Forced Induction Time For A New Motor....???s

[Bob Hughes]

Ok so against my tuners warnings I ran my car pretty hard last weekend in the cold NJ air and either spun a bearing or bent a rod. Not even going to take my engine out right now as I have a teksid block prepped ready for fresh start. My main concern is pistons....I'm currently running an m112 but may or may not jump up to a bigger whipple. I can still drop one pulley size on my eaton but increase air temps with the bigger boost numbers. Should I go with valve relieved flat tops or go with a dished piston? I've seen different cc dish pistons but I'm not sure what's best choice. Plan on doing cams and more than likely heads as well. But the pistons are where I'm stuck. Any help is much appreciated.

 

[trombonedemon]

http://www.google.com/url?sa=t&source=web&cd=1&ved=0CCgQFjAA&url=http://www.badasscars.com/index.cfm/page/ptype=product/product_id=362/prd362.htm&ei=LcCoUoSxO6bIsASxgoJY&usg=AFQjCNH_YJZO0NcItV-0-DaeiUXQldDhnw&sig2=SqfSCfXEz-TJAt0YI_OrRA
Some good info....

 

[Bob Hughes]

Thanks. I'm gonna go with 18cc dished keep my compression down. Blocks at shop now getting inspected and cylinders mic'd. Waiting for specs on cylinders to order right bore. Wanna keep stock bored if I can

 

[sneaky98gt]

IIRC, the stock GT pistons are -18 cc, which give about 9.5:1 compression. -11 cc (96-98 2-valves, I think) give close to 11:1. And flat tops give close to 12.5:1.

If you are only planning to run 93, I'd say stick with the stock -18 cc's. If you were going to run E85 or race gas, I might would consider the -11 cc.

 

[Deleted member 38176]

-18cc here and stock 9.5 cr. I wouldn't go any higher in compression than stock with boost.....unless you're running some serious octane or meth, like sneaky mentioned. Even with that I wouldn't go any lower than -11cc o -13cc pistons.

 

[sneaky98gt]

-18cc here and stock 9.5 cr. I wouldn't go any higher in compression than stock with boost.....unless you're running some serious octane or meth, like sneaky mentioned. Even with that I wouldn't go any lower than -11cc o -13cc pistons.

I will say, though. If I was in his shoes, and definitely wanted to stay with the Eaton, I'd pretty heavily consider doing a higher compression build (10.5ish) and running E85. The higher compression would allow him to spin the blower a little slower and closer to its efficiency range, and the E85 would keep detonation away even with a LOT of timing. I suspect a build like this would net 500+ rwhp.

On the other hand, if going to a better blower or turbo was a strong possibility (sounds like it is), I'd keep it lower compression. The better blower would allow for more boost at a cooler temp, and wouldn't really need the compression to get the same cylinder pressure. And obviously, there wouldn't be nearly as much a need for higher octane with this type of setup.

 

[sneaky98gt]

Also, OP, do you have the specs yet on bore size? If it's stock bore, do you have any reservations about running 03 Cobra pistons? I'll know for sure tomorrow, but I might be getting a set that I'm not going to use.

 

[Bob Hughes]

I've built sport bike motors before never tackled a motor like this and I'm planning on going for around 600hp (currently 455) so I will be swapping out the eaton for either a kb or a whipple but financially that may be waiting. My teksid block is at a machine shop now having the bores all measured if they are all in spec I'm keeping standard bore. Are these cobra pistons u have new? I already have a new set if manley terminator rods for it. Been looking for a cobra crank can't get new any more MMR is out of stock on their 4.6 cranks so still figuring that part out. My other thing is my 3650 not handling the power and I didn't wanna do a t56 swap did research found Hanlon motor sports and they're close to me build track ready 3650s.

 

[flstang65]

I agree with the other guys. I like to build my motors with dished pistons if they are running a power adder.

 

[sneaky98gt]

I've built sport bike motors before never tackled a motor like this and I'm planning on going for around 600hp (currently 455) so I will be swapping out the eaton for either a kb or a whipple but financially that may be waiting. My teksid block is at a machine shop now having the bores all measured if they are all in spec I'm keeping standard bore. Are these cobra pistons u have new? I already have a new set if manley terminator rods for it. Been looking for a cobra crank can't get new any more MMR is out of stock on their 4.6 cranks so still figuring that part out. My other thing is my 3650 not handling the power and I didn't wanna do a t56 swap did research found Hanlon motor sports and they're close to me build track ready 3650s.

I wound up deciding to keep the pistons I got. Don't want to spill the beans yet, but let's just say I think they'll look good in my motor.

If you're only going for 6oo hp, is there a need to upgrade to a forged crank? I was thinking the stock crank was good to around 600 horsepower or so.

 

[Bob Hughes]

I'm setting bar low at 600 figure I have everything apart might as well do it one time. I'd love to have 700+ so beef up everything. I talked to machine shop today I'll have my block back tomorrow and ordering pistons. I'm figuring stock bore manley 18cc dish

 

[Deleted member 38176]

The stock crank is good to over 600rwhp as long as you don't rev the crap of it.

Also, Im not sure of how much the shop would charge (if cost is a concern) to bore the cylinders, but why not bore it out while you have the chance? Looking back, I wish I would have spent just a few extra bucks to bore it to a 3.7.

BTW, ModMax has plenty of forged 4.6 cranks in stock.

 

[Bob Hughes]

It's only $200 on average to torque plate bore and hone around me. I know the sleeves are ok to go .020 over but I'd rather keep the metal in the sleeve if I can. I run the car pretty hard but would rather not damage a sleeve because it's worn too thin. Hopefully I'll have the funds for the crank in the next few weeks Christmas is putting a hurt on my wallet right now. I'll check mod max for cranks

 

[Bob Hughes]

Well I lucked out found a termi crank from a car with 20k miles for $650 just picked that up. Will have to order the pistons in a couple weeks but couldn't pass up the crank.

 

[Deleted member 38176]

Well I lucked out found a termi crank from a car with 20k miles for $650 just picked that up. Will have to order the pistons in a couple weeks but couldn't pass up the crank.

Your car (our cars) have 6-bolt flywheels, all Cobra's have 8-bolt fly's. You'll need an 8-bolt flywheel to make the cobra crank work in your motor.

 

[Bob Hughes]

Yea I was aware of that one thank you for the heads up I figured on another spec aluminum flywheel that's what I've been running with this setup