355 or 383
355 or 383 Okay guys Im trying to decide to go with a 383 or a 355. I will be doing a fully forged bottom end on either. What kind of rpms can these engines see with these bottom ends? And what would you suggest. I want to run in the 10s through an M6 and I can't decide what would be better a little high revving 355 or a stout 383. This car will be driven on the street alot also.
Last edited by TAEnvy; Jan 22, 2006 at 10:47 AM.
396 all the way man they all coast the same.
If you are going to buy a forged crank then go ahead and do the 383. You will make more torque thru the range. The 355 believe me is a good motor, hell i used to have one but it was a stock crank 6" rod job.... However the 6" rod 355 does have the best rod/piston ratio of all the SBC's AFAIK... good dwell time at TDC, less sidewall pressure on the piston= lower operating temps.... 355's are great motors and can make alot of power but costwise if you're going to buy the crank anyway go with the 383....
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From: LT1 land...the "409" of the 90s!
if you are replacing the crank any ways I say 383 with 5.7 rod's 
Remember there WILL be things to clearance
On my 380 we had to clearance the block ,windage tray and oil pan. 396s need even more drastic clearance. 396s also seem to consum more oil due to a less stable piston
To be quite honest a 355 stock crank 6in rod's and good pistons will make all the power a good set of ported LTx castings can feed it you can save a bit of money going that route and still make lots(over 400RW) of hp
Remember there WILL be things to clearance
On my 380 we had to clearance the block ,windage tray and oil pan. 396s need even more drastic clearance. 396s also seem to consum more oil due to a less stable piston
To be quite honest a 355 stock crank 6in rod's and good pistons will make all the power a good set of ported LTx castings can feed it
you can save a bit of money going that route and still make lots(over 400RW) of hp LS1 Tech Stories
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To be quite honest a 355 stock crank 6in rod's and good pistons will make all the power a good set of ported LTx castings can feed it you can save a bit of money going that route and still make lots(over 400RW) of hp
Made 422 RWHP on motor and 407 RWTQ.... With a 6 speed went 11.75@119 on motor all day and i drove it everywhere... And looking back it was by NO means that expensive of a motor... probably cost 8K TOTAL to include a whole new exhaust system, hooker lt's, and a bunch of stuff that I didn't have that I needed.... If I did a duplicate with stuff I have now i could do it for probably about 6K.....
I figure the 355 would be cheaper because the 383 would need better heads and a bigger cam and more machine work. So how does a 7000rpm 355 with Ported GM LT4 Castings sitting on top sound? What kind of cam do you guys think would go good with this? Also would the stock crank handle that kind of power and speeds? I'm kinda not wanting the 383 now because i remeber the one i did a while back on a SBC and it made gobbs of power and torque but it didnt last long.
Also about what is the limit of power (just a ballpark figure) for a setup like that one.(naturally aspirated)
Also about what is the limit of power (just a ballpark figure) for a setup like that one.(naturally aspirated)
Yeah get a killer set of LT4 heads for it. Hell you could do a set of AFR 210's if you wanted to make it a badass 355 that could see 7000 rpms all day. If I were you and you planned on doing something to spin to 7K reliably I'd still do a forged crank..... Get an eagle crank and some eagle 6" h-beams and spin it up!!!!
You'll need a nice cam to get that powerband up if you want something that revs that high..... The cam I had in my 355 was a 236/242 hydraulic roller with .556/.576 lift on a 112lsa.... And it peaked at about 6400-6500 so there was no reason to spin it higher.... If you want 7K you'll probably need something bigger than that..... solid roller sure as hell wouldn't hurt and neither would shaft rockers...
You'll need a nice cam to get that powerband up if you want something that revs that high..... The cam I had in my 355 was a 236/242 hydraulic roller with .556/.576 lift on a 112lsa.... And it peaked at about 6400-6500 so there was no reason to spin it higher.... If you want 7K you'll probably need something bigger than that..... solid roller sure as hell wouldn't hurt and neither would shaft rockers...
383 is the way to go IMO. 
The torque is unbelievable! If you want higher RPMs, then definitely do forged internals because a 383 doesn't like to rev as high as a 355, but it has much better power up to 6500 RPMs. I don't like pushing mine over 6500 RPMs, and that's all I would ever rev that to, but there is no comparison for the powerband that a 383 puts out from idle to 6500 RPMs. You will be glued firmly in you seat until you let off of the throttle. They are both excellent engines, but I have always found it easier to make the 383 into a monster. The torque is what's going to really launch you. You really can't go wrong with either of these motors, but the 383 has always been my favorite. 
