JakeL

Hi Guys -

First post in a long time. Hoping you guys will find this one interesting.

I recently bought back my '97 Corvette, and am planning on doing some road racing.

The previous owner had a 13.5:1 LS2 (6.0L) put in the car. It was a dedicated solo (autocross) car, so the low displacement and high compression was to satisfy rules/weight limits.

The cam in the engine is a 236/244, .605/.625, 113LSA on 111ICL. We think. The original builder is out of business and I can't find anybody that knows anything about what went into the engine, including the previous owner. (not a "numbers guy"). The engine has lots of goodies on it, and makes just shy of 500rwhp on a Mustang dyno. 100 octane only tune. It is possible that it's a Comp grind with XE-R lobes, but I don't find anything in their catalog that quite matches up. Engine was built in the 2006 ballpark.

So, I have two questions:

1.) Is there a way of measuring/verifying what the cam specs are without actually pulling it out and measuring? e.g. can a dial indicator and degree wheel get you close enough?

In particular, I want to know about the cam lobes. Since the car is going to be road raced, I need a cam that is not quite so extreme (less than .600 lift is recommended), unless somehow these lobes are unusually kind on valve springs.

2.) Second question is, in the likely event that we replace the cam, what are some hallmarks I need to be looking for (or looking to avoid) in a cam for a high compression motor such as this? For example, I read in some of the search results here that generally, a bit more overlap will help prevent unduly high cylinder pressures and resulting knock.

There's no problem with the car or the cam today, so one could even do the same profile with just a bit less lift and be done with it I suppose.

So, curious to see what you folks might have to say about this situation, some example replacement cam spec recs (.575-.600 lift), and so on.

Cheers all,

-Jake

A.R. Shale Targa

iTrader: (2)

What I'd do in your situation is get a baseline chassis dyno number and then give all the known combo specs to a camshaft guy. Hell call a bunch of them from Geoff Skinner @EPS, Kip Fabre of Cammotion, Martin Smallwood of Tick, and Brian Tooley. Some of the newer lobe profiles may not make any more peak power but will be more stable throughout the entire power band, giving you more average torque.
Back in the late nineties early otts camshaft companies were retrofitting other lobe profile to the unique sized camshaft blanks. Then some GEN III specific lobes came out and over the years more and more aggressive flanks quickly outran the beehive spring capabilities, and have eventually found the limits of even good duals as well as rocker bearings, push rods, and lifters. Now the "lots more gooder" trend is smoother controlled aggressive lobe's.
Some camshaft guys seem to prefer more overlap and others less. I guess it depends more on the overall package of parts and intended usage. Lately it appears that many of them are keeping the intake lift at or just over .600 with a stock type rocker and backing the exhaust down to .570-.580 range. Apparently most exhaust ports seem to taper off after .550 and don't really benefit from all the lift like the intake side.
I be really curious to see if any of those fellas mentioned could find you a solid 25 more avg. Ft/lbs with a matched camshaft, lifter, push rod, spring combo.

Sales@Tick

iTrader: (3)

In "general", camshafts for high compression engines will have later IC events and earlier EO events than camshafts for low compression engines.

You want to avoid pumping losses on the intake side from closing the intake valve too early and also to avoid detonation.

With elevated cylinder pressure on the power stroke with a high compression engine, more work is being put to the crank than in a low compression engine. This allows an earlier EO event which can help carry power to higher engine speeds and make more HP without losing large amounts of power at lower engine speeds.

As far as the exhaust lobe deal goes that AR Shale mentioned, it has more to do with pressures in the cylinder vs. pressures in the exhaust port than exhaust port flow at different lifts.

JakeL

much appreciated on the responses guys. I'll keep working at it and dig in a bit further when I can.

Spoke with Comp over the weekend, who couldn't find the exact grind with the meager info I had, but it did at least appear that it's likely this cam is a Comp cam with XE-R lobes. Evidently they scribe a serial number on the back of each cam, so if I go through the effort of pulling the cam I can give them that serial number and then I'll actually know what I'm dealing with...and if it should go back in the car thereafter or not...

Cheers,

-Jake

Camaro99SS

iTrader: (4)

A cam with a wider LSA for a more broad, less peaky powerband for road racing. The later IC points on a 114 LSA vs a 112LSA will bleed off allitle more cylinder pressure to help keep detonation at bay. It also means less overlap and a smoother idle.

Another guy to turn to for cam spec help is Patrick G on here, one of the best tuners in the country.


Jason