350 sbc reduce compression ratio or retard cam?

[68maliblue]

Sell the Comp cam, or keep it for another project, with lower compression.
Buy a GM cam # 24502476, for around $150 new. 212/222 @.050", .435"/.460", 112 LSA
https://www.gmperformancemotor.com/parts/24502476.html
Installed on a 110 ICL, it will handle the 10:1

Thanks CamKing. The cam I have is 212 @ .050 except it is on a 108 LSA. Would installing it at 110 ICL be the same or does the wider LSA make a difference?

[rfoll]

I am avoiding most of the dished pistons due to their reduced compression height at 1.540

The H815's are 1.550 By the way the stock 1999 vortec engine is listed as 9.4 to 1

I did a re-ring on a stock Vortec engine and the cr measured 9.1:1. Deck clearances, piston volumes, chamber volumes, and gasket volumes are all theoretical.

[CamKing]

If you put your cam on a 110 ICL, you're also putting it in on a 106 ECL
The 106 ECL will delay the exhaust valve opening, increasing cyl heat. It will also increase the exhaust duration past TDC, during overlap.

[CamKing]

One other thing that helps the GM cam work with the 10:1, is the longer seat duration.
The seat duration on your Comp Cam is 260/268. The seat duration on the GM 602 Crate cam is 270/280.
That means, even if both cams were on the same ICL, the intake on the GM cam would be closing 5 degrees later then the Comp cam.

[rfoll]

One other thing that helps the GM cam work with the 10:1, is the longer seat duration.
The seat duration on your Comp Cam is 260/268. The seat duration on the GM 602 Crate cam is 270/280.
That means, even if both cams were on the same ICL, the intake on the GM cam would be closing 5 degrees later then the Comp cam.

I'm confused by your last 2 posts. Wouldn't the 5 degree later GM ex closing cause even more chamber heat?

[68maliblue]

Thanks for the info CamKing.

[CamKing]

One other thing that helps the GM cam work with the 10:1, is the longer seat duration.
The seat duration on your Comp Cam is 260/268. The seat duration on the GM 602 Crate cam is 270/280.
That means, even if both cams were on the same ICL, the intake on the GM cam would be closing 5 degrees later then the Comp cam.

I'm confused by your last 2 posts. Wouldn't the 5 degree later GM ex closing cause even more chamber heat?

No. The 5 degrees earlier exhaust opening will reduce the heat

[novadude]

Why not just use the dished piston that all of the Vortec engines used and be done with it ? Sealed Power H815P or Silvolite 3470HC if you prefer that brand. My 99 Tahoe runs just fine on 87 octane and has a ton of power.

Agree 100%. H815P also gives the benefit of 1.5/1.5/3.0 rings.

[rebelrouser]

Also when they say retard the timing, most of the time just rotating the distributor is not what is called for. Simply retarding the distributor will make it a dog.

Changing the advance curve is what is called for. Performance trends for example will calculate an advance curve on any engine combination, my experience with the program is it is usually very close to what it needs. Most engine combinations like yours will want to spark knock from 2,000 to 3,000 rpm, so to fix the issue simply retarding the curve takes care of the problem. I have an old distributor machine so it makes it easy to set it up, but you can do it with a timing light some graph paper, and a buddy to raise the engine rpm in increments so you can plot the curve. If you are running a common stock rear axle ratio, you will be driving in that 2,000 to 3,000 rpm range most of the time, which is why it makes it a big problem.

And as mentioned, if you get off some money, and buy a camshaft to work well with your combination, it may be a much more satisfying car when done and you will soon forget how much you spent for the camshaft, as you enjoy the results of your labor.

A large number of my customers over the years want to bring me a pile of parts, and make it run super good, I keep telling them that they have decided how good it will run by the parts they selected, I can polish a turd only so much, but I guess I learned a little, because they keep bringing me piles of parts.

[68maliblue]

I think the CS260AH-8 cam is pretty close for the trans and rear gears, I'm just trying to dial in the compression ratio as I have not bought pistons yet. I have used it in past builds and I like its performance for a daily driver. I don't have pistons yet so I have some flexibility on piston type. Anybody have any experience with this piston? For the cost of buying another cam this will get me to 9.4:1 compression and it looks like it help with quench with the d-shaped cup.. I don't have a problem with opening up the top ring end gaps. I have heard KB had issues in the past but does anybody have experience with these currently?


https://uempistons.com/i-28134-kb-hyper ... cc-2v.html

[68maliblue]

[travis]

Most of the issues people have with the KB hypers is not setting the ring gaps correctly

[rebelrouser]

Most of the issues people have with the KB hypers is not setting the ring gaps correctly

My experience is the same, I have used KB pistons for a lot of builds. I ran a 440 mopar that went 10.90's in a 3,400 lb car that had KB pistons for 6 seasons, with no problems at all. One time I even built a 350 SBC with a 6.71 blower for a mini rod tractor, used KB pistons for 3 seasons ran good, the engine broke a rod, piston was not an issue.

[rebelyell]

By its very nature, proper tight Quench can be Very beneficial in preventing detonation.

run a 0.015" - 0.016" shim gasket, do use a piston w/ thin metric ringpak (as does OE L31 vortec)

FYI, NPR America offers off the shelf piston & rings in Ten Over yes +0.010" for L31 and others.

[68maliblue]

FYI, NPR America offers off the shelf piston & rings in Ten Over yes +0.010" for L31 and others.

I wish I could use something like that but this one is going to need .030" to clean up.