As you read posts on here everyone says that the LT1 heads WILL NOT support 383 cub, to make big power.

Can someome explane to me why, Everything is to be a combo, the overall package will make the power.

If not the LT1 head what head or cmf is required to make big power with the extra cubs.

I have read LT4/2XXAFR/TFS heads so it looks like we are in the 300cfm range..

Or is it the runner size being to small/cfm....

Side note: what heads would you put on 23* if you could to make 500+ RWHP

 

i would use the heads you mentioned and have them worked over by someone other then the manufacturer, LE, AI, Lethal EFI, BRE etc. some of the more well known CZ28 folk for example

i dont think its not that they wont support a stroker motor, its just that the stroker motor needs more air then stock casting can supply to live up to its potential

others hopefully will chime in with much more detail....

 

It's not in the overall CFM as it is the size of the intake runners. The unported/ported volume of a stock casting LT1 head just can't be opened up enough to properly support the demands of a 383 (or bigger) in the upper end of the RPM band. There's such a huge demand for air at high RPM for a 383 that the motor can't get it due to the runner volume causing a restriction. Will they work on a 383, yeah. But, you won't be running at your maximum potential. This is exactly why I went with a 355 instead of a 383 for my rebuild.

Hopefully someone who can explain it better than myself will chime in.

 

My $.02 is to get a bare casting if you're going to get them ported. Send them off to the porter and let them help you with what valvetrain you're going to run in it.

 

240-245 CC intake runner--- 2.080+ valve---- 325CFM Will support 670FWHP on your 383CID. Everything else being perfect.

 

Wouldn't a 240+ CC intake runner be a bit lazy on a 383 with a 23* head? I'd figure 225 would be the largest you'd want unless it was 400+ CID or an 18* head.

 

I don't know your def of LAzy.That head will flow 325 with a MACH # in the low 3's.A 383@6500 is pulling a vacuum on the heads and intake,indicating it needs more port,or bigger valves
You have been listening to to many wives tales.That head would be to big for a 302@6000 but a 302@8500 is a different story.For your engine IF IF you could get a 400CFM port that would be to big at 3500 but not at say 9000.BUT where do you find any that big on a 23* head? CFM is not the issue it is cross section area and there is just so much metal in a head to remove.There ain't that much more in a 23* head.SB-2 comes to mind--another story--
I have installed heads like this (same size) on 383's and made 650FWHP+ EFI below 7000 with NO drivability problems at all.I have also used some bigger with no problems.It depends on your total set up and tune.You also have to have a intake to go with them (not LT-1 or LT-4).The intake can be a big cork in the system.

 

Before we get to the big heads ...Why can't the LT1 heads keep up with the 383....Where are they hurtting..
Is steping up to a LT4 head worth it, or just go to the AFR..

"240-245 CC intake runner--- 2.080+ valve---- 325CFM Will support 670FWHP on your 383CID. Everything else being perfect"

What cyl head can you get 240cc intake runner......Is this an LTX style head or Gen1, would a Gen1 head be a better chose

What kind of intake do you need.....AKA Vic jr....????

 

The LT castings will not flow or can they be made to flow enough to make serious HP without a bunch of exoctic work.The AFR are your best bet,but they need to be ported by someone that can get every last bit out of them IF you want to make serious HP.Now if you want to make 400RWHP the max effort LT-4 will get you there with a good intake.head flow around 285-290CFM because when you bolt anything but a GOOD sheetmetal on your flow is going to fall by 10% or more and 275CFM will support about 565FWHP.
The heads I use are converted small block heads.They are converted for the reverse flow cooling,then CNC ported and then finished by hand.

 

racerdude, I am still learning, so don't think I was correcting you. I am curious though. Why do most people, well at least on this board, say that a set of 215 AFRs would be too big for a 350? Seems if 240 or larger is fine on a 383, then 215s would work perfect on a 350. I understand that rpm plays a role as well, but not many street motors run 8500, and yeah, I would consider a 302 turning 8500 to be a bit lazy on the low end, as it would probably start to pull good at 4000 or 4500. Then again, if it were geared properly, you'd never know.

 

ok, I understand on a max effort 383 the stock heads will never keep up. but what about a 383 that will only spin to around 6500rpm? no way am I paying for a LTX intake and some exotic headwork at this point. I would buy an LS1 before I do that. those heads ported will flow enoughto go 10's N/A. Im expexting to make between 425 and 450 rwhp, seems it wouldnt matter if the eng. was 355 or 383, to make the same power, doesnt it require the same amount of air moving through the eng? so if a set of heads/intake can support 450HP in a 355, shouldnt it be able to support the same HP rating in a 383?

 

NO NO NO

Think about it a 383 requires more air to make HP at 6500 than a 350.It will make MORE HP at the same RPM.SOOOO if you starve it for air it will make the same as a 350 at the same RPM.Care to guess how much to starve it for the same HP at the same RPM.Yaaa Buddy
WHY did you spent the extra money to build a 383 when you don't want it to run to it's potential.Was it the few lbs of extra torque????

It will be fine if all you want is 400-450RWHP

I understand the budget thing,but I don't understand that logic.

If you want to run in the 10's you had better break out the chop saw and torch.A full weight 3600# car MIGHT run in the low 11's with a good 60'( 1.50-1.52).,with GOOD air.

 

yeah, my case is limited budget. I figure that do the short block now while I have to anyways (bad bearings/crank), make more low end torque, and some extra HP too. like I said, there's no way I could get new heads/intake now anyways, just was lookin at it diff. than you. trust me, if I had the money to do what I really wanted, I wouldnt even think of running the stock stuff. but thats not the case.
also, in my case, I figured my eng. in 350 form would make 400-425rwhp on a good day, so pumping up the CID would add some. Im not near what I believe (and what your stating) the limit to be w/the stock heads/intake. ofcourse Im not happy with only 450rwhp, but thats all I can afford right now. makein sure that at my level the stock stuff wasnt hurting perf. with a 383 compared to 350. as in would make more HP w/355 then 383 shortblock. know what Im saying?

 

Yea,been there had to do that.You have the potential for 650+FWHP,with good heads and intake system all the way out to the filter,11.5x1 and a good mechanical roller.It could be made so your wife could drive it at that HP level(not that you would let her)Well, good luck and keep the shiny side up.

 

the problem is not the heads..............some well ported lt1 heads will flow in the 270's or better....................but when you slap on an lt1/lt4 intake........that drops WAY down...........that is why no one is making the power they should.

here as an example thats SAR2k test

"I just tested this on an LT4 intake last week. I used a factory LT4 head that I'm about 90% done with for 95Bird. On the head I've worked the intake side to 205cc and it flows 275 @ .600

With the unported intake bolted up to the head on the bench it flowed 230.5 @ .600

After fully porting the intake (includes raising the runner) the combo flowed 251.8 @ .600"


so even if your heads are badass.......your intake is limiting the power.

brett bauer's and raceprep are both coming out with a new intake that should alleviate these issues..............then the TB and MAF and intake tract will become possible restrictions.