NewbVetteGuy

Not that I plan to actually do any of these things, but I am curious whether any of these cheap L82 performance "hacks" would actually be effective or not.


IF you've already addressed the horrible exhaust and at least gone with no cat, true dual exhaust (and ideally long tube headers), how much would any of the below items help get more power out of an L82?

• 1.6 ratio stamped rockers or 1.6 roller rockers -The lift on the stock L82 cam is pretty low; I know the old heads don't flow well but extra lift has to help, right? -how much do you think this would help?
• Increased CR via thin FelPro 0.015" gaskets; vs. thick 0.040" gaskets static compression ratio improves by 0.5 CR points (no idea how thick the stock L82 heads were) -I've been told that the L82 cam likes more CR; for the price of 2 new head gaskets you can get another 1/2 point-What would that get you?
• Adjusting CAM timing- the L82 cam at least in my 79 is by default retarded by 2 or 4 degrees (I never know whetherr this is CAM degrees or crank degrees) -as I've been playing with dynamic CR calculators, it's become apparant that adjustments to cam timing can rapidly increase dynamic compression ratio- this is a "Free" increase but you have to choose between more torque (and detonation risk) and more HP at high RPMs -free's nice, though

I have heard that the stock heads are shockingly detonation prone so swapping both the head gasket and trying to adjust Dynamic CR upward using CAM timing seems like a pretty risky combination, but I am curious about theoretical gains if you could keep detonation at bay.



Adam

NewbVetteGuy

On the first item, the L82 cam lift is 0.450/0.460 @ 0.050" lift so if I'm doing this right and take those #'s and multiply them by 1.2, I get 0.540"/ 0.552" @ 0.050"; is that going to help these ancient heads?


Adam

GOSFAST

Hi Adam, you're going to see another .030" lift from the rocker change. On the intakes this will go to .480".

Save your money, take another route!

We sell a high number of those OEM L-82 cams during any given year to people like yourself looking for minor HP gains, it is one good street cam for all-around performance.

Thanks, Gary in N.Y.

P.S. On the dyno with the stock-appearing crowd (and keeping the 350" platform, no up-stroke) and using that very cam, we can get in the 400 HP neighborhood with the "right" parts.

Jebbysan

Nope......take the .450/460 divide it by the current ratio = .300/.306
Dividing it gives you the cam lobe lift.
Now multiply by 1.6= .480/.490

GM stamped rockers are horrible......like 1.4/1.45 ratio......A set of 1.6 roller tips is a good deal. Skip the Elgin 1.6 cheater rockers.

Good luck,
Jebby

99 Black Bird TA

Adam, this is a decent article and discusses the impact of raising compression, it might be of interest.

http://www.hotrod.com/events/coverag...ression-ratio/

My opinion for what It's worth : It's a lot of work to replace two head gaskets for half a point of compression quick would yield less than a 4% power increase on a near stock L82. I suspect if 240hp flywheel L82 would gain 10 fly wheel at most if no other changes were made. I would to a proven matched top end package for at least a 100+ hp gain if pulling the heads.

NewbVetteGuy

Again, I want to re-iterate that there's no way I'm doing this, but I am curious about how much increase these items could get you in THEORY. (only to increase my understanding; this is a thought experiment only).


99 Black Bird TA- thanks for that; that's exactly the type of information I'm trying to understand.

So about a 4% power increase or roughly 10 FW HP; maybe 6 RWHP with an automatic trans. For the head gasket swap. -I'm taking that to mean that if you adjusted the cam timing to increase your dynamic CR another 1/2 CR point, you'd also just get roughly another 10 FW HP so that actually kills two birds with one stone. (But adjusting the CAM timing is a "free" 10 HP and way lower labor than a head gasket replacement so possibly "worth it", right?




Great to get the "proper" adjusted lift numbers with a roller / rocker ratio bump to 1.6:1; but what do you guys think that would do perf wise with the stock heads?

Anyone have flow #'s for the stock heads for the before and after lift #'s to help with said estimate?


Adam

Jebbysan

Leave the cam alone and buy a pair of used Iron Eagle Dart in a 64cc chamber with a nice intake and carb would be a fun package......
Put a 1.6 rocker on those heads.......
Boost the CR and get a much better flowing unit at the same time....
This could yield you 50-60 horsepower easily....

