Strating to think about the future and either 383 or 355.

I have a set of stock LT1 heads that are P&P with flow numbers around 260 intake and 190 exhaust. I was thinking of getting the heads ported better and get some more flow for a new cam while i save up for the big project of the 383 or 355.

So my question is how much flow can we get out of stock LT1 castings and what would be ideal for 383 heads to flow.

Its either wait till the 383 project is in the works and get a AFR heads or something, or
Get as much flow out of the stock casting and reuse them with the 355 motor.

either way i would put no more then 200 shot after the rebuild (forged of course)


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Well, there is no such thing as too much CFM. Only too much runner cross section or not enough motor under the heads. I would take as much head flow as possible. I think ~275-280 cfm is about the most I've seen out of stock heads, but I could be wrong. I wouldn't bother anyway. Go AFR if you have the cash.

 

the more CFMs the better.
If you really hog them out you can get 270ish if you do it right, but doing that you will most likely hurt you intake velocity. which doen't matter a whole lot of it is a 5000-8500 RPM powerband circle track car. You would not have much torque below that point. If it is a street car, those heads, and a moderate cam like the cc306 would put you about where my 383 is
499/ 427

 

Those are flywheel numbers right? If not tell me your secret!

 

Yep. I was going to run it on a chasis dyno but ran out of time, last time I had access to one.

 

I was thinking of taking them back to the local shop and ask how much and what would it take to get them to flow around 270 atleast.

Then i would have enough to be happy until the 383 project takes place were i would go for AFR

 

Port velocity can be increased by compression and or cubes. Which is why a 383 is more tolerable of larger cc runners than a 350.

 

DONT AIM SOO MUCH AT PEAK LIFT FLOW
head flow needs to be concentrated in the lower lift areas for maximum performance (.300"-.400" areas)
you see those lift areas twice as much as peak

 

Bump good info.
In one valve opening .200,.300,.400,.500,.600,.500,.400,.300,.200. so focus on .200-.500 (low-mid lift) since they get hit twice .

 

Agreed!

Which is why you should do the AFRs. The low lift flow numbers mop the floor with the competitors.

 

This is a very good post, VELOCITY is such a big word, and the lack of understanding about velocity is growing into a big problem. You can have too much velocity due to too small of port for the cubes under it. Relative to LT1's it's like putting ported LT1 castings on a 383 or 396 and wondering why you don't make any power. Even if the heads flow better than any LT1 head you have ever seen the head port is usually not big enough to support a ton of power, and in fact would probably make MORE power on a 355. You can get into the high 500HP range with a pretty mild SR cam and a set of good ported LT1 heads, where as even with a big SR cam and awesome LT1 heads a 396 is going to only make around 500HP. If you want to spend more money on the bottom end, spend it on the aftermarket castings first because that will really pay off.

Bret

 

So basically, you guys are saying that in my project -383 forged stroker...a set of llyod elliot p/p lt1 casting heads that flow at 272 at .600 isnt gonna cut it at all?

Cuz thats what i have sitting at home and was planning to use..
hmm

 

You said pretty much exactly what I was going to except much better than I could have. It's exactly why I didn't go with a 383 over the 355, because my intake runners are only 175 CC.

 

Lloyd does great work, and his heads are usually big enough to be run on a 383. Usually in the 195-205cc range, which is about the minimum for a 383. If it's a street car that you are not expecting huge HP numbers from and high RPM (over 6000) then those heads will do fine. If you are looking for a drag race motor and want to spin it to 7000rpm then a 355 is a better ticket.

Bret

 

My 383 makes pretty good power up to with
stock LT-4 heads and a pretty mild cc306 cam