buying a car - new motor, supposedly a 383 and has LT4 heads. Looks like the stock LT1 intake and throttle body on there to me.
Any fast and sure way to know if the heads are GM or aftermarket LT4?
I saw a small "GM" cast on the corner of driver side front.
The kid bought it built, motor looks and runs brand new and - it screams like it is what he says - but......
any numbers/things I can look for without pulling off parts?

 

pull the valve cover and look at the casting #

 

Is that the only way?
What is the number supposed to be?

Will an LT1 intake bolt onto LT4 heads?
So if it's an LT1 intake number will I know?

 

Head and intake part #'s for LT1 and LT4 are in a table in this link:

http://www.grandsportregistry.com/lt1vslt4.htm

Intake will bolt up, but it can not have the tops of the runners raised high enough for the LT4 head runners, unless you add metal to the tops of the intake runners.

 

thanks

 

does the head have LT4 cast outside the valve cover? I thought a few years ago I saw that on a set of heads...?

 

casting # for the lt4 intake is 12550631 and 12555690 for the heads

 

thanks guys
12555690 is cast - "LT4" is cast on them as well.
It does appear to have the stock 94 LT1 intake and tb.
This is a 383, well built, made around 500hp on a dyno and 400rwhp on rollr dyno.
Anybody else run an LT1 ntake with LT4 heads?
seems to like it!

 

Well then I'm guessing it will like it a lot more when you actually get the correct intake on it that has the proper-sized runners

 

from the GranSport registry:
"A specific intake manifold was cast for use with LT4 heads. Although the manifold and head intake ports do not precisely match, the manifold was cast with additional material to allow safe machining of the ports to more closely match the LT4's higher head ports. LT4 intakes were powder coated red to differentiate them from the standard LT1 manifold. "
I have learned from old Pontiac building that having a taller/wider port opening into the head can actually be good. It allows the smaller intake manifold runners velocity to enter the head port at greater speed and a straighter charge. And the head intake port's smallest cross section (probably before the radius into valve seat) is where the only restriction will occur.
I'm no expert - but I'm thinking I'd gain little with a port matched intake.
Yup - we all gasket match intakes to heads - but, has anyone tested for a gain in this situation? I think it's a gain when you have big race ported heads and need a full straight charge under maximum RPM. On a street head, the smaller intake that still flows enough to support the head flow may be a torque increase over a big runner race type intake manifold.

 

I did for a little while, and really saw little to no gain going straight to the LT4 intake.

 

thanks - you backed up my theory and saved me wanting to buy one