Thread: Got the rotating assembly / Now what heads?

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The Speed Pro H860CP has these spec according to their web site:

-5 dome volume
1.425 comp distance
530 weight
0.0010 bore clearance
Flat top with 2 reliefs

The pistons are already fitted and the rods are clearanced.

Will I be able to run a standard cam? Isn't that why the rods are clearanced, is for the cam?

I'm thinking I should go with the 72cc heads instead of the 67cc to keep the c r down.

This will be my third engine build. The first 2 were 350's for the circle track race car. Both worked well until we overheaded due to throwing water pump belt. The first one left oil and parts over half the track. The second one got shut off quick enough to keep it all in the oil pan. We haven't got that one out of the car yet to see how bad it is, but I know the cam is busted and 3 or 4 lifters have fallen down. We've started running without power steering to eliminiate that belt (it's the one that goes first and takes out the water pump belt).

Whats involved with clearancing the pan rails? Put the crank in and see where it will hit and then grind it out?

(I've been married 24 years so I am used to filtering out external bickering and useless information, so this conversation doesn't bother me! )

Originally posted by dcoffield
The Speed Pro H860CP has these spec according to their web site:

-5 dome volume
1.425 comp distance
530 weight
0.0010 bore clearance
Flat top with 2 reliefs

The pistons are already fitted and the rods are clearanced.

Will I be able to run a standard cam? Isn't that why the rods are clearanced, is for the cam?

I'm thinking I should go with the 72cc heads instead of the 67cc to keep the c r down.

This will be my third engine build. The first 2 were 350's for the circle track race car. Both worked well until we overheaded due to throwing water pump belt. The first one left oil and parts over half the track. The second one got shut off quick enough to keep it all in the oil pan. We haven't got that one out of the car yet to see how bad it is, but I know the cam is busted and 3 or 4 lifters have fallen down. We've started running without power steering to eliminiate that belt (it's the one that goes first and takes out the water pump belt).

Whats involved with clearancing the pan rails? Put the crank in and see where it will hit and then grind it out?

(I've been married 24 years so I am used to filtering out external bickering and useless information, so this conversation doesn't bother me! )

You will be able to run a standard camshaft.
Go with the 72cc heads or run race fuel
You may have to clearance rod to bottom of cylinder
Put the rotating assy together on a dry run rotate engine, If it hits mark it and grind it then do it again till you don't bind anywhere.

LIST OF CLEARANCES TO CHECK:

crank to block .050"
rod to cam .060"
rod to bottom cylinder .60"

I just looked closely at the Dart heads I'm considering and they
are 76cc's.

784 cylinder
9 gasket squish
-5 piston dome
76 heads

864 / 80 = 10.8 (did I do that right?)

That's a little high pump gas, isn't it?

Ok, a little help here.......

By the formula stated earlier by tech and 3 different online c r calculator we are around 10.4 to 10.8 give or take...

On the Federal Mogul / Speed Pro web site they say these pistons (H860CP 30) makes 9.21 c r with the 76cc heads.

That's quite a difference, why the difference?

Originally posted by dcoffield
Ok, a little help here.......

By the formula stated earlier by tech and 3 different online c r calculator we are around 10.4 to 10.8 give or take...

On the Federal Mogul / Speed Pro web site they say these pistons (H860CP 30) makes 9.21 c r with the 76cc heads.

That's quite a difference, why the difference?

I came up with 9.3:1cr using the measurments:

4.030-bore
3.750-stroke
76cc-head
0.039-gasket
0.025-deck height
-5--piston dome

Dart doesn't offer 76cc heads in none of my catalogs

I think my problem was using -5 for piston dome. I should have added 5 in volume not subtracted 5.

That gives me 9.71 on a zero deck.

Here's the link to the heads. I was looking at a 67cc head and that isn't a Dart standard either. I checked with Performance Auto on the 67cc and they said it's correct. I guess they get them special or something.

http://performanceauto.us/store/prod...110264257a025b

Originally posted by camaro_fever68
I came up with 9.3:1cr using the measurments:

4.030-bore
3.750-stroke
76cc-head
0.039-gasket
0.025-deck height
-5--piston dome

Dart doesn't offer 76cc heads in none of my catalogs

A PRO TOP LINE HEAD COMES IN 76 CC'S AND SO DOES THE WORLD PRODUCTS S/R TORQUER HEADS.

Originally posted by erik erikson
A PRO TOP LINE HEAD COMES IN 76 CC'S AND SO DOES THE WORLD PRODUCTS S/R TORQUER HEADS.

DUH!!!! SO DO A MILLION OTHER HEADS, DART DOESN'T THOUGH, THAT SITE HE LEFT A LINK TO REWORKS THE COMBUSTION CHAMBER TO 76cc

Originally posted by camaro_fever68
DUH!!!! SO DO A MILLION OTHER HEADS, DART DOESN'T THOUGH, THAT SITE HE LEFT A LINK TO REWORKS THE COMBUSTION CHAMBER TO 76cc

THE POINT I WAS TRYING TO MAKE WAS THE PRO TOP LINE HEADS AND THE WORLD PRODUCTS HEADS ARE ABOUT THE SAME SIZE AS THE DART'S AND THEY COME IN 76CC'S.

