11.3:1 CR on pump gas?
Thread Starter
The ORIGINAL and bestest
Joined: Oct 2000
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From: Toronto Ontario
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11.3:1 CR on pump gas?
I have a 406 with Edelbrock Performer RPM heads that I want to switch to AFR units; my current CR is 10.75:1 with the 70cc RPM heads.
If I use the 75cc AFRs, my CR will drop to 10.2:1
If I use the 65cc AFRs, my CR will rise to 11.33:1
I am not changing my cam yet, it is a Comp Xtreme Energy 274 with 230/236 duration and 487/490 lift and 110 LSA.....I will be changing to 1.6 rockers which should add 2-3 degrees duration and change the lift to 520/523.
The AFR techs say that using the 65cc heads with my cam and the 1.6 rockers and 94 Sunoco Gold will be fine at 11.33:1 CR, but I don't think I will have enough duration to bleed off enough cylinder pressure.....am I wrong?
If I use the 75cc AFRs, my CR will drop to 10.2:1
If I use the 65cc AFRs, my CR will rise to 11.33:1
I am not changing my cam yet, it is a Comp Xtreme Energy 274 with 230/236 duration and 487/490 lift and 110 LSA.....I will be changing to 1.6 rockers which should add 2-3 degrees duration and change the lift to 520/523.
The AFR techs say that using the 65cc heads with my cam and the 1.6 rockers and 94 Sunoco Gold will be fine at 11.33:1 CR, but I don't think I will have enough duration to bleed off enough cylinder pressure.....am I wrong?
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
I have a 406 with Edelbrock Performer RPM heads that I want to switch to AFR units; my current CR is 10.75:1 with the 70cc RPM heads.
If I use the 75cc AFRs, my CR will drop to 10.2:1
If I use the 65cc AFRs, my CR will rise to 11.33:1
I am not changing my cam yet, it is a Comp Xtreme Energy 274 with 230/236 duration and 487/490 lift and 110 LSA.....I will be changing to 1.6 rockers which should add 2-3 degrees duration and change the lift to 520/523.
The AFR techs say that using the 65cc heads with my cam and the 1.6 rockers and 94 Sunoco Gold will be fine at 11.33:1 CR, but I don't think I will have enough duration to bleed off enough cylinder pressure.....am I wrong?
If I use the 75cc AFRs, my CR will drop to 10.2:1
If I use the 65cc AFRs, my CR will rise to 11.33:1
I am not changing my cam yet, it is a Comp Xtreme Energy 274 with 230/236 duration and 487/490 lift and 110 LSA.....I will be changing to 1.6 rockers which should add 2-3 degrees duration and change the lift to 520/523.
The AFR techs say that using the 65cc heads with my cam and the 1.6 rockers and 94 Sunoco Gold will be fine at 11.33:1 CR, but I don't think I will have enough duration to bleed off enough cylinder pressure.....am I wrong?
We have built some 383's with 11:3 on compression and we used the Vortec heads which require less timing them most heads and never any problems with 93 pump gas.
You could retart your valve timing a coulple degrees which will lower you dynamic cylinder pressure.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I have a 406 with Edelbrock Performer RPM heads that I want to switch to AFR units; my current CR is 10.75:1 with the 70cc RPM heads.
If I use the 75cc AFRs, my CR will drop to 10.2:1
If I use the 65cc AFRs, my CR will rise to 11.33:1
I am not changing my cam yet, it is a Comp Xtreme Energy 274 with 230/236 duration and 487/490 lift and 110 LSA.....I will be changing to 1.6 rockers which should add 2-3 degrees duration and change the lift to 520/523.
The AFR techs say that using the 65cc heads with my cam and the 1.6 rockers and 94 Sunoco Gold will be fine at 11.33:1 CR, but I don't think I will have enough duration to bleed off enough cylinder pressure.....am I wrong?
If I use the 75cc AFRs, my CR will drop to 10.2:1
If I use the 65cc AFRs, my CR will rise to 11.33:1
I am not changing my cam yet, it is a Comp Xtreme Energy 274 with 230/236 duration and 487/490 lift and 110 LSA.....I will be changing to 1.6 rockers which should add 2-3 degrees duration and change the lift to 520/523.
The AFR techs say that using the 65cc heads with my cam and the 1.6 rockers and 94 Sunoco Gold will be fine at 11.33:1 CR, but I don't think I will have enough duration to bleed off enough cylinder pressure.....am I wrong?
IMO - you would get more power keeping your heads and installing a roller cam with 242/248
Melting Slicks
Joined: Feb 2006
Posts: 2,209
Likes: 0
From: Mo
I ran 12.5 on pg, it's all in the tune for one thing, but also a big cam bleeds off compression kinda tricking the motor. Now I wouldn't try it again, by the time it was detuned it was lazy and was a turd so I just planned 175 mile trips with it. or alot of octane booster
Instructor
Joined: Jan 2008
Posts: 163
Likes: 1
From: Idianapolis Indiana
Depends on where your altitude and gasoline quality in your area. I had a 383 sbc with 10.85:1 in missisippi and it ran great on pump gas. Then I drove the car to southern california. I had to take a lotta timing out just for this area. Cam was just too aggressive. Octane boost in every tank. Gas was good for about 2 weeks then it would detonate.
Racer
Joined: Apr 2008
Posts: 254
Likes: 5
From: ingleside illinois
Well what are you looking for i assume its more power.Your setup doesnt sound to bad the cam is a little small though.If you want the afr heads so bad then get the 75cc and mill the heads a little and you'll have the exact compression you have now.I wuld not do anything over 11.1 and try and run 93 octane.I sure hope you have no n20 and are running 93-Kaboom.DOes afr offer a cnc option on those heads if they do i highly recommend you get it.
Burning Brakes
Joined: Aug 2000
Posts: 1,146
Likes: 2
From: Albuquerque NM
I ran at 11.8 CR on 93 octane
Quench was critical 0.033"
coated piston
6" rod with 3.75" crank...rod ratio
You may want to get the valve coated as they take up a lot of the head's CC surface area.
Or just go with the 10.2 ratio and add nitrous later
Quench was critical 0.033"
coated piston
6" rod with 3.75" crank...rod ratio
You may want to get the valve coated as they take up a lot of the head's CC surface area.
Or just go with the 10.2 ratio and add nitrous later
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