Q: I am in the process of rebuilding a Chevy 350 small block as a 383 stroker. I am going to put the engine in a 1967 Camaro SS. I plan on using a dual quad intake and stock cylinder heads.
My question is this: Should I run a piston compression ratio around 10:1, or should I run a lower ratio? If I go to a lower compression piston, would I have to advance the timing?
Would a stock distributor work OK?
A: To answer your question, we need to get into a little theory. In a naturally aspirated engine, you generally want to run total timing at 38 degrees BTDC (before top dead center) regardless of the compression ratio. More important to timing is the octane of the gas you will run. If you have an 8:1 compression engine, you can run 38-degree total advance on 87 octane pump gas. If you run 10:1 compression, you will need to use 100 octane fuel to have 38 degrees total advance. Since this octane level is well beyond anything available at the pump, you will need to retard the timing to prevent detonation.
As for the stock distributor with that dual quad setup, we recommend you use an MSD 6AL ignition to deliver enough spark to fire all that air and fuel.
I HAVE A 12:1 SBC 406 BUT I ALWAYS HAVE STARTER PROBLM WHEN CRANKING MY TIMING IS SET ON 34 DEGREES TO 36 DEGREES IT KICK BACK I THINK AND NOISY WHN CRANKING.
Hi,
1point:
Spark timing is fonction of the rpm, load and air fuel ratio.
So how can you give such a precise value??
38° is ok but for a rpm around 7000 tr/min and WOT at 1.2 fuel/air ratio.
2 point:
You link CR with fuel octane … but without knowing the DR witch is linked to the R/L ratio and Inlet valve closing (Displacement at the inlet valve closing, thus conditioning the mixture temperature at the end of compression, and so the tendency of knock)
I like your concept of tech advices but please, be more serious…
right, I was thinking the same thing. I have run close to 11 to 1 compression with aluminum heads and 38 degrees total timing without any issues. How can you just automatically assume you need so much timing for so much compression without knowing all the variables like cam profile, type of cylinder head, shape of piston, dynamic compression and Static compression
Building my first Pontiac. The motor I am rebuilding is a Pontiac 400. Had the block checked & it will need to be bored .030″. Using stock #13 Casting heads which are 72 cc heads according to wallace racing. They are 2.11 Int. and 1.77 exh. I have not had them cc ed to verify but will. Assuming they have never been milled. I am wanting to run a rowdy street / strip roller hydraulic cam what compression ratio and cam shaft combo would you recommend. I will be changing the valve springs to match whatever camshaft I go with. WILL BE RUNNING THIS ENGINE ON PUMP GAS. Will also be doing other mods headers, intake, converter, Hei Dist, and gear ratio. If you can recommend a compression ration with these heads I will determine what Pistons to buy to match CR after CC ing the heads and verifying deck height. I have read so many different things I am a little lost, and completely unfamiliar with Pontiac do’s and don’ts.
Thanks!
Your engine builder should know all the answers to your questions If he doesn’t Get a Different engine builder .If you can afford Aluminum heads buy them , you can run higher CR with them= more power more gas mileage.
I have a 305 sbc bored 40 over with mild cam, running 110 gas. What timing would you recommend?
40 degrees total vacuum advance disconnected while checking with timing light