glenb1991

Well guys heres the details ive got on the build. Ill probably be doing a 355ci motor. 4.030 Bore, 3.48" Stroke, 72cc Combustion Chamber. My compression will be between 9.5-10.2 depending on the pistons i buy. so heres my couple questions. I've decided to go with forged rods. SCAT 4340 Forged Pro Stock I-Beam Rods.

1) Do i need to go with a forged crank also, or will a regular cast steel crank such as the Eagle Specialty Products 103523480 work wit this set-up and not get damaged.

2)What pistons should i go with? I realize with the bore, stroke, and CC volume stated above to be in that compression ratio i need pitsons with a volume between 2cc and -4cc so which ones would you guys suggest, or those who run similar set-ups, which ones are you using?

3) Do pistons only come in Hypereutectic aluminum or is there something stronger/longer lasting? All the pistons ive seen are made of this and just wanna make sure this will hold up.

4) Are there any particular bearings you all recomend?

Thanks for the help guys, im really getting underway with this build and just need to order these main pieces before i can start assembling everything.

275HP

I think before anyone can answer your questions correctly, you should tell us how much horsepower you are trying to make, what kind of power adder ( centrifugal supercharger or turbo ) and what your plans are for the car. Are you wanting to drive on the street alot, or are you going to race it at the track alot.

General Answers:

If you have the money for a forged crank get it, it will be a good bit of assurance. 4 bolt or Splayed 4 bolt main caps a good investment to keep the crank from moving around in the block.

I would try to shoot for nothing higher than 9.0 or 9.5 on overall compression, especialy if you are going to drive it on the street. 10.0 or higher compression is asking for serious possibilties of detonation on pump gas.

You should also research your power adder. If you are running a rather large supercharger or turbo charger, the differance of 6 to 10 lbs of boost is dramatic from a horsepower stand point.

You should also research your head and cam combo. You could be running a very effcient set up that only makes 10lbs of boost with a 12lb pulley, simply because it moves air effectively. The total opposite could happen and you run a 10lb pulley and see, 10lbs of boost, but the engine doesn't transfer air as well.

Just some food for thought.

275HP

Sorry, forgot to add. Get forged pistons. Under extreme heat and pressure (something that forced induction provides) hypereutecs tend to come apart. JE and SRP make some good forged pistons.

glenb1991

yea sorry i forgot those details. its gonna be coming off a turbo, and my estimate was around 400 when said an done could be more or less just a guestimate. the 10# is a max, ill probably start of rather low as said at 6#. mainly because i wont havee anytransmission work done therefore i wont be putting all my power to the ground just because i dont want my transmision to blow out on me the first day of driving it. So basically a 9.5 compression is what i want with the minimum 6# and maximum 10#?

275HP

you could get away with a steel crank. The forged pistons are a must. I would say think down the road. If you are pretty sure that you are not going to want to go faster with the same setup, keep your build cost lower by getting parts that will suit your build. If you know that you are going to want something more powerful then buy better parts that can be reused in your later build. All that really matters is that you have a hell of a good time when it's done.

glenb1991

yea. well this is my first project, so i think if i do decide to do another it will be a different car/motor/etc. so myy goals with this are gonna stay no matter what. Like i said around 400hp, start off at 6# go to 10# slowly, and probably in the future go to a t56 and get rid of the auto. i found the SRP Flat Top Forged Pistons and thats what ill go with. Like i said before im gonnas get the SCAt Forged I-Beam Rods, and more than likely if i get some other peoples opinions ill stick with the eagle cast steel crank. appreciate the help 275

slomarao

unless something is wrong with your stock crank i would re use it. Lots of guys have made bid numbers on one. Especially FI apps.

I would shoot for 9.5.1 compression.

glenb1991

well i figure i can get a new eagle cast crank for 190 shipped. so i might as well get one thats fresh and sell mine and get some of that money back. im hoping to not have to do much more internally to this car after this build until the day it just dies on me, so i figure ill buy new this time around especially on essential stuff like crank, rods and pistons.

jsetzer

I wouldn't put a lot of hope into selling your stock one. Even if you do it won't be worth much.

Like others are saying you don't need anything real fancy for your goal. A stock shortblock would survive for a good while if tune right only making 400 on boost.

I'm running srp pistons, and while they are not the best choice, they have held fine so far with me making 640 tq. Avoid hyper pistons.

Did I read in the other thread that you are taking stock heads to 70cc? I did have mine milled a little bit, but my porter had to work to get 60 out of the stockers. I have read 70 before, but never seen it first hand. I did 60cc heads and the -24 srp pistons. I may actually be a bit low on compression, but with my mismatched turbo its ok.

glenb1991

yea today i called the local shop they do A LOT of LT work. he reminded me that i could just keep the stock combustion chamber and get dished pistons, so thats what im doin. getting wiseco forged dished pistons with a +20cc volume.

DirtyDaveW

On the LTx, is there a 'rule of thumb' that for every PSI of boost you get 25 hp? I thought I'd read that somewhere.

glenb1991

never heard of that, but then again ive only been looking into FI for a month now so theres plenty i dont know.

DirtyDaveW

Without a boost controller to regulate it, I'm at about 11 psi and the dyno was 574rwhp which is about right for the 25 per...

boosted-lt1

25hp/psi I would say is pretty liberal. 15hp/psi is pretty conservative. All of our combinations would likely fall some where in between if it could be calculated with any accuracy. Turbochargers are more efficient than mechanically stepped-up impellers and so, by design, would make more rear-wheel horsepower per psi. Whether or not that's intercooled boost, non-intercooled, and a lot of other variables contribute.

My opinion - If you plan to tear the motor down and make the thing reliable at the 400-500RWHP level with boost:

#1 Pistons - get some good forged pistons in there that have thick top ring-land and designed for high cylinder pressures. No need to take the stock head to 70cc's. This would be a dished piston to get you in the 9:1 area. JE/SRP work nice.

#2 Rods - Best bet is to get some solid, inexpensive Scat rods. 4340 I-beams with 7/16 ARP screws are $300 a set from Summit. Don't bother with the stockers unless you don't have 300 bucks at the moment. Otherwise, the stock LT1/PM rod will work OK here if they don't have too many cycles/miles on them and you get some ARP bolts installed at the least.

#3 Crank - Boy, I really wouldn't worry about the stock crank at anything less than 600. I'm starting to think that the two-bolt factory caps would kill ANY crank at really high power levels.

What makes you think that an Eagle casting is going to work better than a factory GM casting?? Personally, if you're stock crank checks out and you stay under 600 (or more) with out detonation, you'd be throwing away money with the Eagle.

-Scott.

glenb1991

really appreciate the help boosted-lt1, and if you go back and read my post #10, it states that im not going with a big head job, just the usual head job, no removing anything from the combustion chamber. Ive decided on the following products for the 3 different parts.

1-Pistons) Wiseco Forged Dished Pistons +20cc $625

2-Rods) SCAT I-Beam Forged Rods $220
SCAT H-Beam Forged Rods $425

3-Crank) Stocker (If in good enough shape @$100 to get redone...???)
Eagle Cast Steel Crank $195

This also brings me to my next question, ive gotten three responses so far, two for i-beams and 1 for h-beams(the guy doing the motor work, aka selling the product)

Is there a huge difference(worth $205) between a forged i-beam and a forged h-beam? or better put into my situation, would a forged i-beam suffice in this set-up and just save the other $205 for other stuff, or would h-beams be worth the extra $205?