Mid-teardown questions...

SadbutTrue · Jun 29, 2008

Finally got the heads off and am now staring at the pistons for the first time. I was wondering if anyone could tell me, by looking at them, whether these qualify as 'flat tops' and how much of a relief they have (for CR calculation purposes). I really have no clue... they were part of an Autozone rebuilt longblock... with 1970 heads and a 1972 block.

So yeah, I took a couple pictures, if anyone can ID them or take an educated guess at how big the reliefs are I'd apprecaite it.

PS: finding out your old heads were D0OE and therefore not worthless ... finding out your engine is bored .060 over and therefore soon to be done

D.Hearne · Jun 29, 2008

Looks like your average dished 351W (1973-up) pistons. Comp ratio's going to be no more than 9.0 to 1. No valve reliefs there, meaning they didn't need em with a stock cam. The 69-72 pistons had valve reliefs. The 72 pistons had a little deeper dish than the 69-71's.

SadbutTrue · Jun 29, 2008

glad i had the heads milled then, hopefully that'll get it to the mid 9s, anyway.

SadbutTrue · Jun 29, 2008

If you look at the close up pic, you do see a minor relief in the piston... does that suggest its a 72 piston then (and maybe slightly better tahn the 73+ ones)?

NewStangOwnr · Jun 30, 2008

You have plenty left with a .060 overbore.
I do haha

D.Hearne · Jun 30, 2008

SadbutTrue said:
If you look at the close up pic, you do see a minor relief in the piston... does that suggest its a 72 piston then (and maybe slightly better tahn the 73+ ones)?

The 72's dish is round, with 4 eyebrow reliefs. I have one each 71 & 72 O.E. std bore 351W pistons I saved from parts motors. At some later point they went to that oval shaped dish in the 351W's.

bnickel · Jul 1, 2008

what you have there is commonly referred to as the inverted dome piston, it's about the bottom of the barrell in performance terms, with a compression ratio generally of about 8.8:1, with milling the heads and the .060 overbore i'd say you're probably right around 9-9.2:1, you have to mill the heads an awful lot to bring that up much higher. what you need is a Speed Pro H-336-CP piston, it is a hypereutectic flat top made especially for the taller deck windsor and will get you right around 10.5:1 with those D0OE heads.

SadbutTrue · Jul 1, 2008

bnickel said:
what you have there is commonly referred to as the inverted dome piston, it's about the bottom of the barrell in performance terms, with a compression ratio generally of about 8.8:1, with milling the heads and the .060 overbore i'd say you're probably right around 9-9.2:1, you have to mill the heads an awful lot to bring that up much higher. what you need is a Speed Pro H-336-CP piston, it is a hypereutectic flat top made especially for the taller deck windsor and will get you right around 10.5:1 with those D0OE heads.

Yeah, my newest calcs give say it'll bump the CR about .3, so if it starts at 8.8:1 then I'm at 9.1:1. New pistons weren't in the bag yet, but in a few years I'll get it rebuilt with nifty pistons and bring it to ~10.0-10.5. Hopefully the CR is at least high enough to take advantage of the cam and heads, still hoping for about 400 hp from this build.

rhyno9 · Jul 1, 2008

The 8.8 compression ratio is generally calculated with 64 cc heads. What size combustion chamber will you be running?

Weren't you going with trickflows?

SadbutTrue · Jul 1, 2008

rhyno9 said:
The 8.8 compression ratio is generally calculated with 64 cc heads. What size combustion chamber will you be running?

Weren't you going with trickflows?

Yeah, Trick Flows milled to 56cc chambers. If thats true it'd be nice, going off the top of my head would yield basically double the gains so I'd be closer to 9.5:1, which I could live with.

Can anyone confirm that? I always thought those stock ratio calculations still used 60cc heads..

bnickel · Jul 1, 2008

rhyno9 said:
The 8.8 compression ratio is generally calculated with 64 cc heads. What size combustion chamber will you be running?

Weren't you going with trickflows?

wrong. those engines used 60cc heads. all 351's had 60cc chambers until the early 80's IIRC, in any case all 71-75 351w's used 60cc heads and the 8.8 compression was with those heads.

rhyno9 · Jul 1, 2008

bnickel said:
wrong. those engines used 60cc heads. all 351's had 60cc chambers until the early 80's IIRC, in any case all 71-75 351w's used 60cc heads and the 8.8 compression was with those heads.

My statement wasn't meant to be a statement. It was meant to be a question. I just missed the ? at the end. When you see the piston in the catalog they show the compression ratio with 64 cc heads.

I know many of the late 70's heads had huge chambers. They were in the 70+ cc range from what I remember reading. I know the e7te heads are supposed to be 64 cc.

Do you know where I could find stock rebuild compression ratio info?

Basically I am struggling with similar issue. I have a reman f4te 351 with a stock rebuild. I want to put windsor jr 58cc heads but I am afraid of the detonation aspect because the bump in compression.

