1971olds350

how do you get 9.5.1 out of an 1971 olds 350 with #7 heads

Wireman134

Get some 10.25:1 6cc dished pistons shave the heads maybe .015" and use a .040 head gasket, or flat tops and minimal cut on the heads. Check this out http://www.csgnetwork.com/compcalc.html

1971olds350

Enter Cylinder Bore Size =4.087 (.30)
Enter Piston Stroke Length =6
Enter Head Gasket Bore Diameter =4.260
Enter Compressed Head Thickness = .051 (mondellos PT-519 head Gasket)
Enter Combustion Chamber Volume In CCs = 82cc (11.9 from head gasket 5cc from 3 angle valve job)
Enter Piston Dome Volume In CCs = -11.9 (mondello #2020+.30 pistons)
Enter Piston Deck Clearance = .020

equals about 9.6:1 comp ratio im a rookie so how did i do

captjim

Couple of little things, it's kinda confusing.
1) Bore 4.087 correct
2) stroke is 3.385" 6" is the rod length, it does not affect stroke.
3) head gasket bore, 4.26" correct
4) head gasket thickness .051 sounds like a lot, but if so, correct
5) chamber volume. This is incorrect, you already factored in the head gasket, here you want the head chamber only, call it 70 cc.
6) piston volume is zero. That is listed as a flat top in their catalog, no dome, no dish
7) deck clearance .020 correct

So, assuming the head volume at 70 (just a guess) Cr is right around 9.5 to 1

1971olds350

the stock head volume for #7 heads is 64cc.. is it true that when you have the machine shop do the 3 angle valve job it adds about 5 cc's more or less?? and how do you set deck height when building an engine i'm confused on that one

captjim

The head volume is usually around 68cc. If you sink the valves, you can add a little, but 5cc sounds like a lot to me. You don't really "set" the deck height. What you do is mock up the engine and measure how far down in the bore the piston is (I check the 4 corners, cylinders 1,2,7,& 8) then disassemble the engine and have however much you want milled off. This is called "decking the block" Zero deck means the piston is even or flush with the top of the block. I recently installed a set of those pistons in my 355 and they say .024 down. When you stated ,.020, I thought that you had measured it. To get an accurate CR, you must measure everything.

1971olds350

im gussing your cr is around 10 to 1 if your using .040 head gaskets. so decking the block is done by measuring the deck height first then machining the block down to where you want it or do you machine the pistons to where you want them

captjim

You don't normally machine the tops of the pistons. In most instances, the pistons sit down in the bore, seldom do they protrude out the top of the bore. So, to get it where you need it to be, you generally deck the block. This also squares it off, making it mice and flat, too.

88 coupe

What do you mean by, "mock up"? How is it done, and why?

Norm

captjim

The guy who started this thread has not been here for 4 days, so he is not interested. I know that I know how to do it and I'm pretty darn sure that you know. So, what reason can there possibly be for this post? Obviously, trolling for an argument. Stirring up shyt, like you always do. Just like your last post in this https://classicoldsmobile.com/forums...pedestals.html thread. You love drama and conflict, and if there isn't any you will try and create it. I'm not biting. BTW, do you think you would have been as nice to 1971olds350 as I was when pointing out his mistakes? Rhetorical question, obviously.

1971olds350

not interested?? i love oldsmobiles and aren't fourms for people that want to help one another i'm going to start building my 1971 olds 350 real soon and needed a little guidiance, is there a problem with that if so you should of never replyed

88 coupe

A "gearheads" thirst for knowledge, would be one of many.

You will find out, as soon as I begin addressing his/her original post.

You asked two questions, and I answered both, in good faith.

I have no doubt that you do.

As a matter of fact, I have no idea what you were talking about. Which goes back to your original question:

It was, a simple request for clarification.

It was not, to provide another "soapbox" for you to continue your childish rants.

Norm

z11375ss

Capn, haven't you had enough of "Norm"? Ignore list him. We all know what a mock up is for goodness sake. 1971olds350, wait util you've been "Normed" a couple of times. Your tune will change.

88 coupe

I don't think so, Tim.

