Hemi questions

I posted most of this information in another thread, but haven't gotten much feedback, so I thought I'd post it again here.

My machinist built a motor to put in another car that he has offered to sell to me for a much cheaper price than I could even build a wedge headed motor from scratch. It is an AR Hemi motor. It was initially intended to use a 14-71blower with alcohol, but I will be placing the motor in a 2010 Shelby GT500 backhalf Outlaw 10.5 car and will be using twin turbos. The car should weigh around 3000-3100 with driver. Some of the specs are listed below.

604 cid
AR aluminum block with 11.200" deck height and front gear drive/mag drive
4.50" bore
4.75" stroke
Bryant billet crank
AR Hemi heads (2nd generation, not raised intake runner?)
2.40" titanium intake valves and 1.90" titanium exhaust valves
Brooks aluminum rods
Arias pistons yielding 11.7:1 comp ratio
dry sump oiling system


I'm gonna likely run twin 88mm turbos from Precision. The fuel will be alcohol. It will be EFI controlled by Big Stuff 3. I'm planning on using a crank trigger and MSD Pro Mag 44 for the ignition system. The tranny will be a Powerglide.

I'm considering switching out the exhaust valves to Inconel, as I'm not sure that the titanium exhaust valves could withstand the heat generated by the turbo setup, particularly preceding the launch when timing is retarded to help the turbos spool faster.

I do not believe that the heads are the most recent version with the raised intake runners, but for the price that I can get the motor it is hard to pass up. Am I going to regret not having the best available hemi heads? I suspect that the motor will make more horsepower than I will ever be able to use even without the better heads.

What would be a reasonable maximum rpm to turn the motor and what would be the longevity of such a motor between teardowns. My machinist thinks that I can get 60-70 passes out of the motor if I limit rpm to less than 8000.

I'm looking forward to any feedback or questions that you guys may have.

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The block has been previously run, but the entire rotating assembly and valvetrain is new. I'm thinking 15-20 psi boost initially for 1800-2000 hp with eventual plans to increase to 30 psi for 2500+ hp.

That sounds really nice. Heads are certainly important, but quit worrying about having the "latest and the best" heads and instead work on your existing combo and you have the potential to be right up there with the other guys. The additional power gained from replacing those heads with the latest version might not justify their final, total cost.

Paul

i would'nt think a 4.75 stroke would like 8000 too much.JMO.......and it should make an ass load of power with twins way before 8000 too.

80-100 runs is very reasonable with a turbo motor. Dont worry about the heads in this build the turbos will be the limiting factor no matter what size you choose. the inconel valves would be a plus.

as far as the rpm, I don't know much about those heads or your camshaft and such but I will say that most of the major turbo racers are using much higher rpm's than most think. I know some of the local racers, which are pretty fast in the turbo world, spin their big blocks 10,000+. Not saying that you need that but I was just giving you a reference.

If you want to turn high RPM I'd say more bore and less stroke would be a good idea. You need to consider the piston speed, not to mention valvetrain - springs get expensive. Don't quite get why they used a 4.5" bore. A 4.6" bore x 4.5" stroke would have been 598 ci. Think shoud focus on how to make the power with the turbo's in the 5,000 - 7,000 RPM range and not worry about the latest heads or spinning it like a N/A.

Steve