Question for the HEMI guys

[Bigal75]

I've always heard that you could run more compression in a HEMI certainly with aluminum heads- any one running 12:1 on pump gas?

 

[Meep-Meep]

I have an iron head one in my 66 Charger. I didn't build it but it blows about 215 PSI and idles like a 318 so I'm thinking it has the repo cam with factory compression. I am running pump 91 and can get it to ping under heavy acceleration but normal driving seems to be OK. I think 12:1 with pump gas is a stretch at best, even for a hemi, but I can't say for sure. On E85 it will work and probably want more.

 

[Bigal75]

I'm talking regular fuel - 94 octane. It's just I've seen people build them from 9:1 to 11.8 and these people claim no issues. I would hope not to have issues at 9:1 - in fact I would think that's too low.

A buddy of mine runs 12:1 in a 383 SBC, aluminum heads and decent solid roller. He's never had issues running pump fuel.

I was just curius to see what people run.

 

[Meep-Meep]

94 octane is a dream here in CA!!

 

[Sixpack70]

9:1 in a hemi is blasphemy! Lol

 

[HEMI-ITIS]

I have 8:1 in mine with steel heads:grin:
The hemi head is more resistant to detonation than any wedge design.12:1 might be pushing the limit depending on the cam & ignition timing:eusa_think:

 

[super-bee_ski]

nope,
I'm a "May 1969" Hemi with Hansen Stage V Aluminum Heads, and like a 9.8-1 compression...(I think)

 

[george68hemirr]

572 keith black aluminum block/stage v big valve aluminum heads.....11.5 to 1 compression max running 93 octane......no problems

see how it runs
http://www.flickr.com/photos/dodgeautos/5189537576/

runs 10.38/128 at the track

 

[b-star69]

Must see

572 keith black aluminum block/stage v big valve aluminum heads.....11.5 to 1 compression max running 93 octane......no problems

see how it runs
http://www.flickr.com/photos/dodgeautos/5189537576/

runs 10.38/128 at the track

The guy in the video said it all! very cool roadrunner.:3gears:

 

[snakeoil24]

What are you doing with the motor?

Mine is 9.6:1 472 single 4 mechanical street roller. Gas sucks E85 would be far better. Why do you want Hi compression? Iron heads up to 10:1 after Stage 5 heads only!!!!!!!

 

[Hemirunner]

I run an aluminum headed 572 hemi with 12:1 static on 93 octane pump. I run straight 110 or a 93/110 blend when I race as we're spraying a 300 shot.

 

[Bigal75]

I run an aluminum headed 572 hemi with 12:1 static on 93 octane pump. I run straight 110 or a 93/110 blend when I race as we're spraying a 300 shot.

So no issues at 12:1?

 

[Hemirunner]

It's all about dynamic compression ratio. The cam's intake closing point is taylored to keep the dynamic compression at a level that will tolerate 93 octane. This motor made 735hp on the dyno and put 1050hp to the flywheel on the spray. Stock appearing engine with all the nitrous hidden using hand ported early MP aluminum heads.

 

[Budnicks]

11:1 is very manageable, especially on the street & 94 octane gasoline {we would love to have 94 oct. here in Ca., freaken Liberal Environmental ****}, 12:1 with E-85 maybe, or using the proper camshaft, bleeding of compression with valve overlap {but that can kind of, defeats the purpose of having higher compression piston} also the ignition timing & fuel tuning, "maybe" will work on 94 octane gasoline "safely"... There are electronic devises out there that will back of/retard ignition timing under loads, to help with detonation issues {maybe even you could add a knock sensor, in the valley pan or somewhere else, like they have on modern EFI cars, to trigger the ignition retard}, you could also add Methanol/water injection, that will help a ton... But, either way you go, make sure you have/leave "no sharp edges" on any of the components in the combustion chamber or on the piston tops, valve reliefs, edge of the cylinder, combustion chamber etc., they will make any "possibility of detonation", much much worse, they will cause hot spots on any engine, not just the HEMI... Do nice smooth radius's on everything Have fun & Happy Moparing