Ok i have two problems with my build

[Yellow76]

First i bought some new heads and i dont no what push rods i need to buy or even if i need new ones.

Alright second i dont no how much compression im going to be running.
Thanks for any help!

My motor...355 flat tops, this cam http://www.lunatipower.com/Product.aspx?id=1984&gid=287
the heads i have are some holleys cant really find info on tham exept thay have 2.02 intake and i think 68cc combustion
rpm performer
holley 750

[Captainfab]

You aren't going to know what length pushrods you will need until you bolt the heads onto your short block and measure for them.

As for compression, you will need to provide more detailed info. such as your deck height, compressed head gasket thickness, and the total volume of the valve releifs in your pistons.

Regarding info on those heads. I believe I posted all of the info available on those in your other thread, with the exception of combustion chamber volume. I somehow missed that as the exhaust port and the chamber volume are the same. I made that addition to my post in your other thread.

[Yellow76]

Alright i looked up the pisstons and the dome volume is -5cc is that what you wanted? As for the deck height i dont no can i measure that or what and depending on what compression i have i can pick what head gaskets right cause im just trying to as close to 10 to 1 as i can. Thanks for all help again

[Maxxd07]

This link could help with the compression.

[Super73]

What is your reason for the 10-1 compression ratio target?

If you don't have heads on the block and all the parts are together, you can figure out how far the piston sits in/out of the hole with a piston stop and dial indicator with stand.

[Yellow76]

I wanted close to 10 to 1 cause i still want to run pump gas in it

[57sailplane]

hey guys,

its been a while.

if you don't have a dial indicator then do you have a good straight edge and a feeler gage?

You will need some help. put the straight edge across the cylinder of course this is with the head off. then put the the feeler gage under the straight edge between the the flat of the piston. i would start with .025. have somebody else run the crank around if the straight edge is lifted then you have to much gage. you want the point at which the straight edge is just not lifted. this will get you a good guess on deck to piston clearance. of coarse i say guess. you really need the dial indicator.

later Andrew k

[Super73]

Static compression ratio has less to do with pump gas than the full combo. You could be leaving power on the table with a 10-1 CR motor. Look here: http://67-72chevytrucks.com/vboard/s...d.php?t=419877

Marv, myself and a couple others go over this is better detail.

[C20-67_N_MO]

Originally Posted by Super73

Static compression ratio has less to do with pump gas than the full combo. You could be leaving power on the table with a 10-1 CR motor. Look here: http://67-72chevytrucks.com/vboard/s...d.php?t=419877

Marv, myself and a couple others go over this is better detail.

100% agree with Super.

These guys now their stuff in vivid details.

[Yellow76]

Alright well the combustion chambers are 68cc i havent taken the deck hight yet but ill find out as soon as i get the other heads off and i have .40 head gaskets thanks for the help guys

[Yellow76]

And the deck hight of the head is .500

[Captainfab]

That would be the deck thickness of those heads. That has nothing to do with calculating the compression of the engine. You need to measure the distance from the top of the piston at exactly TDC to the deck surface of the block

Originally Posted by Yellow76

And the deck hight of the head is .500

[Yellow76]

alright well its been awhile i have been busy but i finaly took the head off my truck and the piston is almost flush with the block but i cant turn my motor to get it to TDC for some reason when i bolted it to my tranny i cant turn it over with my hands

[Super73]

You may need to put a 1/2 drive socket wrench or breaker bar on the crank bolt to turn it over. It should not take more than 60-70lbs connected to the tranny.

[Yellow76]

alright well i got it to TDC and its .040

[Yellow76]

well i did a dynamic compression calculater thing and it said my motor was 9.26 :1. Doesnt that seem to much?

[Marv D]

Give us every detailed diminision your using to calculate the compression and let's talk about this. If you have a set of KB builder pistons I can believe they are .060 down the hole, but let's talk about it before you say you got it.

FIRST, did you measure the deck clearance with a straight edge and feeler gauges? or a dial indicator and a bridge?

If you used the ANYTHING but the center of the piston, and / or measured along the axis of the piston pin, you likely introduced piston rock into the mix and have a bad number there.

Maybe I missed it in there somewhere, but i did not see your cam specs either.

[Yellow76]

Well i re measured and i was wong its .046 and this is what i have for specs.
Number of Cylinders :8
Bore in Inches :4.030
Stroke in Inches :3.48
Rod Length in Inches :5.7
Static Compression Ratio : 9.98
Inlet Valve Closes ABDC : 39.5º
Boost Pressure in PSI : 0
Target Altitude 200


This gives me 9.19 dynamic compression with a .040 head gasket. Would this set up run pump gas (91)?