Compression Ratio Question?
Junior Member
Joined: Jun 2006
Posts: 343
From: Canton PA
RE: Compression Ratio Question?
ORIGINAL: 2000BlazerSS
Your heads aren't possibly Vortec's they were released on trucks in 1996 (V8's). You have plain ordinary combustion chambers and a plain ordinary cylinder head. As far as running 12 point anythings on the street you have to have an engine designed for that compression and no octane, or your going to go into detonations anytime you get in it. When THAT ahppens don't have a knock sensor still on your engine.
To eliminate detonation, which is the biggest destroyer of engines you have to have cool EVERYTHING, and you'll see that when GM started raising compression to near 10 to one they did it on engines with aluminum heads, USUALLY you can run 1/2 to 3/4 point MORE compression with aluminum heads over iron heads. Cool air is a MUST with higher compression, it helps prevent/delay detonation, the cooler the better.
Camshaft design also affects how high a compression ratio you can run. Anyone who's racing in the "pump gas" class knows what it takes to run high compression and 93 octane gas. Read about it when Hot Rod or Car Craft runs article on pump gas drags, and what they do to the engines.
A 4.3 can't run 12-1, can't run 11-1, and is pushing it at 10-1. I say can't because it can't, the special cam and aluminum heads aren't available to begin with.
In YOUR case, with YOUR engine, may I seriously suggest nitrous?. That's the only way your going to afford over 250 real horsepower.
Your heads aren't possibly Vortec's they were released on trucks in 1996 (V8's). You have plain ordinary combustion chambers and a plain ordinary cylinder head. As far as running 12 point anythings on the street you have to have an engine designed for that compression and no octane, or your going to go into detonations anytime you get in it. When THAT ahppens don't have a knock sensor still on your engine.
To eliminate detonation, which is the biggest destroyer of engines you have to have cool EVERYTHING, and you'll see that when GM started raising compression to near 10 to one they did it on engines with aluminum heads, USUALLY you can run 1/2 to 3/4 point MORE compression with aluminum heads over iron heads. Cool air is a MUST with higher compression, it helps prevent/delay detonation, the cooler the better.
Camshaft design also affects how high a compression ratio you can run. Anyone who's racing in the "pump gas" class knows what it takes to run high compression and 93 octane gas. Read about it when Hot Rod or Car Craft runs article on pump gas drags, and what they do to the engines.
A 4.3 can't run 12-1, can't run 11-1, and is pushing it at 10-1. I say can't because it can't, the special cam and aluminum heads aren't available to begin with.
In YOUR case, with YOUR engine, may I seriously suggest nitrous?. That's the only way your going to afford over 250 real horsepower.
http://www.hotrod.com/techarticles/e..._engine_build/
They made over 250 HP. But they were not using a 12:1 compression they ended up using 9.08:1
Jackal: You may want to look into to what they did. If you do let me know how it turned out and roughly how much you spent. Is yours FI? If it is I defenately am interested. I need more power out of my blazer for towing and running the larger tires. besides trying to do a front and rear gear change to 3.73 or 4.10's
I don't know everything about motors Yet! But will be getting my head filled with the knowledge there is here shortly.
Thread Starter
Joined: Dec 2006
Posts: 48
From:
RE: Compression Ratio Question?
Thanks Bro...
I deffunatly will, i am running 12:1 cr. You may not want to do that for towing. I also do not know everyting about engines. If knowledge was a beach i would the amount of a grain of sand! I am hear to learn, thats why i am trying to build power below my cams capabilities. I have ran 12.5:1 one on many Street cars so it depends on what your looking for. An engine simply needs to breath, wheather its a cam, headers, heads, back cut valves, and so on. Your looking for ways to increase Volumetric efficiancy, which is a fancy way of saying what percent of air fuel mixture you can squaze through a 4.3l.
