Can anyone tell me what the estimated compression ratio is for a 350 with vortec heads and flat-top pistons?

Can I run on 93 octane without any problems?

I don't have a pressure gauge handy.

I'm having problems getting the car timed too. I think I'm doing something wrong with the timing light. It says the car is runing great at 35 deg of timing...surely this can't be correct.

Any help would be greatly appretiated.

Thanks,
Shannon

 

really need to know volumns of the gasket, chamber valve reliefs and, how far in the hole the piston is to figure compression. good guess would be 9.5-10.0 range. what do you want to do with a pressure gauge? should be no problme with 93 or less. what car/engine? is the est unplugged when you set timing? sounds like it isn't

 

Sorry that was a little vague.

I'm not real sure on the volumes of the gaskets or the valve reliefs. I was just looking for a ball-park figure. I had been told by other engine builders that I needed to run dished pistons with vortec heads...said it would have a high compression ratio if I didn't.

This has been an ongoing project over the course of the winter.
The car is a '91 firebird.
The motor was originally built by my dad in '87 for his '68 Nova. This was his race car at the time. The motor was never ran on the track after the rebuild in '87. The only thing we did was change from the 375 hp heads that he had on the motor to vortec heads. This change was made to allow the mounting of the late-model A/C bracket. I also switched from TBI to carb.

The issue with setting the timing on the motor:

I brought the #1 piston up, pointed the tip of the distributor toward the #1 piston, pulled off the vac lines connecting the distributor and the carb.
To get the motor to start I have to turn the dist. CCW several degrees. Throw the timing light on it and it says 35deg.?? I haven't had the exhaust ran on the car yet, so it's open-headers. There is also an insistent POP in the headers. If we turn the dist. CW to bring the timing back to some normal range, it backfires through the carb.

Sorry for the long post...it's just been a long winter, and I'm ready to race. I would like to completely finish this myself, however I'm strongly considering tailoring the car to someone else’s shop to get the car finished.

Thanks for your prompt reply.

 

pointing the distributor towards the #1 plug serves no useful purpose and is or can be counterproductive. pull the vacuum and plug it. why don't you try settign the timing with the light instead of checking where you've moved the timing to by moving the distributor? after the timing is set where you want it reconnect vacuum.

 

also make sure the balencer's outer ring hasen't sliped, or isen't mached to the timing cover's tab (they changed the location of the tab somtime between '71 and '84 'cause the '71 balencer worked with it's respective cover but was way off with the '84's cover.)

 

Excellent point. My grandfather was an old-school mechanic and owns a junkyard/wrecker service, however his expertise is in Mopar not Chevy. The motor I have was originally hooked up to a 4-speed, so I changed harmonic balancers. I just took the first thing my grandfather gave me and slapped it on. The timing marker and timing cover are both from Auto Zone. It would be my luck that the two aren't lined up correctly.

How do I check or confirm this scenario?

 

Don't quite know how the motor being "originally from a 4 speed" makes changing the balancer nessessary but it definately sounds like you have mismatched parts.

You can find true TDC and remark the balancer or move the timing tab. You need a "Piston Stop" to find true TDC.
The piston stop screws into the spark plug hole.
by turning the motor over (by hand), first one way then the other and noting where the piston contacts the stop, TDC will be at a point on the balancer exactly half way between the two stop points. You must loosen off both valves on that cylinder while testing this so they do not jamb into the stop. Your compression ratio will not be too high with flat top pistons and vortec heads. But you will need to use high octane pump fuel (92-94 octane)

 

Here's a pic of a Piston Stop

You can also make one by knocking the porclein out of an old spark plug and welding a length of steel tube or a bolt into it. (In your case a Vortec spark plug)

 

We've changed so many things on the three cars I've been working on over the course of the winter that I have forgot which changes were made to which car....Dad says we didn't change the harmonic balancer, but we did change the timing marker. You would have thought that between the two of us we would have noticed that the one we pulled off and the new one we put on were different.

Is there any harm in setting the timing where the car runs the best; regardless of what the timing light says. I would just use this as a reference for now...just to get the car out on the street. I will correct this problem later.


I have a feeling that timing will be the least of my worries the first time I shift the stock 700R-4 @ 6800rpm. I have heard that people have ran these trans hard with limited problems. I don't plan to run sticky tires any time soon.....maybe it will hold up.

Thanks guys.

 

Why don't you just spend 1/2 an hour and fix the timing
pointer problem? Get your head outa your ......

 

Already done.

Dad said he fixed it last night. I'm still in college, so I only get weekends to work on it. I'll let ya'll know how it turns out.

Thanks