Thanks
RV

D.Hearne · Jul 1, 2008

rhyno9 said:
Basically I am struggling with similar issue. I have a reman f4te 351 with a stock rebuild. I want to put windsor jr 58cc heads but I am afraid of the detonation aspect because the bump in compression.

Thanks
RV

Going from 64 cc to 58 ccs in a 351 will bump the ratio about a half point at best. No need to worry about pinging in your case. I run 93 octane gas in a 10.4 to 1 331 with Canfeild heads & a Z303 cam. It'll probably digest 89-90 with no more than a change in the timing. Now if you're planning on keeping the F4TE roller cam, then you may get into detonation problems. I run that cam in a carbed roller 5.0 with ported E7 heads and it'll ping in summertime with 87 gas and 12 degrees timing.

bnickel · Jul 1, 2008

rhyno9 said:
My statement wasn't meant to be a statement. It was meant to be a question. I just missed the ? at the end. When you see the piston in the catalog they show the compression ratio with 64 cc heads.

I know many of the late 70's heads had huge chambers. They were in the 70+ cc range from what I remember reading. I know the e7te heads are supposed to be 64 cc.

Do you know where I could find stock rebuild compression ratio info?

Basically I am struggling with similar issue. I have a reman f4te 351 with a stock rebuild. I want to put windsor jr 58cc heads but I am afraid of the detonation aspect because the bump in compression.

Thanks
RV

i'm not sure what the compression on later model windsors is, but i know of the did have a smaller dish to the pistons so with a 64cc chamber i can see it being around 8.8 still. pretty sure the 90's 351's had the smaller dish like Lightning motors for instance

rhyno9 · Jul 1, 2008

SadbutTrue said:
Finally got the heads off and am now staring at the pistons for the first time. I was wondering if anyone could tell me, by looking at them, whether these qualify as 'flat tops' and how much of a relief they have (for CR calculation purposes). I really have no clue... they were part of an Autozone rebuilt longblock... with 1970 heads and a 1972 block.

So yeah, I took a couple pictures, if anyone can ID them or take an educated guess at how big the reliefs are I'd apprecaite it.

PS: finding out your old heads were D0OE and therefore not worthless ... finding out your engine is bored .060 over and therefore soon to be done

Sorry to sidetrack your thread with my issues. I have basically the same dish without the reliefs and I have been trying to ascertain the same info.

After looking at the first pic I can see a portion of what would appear to be the part number under the dish. Clean the rest of that off and then maybe you can provide a part number which will assist in locating the specs for the piston.

Thanks to everyone and to the internet. Sharing of ideas and knowledge is a wonderful thing.

bnickel · Jul 2, 2008

rhyno9 said:
Sorry to sidetrack your thread with my issues. I have basically the same dish without the reliefs and I have been trying to ascertain the same info.

After looking at the first pic I can see a portion of what would appear to be the part number under the dish. Clean the rest of that off and then maybe you can provide a part number which will assist in locating the specs for the piston.

Thanks to everyone and to the internet. Sharing of ideas and knowledge is a wonderful thing.

guess i'm not seeing what you are but i suspect that what you are seeing is probably an 060 which is just an indicator that the piston is .060 oversized

SadbutTrue · Jul 2, 2008

rhyno9 said:
Sorry to sidetrack your thread with my issues. I have basically the same dish without the reliefs and I have been trying to ascertain the same info.

After looking at the first pic I can see a portion of what would appear to be the part number under the dish. Clean the rest of that off and then maybe you can provide a part number which will assist in locating the specs for the piston.

Thanks to everyone and to the internet. Sharing of ideas and knowledge is a wonderful thing.

Not an issue

SadbutTrue · Jul 3, 2008

Okay, pushrods coming in today. So a few questions before we start-reassembly.

1) I have a degree kit from summit. After donig some research on compcams' site and others, it seems like its a decent idea but for my purposes perhaps not worthwhile. I keep reading that the purpose of degreeing is to 'compensate for machining errors etc'... how exactly does it do that? More importantly, should I bother?

2) Camshaft endplay... how is the best way to check that?

3) Anything else I absolutely need to make sure is perfect or need to not forget when I'm putting it all back together?

Thanks for all the help!

D.Hearne · Jul 4, 2008

I've never degreed a cam. Never had reason to think I needed too either. End play? Install the cam, then the retainer plate, then the timing set and then see if there's any movement forward or back in trying the move the cam gear. There shoudn't be much if any. If there is, you may have the wrong timing set.

SadbutTrue · Jul 5, 2008

Okay next question... what do you Trick Flow (and perhaps other heads) guys do with the alternator mounting bolt on the one head? The threaded side inside the insert is way smaller than the alternator bolt from the stock heads. Do you use a smaller bolt and sleeves? Do you drill out a bigger hole in the aluminum? Do you fab up some sort of bracket to hold the alternator via other bolts?

I've already had an alternator bolt shear off and that was a full-sized one, I imagine the smaller one won't last long...

Thanks!

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