[Schurkey]

Originally Posted by ericwoo

my car is still kind of sluggish IMO.

I have a hard time seeing my 350 producing much more than 300 horsepower.
[*]600 cfm double barrel Holley carb (I tried putting a 750 double pumper and it was bogging down the engine)[/list]
Any idea of what I can look at that may be wrong with this set up? Or what upgrade I should do to get this thing to over 350 horsepower?

I was expecting some decent power but boy this thing is kind of a dog.

PRIMARY problem is that you started with a 350 when there's no penalty for going 400+ cubes. On a mild engine, every cubic inch is one horsepower and 1 1/4 ft/lbs of torque. ~50 cubes = more better. 100+ cubes = happiness.

Secondary problems:
600 cfm DOUBLE BARREL Holley carb??? Apparently with no tuning

Cam installed "dot-to-dot" when there's a half-dozen things that all are needed to be precisely machined for that to be accurate--and "accurate" may still not be "optimum".

No mention of timing advance tuning

No mention of piston design/quench distance/ring package/block honing


As said--compression test needed. Fuel pressure test needed, with engine at WFO and max RPM. Verify throttle plates open fully, and the trans TV cable and shift-points match the torque curve.

[ericwoo]

Originally Posted by Schurkey

PRIMARY problem is that you started with a 350 when there's no penalty for going 400+ cubes. On a mild engine, every cubic inch is one horsepower and 1 1/4 ft/lbs of torque. ~50 cubes = more better. 100+ cubes = happiness.

Secondary problems:
600 cfm DOUBLE BARREL Holley carb??? Apparently with no tuning

Yes, a 400 would be great. If I can get this 350 to produce 375 horsepower with some adjustments, I would be happy though since I am not into competitive racing. Just want a high performance street vehicle to take racing a few times for fun.

opps, I meant to type 600 cfm four barrel holley carb. It actually has a vac secondary. The other one I tried was a 750 double pumper but sold it since it was too much carb

[ericwoo]

Originally Posted by steve25

So you did a cranking compression test with all the other plugs in?

If so then now you have to do that test again or make a leak down test before you say that removing the heads is needed.

Be sure to kill the power to the HEI before making these test.

Originally Posted by Jay S

At very least you need to do it again before make any conclusions.

I had a Pontiac that the factory deck machining height was off .018” between banks.

So I adjusted the valves again just to get the hydraulic lifters to zero lash, then tightened 3/4 turn. Then tested the compression a 2nd time with the below. Took all the spark plugs out and the engine warm. Overall, the readings seems to be similar +/- 5 psi. (not sure how precise my old gauge is)

Driver side head
# 1: 155 psi
# 3: 160 psi
# 5: 155 psi
# 7: 158 psi


Passenger side head
# 2: 195 psi
# 4: 194 psi
# 5: 200 psi
# 8: 187 psi

I am ordering a leak down tester to see if there is leakage in that driver side head. Hopefully I should get that complete early next week.

The next thing I realized, is the pushrods are indeed a little too short. See the test I did in the attached photos

Passenger Side


Driver Side

[Schurkey]

Originally Posted by ericwoo

I am ordering a leak down tester to see if there is leakage in that driver side head. Hopefully I should get that complete early next week.

There's a hundred companies selling leakdown testers for automotive use, and NONE of them are trustworthy...until you've either confirmed them with a Master Orifice, or you've tested known-good cylinders of the same approximate bore diameter as what you have. If you test enough engines, with enough different bore sizes, you can have a good idea of how your leakdown tester works--but the Master Orifice is WAY faster.

There are no "industry standards" or legislation/regulation of automotive leakdown testers. They build whatever they want, and depending on how they're built, they can give WILDLY different results on the same cylinder.

However, the FAA has standards for AIRCRAFT piston-engine leakdown testers, and the ones suitable for 5" bores and smaller aircraft engines are also suitable for automotive engines.

Even better, Continental/Teledyne came up with the "Master Orifice", a calibrated leak that is the equivalent to the MAXIMUM leakage allowable in their engines. You'd plug a leakdown tester into a Master Orifice, note the reading. Then if the engine has less leakage than the Master Orifice, it's considered "good". My standards are higher than that, so I only allow about 2/3 the leakage of the C/T Master Orifice, and only then if it's past the rings--not past the valves, or into the cooling system.

I bought an aircraft-spec leakdown tester with a built-in Master Orifice a dozen years ago. Very recommended. It normally ships with an 18mm cylinder adapter, they'll supply a 14mm automotive adapter on request...or buy several sizes and be able to do motorcycles and old Fords and Mopars.

https://www.aircraft-tool.com/detail?id=2EM

Originally Posted by ericwoo

The next thing I realized, is the pushrods are indeed a little too short. See the test I did in the attached photos

Passenger Side


Driver Side

The first witness mark isn't readable, the second one is not bad, but wider than optimum. Adjust the pushrod length to minimize the sweep (narrowest pattern) even if it's somewhat off-center on the valve tip.