I have been reading allot of threads on what compression you need for pump gas, but havent found much about higher octane. I am thinking about building a stroked 400 (434). It will be used for mud racing. I can get 110 octane at $5 a gallon or 114 for $6.50 a gallon. I want the compression as high as possible and be able to run 110. The classes I run require iron heads. I have a set of 74.5cc open chamber 2v heads that I may use. With these heads what would be the max DCR I can run with 110 octane and not have a problem with detonation. I will be running a 160 thermostat.
Thanks

 

http://cochise.uia.net/pkelley2/dynamicCR.html

this link might help you

 

You cannot build a 434 motor with 75.4cc heads and a cam like a 255DEH that will detonate with 110 Octane fuel, unless you have popup pistons to get the static CR well over 11:1.

Check this out.

http://www.popularhotrodding.com/tec...eze/index.html

Also

www.edyno.com

 

Thanks for the site information. My combination will involve a bigger cam than a 255DEH. I am looking at a combination that is in the range of 11.5:1 static compression and 8.8:1 Dynamic compression. What I have read says 8.8 DCR will work with 110 maybe less. Just wanted to get some ideas from guys that have run these motors outside the normal to see if the 400 will work with this setup. If I have a reason to believe 8.8 DCR will not work then I will lower the Static compression or go even bigger on cam.
Again thanks for your any information.

 

You should be able to run on 98 Octane with 8.8 DCR.

The highest static CR you can get in a 434 with zero deck flattop pistons and 2cc valve relief and 75.4cc combustion chambers is 11.3:1.

 

9.3:1 or so from what i've read. there will be some heat issues and the engine won't last long..comparably...but many hp racing engines push into the 9 range. if you go nuts with a cam you could probably get up to 12 or 13:1 static.

 

what would be the cr with aussie heads 57.8cc way to high i guess

 

someone needs a desktop dyno...and the book to make it work right etc. If you can't get what you want from 11:1 you need to go with a 460 bored etc.

Playing with ultra high numbers will cost you big time $$$ and you will likely not be competitve cause you will break and bleed. Go with a bit more than whats proven thus far but if you go much beyond you will end up putting in too much powder and blowing the thing up so to speak.

Those that build these monster engines either buy a proven kit that tons of research has developed or do tons of research and build up to it..like reloading ammo...a bit at a time. There is no proven kit beyond what tmi has put together...mess with the static and dynamic due to expected octane but keep it reasonable like, maybe 10.5:1 scr and 9.0 dcr- get the cam to make that work then try to get the supporting parts ie heads, intake and exhaust to support that. It will be a screamer with torque that will bust parts but it is more likely to produce something viable than shooting for the moon out of the gate. And you will be adding some K to those who are working with the 400.


My .02

 

roger what do you think of 7.96 dynamic cr and 9.25 static cr for 400? xe256h-10 cam?

 

http://www.tmeyerinc.com/pistoncompare.html

 

That should be a nice combo, plenty of low end torque. You should do some porting work to take advantage of the extra lift from the XE256 cam and extend the RPM range. Roller rockers, double roller timing chain, headers, and 600 cfm carb are also desireable.

 

can i install roller rocker with my cam without machining my head? I tought i need a retro cam kit. Did hydraulic roller tappets will work? For the porting,should i port only the exaust side?

 

You can get Scorpion Pedastal Mount Roller Rockers. You do not need to machine the head.

Use regular hydraulic tappets with the XE265 cam.

Do not port the intake side, just clean up the valve pockets and smooth out the exhaust port.

 

thankx a lot guys.