mn_vette

I know this topic has come up before but I want to see if there are any new opinions. How much less durable is the 396 in comparison to the extra horse power it gives.

I'm doing my rebuild fully forged as soon as my tax refunds come back(yes I filed late) and I'm trying to figure out which one to go with. I'm also planning on putting an N2O shot on top of it probably between 150 and 250 hp. Any comments and opinions would be helpful.

Thanks

gkull

Durability is not an issue on a modern well put together project motor if you keep the rpm down to 7000 or less. I'm a 396 fan. I am not a fan of 4 inch stroker stock small block chevys. We do have a 408 ci 4.030 bore super charged here on the forum with 600 RWH.

All you need is a crank and rods designed for 750 - 800 hp and the 250 shot of NO2 will be no problem. Your parts aft of the engine might complain though!

mn_vette

I was planning on 6500 rpm max. I'm not planning on rebuilding my engine for quite a few years after this and I need to get the most out of it.

I do hear you about the aft parts, the tranny will be the first thing to go. I'm going to "try" and take it easy until I get it rebuilt.

blue_stingray

i'm trying out a 383 now, for lack of finding a big block, and slightly because of weight differences. all forged, all studded, victor jr intake and heads, hyd roller cam- all good stuff, plus a 100 shot of nos when it's broken in.

what i'd really like to have is an aluminum small block- anyone got one laying around they don't want?? yeah right.

anyway-- a little off topic here, but do you run your electric water pump on the street? i'm looking into getting one, but i am a little hesitant since i'll be driving the vette alot during the summer once it's finished. how durable has yours been?

mn_vette

I put mine in this winter with my cam change and it's been just fine. The only problem I've ever had with it is if you leave your key in the "on" position without the car running it does drain on your battery. But I had an old battery which I just replaced because it was cracked. So you never know

But back to the topic at hand....

Taijutsu

All I can add to the good advice given is this. Those extra inches will not do much unless you have the heads to fill the bigger cylinders. Forged and studded is a good start. I'm not sure how much flow a 396 will need but big ports will be required for high rpms. Also be aware of quench to aviod detonation. A long rod will be difficult w/stroker. Good luck

blue_stingray

do you mean running a 6" rod as opposed to a 5.7" will be difficult in a 383?

right now i'm building mine with a 6" rod and 1/16 inch rings on forged flat tops. about the only diff are the rings supports supplied with the pistons and maybe a little more grinding to clear the rod bolts.

this will be my second engine running 6" rods, and if anything i have noticed slightly higher rpms using them, although i don't plan on racing this one above 6800. the last engine i had i could run at 7K with no problems, but that was a 355.

Taijutsu

Don't get me wrong. I am a big believer of longer rod! In a 350 the piston pin doesn't get into ring space on piston. On a 383 it does a little. I'm not sure if you can run 6" rod w/396. And if you can, how much will the pin highth effect ring/piston strength? Not to mention expensive custom parts. I could be wrong on all this. If I am, someone will be quick to set me right I'm sure! I have a 6" 355 that runs 10.25 cr on 91 gas.

blue_stingray

there's a lot of opinions out there for/against 6" rods. some articles say they do make a differance, offers claim they don't. they cost the same and they haven't been proven to hurt, so why not.

my bad-- when i heard 396, i instantly thought of the BBC, i didn't even consider a 396 small block. guess the 3.85/4" stroke hasn't caught on yet to the average SBC crowd. :confused:


[Modified by blue_stingray, 6:46 PM 7/3/2002]

mn_vette

Actually I talked to someone from Speed Demon Motorsports and you can get 5.85" rods from Callies and an SRP 14cc dish piston to go with it on the 3.875" stroke for the 396.

Even if I move the same amount of air as the 383 the 396 should give me more horsepower due to the larger crank, and the guy doing my heads has conficence that he'll be able to get it right.

What is a "quench to avoid detonation"?

Taijutsu

Quench is piston to head clearance. About .040 is good. This minimises detonation and improves combustion. Using thicker head gaskets to lower cr is not good. The tighter quench, even if it raises cr will burn better w/less detonation. Stroker motors often have excess cr. Dished pistons and larger combustion chambers are the way to go. Good luck, keep us informed.

AKS Racing

That would be me? In a 4" stroke (350 block), you are unable to run a 6" rod with 9.5 or less cr when using 58cc or less heads. A 5.875 will fit, but no 6". If it is to be normally aspirated and 11:1 is OK or 76cc heads are you flavor, then the 6" rod may be utilized.

I have built the 396 prior, but I wanted to do what others said could not be done. Now I hear the 4 1/8" stroke is impossible in a factory block, I do not think I will try this as I just happen to have an aftermarket block that has already spoken for the crank.

Go with the extra cubes and lots of head flow.

Aaron

NOS11secvette

I have the 396 stroker kit from Callies. Great kit. No complaints here and I have over 3,000 miles on the new motor. I agree go with more cubes.

MoMo

IMHO, the 396 wouldn't be worth what you're giving up in reliability. If it was to be a torque motor only, and you don't care about much rpm, then build it, but with forged everything!

The piston speeds that are permissible on a 383 are already slightly compromised, but they can still be built to rev okay. The 396 is similar to its big block brethren ONLY in the displacement. The rod/stroke ratio of the 396 BBC is the same as a 427, and is pretty good. Plus, the heads flow the air that is required for that many cubic inches, whereas, you'll be severely flow-challenged with that many cubes on a small block.

If you do build the small block version, get good heads. Something like Brodix or Dart, with at least 2.08/1.60 valves, if not bigger.
And don't look for more than 5000 rpm at the most. You'd need pretty trick components to exceed that.

mn_vette

I was hoping for 6000-6500 for a 396ci. What happens if I over rev it??? the valvetrain should be able to handle it. Would rods start comming apart? or would something happen because of all of the sidewall forces? I've never destroyed an engine so I'm kind of curious.

MoMo

I have the automath formula at home. I'll post it in a few hours.

But yes, you could overrev it for brief periods and get away with it for awhile, but you'd be pushing it. With that much stroke, you'd have pistons speeds somewhere between 5000 and 6000 feet per minute, and forged components can typically take about 4000 safely, and up to 5000 in spurts.

So keep your AAA membership up to date, just in case a rod gets sideways in the bore and the crank breaks in half.

Red Rocket

Happy with my MTI 396. Hope to get as many miles as the Thunderchicken MTI 396. The Thunderchicken has been rode hard and hung out wet at 6,000 RPM's on a daily basis and keeps coming back for more abuse.

mn_vette

If you could post that equation, I'd really appreciate it. I'd like to see the determining factors.

Do you know how many ft/min stock stuff will take then?

Lt1er

The equation is simple logic.

stroke * 2 * rpm / 12 = piston feet per minute So for example.

3.75 * 2 = 7.5 7.5 * 7000 = 52500 52500 / 12 inches = 4375 fpm

mn_vette

I can't be quite that simple. That would be a constantly moving piston. But with each rotation the piston moves slower at the top and bottom of each stroke. This means the piston must move faster in the middle of each stroke to equate out to the average number which your example gives.