If you have a stock L48 block with 8.5:1 compression, what would be a good way to improve(raise) compression? Decking the block and/or pistons and/or heads?

 

You can pick up a point just by switching to 62-64 cc. heads. Any more than that and it's piston time.

 

Go to 64cc heads, I have just been asking a similar question and while your at it look at going to aluminium with big valves.

 

L-48 cam was very weak so a new cam is a must.
Do a forum search on this topic
There have been many posts regarding upgrading the L-48

I'm in the same boat and have had many suggestions from the forum members which I greatly appreciate..... unfortunately, none seem to agree 100%

Do some reasearch and then make your decision.

ps: let me know how you make out....

 

Chevy has some .016 thick head gaskets, that will raise your compression a half a point.

 

world products 170 runner 58cc combustion chamber head.

 

Depends on budget but most of the time you would want to swap the heads. Pistons can be cheaper but more work is involved. Decking the block is possible but not always done if you can play with the gasket thickness.

-Mark.

 

I'm also in the same boat. I'm thinking AFR heads, cam , headers .
But I don't know which ones as there are so many combinations. I'm looking to get about 60 to 80hp on my stock L48 with true duel exhaust. Any good info here is appreciated.
Thanks

 

Regardless of what SCR many folks think their stock L48 has ...

... with a stock 4" bore L48, an inexpensive set of SpeedPro/Sealed Power flattop pistons P/N H345NCP (-5cc dv, 1.560" cd) along with an inexpensive pair of Felpro thin shim gaskets P/N 1094 (3.2cc) will yield right at 9:1 SCR. With a thirty-over bore, same combo'll yield right at 9.1:1 SCR. Both combos have a pretty good quench height that's right at 0.040".

 

This is becoming a popular topic right now, isn't it? That's a good thing, though; add me to the list of people who are looking into this. So if a set of 62 cc heads and a .016" set of steel head gaskets brings a compression ratio to, let's say, 9.4:1, how much cam can we use with the good ol' TH350 tranny and 3.55 gears? I'm assuming this combo will make a decent power increase without destroying half shafts, gears and solid u-joints. . .

- Chilli

 

Summit 1103
*addendum*
SOS ... Nothing new under the sun ... same freakin' Q&A and accompanying disbelief/disregard week-in, week-out all year. Folks see 400hp head-cam combo advertized & don't realize/won't believe it won't happen with dish pistons way down in hole that yield low compression. Even when advised they don't wanna believe it & go ahead a stick too big a cam in there anyway. Novice builders/tinkerers constantly making the most common mistake of all; Overcam. Result: low vacuum and crappy traffic performance. SOS.

 

 

Who would be the best person to talk to about head - cam combo .
I do not want to screw this up.

 

I'm not saying I take any of these ads as law, especially with dished pistons. I still think aluminum heads on the stock L48 is a good idea, I just don't know what to do for a cam. As such, I'm not going to sink any $$$$ into a cam/heads "package." I'll put my own cam/heads combo together . . . as soon as I can figure out what a good cam would be to go along with said aluminum heads and dished pistons. I can live with a cam offering less than .500 lift if that's what is necessary.

- Chilli

 

Here is what I just did to my son's '76 L-48. I measured the bore and it had less than .001" of taper and only a few scratches. I just used a fine ball hone and did a quick pass on each bore. Then we pressed off the dished pistons and installed Speed Pro H631CP Flat tops w 5cc reliefs. Since they are relatively close in weight to the stock pistons the machinist said save our money an not bother balancing it. Since the cam was flat I installed a GM "151" cam, advanced it 4 degrees for more bottom end. I had an older set of '041 heads with 64 CCs with 1.94" and 1.5" heads. I spent about 10 hours porting them and opening up the bowls. With a NAPA/Victor Reinz P/N 5746 head gasket the SCR came in at 10:1. With the "151" cam's late closing inlet valve we have a DCR of less than 8:1, fine for pump gas and great for a dailey driver.
The cam sounds mild but very healthy and will work fine with the stock converter with the auto trans.

We found an older Weiand 8004 intake on Ebay for $20, and cleaned that up and then installed the Q-jet with a new choke pull off. Bought a nice used set of Hooker Headers from the parts section for less than $100 and installed them. I recurved the distributor for 34 degrees total at 3,000 RPMs and installed a used LT-1 style air cleaner we found on Ebay for $25 and we are good to go.

Engine Analyzer predicts:
151 cam, 4 deg adv........349ft/lbs@3500, 80% torque bandwidth =1950-5500 RPM, 307HP@5000

So not too shabby for very little money. Now I just have to finish the frame and get it back together.

 

Chilli, is your car an auto or manual. If you go too big on the cam you need a little looser converter to allow it to idle without pulling down the trans. The L-82 engine used a little looser converter with it's cam, which in my opinion would be another nice, very dependable street cam to use.

 

BINGO!
Numbers look good & agree with other references. And a very good & smart approach too! Others should consider this as a solid example of what to expect & a standard for comparison. Good Job

 

It's an auto (TH350). How much difference is there between the L48 and L82 original cams?
I totally agree that putting in flat top pistons is a good/better idea, but I don't trust myself to do that kind of work - I'm a halfass driveway knucklebanger on a GOOD day. I'm sure my best bet would just be to get a GM crate motor, but that's a big $$$$ issue.

- Chilli

 

There is a relative big difference between the two cams. The L-82 will work best with at least 9.75:1, preferably with 10:1. The L-82 has 224 degrees of duration, around .450" of lift.

You can use the stock L-48 cam to produce excellent low end torque for a nice driver with an auto and 3.08 rear gears. It will like 9.75:1 max and retard it 4 degrees to increase the useable rev range to about 5,500.

 

In my opinion...... Jackson
But you need to give him all the information that he needs.....which will require removing a cylinder head or both
And he can get it done on a budget as well