I'm doing a 383 build with 5.7 forged I-beams and 53cc LE3 heads shooting for 12:1 SCR on E85. I was looking at 12cc forged Speed Pro pistons and the Impala gasket at zero deck it should give me what I need. Is the Impala gasket too thin or would that be ok as far as piston to head clearance. I cant afford to pull the motor again after its built and want to make sure that it is right the first time.

 

.028 on a zero deck is cutting it mighty close! and you better have a damn good engine builder because if it closes up any more then that you will have a fair bit of piston to head contact. some holes will vary a few thou, due to piston design, rod length and crank variances, stacking tolerances. id suggest leaving the slug in the hole a bit around 10 thou to net around .038, so no zero deck. tight quench does good for preventing detonation but you are running E85 so you dont need to play that dangerously. also excessive quench doesnt make anymore power up to a point, you are just slapping aluminum together for no real reason, especially on e85.

 

on a side note, i am also building a 383 right now with an advanced induction top end. compression will be in the ~12.1:1 area on pump gas

 

First off ... yes .... using the Impala head gasket with it's .029" compressed height with a zero deck height will give you, (of course!) a .029" piston to head clearence. You really want to have a minimum .034"/.035" clearence here. Either .... 1) leave the piston .005"/.006" "in the hole" when you have the block decked and use the Impala gasket, or 2) use the Fel-Pro 1074 head gasket at .039" compressed height with a zero decked block.

Also, if you're setting up the motor for E85 .... why not run a 6cc flat top piston, instead of the 12cc "dished" piston you're considering using, and aim for around a 12.5 to 13.0 to 1 SCR. E85 motors love higher compression, and, a bigger cam with a late IVC point will, of course, "bleed off" much "static" compression. Also, why 5.7" rods? If(???) the motor is being set up for naturally asperated performance, a 6.0" rod will give you a better rod/stroke ratio on your 383 (i.e. stroker) motor build, yielding less piston side loading and internal friction, while still keeping your oil control ring out of the wrist pin area on a 3.75" stroke crank (i.e. 383) motor.

Just some "food for thought" as you consider this build???

 

I've considered the higher compression since its E85. Might just go that route with the .039 Felpro. The reason I'm using 5.7 rods is I already have a Scat cast crank (part 9-350-3750-5700L) and it suggests 5.7 rods for it. I plan on keeping the shift point no higher than 6500 also.

 

I believe rod suggestions are for balancing purposes, you can run whatever rod you want.

 

Rod suggestions are for counterweight to piston pin clearance, and somewhat on the bobweight. Most cranks like he has are balanced to a fairly heavy target weight anyways so they can work even with the heavy speed pro pistons. Everything should still balance or come close even with those lead brick speed pro pistons. Let your balance shop worry about the best way to deal with that though.

.029" is too close, and not at all worth it on a street car imo. You can probably get away with it if you measure piston rock etc, but what are you doing to do when the bores wear a little and it gets loose and rocks farther? Its probably going to leave an impression of the piston on the cylinder head.

With 13:1 you're going to have to run a very large cam to keep cranking compression anywhere near sane. E85 will work good with high compression, that doesnt mean you need it or want to maximize it.

 

So since the crank is setup for the 5.7 rods, should I just stick with that, or can I use 6" rods? The crank is the only part I have so far with the heads coming next week. If those pistons are too heavy, then what pistons should I go with? I want to keep the costs as low as possible with this build while still being reliable. Lloyd Ellott suggested with the cam I am looking for (shifting about 6500) that I want to shoot for 12:1 SCR on pump gas, which I want to leave as an option just in the rare case the 2 E85 stations in my area happen to disappear.

So that I can go ahead and order the pistons and rods, which ones should I go with? Also do I need the 7/16 bolt rods or are the 3/8 rods enough?

 

Same here

 

You can use whatever rod you want on it, 6" rods will have lighter pistons. (do not read too much into rod length there isnt squat to be had there)

If you go with the 6" rod I would stick with a mahle piston and ring setup. Those particular ones do not have the piston pin in the oil ring rail which i prefer over the ones with the pin in the rings. There it nothing to this either its just merely what I prefer. They are not that bad in price considering what a piece of eye candy they are and the finish work on them is top notch.

There is nothing wrong with speed pro pistons, they are just fairly heavy when compared to most other manufacturers. Look somewhere where they show the weight of the piston in grams. They also have the advantage of being one tough cookie due to not being lightened up. May be better for you here.

If you want to stay cheaper on the pistons look into some keith black forged stuff. Its not as expensive as you think, and I have personaly had very good luck with them in half a dozen engines, also seem to be lighter than the speedpro forgings.

You will be fine with any of them.


Run 7/16" cap screw rod bolts, the strength of rod bolts of equal material is going to be directly related to thier area of the rod bolt. To illustrate the increase in strength you just need to take a look at the change in radius squared.

3/8 bolt has a radius of 0.1875" which squared is 0.03515625 sq in.
7/16 has a radius of 0.21875" which squared is 0.0478515625 sq in.

calculating % increase allows us to ignore pi in the area equation because it will cancel here. A little division gets you about a 36% increase in load capacity. Pretty simple choice considering that rod bolts are the hardest working fastener in an engine. The upgrade is cheap as well.

I prefer the scat rods to the eagles, they're just easier to fit in the crankcase in my experience. I only ever use i beam rods as well. If it looks like your block has a lot of core shift, talk sweetly to your machine shop and have them spot face where the rod bolt head fits on the cap deeper into the rod, and then cut down the top of the cap screw a little bit where your wrench fits it. This may save you considerable time clearancing if it wont just drop right in. Dont get all crazy with the clearancing either its too easy to find water. I like to use either heavy zip ties or a piece of solder of known size to check clearance. You need about .050-.060" clearance or so to be absolutely safe.

Also make sure and tell Lloyd you're running a 383 so the cam base circle can be ground smaller and avoid that pita right off the bat.

 

e85 is nice for being able to add timing into the motor, or adding a bit of compression. Really, i would sacrifice a little compression for more timing though

 

I think I, going to go with the 6.0" Scat I-beams with 7/16" bolts, Clevite coated bearings, and KB 6.4cc dished pistons, Felpro 1074 .039 gaskets and .005 deck. Should put me 12.3 SCR, then have Bret spec me a custom cam to peak around 6400 and DCR close to 9. What do you guys think of this setup?

 

That'll do well.

Are you going with the kb forged pistons?

 

It's too close and is not needed.

Rich

 

What is too close, DCR? I was just guessing on that, I would leave the cam spec'ing up to him of course.

Yeah going with the 6.4cc dished KB forged pistons and 6.0" rods.