Jebby

NewbVetteGuy

I don't know why, but I think it's really interesting to consider what perf you could just squeeze out of an L82 with a bone stock motor (the exhaust is horrible and must be replaced at all costs).

-Again, I'm NOT in the "keep it stock forever" camp at all and I'm NOT going to be doing any of this stuff, but I think there's something to be learned in exploring what COULD be done with the stock block, intake, heads, and cam to maximize power.


Adam

jb78L-82

FWIW its worth, my OEM L-82 all stock 4 speed but 1.52 roller tipped rockers with shorty headers and 2.5 duals with a weak compression #6 cylinder did 233 RWHP on a dynojet with no emissions which is about 310 GROSS HP. Forum member, Karol, with a similar setup as mine, OEM components (100k miles on L-82) except cam of unknown origin with stock 882 heads, no headers but 2.5 duals did 248 RWHP on the same dyno (325 gross HP, same as 71 LT-1 with 330 gross HP). The L-82 is VERY similar to the LT-1 330 GROSS HP C3's....pretty stout for a 70's V8. 1.6 RR, LTH headers, and 2.5 duals will net you noticeable HP....

NewbVetteGuy

Yep, I've seen you quote those impressive and informative numbers elsewhere.

I'm curious how far one could go with 0.015" felpro gaskets and 1.6 roller rockers. -A bit more airflow and a bit more CR. Sounds like the 1/2pt CR would only net you another 7 HP with a manual trans, maybe.


It just goes to show that the change in the way HP was measured, the tendency to underrate at this particular point in time, and the horrible exhaust have all really combined to unfairly destroy the reputation of the motors from this era. They really weren't bad; the exhaust was terrible and the heads by modern standards pretty poor, too, but they really did far better than the official on-paper numbers would lead you to believe.

The L48 I find it harder to defend quite so much, though and won't try.

Adam

gkull

When I first bought my L-82 I didn't have a lot of money for major mods. So my first changes were to rotating and car weight. Lighter 8.5 inch american racing wheels, spare carrier removal, shift kitted and valve body mods, no emission, headers and free flowing true duals, SS flex fan, timing , and open element air cleaner.

I don't think that compression goes up much with a gasket change.

Later on I did heads, cam and 1.6 crane roller tips

99 Black Bird TA

I wouldn't discount any 350 - they all respond to hot rodding.

The L48's basically responds to the same mod's as the L82. Once mod'd to the same level since both are 350's they are pretty similar in power.

Back in the early 80's my 72 had it's orginal base engine (L46 or ZQ3) with headers & cam it and easily beat several stock/near stock L82 corvettes (both auto's and 4 speeds) from a roll or stop light to stop light. Pulling 3 to 4+ car lengths in most cases. Each of the L82 owners made ugly faces getting shown up by a base model L46/ZQ3 - which was priceless at the time to me.

NewbVetteGuy

Every time I use a compression calculator and swap the gasket size from an 0.040" to an 0.015", it shows a CR increase of 1/2 a point.

-I was just as shocked but I find a lot of posts here on CF saying the same thing.



Adam

7t9l82

I've seen more than one corvette run in the 12 second range with that same so called low lift cam. The extra lift from 1.6 rockers and a set of better heads with 64 cc chambers have a big impact.I've done more than that to mine but my shortblock is stock and I make a laughingstock out of c5 corvettes,not that I think they are all that much. People underestimate old stuff and it's abilities all the time but it's just silly.

gkull

I just ran some calcs. I'm not sure of the negative cc on a dished L-82 or the exact head cc, but using the -.025 piston to deck you are gaining @.4 C/r going from compressed .038 to .015 gasket.

You only get up to about 9 c/r

The13Bats

you guys must all have more toad pelts than I do adding heads isn't cheap in my world....

But hey I got as question no other tweak or mod what will the 1.6 rockers do by themselves?

AirBusPilot

I added 1.6 rockers to a stock 85' vette.

*** dyno confirmed 20hp. You could feel it.

7t9l82

L-82's had flat top pistons not dished.

NewbVetteGuy

The "flat top" pistons still have a 5cc relief, though, right?

And started with 9:1 CR, no?


Adam

bluedawg

GM's stamped rockers are 1.52 to 1.