11.25:1 compression...bad news?
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
11.25:1 compression...bad news?
I have a .003 deck, -4cc flat top pistons, 4.030 bore, 3.75 stroke and a .039 compressed head gasket which equates to @ 11.25:1 compression. The cam is a hydraulic roller with 242/248 duration @ .050 and the motor is carbed with alum heads.
Will this thing run on premium pump or am I gonna have to use race gas? Is anyone here on the forum successfully running this much compression on pump gas?
Will this thing run on premium pump or am I gonna have to use race gas? Is anyone here on the forum successfully running this much compression on pump gas?
Le Mans Master
Joined: Oct 2002
Posts: 5,714
Likes: 6
From: Silver City NM
St. Jude Donor '05-'07
Originally Posted by nastee383
I have a .003 deck, -4cc flat top pistons, 4.030 bore, 3.75 stroke and a .039 compressed head gasket which equates to @ 11.25:1 compression. The cam is a hydraulic roller with 242/248 duration @ .050 and the motor is carbed with alum heads.
Will this thing run on premium pump or am I gonna have to use race gas? Is anyone here on the forum successfully running this much compression on pump gas?
Will this thing run on premium pump or am I gonna have to use race gas? Is anyone here on the forum successfully running this much compression on pump gas?
http://www.maxlead2000.com/
Dep
Pro
Joined: Oct 2003
Posts: 641
Likes: 2
From: Storm lake Iowa
Maybe...the guy a bought my car from claimed compression is 11.25:1, but he's not a completely reliable witness. I run 92 or 93 octane pump gas, add a little lead additive/octane booster to every tank, and it runs fine. I don't get pinging (since I adjusted the timing...12 degrees initial), but I DID get horrible dieseling when I had to put 5 gallons of 89 octane in one time when I ran out of gas. There are many factors involved in this though...I'd suggest you tank up and try it. If you get pinging, retard your timing a little until it stops, then consider a more permanent solution...I'm sure lots of people will chime in with suggestions. My guess is you'll be able to pull it off.
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
EddieJ82 runs 12:1 on pump gas with aluminum heads..
However, I doubt that you have that much compression because I believe that your bowls are blended.. This increases the size of the bowls and drops the compression..
My compression would be over 12:1 with the bowls untouched, but it is 11.71:1 with the bowls ported..
However, I doubt that you have that much compression because I believe that your bowls are blended.. This increases the size of the bowls and drops the compression..
My compression would be over 12:1 with the bowls untouched, but it is 11.71:1 with the bowls ported..
Last edited by GrandSportC3; May 8, 2005 at 10:02 PM.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I am running 11:1 with the same duration cam, I usually run 94 octane but is OK with 92, had the timing up to 40 deg with no pinging, I don't run a vacuum advance which probably helps 
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
I have several factory engines over 11-1, a 1970 LT1, 1966 L72 and a L78 in a 67 Camaro. All work very well with premium pump gas and without additives. My total advance is 36-38 degrees at 3000 rpms.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by DJ Dep
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by GrandSportC3
EddieJ82 runs 12:1 on pump gas with aluminum heads..
However, I doubt that you have that much compression because I believe that your bowls are blended.. This increases the size of the bowls and drops the compression..
My compression would be over 12:1 with the bowls untouched, but it is 11.71:1 with the bowls ported..
However, I doubt that you have that much compression because I believe that your bowls are blended.. This increases the size of the bowls and drops the compression..
My compression would be over 12:1 with the bowls untouched, but it is 11.71:1 with the bowls ported..
By the way, can you run pump gas on a regular basis?
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by MotorHead
I am running 11:1 with the same duration cam, I usually run 94 octane but is OK with 92, had the timing up to 40 deg with no pinging, I don't run a vacuum advance which probably helps
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by turtlevette
what's the cc of the heads? You are probably calculating it on the high side. Its hard to believe you can get that high of a compression with flat tops and thick head gasket.
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Originally Posted by SkunkApe
Over at the Viper forum, some owners are running water or water/methanol(?) injection systems to prevent detonation. Not sure if this would help your situation.
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Originally Posted by nastee383
I'll find out what the bowls look like soon. I'm changing valve springs to beehives. Mark said it was about 10.7:1. I'd feel better about that.
By the way, can you run pump gas on a regular basis?
By the way, can you run pump gas on a regular basis?
A lot also depends on the duration of your cam.. My cam is HUGE and bleeds some of the compression off......
BTW - your cam is also a pretty big cam (not huge but big) and should bleed some of the compression off. There are some sites where you can calcuaste dynamic compression ratio... I'm pretty sure that even with 11.25 : 1 and aluminum heads, you should be ok..
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
On my old iron head 383, I did the math and the CR that I calculated was 10.50 : 1 and the engine was advertised as 9.8 : 1. I called AR and they told me that blending the bowls chaned the compression ratio and that it was somewhere around 9.8 - 10.0. I always ran 93 octane in that engine without any issues... 10.0 is supposed to be the highest that you can go with iron heads...
If I remember correctly, they ported the chambers from 64 cc to 68 cc...
If I remember correctly, they ported the chambers from 64 cc to 68 cc...
Last edited by GrandSportC3; May 9, 2005 at 12:19 AM.
Le Mans Master
Joined: Oct 2002
Posts: 5,714
Likes: 6
From: Silver City NM
St. Jude Donor '05-'07
Originally Posted by nastee383
That's what I DON'T want, to have to add additives every time I fill up.
Dep
Race Director
Joined: Jun 2000
Posts: 10,051
Likes: 677
From: FL
Here is a great quote:
"Because without reference to the camshaft specs, talking about (static) CR is next to meaningless!"
http://www.kennedysdynotune.com/Dyna...ion%20Tech.htm
What you really need to concerned with is your "Dynamic Compression Ratio". The above link is to a good tech article and a Google search will yield some free DCR calculators.
EDIT: Better link with a downloadable calculator: http://members.uia.net/pkelley2/DynamicCR.html
"Because without reference to the camshaft specs, talking about (static) CR is next to meaningless!"
http://www.kennedysdynotune.com/Dyna...ion%20Tech.htm
What you really need to concerned with is your "Dynamic Compression Ratio". The above link is to a good tech article and a Google search will yield some free DCR calculators.
EDIT: Better link with a downloadable calculator: http://members.uia.net/pkelley2/DynamicCR.html
Last edited by SteveG75; May 9, 2005 at 09:31 AM.
Le Mans Master
Joined: Oct 2002
Posts: 5,714
Likes: 6
From: Silver City NM
St. Jude Donor '05-'07
Originally Posted by SteveG75
Here is a great quote:
"Because without reference to the camshaft specs, talking about (static) CR is next to meaningless!"
http://www.kennedysdynotune.com/Dyna...ion%20Tech.htm
What you really need to concerned with is your "Dynamic Compression Ratio". The above link is to a good tech article and a Google search will yield some free DCR calculators.
EDIT: Better link with a downloadable calculator: http://members.uia.net/pkelley2/DynamicCR.html
"Because without reference to the camshaft specs, talking about (static) CR is next to meaningless!"
http://www.kennedysdynotune.com/Dyna...ion%20Tech.htm
What you really need to concerned with is your "Dynamic Compression Ratio". The above link is to a good tech article and a Google search will yield some free DCR calculators.
EDIT: Better link with a downloadable calculator: http://members.uia.net/pkelley2/DynamicCR.html
Most custom grinds are $349.95.
Hmmmm....always follow the money trail.
Dep