The torque is unbelievable! If you want higher RPMs, then definitely do forged internals because a 383 doesn't like to rev as high as a 355, but it has much better power up to 6500 RPMs. I don't like pushing mine over 6500 RPMs, and that's all I would ever rev that to, but there is no comparison for the powerband that a 383 puts out from idle to 6500 RPMs. You will be glued firmly in you seat until you let off of the throttle. They are both excellent engines, but I have always found it easier to make the 383 into a monster. The torque is what's going to really launch you. You really can't go wrong with either of these motors, but the 383 has always been my favorite. 
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Originally Posted by 572BBC4thgen
VERY TRUE! my old 355 with a set of Stage II heads that didn't flow all that great (258 cfm at .600 intake, 203 cfm at .600 exhaust) with SRP pistons, eagle h-beam 6" rods, stock crank, with a 236/242 .556/.576 112lsa cam, ported manifold, and 58mm throttle body....
Made 422 RWHP on motor and 407 RWTQ.... With a 6 speed went 11.75@119 on motor all day and i drove it everywhere...
Made 422 RWHP on motor and 407 RWTQ.... With a 6 speed went 11.75@119 on motor all day and i drove it everywhere...
If you drove your 355 everywhere, my cam is 240/246 .573/.582 113 lsa ,so I shouldn't worry about drivability for my 383cid.
If looking to skimp on the heads to do a 383 then forget it I would do a well headed 355 WITH THE STOCK CRANK first. On the heads everyone loves to believe they need LT4s or aftermarket when there are a lot of companies doing amazing things with ported stock castings who will steer you towards ported stock heads before they would even try to sell you the aftermarket heads they themselves offer.
Joined: Nov 2001
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From: LT1 land...the "409" of the 90s!
I made 395RWHP on my stock bottom end 350. Through and UN-LOCKED A4 and a 12 bolt! this would be the equivelent of 425 through a M6 the power peaked at 6,900 with a GM 847 cam.
The problem we run into with bigger cubic inches and 90% of the heads out there is to much velocity yes you want good velocity but when it goes to high it becomes a problem.
The new engine in my car is a 380Ci LT1. the heads were xtensively modified by Lloyd as per my directions and his port work. Only time will tell if it was enough. I know the money I spent to get here.
All of these reasons are why I say go with a 350 build up and a good set of ported LT1 heads.
to be quite Honest the only reason I even finished the 380 Lt1 was because I do not have all of the parts for the 18 degree LTx engine yet I had ALL the parts for the 380 here they just needed machine work
good luck on what ever Direction you take
the power peaked at 6,900 with a GM 847 cam.The problem we run into with bigger cubic inches and 90% of the heads out there is to much velocity
yes you want good velocity but when it goes to high it becomes a problem.The new engine in my car is a 380Ci LT1. the heads were xtensively modified by Lloyd as per my directions and his port work. Only time will tell if it was enough. I know the money I spent to get here.
All of these reasons are why I say go with a 350 build up and a good set of ported LT1 heads.
to be quite Honest the only reason I even finished the 380 Lt1 was because I do not have all of the parts for the 18 degree LTx engine yet
I had ALL the parts for the 380 here they just needed machine work good luck on what ever Direction you take
Launching!
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Doin a 396 here, i went with the big cubic inches. I got a 96 vette blocked that was already machined and notched for the crank and rod cleareance. Loyd Elliott custom ported trick flow heads and LT4 intake port matched. Callies Dragon slayer crank. Eagle 6' rods. Custom cam by Loyd Elliott. Oliver 4 bolt billet main caps and arp studs and bolts that came free with the block. Hopefully gonna make some good power on all motor then spray it later on down the line.
There is nothing wrong with having the added cubic inches believe me. The torque is going to be more under the curbe cause there is still no replacement for displacement....
But a properly thought out stock cranked 355 with good rods, pistons and heads can make a shitload of power.... My 355 was downright animalistic when you'd get on the throttle. Great throttle response and considering I had heads that didn't flow a TON Of air the velocity like what TwoFast said was definitely there....
Sometimes a smaller port with a good shape to it that only flows say 258cfm at .600 like mine did will help make power cause the velocity stays way up there flowing thru the smaller port...
But a properly thought out stock cranked 355 with good rods, pistons and heads can make a shitload of power.... My 355 was downright animalistic when you'd get on the throttle. Great throttle response and considering I had heads that didn't flow a TON Of air the velocity like what TwoFast said was definitely there....
Sometimes a smaller port with a good shape to it that only flows say 258cfm at .600 like mine did will help make power cause the velocity stays way up there flowing thru the smaller port...