Maybe in a wet dream One thing for the OP to investigate is when the motor was rebuilt what P/N pistons were used. My guess is generic flat tops that typically have 2 or 4 valve reliefs, in which case he could have a little better compression. Regardless, some decent performing heads, a cam, true dual exhaust and a distributor recurve will wake up that motor. The cam I like to use for customer's top end replacements is a Engle 1018H with 216/228 duration @.050" on a 112 LSA with .458/.468" lift.

 

Just a followup to my original question about just a cam change with stock heads and to confirm that I am not crazy about my original assumption about a cam change only on stock engines.

Spoke with 2 forum members that have L-82's, not L-48's-the L-82's have bigger valves in the head than the L-48's but still smog heads.

Forum member #1: Stock L-82 with stock cast iron exhaust manifolds and 2-1-2 exhaust with no cat-Dynoed at 192 HP rear wheel-Not Gross or Net at the flywheel.

Forum Member #2: Stock L-82 with VERY mild cam (does not know what type exactly) with headers and true dual exhaust-Stock heads-Dynoed 225 rear wheel HP-Not Gross or Net

If you assume that the OEM cat on example #1 would deduct another 10-13 HP from the equation, a basically bone stock L-82 would have dynoed rear wheel HP on or around 180 rear wheel HP. So, headers, true duals and a VERY mild cam change produced 45 rear wheel HP on a stock L-82. Adding a more aggresive cam to the equation with the same headers and true duals, one could expect somewhere of around 55-60 HP rear wheel which is a ton on a stock L-82 motor with stock heads even if they are smog heads. It's not an L-48 but it does illustrate the gain that can be had with minor changes such as headers, true duals, and a cam change only on stock heads/motors. These real world examples also reinforce my experiences in the late 70's of changing cams only on smog V8's with smog heads from that era that transformed the cars with MUCH more HP. As stated earlier, big HP gains require cam and head change but this notion that doing a cam change will not result in appreciable HP gains with a cam change only on engines with smog heads is false.

 

a camshaft is about the only part that CAN add100 HP. not in this case. in 78 i had an l-82 pacecar i pocket ported the. heads freed up the exhaust and advanced the cam added a l-t1intake and 3310 Holley nothing of its era could touch that car.i never raced that car for time as i had a drag car at the time

 

I am not trying to argue with you about it at all, it's just that after looking around the internet, I am still not exactly sure what the dish volume on those 8:1 CR chevy 350's was, I have seen 12, 13, and now 15cc. I used 12cc on my calculations to play it safe, but if I could get a more accurate number to work with, that is always better. How sure are you about the 15cc dish, and what is your source, etc. If you choose to reply, thanks in advance for the info.


Scott

 

Hi Scotty
There are at least two versions of the L48 piston that I know of. A dished (or sumped) version and a dished with 4 Valve Reliefs (4VR). The only way you will know what your piston volume is for sure is to cc them. You are right, there are numerous specs floating around on the internet, even the NHRA specs them differently, I've seen 9.9 and 12ccs listed. I used a burette, plate of glass and alcohol to cc the originals that were in my kids '76, its been a few years but I recall those measured at 15cc. Hope that helps out.

 

Thanks for the reply, I"m not tearing the whole engine down, so I guess I'll just go with 12cc to be on the safe side.

I feel like I have highjacked the thread, so let's get back to the kid who wants to soup up his 'vette! I have already said my piece, and I still stand by it: changing heads will cost more than a new cam, but I think that he would be happier with the results. I think new heads is the way to go. Look into the vortec heads if you wanna stay with cast iron, or dont wanna spend alot of dough. They have a great reputation for adding power to small block chevys for pretty short money.


Scott

 

I did a top overhaul on my '77 L-48 about 8 mlos ago and heres what I did and I'm very pleased with the performance. Talked to a good friend who builds racing engines and asked him which way to go. He said he had a set of '68 Camero (?) Z-28 heads that he would rebuild. He recommended what cam, intake (Weiand alum), lifters, carb etc to use. I replaced the timing chain & sprockets etc

The rebuild was pretty simple (actually pulled and installed cams with radiator in place (it was close..). I have a listing of mfg part #s I can dig up.. I highly recommend you do a proper engine break in so you don't do damage ot cam/lifters.

I also got rid of the cat-convertor and X-over exhaust BS (muffler shop did that) and running a Holley 650... Big difference in HP now vs factory output....

Terry

ps. I would NEVER does this again without pulling the engine...

 

L48 needs more compression ... much more.

Only head and/or piston swap can make that level of change in L48.

If ya won't swap L48 heads, then consider change to pistons with small dome such as sealed power p/n H618CP (about +3.5cc dome volume). But I'm w/ ScottM; 58cc alum ZZ4/L98heads are good choice.

never ceases to amuse when a member offers advice on cam choice along w/ horsepower predictions ... when not so long ago that same expert asking here for cam choice advice for his own stock motor. Don't forget to check your oil.