409 068 truck block compression

[Windingout]

Hi guys I am planning my engine build and I would like some opinions on the compression ratio I should run. I have a 62 truck block casting 068 going into a 63 Impala 2 door hardtop. Iam going to run the car 90% street and 10% strip or something like that. You know how the racing bug creeps in. The car has a M21 and a 12 bolt posi with 456 gears which I will likely have to change to 3.73. I plan on Edelbrock heads, a solid roller cam, maybe around .6 lift and I have a 881 manifold with (2) 500cfm AFBs. The engine will be bored .030.The question is how much compression can I run on pump gas with out additives. I was thinking based on a drop of 1 point to be around 10:1( from previous discussions that I can't find). But maybe I can squeak out 10.5:1. I was thinking about the Ross pistons 11:1or 11.5:1 and Eagle I beam rods. If any of you guys with more experience on this subject can help me out it would be appreciated. Can anyone estimate what horsepower this set would make. I am not after the ultimate drag car but I would like to get below 12 seconds.

 

[Dr Richard Kimble]

with aluminum heads , yes , a real 10.5:1 1 is the place. With that , the aftermarket 6.135" BBC rod is ideal .
I say "real 10.5:1" , because production pistons will not get you there . a custom made piston, lightened , with the deck height set properly , and the correct valve relief for your cam , will make the best combination .
yes , the pistons cost is bad

 

[Fathead Racing]

The 068 casting is listed as a passenger car block. Anyway, with aluminum heads you will be safe coast to coast with a compression ratio of 10.5. No need to go past this for a 90% street engine. Very little to gain going over this comp. for the street. You could probably get away with 87 octane in a pinch with aluminum heads with 10.5. Pick the right cam and your dynamic compression ratio will not be a factor. You can actually have a monster at 9.5 comp. ratio but I'll probably get beat up enough by suggesting 10.5.

 

[Don Jacks]

Others may to "beat you up" for suggesting 10.5 Ray,but not me! After all ,your "little" stock stroke 409 went low 12's in your 4,000 60 Impala with a 9.7-1 ratio,and a cam of 230-240 @ .050.You speak from having "Been there,Done that".

 

[Phil Reed]

Get Bob Walla heads instead of Edelbrock!!!

 

[Windingout]

Yes,the 068 is listed as a car block and I thought I hit pay dirt until I found out from you guys what those big notches were for. This motor came out of a fire truck and is a Canadian motor. The plant code off the front pad is T03210D and is not listed. I suspect this may have come out of the St. Catherines Ontario engine plant and those listings are US data. GM Canada operates a little differently than the US.
.

 

[Fathead Racing]

Yes,the 068 is listed as a car block and I thought I hit pay dirt until I found out from you guys what those big notches were for. This motor came out of a fire truck and is a Canadian motor. The plant code off the front pad is T03210D and is not listed. I suspect this may have come out of the St. Catherines Ontario engine plant and those listings are US data. GM Canada operates a little differently than the US.
.

I'm running the truck block with some success.

 

[63 dream'n]

I can't speak with 1st hand knowledge but, it stands to reason and I've read that the compression relief on the truck block actually helps it perform by unshrouding the valve to aid with flow. You just have to plan accordingly as to not loose compression with your piston choice.

 

[Fathead Racing]

Yes, the notch does unshroud the exhaust valve but mainly above 11.5 piston. The truck block with its notch befits a race engine more than it would a lower compression street/strip mill.

 

[Ishiftem]

I'm running the truck block with some success.

I would say so!

 

[Don Jacks]

The "Rule off thumb " is that,in a truck block,order 11-1 pistons in order to end up at 10.5-1.Phil makes a good point in that Edelbrock states that the recess area around the valves is 15 cc's which will further reduce the compression,where as the Walla heads have none,giving you more compression than the Edelbrock's,and they flow better.

 

[63 dream'n]

The "Rule off thumb " hat,in a truck block,order 11-1 pistons in order to end up at 10.5-1.Phil makes a good point in that Edelbrock states that the recess area around the valves is 15 cc's which will further reduce the compression,where as the Walla heads have none,giving you more compression than the Edelbrock's,and they flow better.

So quench needs to be tighter with the eddies.....opinions on what is ideal....????

 

[Fathead Racing]

So quench needs to be tighter with the eddies.....opinions on what is ideal....????

Quench is not related to compression.

 

[63 dream'n]

[QUOTE Fathead Racing, post: 276943, member: 61"]Quench is not related to compression.[/QUOTE]

So what's the terminology for actual distance between piston top( flat) to cylinder head. Which would equal your head gasket thickness ,if piston is even with deck surface.I read this distance is critical to make or loose compression/ power

 

[Fathead Racing]

[QUOTE Fathead Racing, post: 276943, member: 61"]Quench is not related to compression.

So what's the terminology for actual distance between piston top( flat) to cylinder head. Which would equal your head gasket thickness ,if piston is even with deck surface.I read this distance is critical to make or loose compression/ power[/QUOTE]
Gets a little complicated. I and others will be on this like ugly on a gorilla tomorrow I'm sure. My comment was made to start this conversation.

 

[63 dream'n]

You are a damn good fisherman..........hooks set......

 

[Fathead Racing]

You are a damn good fisherman..........hooks set......

I have gobs of info on this subject. Your on the right track. My perfect quench with a steel I beam rod with .004" Piston side clearance and .002" rod bearing clearance is .035". Different with aluminum rod and race piston, different when giggle juice is squeezed in there. Can be as much as .065". As little as .028. Shape of piston determines compression in the W engine combustion chamber, cylinder heads in others with flat piston wedge head design.

 

[63 dream'n]

So if the Walla heads don't give up the 15 cc's the eddies do,given the same piston to head clearence,the quench is the same,combustion chamber volume is different with more volume or slightly lower compression with the eddies.......no............?????

 

[Fathead Racing]

So if the Walla heads don't give up the 15 cc's the eddies do,given the same piston to head clearence,the quench is the same,combustion chamber volume is different with more volume or slightly lower compression with the eddies.......no............?????

Yes, but that is not the determining compression factor. That's still within the quench area.. Has slight affect on compression, your right.

 

[Dr Richard Kimble]

piston to head clearance
I have personal experience running a 427 cranked stroker to 7000 RPM , with .036" piston to head clearance . heads have been off ,. keeps things "clean" inside , but absolutely no problems .
the typical felpro gasket is about .043" compressed thickness . in a perfect world , pistons set to .006" - .007" above the deck .
During mock up assembly , check this by "rocking" the piston as well , getting a "high" and "low measurement . Depending on your piston to wall clearance , these readings can be as much as + / - .010"
again , don't buy an off the shelf piston , and then deck the block away , just to try and get the ideal deck height .
take advantage of custom made pistons