784 cc's in the cylinder, 76 cc's in the head, 8.43 cc's in the gasket (4.100" gasket bore x 0.039" compressed), 5 cc's in the reliefs and a zero deck will yield 9.76:1 c.r.

With less static compression ratio by using a 76 cc head, you can lighten up on the cam a little and have more bottom end in the motor with maybe a little less converter.

Originally posted by dcoffield
I think my problem was using -5 for piston dome. I should have added 5 in volume not subtracted 5.

That gives me 9.71 on a zero deck.

Here's the link to the heads. I was looking at a 67cc head and that isn't a Dart standard either. I checked with Performance Auto on the 67cc and they said it's correct. I guess they get them special or something.

http://performanceauto.us/store/prod...110264257a025b

I checked out them heads and that company sort of modifies'em a little bit. Nothing at all wrong with that. They will work great. I did the computations with your CH on your pistons and you can bring your block and pistons to the machine shop and get to clean check bore torque plate hone and deck to 9.0 parallel to the mains. Use fel-pro hi-perf. head gasket and your good to go. You miight have some minor clearancing like I mentioned earlier. I came up with 9.8 on the compression though. When you Zero deck it make sure you use pre-flattened felpro 0.039 gaskets.

Originally posted by techinspector1
784 cc's in the cylinder, 76 cc's in the head, 8.43 cc's in the gasket (4.100" gasket bore x 0.039" compressed), 5 cc's in the reliefs and a zero deck will yield 9.76:1 c.r.

With less static compression ratio by using a 76 cc head, you can lighten up on the cam a little and have more bottom end in the motor with maybe a little less converter.

Tech,

I know you can under compression a motor with a big cam and totally kill the engine. (over camming) I know if you match the compression to the cam pretty good, you won't lose a lot of bottom end.

What I don't understand is your point on if you got a high CR you got to run a big cam. Are you trying to bleed off cylinder pressure, if so why? In my experience a short cam and 9-10.5 CR makes for a stout low-end torque monstor. What are the negatives your trying to avoid.

I try to build my street engines to have 200psi cranking pressure. Anything less is over cammed, I have built 220psi cranking pressure engines with good quench with no problems. This blower motor I'm running now only got 170psi because when I got the blower I changed my order on the pistons to 9.0 instead of 10. And my cam is long 248/258 @0.050

I don't see why I couldn't have a 10.0:CR and a stock cam. It would be more efficient. Especially at cruise because of VE figures.

I'm not going against you, just want to know your reasoning.

Originally posted by camaro_fever68
Tech,

I know you can under compression a motor with a big cam and totally kill the engine. (over camming) I know if you match the compression to the cam pretty good, you won't lose a lot of bottom end.

What I don't understand is your point on if you got a high CR you got to run a big cam. Are you trying to bleed off cylinder pressure, if so why? In my experience a short cam and 9-10.5 CR makes for a stout low-end torque monstor. What are the negatives your trying to avoid.

I try to build my street engines to have 200psi cranking pressure. Anything less is over cammed, I have built 220psi cranking pressure engines with good quench with no problems. This blower motor I'm running now only got 170psi because when I got the blower I changed my order on the pistons to 9.0 instead of 10.

I don't see why I couldn't have a 10.0:CR and a stock cam. It would be more efficient. Especially at cruise because of VE figures.
S
I'm not going against you, just want to know your reasoning.

YOU DON'T KNOW WHY YOU WOULD WANT TO (BLEED OFF CYLINDER PRESSURE).I THOUGHT SOMEONE LIKE YOU WOULD UNDERSTAND THAT SIMPLE A CONCEPT.DUH!!!

Originally posted by erik erikson
YOU DON'T KNOW WHY YOU WOULD WANT TO (BLEED OFF CYLINDER PRESSURE).I THOUGHT SOMEONE LIKE YOU WOULD UNDERSTAND THAT SIMPLE A CONCEPT.DUH!!!

I AM CONVINCED THAT YOU HAVE NEVER BUILT AN ENGINE ANYWHERES BUT ON PAPER. THERE IS NO REASON TO BLEED OFF CYLINDER PRESSURE UNLESS HE WOULD'VE HAD ABOUT 10.5:1 OR MORE COMPRESSION SO HE COULD RUN PUMP GAS. I THINK YOU READ TOO MUCH. PLENTY BOOK IDEAS, NO REAL WORLD EXPERIENCE. HE HAS A 270H CAM FOR THAT ENGINE HE BUILDING AND IT WILL RUN GREAT WITH A GOOD QUENCH ALL THE WAY TO ABOUT 10.3:1 AND HAVE RIGHT ABOUT 200 PSI CRANKING PRESSURES, ACCORDING TO VE AND CAM SPECS. IF YOU TRY TO FIGURE IT TO SAY I'M WRONG, DON'T FORGET THAT THAT CAM HAS 4 DEGREES ADVANCE GROUND IN IT.

"What are the negatives your trying to avoid."

Detonation from currently available pump fuels.

I'm impressed with your figures and would be interested in knowing what fuel you're using. I've built a bunch of Chevies, but shoot for around 170 on street motors after talking with cam grinders over the years. Maybe I'm just too conservative, but I have an obligation to err on the side of caution in answering questions on this forum, 'cause I'm spendin' someones else's money.