[steve25]

First and foremost what is the motors hot cranking compression?

Larger port higher flowing heads will not help at all in terms of better acceleration below 4000 to 4500 rpm so strip that notion out of your mind.

Your leaving too much in hands of so called experts when it come to distributor timing, and not being able to check it yourself is leaving you behind the 8 ball .


You car set up right and with those rear gears should anniilate the rear tires at will!.

Here’s how your HEI should be set up.

[HWYSTR455]

Your total mech advance, if I'm reading it right, is only 12 degrees total. I would try making your initial timing around 16-18 as long as it cranks over ok. Then see if it's an improvement.

If so, you need to have the distributor recurved to have about 16-18 total mech advance with 16 degrees initial advance.


.

[petes67bird]

Originally Posted by HWYSTR455

Your total mech advance, if I'm reading it right, is only 12 degrees total. I would try making your initial timing around 16-18 as long as it cranks over ok. Then see if it's an improvement.

If so, you need to have the distributor recurved to have about 16-18 total mech advance with 16 degrees initial advance.


.

Thank you, I plan on taking it to another shop once it warms up in the spring to get it looked at once again. I am hoping that timing adjustment livens up the motor a bit.

[petes67bird]

Originally Posted by steve25

First and foremost what is the motors hot cranking compression?

Larger port higher flowing heads will not help at all in terms of better acceleration below 4000 to 4500 rpm so strip that notion out of your mind.

Your leaving too much in hands of so called experts when it come to distributor timing, and not being able to check it yourself is leaving you behind the 8 ball .


You car set up right and with those rear gears should anniilate the rear tires at will!.

Here’s how your HEI should be set up.

When you are asking about cranking compression, do you mean per cylinder. If so, they all measured between 159-166psi. The only reason I started thinking about heads is because that is what I was being told by people more knowledgeable than me. Butler, KRE, and Cliff all said that changing my heads would give me more air that the motor needs and generate the power I was lacking. I was told that the 96 heads do not flow great ( I only have the 3 angle and milled a little) and that I want to increase my compression for my cam. 2 of those three mentioned that the cam needs to be put 4 degree forward to 109, and that on center, it will be sluggish. I asked the builder about my concerns and he sent me videos of the same build in a Firebird and it seemed very lively.

I will be honest, I do not know what moving the cam will do to my driveability etc, I am just disappointed in my current setup and for the spring, I would like to wake up my setup or get it set properly if it is not. I am happy to save money wherever I can obviously as I would prefer not to spend 5k on heads/rockers etc. My vehicle prior to this was a 1980 z28 with a 350 crate motor, reverse valve body TH400, 373 gears, that was feel it in your pants way faster

[chiphead]

I broke out the calculator on that distributor setup. Since the dist turns half as fast as the crank, you double the degrees and RPM stated on the Sun sheet to calculate the timing at the crankshaft.

I get
16 degrees advance at 2000 RPM
20 degrees at 2600
24 degrees at 3400

Assuming the typical Pontiac engine wants total timing to be 36 degrees (which includes base timing) you subtract 36 from the 24 degrees of dist advance to get 12 degrees at idle. So the base timing would have to be set at 12 degrees BTDC to give 36 degrees at 3400 RPM. Base timing (which you set) plus dist advance curve (calculated above) gives the total timing the piston will see at a given RPM.

The total timing at those RPMs with 12* base would be
28* at 2000 RPM
32 at 2600 RPM
36* at 3400 RPM

So take a timing light and verify you have 12* of base timing. This is your starting point for tuning. What's interesting to me is that there is a decent amount of timing from 2000-2600 RPM, but it takes another 800 RPM for the curve to come all in. I assume they did this to provide a safe tuning window that won't rattle the bearings due to too much timing too early.

At low 9s static compression, on 93 octane gas, I would think it safe to quicken the second half of that curve. Basically have all the timing in at 2900-3000 may increase some power in that range. Maybe 15-30 HP depending on what the engine likes.

But that's not going to provide a world of difference unless the actual timing is vastly different from what I estimated above. For comparison, my 400 motors tend to like 14-16* of base timing and 34-36* at 3200. So shoot the timing with a light and report back.

Cranking compression is a decent estimator of how an engine will behave, if engine size, compression and camshaft is known. Manifold vacuum at idle will help tell if an engine is tuned properly, at least at idle. You put the two together to estimate an engine's power potential and if the tune is in the ballpark.

Edit- I just saw that your cranking PSI is in the 160s. That's not bad. My 400 with 2802 and 9.7:1 compression pumps 165 and it's no slouch. I'd look at ignition timing and carb settings first. How about shift points? How long does the 2004R hold 1st gear at heavy throttle?

I do think that the biggest gains would be heads. Its not just airflow. Going from 9.3 to 10.3 compression is going to pick up power everywhere. The power production above 4500 is going to benefit from headers and 3" exhaust, but down low, cylinder pressure rules.

[HWYSTR455]

Ok I see the hand written notes now.


.

[ta man]

I would confirm that the harmonic balancer hasn't slipped. Timing can be way off.

[petes67bird]

Originally Posted by chiphead

I broke out the calculator on that distributor setup. Since the dist turns half as fast as the crank, you double the degrees and RPM stated on the Sun sheet to calculate the timing at the crankshaft.

I get
16 degrees advance at 2000 RPM
20 degrees at 2600
24 degrees at 3400

Assuming the typical Pontiac engine wants total timing to be 36 degrees (which includes base timing) you subtract 36 from the 24 degrees of dist advance to get 12 degrees at idle. So the base timing would have to be set at 12 degrees BTDC to give 36 degrees at 3400 RPM. Base timing (which you set) plus dist advance curve (calculated above) gives the total timing the piston will see at a given RPM.

The total timing at those RPMs with 12* base would be
28* at 2000 RPM
32 at 2600 RPM
36* at 3400 RPM

So take a timing light and verify you have 12* of base timing. This is your starting point for tuning. What's interesting to me is that there is a decent amount of timing from 2000-2600 RPM, but it takes another 800 RPM for the curve to come all in. I assume they did this to provide a safe tuning window that won't rattle the bearings due to too much timing too early.

At low 9s static compression, on 93 octane gas, I would think it safe to quicken the second half of that curve. Basically have all the timing in at 2900-3000 may increase some power in that range. Maybe 15-30 HP depending on what the engine likes.

But that's not going to provide a world of difference unless the actual timing is vastly different from what I estimated above. For comparison, my 400 motors tend to like 14-16* of base timing and 34-36* at 3200. So shoot the timing with a light and report back.

Cranking compression is a decent estimator of how an engine will behave, if engine size, compression and camshaft is known. Manifold vacuum at idle will help tell if an engine is tuned properly, at least at idle. You put the two together to estimate an engine's power potential and if the tune is in the ballpark.

Edit- I just saw that your cranking PSI is in the 160s. That's not bad. My 400 with 2802 and 9.7:1 compression pumps 165 and it's no slouch. I'd look at ignition timing and carb settings first. How about shift points? How long does the 2004R hold 1st gear at heavy throttle?

I do think that the biggest gains would be heads. Its not just airflow. Going from 9.3 to 10.3 compression is going to pick up power everywhere. The power production above 4500 is going to benefit from headers and 3" exhaust, but down low, cylinder pressure rules.

If you did heads, do I go edelbrock or kre? Also I was thinking either 72 or 74cc.