12.5:1 355 on pump gas, with a little bit of juice safe?

[chrizar]

So I've been wanting to build a 383 for a while, and decided a 355 is more cost effective and will meet the HP goals I have for now. I spun bearings in my 4 bolt motor and killed the stock crank, my main concern is will a stock crank be up to the job is spinning near 7k on the reg, since I know these motors can handle a 150 shot on a perfect tune stock. I'm not looking to run a big shot, 100 at the most and it's not a track car, just a fun street car that see's a tiny bit of track time and lots of goofing off on the street. I have 93 at the pump, and plan on running that or E85 if I have to.

My current thoughts on the parts combo for my 355 would be:

Compstar comet lightweight crank, stock stroke (or stock crank if I can find a good used one)
Eagle forged I beams with ARP fasteners
Some sort of a forged piston, Mahle, JE, etc -5cc relief
AI 200CC stock castings 52cc chamber
port matched intake
58mm tb
AI matched cam, will probably end up being a custom grind but for the time being I'm looking at a 234 242 .576 .580 with a 110 lsa.
of course proper springs etc etc
ls7 lifters
comp pro mags 1.6's NSA guides, hardened pushrods 7/16th studs etc
not sure on HG yet, I have to figure out what my deck height will be after the block is machined but most likely an .026 or .029 MLS one.


I'm mainly looking for about 430whp through an a4 on motor hoping for 520 give or take on spray, mainly looking for opinions of if this will work for what I want or if i'm way off on my parts list here. I posted this on LTXtech with no replies so I'm putting it here too.

[Nocooler]

I don't see how you could hurt it with 100shot.

[farmington]

make sure you have a fuel system capable of supplying enough fuel, a way to pull 4 degrees of timing when you spray, always purge before you spray to get liquid N2O to the solenoids

[jrkirkpa]

Not positive, but I don't think you'll get 12.5:1 with flat tops, 52cc heads, and stock stroke

[TB2]

You can save a lot of money with a good condition factory forged crank. It will take that horsepower, but is heavier than the callies. I think your pushing too far on compresion with pump gas. You may be able to get away with it if you use a good methanol injection. Depending on where you drive, e85 would be a good alternative. If you do decide to use only e85, you should consider taking the compression higher since e85 will allow you to do so. That cam is pretty small for that kind of rpm. That aside, the main things the motor will need to see 7000rpm on a regular basis is good internals. I would use h-beam rods, main studs, and make sure you get it all properly balanced. And good valvetrain components would be a must.

[dawdaw]

You can do it, you'll have a very small tuning window though.. You don't need to be looking at static compression as much as you need to look at dynamic... Cam timing has a ton on determining how much cylinder pressure you can make.. Also make sure your cooling system is up to par, and like stated before the tuning is going to have to be spot on. I would have ai grind your cam, they seem to put alot of there cams on a 108 which will help bleed off some of that cylidner pressure... FWIW, we took my neighbors motor on an egine dyno and made about 30 pulls and played with cam timing and we were able to get the cylidner pressure as low as 140 all the way to 190 just by advancing and retarding it... With that said in my opinion i would just tell ai you want a 12.5:1 motor on pump gas and they'll grind you a cam and tell you where to put it, and the tuning and cooling system is gonna be on you. Your headed in the right direction though.

[chrizar]

Well I was following a thread on LS1Tech about compression and pump gas for LT1's and some say they run near 13:1 but your tune has to be perfect. I have a lot of reading to do on Nitrous but it's going to be an on going project for sure. I'd like to build my shortblock this winter, and get my heads done next year and pick the cam up.

As for fuel would a simple 255 pump be enough, I'll probably change all the lines out for stainless braided anyhow. Just to make it cleaner, and know I can run anything fuel wise in it. Plus if gas does not come down I'll swap to E85 anyhow as long as it stays over 1.00 or more cheaper a gallon than 93...

Now as far as a tune/tuner goes I'll have to do some searching on who to take it to around here. I'll have to get a converter made I'm guessing since I want to spray it, or is 100 shot not enough to matter with just tossing a yank SS 3600 stall in it?

Other thing I'm curious of, is if I'm set on Ethanol what does it take to get to 13:1 comp? Domed pistons, but then valve clearance comes into play? I'm obviously still learning but I think I have a solid idea to build from here.

[dawdaw]

If you did a 383/396 not much, flat tops,.have the heads milled a tiny bit and run a thin headgasket to keep the quench down. A stock stroke is gonna need some domed pistons to achieve that high of compression. A common 355 build with a 52 to 55 cc chamber on a thin head gasket is usually Round 11.8ish.

[chrizar]

Only downfall is going to a 383 or 396 is machine work is that much more. Plus I've read it's not easy to make a big cube LTX, can't remember what the reason was though. A 396 would be fun, and one hell of a torque monster... but Ethanol is only E85 from like late may to early august then drops to E80 and down...

Now back to the whole domed pistons thing, valve clearance can be an issue if I'm not mistake. The 7k rev limit on the pcm would be no problem as I don't think the big cube motors normally like higher rpm's most of the time?

[dawdaw]

Only downfall is going to a 383 or 396 is machine work is that much more. Plus I've read it's not easy to make a big cube LTX, can't remember what the reason was though. A 396 would be fun, and one hell of a torque monster... but Ethanol is only E85 from like late may to early august then drops to E80 and down...

Now back to the whole domed pistons thing, valve clearance can be an issue if I'm not mistake. The 7k rev limit on the pcm would be no problem as I don't think the big cube motors normally like higher rpm's most of the time?

ya you are going to have to clearance the block for a 383/396 or anything bigger, it's usually the rod bolts that hit... it's not difficult to make a big cubed lt or ls or anything, just take it to a machinist that knows what he's doing... And yes e85 usually goes down to e70 late fall and you get it early spring as well, i tested like 10 batches of it all the way to november though and never got e70, it was all e85... Valve clearance shouldn't be an issue if you spend some good dough on a piston with some good sized valve reliefs, you may have to fly cut, all depends on how much duration you have and where you put the cam in at... You can spin a big cube motor extremely high, all depends on what your wallet goes to and what your wanting to do, hell look at the pro stock cars.. there what 800 cubes? and spin 10,000 rpm lol... there's a guy down at the ltx shootout named Mike out of Rhode island, he has a 385 lt1 with a edlebrock efi intake manifold, big solid roller, fast xfi, and a billet rotating assembly and he's turning that north of 8,300 i believe he said threw the traps.

[chrizar]

He has that quazer blue Z if i'm not mistaken, he is on tech quite a lot. I'm not going to spend a fortuen on this setup anyhow, probably around 6k when it's all done. not going to half ass it, but I don't have some huge budget either. I may end up being forced to sell my block now anyhow...