350pride

Why is there no reason to build a 408...besides bragging rights? (in reference to the 383 or 396 comment). I read where it stated the hp output for the 383...are you saying that there is no more hp to be gained from an lt1 motor greater than a 383 just torque, or are you saying that the (hp/reliability) to (cost to build) ratio is really small?

hope Im not hijacking, but... what would be the most ci to get the most hp and tq with the greatest reliability.

Sorry, just currious (i was always told that if you didnt know, you should ask)

Pride

reamo04

reliably and safely a 383. 396 has too much of a chance to hit water, so unless you have a few extra blocks, or a good machine shop, 383 is the way to go.

Formula408

I do know the original Kit I looked at had a 5.85 rod; I believe it was a JE piston don't recall for sure. It was discontinued though. I ended up with the 6inch rod and Ross customs. I can say my piston to counterweight clearance is pretty tight. maybe 1/8 inch or something like that. a lot in machinist terms but still close enough for me.
I figure if I end up with a non repairable leaker I will get a dart block and start over. I own an ice company so I get to play very little in the summer and wanted to do something a little different. I probably could count the times I've had my car out in the past 4yrs. on 2 hands.

AdioSS

cut the deck down a little more and use a thin gasket to get the same quench.

Given the same combustion chamber size @TDC, if you increase the stroke, you increase the compression ratio.

AdioSS

Usually people use OE LT1 or LT4 castings which are limited in how much air they can flow. That limits total horsepower. Theoretically with the same heads you can make the same horsepower no matter the cubic inches. The thing is a smaller engine will make that horsepower at a higher RPM than a larger engine. However, like I mentioned before, the larger engine has the ability to have a higher compression ratio, but in a street engine, you'll keep that low anyway.

The larger engines are limited by OE castings. That's why most people say that there is no rason to build a 408" LT1.

I counter that it will make more usable power. And if you are going to use heads that can take a 408" engine to over 7000RPM, then why not?

AdioSS

thanks for that info

rock1501

I went 383 for this very reason plus the hp to be gained from the extra 13ci cant be too much prolly 5rwhp or less

rskrause

Look, this is simple. More cubes always improve performance on a street motor and usually on a race motor as well. But there are limits related to basic block architecture. Once you start approaching them, the cost/benefit ratio will become unfavorable. And there is a point which to go beyond is basically impossible. A 408 LT1 is certainly approaching the point where most people would say "not worth it". But to each his own, variety being the spice of life and all that.

Also, the potential power gains per ci start to become less as the bore/stroke ratio becomes less favorable, limitations of the available heads start to be approached, etc. These are all things that have been discussed here, for some reason I felt like a little summary. Maybe later I will go into some detail about real worl examples, because I have been there/done that or have had buddies who have. done so. It really is true that IF you use the same heads, cam, etc. and just increase the displacement by stroking the motor, there will be NO gain in hp, though low end torque will improve (not peak torque though) and you will make the power at lower rpm. Increasing the bore is better, as it promotes head flow, but the ability to do that is strictly limited by the block casting.

You can think up some very wierd examples that don't follow the above scenario, but they are seldom encountered in real life.

Rich

mdacton

don't get offended but I have a really good feeling your going to be pissing water in the oil pan.

I hope not, but once that block leaks its pretty much going to leak.

Formula408

no offence taken. I posted here knowing I would get a difference of opinions. Pressure check went good though. As long as the devcon holds like others say it has for them I should be ok. I just worry about the first heat up. My engine builder did a 383 that went through and he was able to pin it successfuly. but I am aware if it leaks its a BIG issue.

mdacton

If it makes you feel any better...a 460 block someone left water in and split the block.....Well they used some type of epoxy on it from the outside. Been running it 2 years now without a problem.

But I have seen others leak inside the engine later on. I'm not really familiar with the different epoxy types etc.

Formula408

Rich,
I believe you said you broke through on yours. What did your repair consist of besides the devcon? that is if you don't mind me asking. How big of a hole did you have in yours? has it caused any issues ?
thanks in advance.

rskrause

I have done the 383 LT1 build three times. One cleared with no problems, One we broke into the water jacket and used Devcon followed by Hard-Blok with no leaks. One we broke through and couldn't fix the leaks. I think there is a lot of difference betwen castings.

Rich

edit: I meant four times, twice no problem.

marshall93z

100% truth.

Formula408

Just wanted to let everyone know the 408 is alive! I've had it running a few times and had it up to temp a couple of times with no leaks so far. (pray for me please... lol)
It has been a interesting ordeal to say the least. Thanks for everyone's input on the subject and I will try to give updates as to weather it fails or not.