slickfx3

there is a debate that i would like to clarify, so any guru horsepower authorities chime in,...

Demonic85

396 will cost more to build, more "meat" has to be taken off the block to get the new crank to fit. Yes it would make more HP though if built with the same kind of parts (cam, intake, heads, etc).

slickfx3

keep it comin'

neat

To my knowledge, no one makes a 3.875 crank that is cast, so to go 396 you must use a forged crank. If you don't plan to stay NA and keep it under 7000 RPM, in my opinion there is no need for a forged crank, so that would be a cost benefit to the 383.

Also to the best of my knowledge you must use a 5.85 rod with a 396, where you have some options for rod length with the 383.

I think the 396 will make more power, but the rod angularity and piston speed differences between it and the 383 make the 383 a better engine, IMO.

slickfx3

eloborate on the piston speed thing and angle please

StealthLT4

Someone else may be able to elaborate better, but here's what I know:

The higher stroke means that, when the piston starts moving downward on the power stroke, the con rod is at a greater angle from vertical (wrt the piston), and therefore more of the force is put on the sidewall of the cylinder instead of down to the crank. This is a bad thing. Also, with the larger stroke, getting the same rpm will mean higher average piston speeds, which presents an engine longevity issue.

A 396 will still make more power, but may not rev as freely as a 383, and might not survive as long at the higher revs. That's only comparing 2 identical engines though; quality components will make either build work well.

slickfx3

so far so good, were not talkin small block fords here, okay chevy guys wadup?

tpi 421 vette

A 396 is the same stroke as a 421. You can use a 6.00" rod with a 1.062" compression height piston. So the rod ratio and angularity with that configuration isn't too bad. Like mentioned... a 396 will require a forged crank, which adds alot to the price.I would also recommend some good stroker rods. If your budget allows, I would do a 396 over a 383. You could also go a 4.00" stroke which would give you a 408.XX or a 409 as alot of people like to call them. But it takes alot of clearancing, and you can go 6.0" rod with a 1.00" piston compression height. Or use a 5.85 rod with a 1.150" compression height piston. I have done several, but a 4.0" stroke starts to really push the limits. I have also done a 4.125" stroke, but I don't know if I would recommend it after all I went thru to make it work.

I think you would be happy with a nice 396.

Orr89rocz

Go 383, especially if not needing a forged crank

difference in power is marginal, 10-15hp with same cam/heads but will lose some torque with 383.. 396 will make abit more torque and possibly abit more midrange hp but i dont think the price is worth it

slickfx3

hmmmm. great answer for a question i have yet to think about.

nominal increases with the same cam, is that across the board, or will a bigger cam benefit the bigger motor better than the smaller?

i know that's a tough question to answer because they would taylor the cam to use and engine size, but that is the base line question.

JimiHendrix

I've researched this issue over a period of time. I've spoken with lLoyd Elliott of portworks, and I spoke with Andy Jensen. . . in person. . . Andy owns a machine shop in northeast PA. Both experts were in agreement that; 1) 396 will only make slightly more power than a 383 because the intake and heads cannot feed the 396 engine any more power. 2) The combustion chamber and head design severly limits the 396's ability to make much more power than the 383. Just look at the heads on a big block compared to the small block. 3) if there is any bit of core shift, you WILL grind thru to the water jacket on a 396. 4) more parts options with a 383 (especially pistons).

So, the verdict for me was: to go with a fully forged 383 with a good package. Aim for optimum cam and heads. There are a whole lot of 350s putting out more torque and hp than a typical 396. There is one guy here running a 370 that is putting out 475 rwhp!!! The secret to power in these engines. . . are in the cylinder heads

To sum it all up. 396 aint worth the extra headache. Andy told me that I will be more than surprised with a healthy 383 street machine, set up with a mild stall and 3:07 gears. He told me that if I wanted a significant 383 street machine with close to 500 rwhp, to have a sheet metal intake fabricated, high lift moderate duration solid roller cam, and install race heads.......nahhhhh. IT needs to be driveable.

Anyway, that's my take on it.

Muffin

The latest issue of Chevy High Performance goes into this in detail. Confess I just scanned it cause I have all the parts and pieces for a 383.

pologreen1

I would like a 396, but I also figured that a 383 is more suitable and practical for my car when I do it.

mseven

1)what cylinder heads and intake can't feed it enough ?
2)what cylinder head design "severly limits" it to making more power ?
3)not at 396, going bigger bore may run into problems though
I have no idea what you are talking about here, but you need to keep researching. If you are talking about using a 113 head and a TPI, then ANY motor would suffer from achieving it's max. potentilal.

JimiHendrix

Hello, we are talking gen I SM here.....am I correct?

It's pretty simple. Imagine taking a small block head and placing it on a big block engine. The cylinder head design concerns the limited valve size that you can put in a small block head, and the small combustion chamber shrouds the valves, inhibiting the volume of fuel air mixture you can put in cylinder. Even the GEN II LT1 intake is very limited as to the volume of F/A that it can feed a big block sized engine.

There comes a point where you get less of an increase of power. . . when you increase the size of the engine and change nothing else. That point of diminishing returns is at the 383 to 396 displacement change.

If it were true, you would get nearly twice the benefit from going from a 350 to a 383....vs. 350 to a 396. But, you don't even get 5% overall more power out of a 396, compared to a 383. (you get approx 4% more hp and 6% more torque). Reason: F/A intake restriction.

Show me a 396 putting out more power than AI's featured 383 NA engine getting 10 second quarter miles....."show me show me.....that you really love me.....actions speak louder than worddsssss" ahhh, that's a 80's song lyric...

mseven

Once again, here is a fountain of misinformation. If cylinder heads were a restriction then there would not be a cylinder head available to support anything above 350ci..according to you, or at least make power. As to intakes, an LT-1 is not the only intake available on the planet. You want to make compares to a track car ?
I think your point would be better illustrated by showing all of us your motor combo, dyno sheet, et's etc.
since you like to make compares, here is a bosted 406ci...(not enough cylinder head)
http://www.youtube.com/watch?v=gQiyH-kKgRo

AKS Racing

This is true when going to a boosted application, but on N/A you can still use the 6.000" rod in a 3.875" and a 4.000" stroke application.

This should not be an issue with the L-98 blocks. The old 400 blocks, yes, more modern blocks, no. Also, by judicious selection of components (rods, crank, etc), much of the grinding required is reduced.

A lot of good info above with one slight edit for clarity. I have done similar builds and experienced the same. The 421 using the 4.125" stroke in a 4.030" bore (350 based block) tends to be more trouble than it is worth. The 421, using the 400 based block (like Jim typically builds), is certainly worthwhile.

And there are plenty of heads on the market that will easily support the HP goals of these large CID type builds.
Aaron

95wht6spd

I think Lloyd is referring to a 396 with GM LTx ported head castings, he feels they cannot provide enough CFM even at max porting for a 396. (I could be wrong, but when I spoke to him this is what I took away.)

JimiHendrix

For crying out loud....that engine is not normally aspirated. We aren't getting our points across to each other....so....leave it alone.

Ummmm, I see your point mseven. (that is.....you don't see mine....)

tpi 421 vette

Good point Aaron. I forgot there are 2 different ways to do a 421. I was talking about the common 4.155x3.875. The other 421 is rare 4.030x4.125.