Hey guys.
I am looking to put together a sbc 350 (LM1) out of a 1980 z28 4-speed (with only 32,000 miles on it) to get the best performance I can and still use 87 octane (regular) gas. The car will be used as a daily driver and will see an occasional weekend at the track. I know that this is not a corvette but it still has an engine with similar specs as used in corvettes. Now the catch is I have to use the existing numbers matching short block. I was instructed that I have to leave the short block original, everything else can be changed.

Here is what I have to work with:

SBC 350 stock bore and stroke (4.00 x 3.48)
Stock dished pistons (16cc dish)
Piston to deck height (.030)

It already has 1 5/8" headers on it so they are staying.
I need to get:

Heads
Cam and lifters
timing chain and gears
Intake
Rocker arms
push rods
Head gasket etc.

Any idea's?

 

Difficult question. I don't know of any numbers for static and dynamic compression ratio that will allow 87 octane fuel. The old standard thumb rule for 91 octane is 9.5 max static compression with iron heads and 10.5 for aluminum heads. This assumes good quench and fast burn chambers. Dynamic compression should be less than 8.2 for aluminum heads and not sure what iron heads would be.

The only advice I have is use what GM/Chevy sold in their cars for 87 octane and what their compression was. You really need to measure the above piston and head chamber volumes for an accurate ratio.

Well no one sells a knock sensor as a gauge anymore (MSD used to). So you have improvise some ear cup with heater hose to listen for knock while driving - you won't here knock from drivers seat w/o some aid before it's bad enough to do damage.

Good luck.

 

Food for thought, with aluminum heads and 10:5 compression you can get away with 91 (midgrade) gas, that's what I use in my 600HP 427ci sbc. I will bump it up to 93 octane if I go to the track.

 

My OEM 355 with AFR aluminum heads, 10.2 compression, and roller cam (.525 lift, duration 219/225, LSA 110, Operating range 1,500-5,600 RPM), and 1 3/4 inch headers runs perfectly on 89 octane with zero detonation.

 

Detonation resistance also drops as a function of temperature; with air intake temperature playing a particularly large role.

-A cold air intake and blocking the exhaust cross-over in your intake if it's got one I think is good for an 0.7 CR worth of detonation resistance, if my memory is right.


I think there's a David Vizard quote floating around about equivalent octane detonation resistance gained from intake temperature reduction.


You could always build a static CR like you're going to be running 91 octane - shoot for 10.2 and then 7.8-7.9 on your dynamic compression with your cam selection and then make sure you block that crossover and get a cold air intake.

A good radiator and reduced oil temps can get you a few more degree temp drop and detonation resistance. -You can also pull a bit of timing out of your tune, or slightly retard your cam if you get a little bit of knocking when it gets hot outside.

(If you do a TBI EFI conversion like the Holley Sniper- you can just jump into the touch screen and pull the timing out during the hot months of summer only and then put it back in when the weather cools back off again with just a few presses of a button. Or when gas is cheap buy 92 octane and bump the timing up and when it gets expensive press a couple buttons and put the 87 octane in.) -Computers are great!

To make it easy on you: just do the calculation of your static CR with the assumption that you'll be going with 64cc combustion chambers and aluminum heads and I think the numbers will like you. With my 5cc valve reliefs flat top pistons 0.025" down the hole, and a 0.015" FelPro gasket I ended up at only 10.2:1, so you'll be less than that with your 15cc dish and pistons further down the hole so just make sure you've got a cold air intake in your build plan and don't go nuts on the ignition advance and I think you'll be fine barring some really crappy gas.

The 0.030" down the hole pistons means you'll have a quench that's just slightly larger than ideal with even a FelPro 0.015" gasket so don't go with a thick gasket for sure.



Adam

 

or you could just spend 30 cents/gal more for premium

 

Thanks for the responses.

This car will see approximately 60 miles a day, so they want to use regular (87 octane) gas. Trust me I tried talking them into running a higher octane fuel. No dice. For some reason 18 year olds that go to school don't make a lot of money.

Originally the engine was rated at 8:2:1 compression. By my estimate it was more around 7:9:1 or less.
If I put a 62cc combustion chamber head on it with a .015 gasket I could get the static compression to approximately 9:2:1 Depending on what cam I can use I was hoping that this would be able to run well on 87 octane and still get some good HP out of it. Trying to get something to run and run well on 87 octane is new territory to me. I've never had to worry about that before.

 

Hey Joe, I can't offer much help here, but have a good Thanksgiving.

 

Thanks Bruce, I hope you and your family have a great thanksgiving as well.

 

So methanol injection and use -40 wiper fluid? That will get your temps down and fluid is cheap....but likely not much, if any, cheaper than the 30 cents per gal for Premium. The thought of a programmable ignition makes sense or just run a conservative timing curve to aid in the goal.

 

I have a programmable Mallory Max Fire. Change your timing curving in a few minutes with a computer. Guys in here are missing out in maximizing their timing curves without some kind of programmable ignition. I read that any performance chevy likes 20+ initial timing to get the most out of it. Problem is, how do you easily reduce the mech'l advance to compensate for the high initial and adjust vacuum advance? Problem solved with my Max Fire and similar products. I would never go back to a standard electronic/points dist'r.

 

9.2:1 could work with good timing and fuel tuning. A timing setup like resdoggie posted could sure help to pull timing just where it detonates while still giving it the timing for good performance everywhere else. Being a 4-speed helps if it's driven so it's not lugging the engine where it's most likely to detonate.

I run my LT1 with 10.4:1 compression on 87 all the time and it was good except around 2400rpm where it would detonate a bit. It has the advantages of EFI and reverse cooling but you dropping 1.2 points on the compression should counter those advantages. Being an EFI setup I removed a bit of timing just in the area it detonated and got more aggressive with the automatic shifting so it doesn't lug in the area it was pinging. Everywhere else it runs good on the cheap stuff.

 

The factory timing specs are for smog motors. If one lives in an area where the smog equipment can legally be removed and want more performance, the timing will need to take on a whole new curve. Currently, my initial is 22*, mech'l 10* and vacuum 8*. At cruise I noticed some ping (over the sound of the sidepipes, lol) with 10* vacuum advance so I just hooked it up to the computer and 5 minutes later it was reduced to what I have now, 8*. Ping seems to have gone. What surprised me the most with 22* initial is the ease of cranking it over at startup.

 

76Rat you have to try retarded timing for your self to see if you can live with it. I retarded a Oldsmobile one time to get it to pass smog and hated driving it like that. It would bog, backfire and had almost no acceleration. Also when ever I put 87 octane fuel in my '94 EFI Camaro LT1 it bogs and surges just trying to get on the freeway though it will cruise w/o problems. IMHO retarded timing is no solution at all to high compression and detonation. This is why I say you have to try driving one of your cars for yourself with the timing retarded as you can see many others say their performance is acceptable.

Just my 2 cents.

 

If you are installing cast iron heads, you will probably need to use mid-grade fuel with a CR of higher than 9.0. You can try the combo you described, but my bet is that you will need to back off the ignition timing to keep it from knocking...and that means de-tuning it from best performance.

If you can find some 62cc aluminum heads, you would be OK.