I deffunatly will, i am running 12:1 cr. You may not want to do that for towing. I also do not know everyting about engines. If knowledge was a beach i would the amount of a grain of sand! I am hear to learn, thats why i am trying to build power below my cams capabilities. I have ran 12.5:1 one on many Street cars so it depends on what your looking for. An engine simply needs to breath, wheather its a cam, headers, heads, back cut valves, and so on. Your looking for ways to increase Volumetric efficiancy, which is a fancy way of saying what percent of air fuel mixture you can squaze through a 4.3l.
Thread Starter
Joined: Dec 2006
Posts: 48
From:
RE: Compression Ratio Question?
Heres the cam i am going to run.
LUNATI Solid Lifter Camshaft for the Chevrolet V6 262 Engine. Part # 43507 Grind # M-239-249 Serial # T6KT Lobe Sep 106. Ex Closes @ 14.5 ATDC Ex Opens @ 54.5 BBDC In Opens @ 17.5 BTDC In Closes @ 41.5 ABDC. Duration @ .050 is 239/249 Advertised is 278/288. .517/.542 Lift, with a 1.5 Rocker and valve adjustment is .018/.020. it should be pretty sweet!
LUNATI Solid Lifter Camshaft for the Chevrolet V6 262 Engine. Part # 43507 Grind # M-239-249 Serial # T6KT Lobe Sep 106. Ex Closes @ 14.5 ATDC Ex Opens @ 54.5 BBDC In Opens @ 17.5 BTDC In Closes @ 41.5 ABDC. Duration @ .050 is 239/249 Advertised is 278/288. .517/.542 Lift, with a 1.5 Rocker and valve adjustment is .018/.020. it should be pretty sweet!
Junior Member
Joined: Jun 2006
Posts: 343
From: Canton PA
RE: Compression Ratio Question?
I'm not sure. I just tried the link and it worked for me.
Here is the orginal post it was brought up in.
https://blazerforum.com/m_63537/tm.htm
There is 2 links in that one from hotrod. I couldn't figure out what issue it was in.
Here is the orginal post it was brought up in.
https://blazerforum.com/m_63537/tm.htm
There is 2 links in that one from hotrod. I couldn't figure out what issue it was in.
Joined: Dec 2006
Posts: 45
From:
RE: Compression Ratio Question?
After ceanern posted it worked I posted I went to the site using his link. The story was about a 262 that was built by Hot Rod. The engine is TOTALLY a street/race engine, but go there using the link and see. I figured when it didn't show up you deleted it because I refered to Jackle as Jerkle. There was more to what I said than just that but the article is on an engine that wouldn't pass a smog test, and they speak of having a super hard problem coming up with a decent set of heads. If the 96 and/or later 4.3's had true Vortec heads they would have used those, they didn't they spend big money trying to get a stock head to work. Like I say, unless I look at a96 and later 4.3 head and compare it to the V8 vortec on my bench I'll wait.
PS: Around 86/87 I built a "performance" 90 degree V6 for display at the engine plant. I built it using a set of aluminum heads and intake donated by Chevy in Michigan. The intake looked like an old "Smokey Ram", neat as hell. But not available for years. Chevy made a bunch of stuff like this back in the 80's.
PS: Around 86/87 I built a "performance" 90 degree V6 for display at the engine plant. I built it using a set of aluminum heads and intake donated by Chevy in Michigan. The intake looked like an old "Smokey Ram", neat as hell. But not available for years. Chevy made a bunch of stuff like this back in the 80's.
Thread Starter
Joined: Dec 2006
Posts: 48
From:
RE: Compression Ratio Question?
I will be running my 97 vortec heads, which are steal. I am running the older bottum end, before the balance shaft. I am certain you know your stuff, things are probaly getting lost in my deciffering of what your trying to say. I do not have to pass any smog tests here. Also stop living in the 70's and 80's cause that was 37, and 27 yrs ago. To be honest i don't even know how to rebuild a carburator, but to me that would be asking me how to tune a steam engine, i have no use for knowing that.