I just picked up a rebuilt 69 350 w/#5 heads on it. I was told that it has the KB Silvolite pistons, which are rated at a compression ratio of 8.4 to 1 on their website. Of course, it does not say with what size combustion chamber head they used to figure out that ratio. My motor has the #5 heads which I believe have a 62cc combustion chamber. Assuming that the heads were not milled, does anyone have a rough idea what the compression ratio range would be?

 

I checked the KB-Silvolite website. Search of the Silvolite section, showed nothing for Oldsmobile. KB search showed only 403/455 pistons.

Post a link to the site, where you got that number, and we can go from there.

Norm

 

Here you go Norm.
http://kb-silvolite.com/spistons.php?sort=S_Div

http://kb-silvolite.com/spistons.php...tails&S_id=566

 

I did receive a reply from their website stating that the compression ratio would be around 8.6 to 1. I was really hoping for a higher number in the 9.5 to 10 range that would run on pump gas and run strong. I have headers and flowmasters as you can see in my sig, but they probably would not help this motor that much due to the low compression. I also wanted to put on a performer RPM manifold and a more aggressive cam, but I believe I need to put in a set of pistons that will bump up my ratio first. Some other posts mentioned badger pistons. Are they the best choice? Am I on the right track with this? Please let me know. Thanks.

 

I like the Speed pro forged flat tops.

 

Thanks.

Using the numbers, from that site:

From one of captjims posts. The one he deleted.

From the opening post.

And assuming nominal (plus or minus nothing) factory dimensions, for the rest of the short block:

.040" gasket = 8.01 to 1
.015" gasket = 8.40 to 1.

My information says they are 68 cc. I don't know, as I have never cc'd one.

For what it's worth, here are the numbers, using 68 cc:

.040" gasket = 7.62 to 1
.000" gasket = 8.20 to 1.

Norm

 

I am definitely not happy with those compression numbers from a power standpoint. I may just throw it in the car and see how it runs, but I guess when I have the money, I will need to buy a set of flat top pistons to get the compression ratio higher. Thanks for the info Norm, greatly appreciated

 

8 to 1 can, and will, run, very well, on pump gas.

Excellent product.

Depends on many factors: What is your goal? Budget? Driving habits? Family car? Daily driver? % street? % race? % other?

How much loss in MPG/driveability can you live with?

Which track you use, depends where you want to go.

Norm

 

Too many people are hung up on "static" compression numbers. Sounds like you have been listening to some of them.

Good start. You can find out what you actually have, before you start "fixing" it.

A cam change might, very well, be a better investment.

I suggest you consult with a good engine machinist/builder, before you start throwing money into the pit.

Norm

 

[PHP]Too many people are hung up on "static" compression numbers. Sounds like you have been listening to some of them.[/PHP]

I have just heard from engine builders and even Summit Tech line that I should have around 9.5 to 10 for a streetable compression ratio that yields the most power.

[PHP]Depends on many factors: What is your goal? Budget? Driving habits? Family car? Daily driver? % street? % race? % other?

How much loss in MPG/driveability can you live with? [/PHP]

This is not a daily driver/family car. It is going to be a fun car that I want to be reliable, run on pump gas, etc. I don't have a track around me so it won't be for racing. I do want to run it on the street with good pull off of the line. I am hoping for this car to be capable of running in the 13's. I have read some other 350 builds on OldsPower, and with minor enhancements these motors can run in that speed range.

I probably will just throw it in first to see how it runs and go from there. Thanks for the advice.

Darrell

 

Tech section on this web site lists #5 heads with 64cc chambers.

 

although I'm a new guy here, I've been running my olds350 with 5 heads since 1968 and I have to say over the last fourty years I have seen #5 heads listed at 62 , 64 , and 68 cc. I for sure will be ccing my heads the next time I have them off.

 

I don't know which "engine builders", but "Summit" is not well known for accurate tech information.

As stated, I doubt that you could ever find anyone who would disagree.

It's a "cut and paste" from 442.com. Nuff said?

In a '33 Plymouth?

Norm

 

Yes , in a '33 plymouth., with a '63 olds rear end

 

I like the way you think.

Norm

 

I sure like the look of that too.

 

I think between 9.5 to 1 and 10.1. I think the #5's are 64cc.

 

I think they're 64cc.

 

I have a question that relates to this topic . . . what's the piston dish volume of the '69 SBO 350 that has 9.0:1 compression?

- GoldOlds