Ok, I finally decided to go turbo for my project. Turbo setup is being fabricated. Anyway my next step is to send my block to the machine shop. And I have to decide either 355 or 383. Your opinions please. Thanks!

 

That's an interesting question. It really depends on what turbo you're using, though. Many people say that the largest of the "T-series" turbo's (the T-76) is borderline too small for a 383 and up. The reason being that the small exhaust housing will cause excessive backpressure for the large engines. I'm not sure if I totally buy into that because X hp means X amount of exhaust flow regardless of the cid of the engine. Be that as it may. . . people have made lots of power (800 - 1000 rwhp) with a T-76 and 186 (Supra) - 281 (4.6 Cobra) - 355 (LT1) cid. I'm trying my luck with a 383 and a T-76 and I can say that the midrange torque is ridiculous (spins the drag radials from 60 mph in Drive). However, I do believe a T-88 is better suited to 383 cid in the end.

 

Well I did opt for a T-76. And I was told that the T-88 required more modifications for it to fit. And also between the two (76 & 88) power level is very marginal.

 

If you are talking about whether or not to go with a 383 ci or a 355 ci, I guess it just depends on personal preference. Some engine builders are going to tell you to even go as minimal overbore as possible to keep the cylinder walls as thick as possible because of the added cylinder pressures of the boost. Defintiely .30 over should be the max (which is what you will have with either 355 or 383). If you have the money to go the stroker route, go for it. The actual parts will cost pretty much the same, you will just have more in the machine work or labor on the block for clearancing for the added stroke. I opted to get a 3.50 inch stroke forged crank to stay near stock because I didn't want the added expense of building a stroker and personally, with me planning on running about 18 pounds of boost on a well built 357 LT1, I don't htink that it will make that much difference, your already talking about a lot of power for a street car. From what I understand, you will gain some torque with the stroker but very minimal horsepower. It's just what you want to do. If you've got the money, "There's no replacement for displacement."

 

Since you asked for preferences, I prefer the 355. My reasoning is the simple fact of piston design for both rotating assemblies. on a 383, the piston pin hole is pushed further towards the crown of the piston meaning closer to the ring lands meaning having to move the ringland further up toward the top meaning less material to withstand any tuning mishaps. also a stroker will need to be clearanced, which means removing material from the block and getting real close to the water jackets in the block.. just some I personally don't like to do, but many have done with great success. I would not build a 383 with a 5.7" rod personally due to the fact that with that much more throw in the crank, your rod angle get pretty steep, and going to a 6" rod is going to move the pin hole even further up the piston to achieve proper compression height in a standard deck block with .025" from the factory, and after a cleanup of at least .005" you are left with .020" deck not enough on a standard block to get your compression ratio down with a shelf piston and 6" rod on a 3.75" stroke, so custom pistons with proper deck will be required or going to an AFR head with the 76cc chamber. those are the only two ways I would personally achieve a lower static compression ratio, that will allow for optimal quench area still and you can use a head gasket of nominal thickness.

can you build a low compression 383 that can withstand high boost? of course, several have done it, if money is a deciding factor, you may look into spending the extra money on stronger components in a 355 and turning the boost up a little more. for the slight difference in power/torque you will see at peak boost, I personally don't think I would go that route, but some who have previously built a motor for boost with superchargers etc.. may have simply opted for lower boost on a slightly higher static compression motor, or spent the extra money to achieve a properly built larger cube high boost turbo motor. at the end of the day you have to ask yourself how often you plan on driving a car with VP116 octane fuel at ~24 pounds of boost trying to maintain 1000+ rwhp and keep it glued to the street, or if you just wanna be able to accomplish it once in a while on the dyno while a more street friendly tune and lower boost achieving 650-750 rwhp (which is still more then most have experienced on these boards) will satisfy your thirst for acceleration and power on a day to day basis.

If your planning on going for speed records, scrap the LTx block, get a little M and go 434CI small block, complete aftermarket engine management, and a 100+mm single turbo and be done with it.. otherwise IN MY HUMBLE OPINION, a 355 built properly with high end components a bullet proof fuel system extra money spent in well above adequate intercooling, and a long pondered well engineered turbo system you invest countless hours of research in developing and more money then you ever considered spending on it, and you will still at the end of the day have more power then you are probably bargaining for at this present time.

My strongest recommendation is to find someone with a well built well performing forced induction car around the power level you are currently seeking to build for, and have them take you for a full tilt boost wide open run. when you finish apologizing for soiling there plush leather seats, you can thank them for helping you understand what 1000RWHP feels like. lol this is not a flame but a simple observation made by yours truly before the numbers posted here had any real relevance beside a cool big number to shoot for. once you experience this level of power you will truly not worry about the difference between 900 and 1000 rwhp..lol can you feel it.. i strongly doubt it, at this level counter steer at 100+ mph speeds are far to pressing to measure the seat of your pans distinction between those levels.

again just my opinion! derived from personal experience!

Chris

 

.This 355 buildup is sounding very interesting. I mean does one really need the extra cubes when its a FI project? thanks for your opinion.

 

I say go with the 383. Extra cubes never hurt, and you're going to pay pretty much the same for a forged 355 assembly as you will for a forged 383 assembly.

 

Cost will pretty much be the same since only the crank and pistons will be different and probally the same price (and assuming your will be replacing). Will take a little more machining/clearancing for the 383 but, minor in the final cost of things. If you are looking at a mild combo maybe 15psi or less the 383 will probably be the way to go. If you are looking for an all out boost project at 15-25psi the 355 maybe be the way to go with more piston skirt area as discussed above.