L88 cam in L78?

[Seattle Sam]

Thanks for all the responses, I would pity the fool that puts an L88 cam into a 396 with cast iron exhaust! [img]/ubbthreads/images/graemlins/no.gif[/img] [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/no.gif[/img]

At least, I will be sticking with the 143 cam. My goal is to blueprint the motor when I pull it out, and do a few things to improve air flow (like port matching the manifolds). I plan to drive this car on the street a lot, but I would also like to see 12's on bias-ply tires with it..

Seriously, I started looking at the specs as listed in the Chevrolet by the numbers book, and the L88 and ZL1 have tons more duration than the L72/L78 cam, as well as more lift.

Lift and duration, per Chevrolet by the numbers 1965-69 These must be at 0.000" lift..

L72/78 cam, pn 3863143, lift .520 intake and exhaust, duration 316 degrees intake 302 degrees exhaust.
L88 cam, pn 3928909, lift .562 intake, .584 exhaust, duration 354 degr intake, 360 degr exhaust
ZL1 cam, pn 3959180, lift .579 intake, .620 exhaust, duration 354 degr intake, 360 degr exhaust

I do have a question about the duration of the 143 cam, Chev by the numbers lists duration (from .000 lift I assume) as 316 / 302, the aftermarket cam sellers list their "143" cams as having 240 deg of duration for both intake and exhaust(I assume this time at .050" lift). Does this mean that the 'ramp" in the factory cam for the exhaust side is steeper than the intake side? What do you think the intended effect was for this steeper ramp?

The other two (bigger) cams have more lift and more duration for exhaust over intake (at least at the baseline), what is the benefit of this configuration?

I think I have read that at high RPMs the open exhaust valve can create a low pressure zone within the cylinder, helping to draw in the intake charge before the piston starts the down stroke - is that it?

Thanks again,
-Sam

[JoeG]

You could lighten up your valve train with stainless valves and push rods.Or you could put the larger valves of the L-89 in your cast iron heads.--- JoeG----good choice 143 cam.for your application.

[JLerum]

Sam;

The reason you find more duration on the exhaust side of the cams are because only until recently cylinder heads big restrictions were the exhaust port. Chevy has a really good one for a stock head compaired to the other manufacturers. On a flow bench they would flow about 70% of the intake which for their time of design was really good. You will find that alot of the after market manufacturers are around 80%. To compensate for the lesser design you would hold the exhaust valve open longer to help it out. The kicker again is the longer you hold the valves open the more compression that is required to aid in cylinder filling. Keep in mind we are talking about a cam made for all out performance for the L-88 and ZL-1 cars. [img]/ubbthreads/images/graemlins/beers.gif[/img]

If you look at Buick stage 1 motors their exhaust is an extra 10 or 12 degrees. The 440-6 pak motors from Mopar also have an extra 10 degrees designed in. These are just a couple off the top of my head that I know of that com from the factory with a cam to aid the exhaust port.

JIM [img]/ubbthreads/images/graemlins/headbang.gif[/img]

Yes...........those cam numbers are off the lobe not at .050 which seems to be the standard today.

[COPO PETE]

With all due respect for Waynes car, the cam is is running is a made up cam. We really don't know much about it. If he had a GM L88 cam in it, it would peek around 6800 rpm or more with his manifolds. I shift a 7000 rpm and go through the end at around 7200 with my lesser manifolds. If I shift at a lesser rpm, the car slows down a lot. His lobe separation and ramp speeds must be quite different than a GM L88 shaft. He has obviously done his homework, but it would be real interesting to see what the car does with the GM shaft!
Peter

[GMH454]

Sam lots of good advice here. Don't use the L88.
Drove a A/Prod Vette car around a track once. Memorable experience. Car weighed 2700lbs blueprinted crate L-88 1974 vintage (cost around $540 for the short block in 1974 )Holley 850 factory intake 074 alloy heads, sewer sized side pipes and big 10" racing wheels and tyres.
Going around the track under 4000 rpm was very disappointing. Start pulling in the hi 5000s and all hell broke loose.
Very peaky. NO torque down low.
At around 5400 rpm it would break the tires loose in 3rd gear at around 120 mph.
A great racing legend best left on race tracks
Have fun.

[Born30YrsLate]

I'm still trying to figure out all this camshaft stuff...the question I have at this point is that the powerband for the 396/375 cam is 4000 rpm (2500-6500) but the powerband on the L88 cam is 2600 rpm (4400-7000)...what makes the powerband so short in the L88 cam? [img]/ubbthreads/images/graemlins/confused.gif[/img]
Also - the next motor that I build is going to be an L88...I will be using the 074 heads and 198 intake as well as all the other correct parts for this motor, now after reading about the L88 cam I'm thinking that I don't want to use factory cam!.....What is a good cam that I can use instead of the factory L88 cam for a good powerband up to 7000 rpm?....this car will be driven on the street mostly and that won't be very often and maybe a couple passes at the track. This motor is coming with the car I'm buying which is why I'm building this L88 and I'm looking to get at least 525 peak hp between 6500 and 7000 rpm out of it.
As a side note the motor will be backed up by an M22 and 4.56 posi and will have either 255/60R15 or 275/60R15 rear tires if that helps any?...... As always everyone's input is greatly appreciated...... [img]/ubbthreads/images/graemlins/beers.gif[/img]

[Chevy454]

Are you gonna run headers, Fred? Back in the day the hot ticket was to run the 143 cam (L-78/L-72) in the L-88s. 525hp shouldn't be too tough for an L-88.

[Born30YrsLate]

Rob - yup I'll be running headers that go into mid year corvette side pipes with the capability of running the headers open.
Another quick question - will the L78/L72 cam perform just as well as let's say a Comp Cams Magnum mechanical camshaft which has the same powerband range? I noticed that that Comp Cam has a significantly higher lift for the same rpm range?
Thanks again....... [img]/ubbthreads/images/graemlins/beers.gif[/img]

[Chevy454]

Fred:

Some quick guestions on the engine combo. What intake/carb are you gonna run (L-88 stuff?)? And this car will mainly be a street car, with a trip to the track once in a while?

The thing with the magnum muscle cam is there is just a tad more duration (242 vs. 250) on the exhaust side, but is identical on the intake, but it's got a TON more lift and a LOT tighter LSA (110). That LSA worries me, as that's a borderline race car spec. That means it's gonna have a choppy idle, and may have a vacuum problem. But, I'd give Comp a call and ask. Also something to consider is the more RPM you wanna run, the better your valvetrain has to be, and the more wear and tear on the engine. Just food for thought.

[JoeG]

Born30YRSLate, Just some seat of the pants info that was tried aways back,
With the 143 cam you get very good street response with a 456/410 of course the steeper the gear the better the low end response with the 143 cam. The higher the lift and close LSA ,you are going to have to stay with 456/488 to give you that acceptable low end response.Bottomline as everyone has more or less agreed the 143 is an excellent compromise between street and strip.Listen to what the fellas are saying you won't be dissappointed,-----if you are only going to make an occasional trip to the track and mainly street drive it. .Just some input,-----JoeG [img]/ubbthreads/images/graemlins/[/img]