustics. To give you some idea take a look at Carl's website and the video of his exhaust system for the 87 to 95 models.
http://www.928motorsports.com/productdemos.php

His system has a muffler that can be reversed to give a different set of acoustics . Roger also offers an exhaust system but no idea if he has a video demo on line. doing other things like an x-pipe will also make some difference.

If you really want to regrind the S3 cams for whatever reason it has been done previously using lash caps on the reduced base circle but that was racing performance driven and Jim Morton is your man on that one not to mention others who may have done so. However I would not be too surprised if the re-grind would cost you more than a set of Colin's cams for instance. Then of course if you do go for an upgrade of the cam profile what price the tune of Ken's chips?

Rgds

Fred

The Forgotten On

I would do all of the other upgrades you are considering before a regrind to make absolutely sure it is worth it to you. As said above, it is no small undertaking.

JakeS2

My 2c. Do what you do, but invest into wbO2, ST2 and PEMs from JDS.

docmirror

I looked into cam grinds back when I had a S3 cam modified for my GT. I figured once I had them out, I should check into it. Here's what I found. You can call any major cam grinder, tell them you have a SBC, and what you want to do, they will ask about your intake and FI, and advise you because there's millions of hours of engineering and testing behind the Chebby engine, intakes, C/R, cams, valve sizes, ports, chambers, etc. There is almost NO engineering done on aftermarket cams for the 928 engine. And - the few people who have done that work aren't sharing for free. I'm not blaming them, the engineering of the cam/intake geometry/port etc is complex and costly.

So, you don't just wing it and start grinding. There's other issues too. The 928 uses a double spring, and you might face coil bind. Also the lifter question, concerning weight and hyd adj range. Of course, duration and timing come in to play as well.

I'm guessing again from my investigation long ago that you could sneak in a little duration and get a lumpy idle, and lousy mid-range performance at a slight gain in very top end, but then again, you might make 80% of the useable range of RPM much worse to make 20% of the unuseable range of RPM better(5300-6100). Anyway, when I looked at it, and saw the already ugly amount of combustion products in my intakes, I shied away from trying anything.

YMMV, objects in mirror, contents have settled and may cause **** leakage.

mark kibort

thats not really a cam sound, its more the exhaust and its very raspy in my opinion. a simple two in to one pipe with a rear borla will give you a very nice song.

mark kibort

I think many have increased hp in the "unusable range" (now that is funny , considering thats where all the HP is located as well as the "full song" of the exhaust note) if you are operating below 4000rpm, that isn't where there is any HP to make you go! and most cams that we have seen dont hurt anything below 4500rpm which is exactly where you want all the HP to be.. 4500 to 6500rpm... i have the S3 cam, which is near the same as the GT cam and it works well. mod'ing it to make more overlap would give more a lopy sound.
1mm grind off the base circle has been done and doesnt hurt much of anything, only gains.
Scot has the devek B1 cams and everyone LOVES the sound of his car and his idle. a lot better than the car in the video.

docmirror

Well, since you want to snark at me after I posted the YMMV disclaimer, I'd like to see a show of hands of drivers that tootle around between 5300-6200. Bueller? Bueller? Bueller? Yeah, I thought so. The OP mentions his desire for a lopey idle, so you come on with your obtuse racing crapola just to be a ****. Most cars have a 2.20 or 2.54 rear end, so 2nd gear at redline will be a speeding ticket in almost all locations.

Did you do those 10-20,000 of hours of trial and error with the S3 cams? No? So - your opinion on what changes to make are about as useful as EF(equine feces). got a dyno chart? You prolly have ONE dyno chart from a diff cam. hehehehhe.....

olmann

Where is a good place to use to modify the S3 cams for S4 use?