Norm

csstrux

OK I"ll bite. I have never done more than put a cam in a sbc and minor work, so this isn't smart assed anything. I'm a tin knocker not a whench. WTF is "mocking up" how is it done, and what does it do, or a better question would be what are the bennifits? This my first serious attempt at a solid build up, and would like to know as much as possable before I find out the hard way that I'v stepped in it.

88 coupe

Not true.

If you would like to discuss the subject further, do it in a PM. Or, if you need to discuss it in public, you can start a new thread, in the proper forum.

And so you know where I stand: BS/inflammatory posts, such as this one, belong on OP (Oldspower) and/or ROP (Realoldspower).

It does not belong, here, on CO (Classic Oldsmobile).


Back on topic: We are waiting for captjim to tell us WTF he is talking about.

Norm

captjim

" Back on topic: We are waiting for captjim to tell us WTF he is talking about."

Thanks anyway, but I think I'll pass on that. If I answer, I'm "arguing" and statements like this get made by Wireman
" Captjim will argue with a tree"
or this by Bosco1956
"captdumbass is more like it "

If I don't answer, I get smart-a$$ comments like these from 88 coupe
"Would it be fair to say, this silence is deafening?" or
"Anyone else, hear all the crickets?"

You can't have it both ways. Either the site is conducive to guys feeling comfortable exchanging their thoughts and ideas without fear of being humiliated and insulted, or it isn't. And it isn't, IMO. So, I am off to the shop, we just finished up a BBF pump gas stroker that made 875 HP that I got to help build and I need to get it off the dyno. Big fun!!

88 coupe

This "excuse" did not stick to the wall,

any more than this one.


Here it is again:

We know, we can expect "excuses" from any common BS artist.

Norm

captjim

https://classicoldsmobile.com/forums...html#post44638

Order all the parts, bearings, pistons, etc. Get your block machine work done. Once you get them, mock up the engine with the crank in place. Have the pistons pressed onto the rods. Install 4 piston/rod assemblies into the 4 corner cylinders, #1, #2, #7, and #8. Do NOT install the rings. Torque the rods and mains down to the desired specs. Rotate the engine and measure how far from the top of the block each piston is at TDC using a dial indicator or depth gauge. Use a Sharpie and write the # down on each corner of the block. Say that the pistons are .025 down in the hole on average. There may be a slight variance, and usually is, not a big deal. You want the pistons down .010, not .025. So, you remove everything and send the block back to the machine shop and have the deck milled .015. .025 minus the .015 you mill off will leave you with the desired .010 deck clearance. You could also not mill any off and use a .028 gasket and get 9.6 to 1. Or, zero flat top pistons deck and have a custom 8 cc dish milled into them to get 9.7 to 1. You could use a flat top piston zero decked and a larger chambered #8 head and mill it down to 75cc and get 9.7 to 1. There are several ways to get what you need using the 4 basic factors that I mentioned in the beginning of this. I do like having the block milled, then you know that you have a nice flat, square surface, along with fine tuning the Cr.

smcurro

That's some great info! Reading your post really helped me figure out the way I want to go with my 350...

88 coupe

Now, that wasn't hard, was it?

Norm

captjim

Glad to help. We are limited in piston choices, but there are several head and gasket options to get the desired Cr.

88 coupe

Assuming, your engine is still at factory specifications, the pistons are the only change, and guessing 5cc for the valve reliefs.





Norm

Oldsguy

Very interesting information. I appreciate the help. I have never assembled a short block myself (always taken the easy route and had the machine shop do it, get back a block, crank, rods, pistons and all the bearings and rings assembled and ready to go). This is the kind of thing we need on Joe's tech forum.

captjim

The entire article is in that link, feel free to use it if you think it might be of value to anyone.

88 coupe

Still using factory numbers and Mondello 2020+30 pistons, but substituting PT-513 in place of your PT-519:





Mondello "tech line" can tell you the actual volume of the valve reliefs, but the chamber volume, piston to deck, and deck height, cannot be verified until you take the engine apart.

Norm

88 coupe

Are you still with us?

Norm