Air-Adam

I'm just curious, as I've heard alot of conflicting info on this...

What is the actual difference between the LT1 and LT4 intake manifolds? I know the LT4 intake isn't an 'upgrade' from the LT1 manifold, as they are basically the same internally. I've heard its just that the LT4 manifold has a taller lip around the port sealing surface to cover the taller ports on the LT4 cylinder heads.

So why is it some heads are listed as needing the LT1 manifold, some as needing the LT4? Is it just the larger sealing surface on the LT4 manifold to better cover large ports on cylinder heads like the LT4s? If thats the case, can the LT1 intake not be welded to add a bit more metal around the sealing flange, and then machined flat again?

I'm just asking because I may be upgrading cylinder heads in the future, but I see lots of sets designated as 'LT1 heads' and lots as 'LT4 heads' though the only real difference I can see in the sets is the ones listed as 'LT4' are anything 195cc and up.

I'm not new to working with cars, especially the GM stuff, but the LTx stuff is still somewhat new to me..

F6

You can't put a LT4 manifold on LT1 heads, the manifold is milled at a different angle. You will, just like I did, have to get yourself LT4 heads and then everything will work out fine.

RamAir95TA

They aren't milled at a different angle. The LT4 uses raised ports that won't line up with LT1 heads. They are identical otherwise.

96capricemgr

I see why you are confused. You have a better handle on the differences than the two guys who "answered" your question INCORRECTLY.

As you have read there is more material above the port to seal to the taller port in the heads. TALLER, same location just TALLER so the intakes all line up. The LT4 manifold will have enough material to allow port matching to the TALLER port LT4 heads, but GM cheaped out and in stock form made it internally the same as the LT1.

Yes you can weld on more material to an LT1 intake and make it port matchable to LT4 heads.

All that said, skip looking at LT4 stuff, despite the hype the results just aren't really there. Ported GM LT1 heads are capable of BIG power, if you want more than that then the Trickflows are the only aftermarket LT1 offering I would consider.

My opinions on this stuff are very definetely in the minority, you will learn though that "conventional wisdom" and popularity have little to do with right.

Air-Adam

Yea, I wasn't planning on using the GM LT4 heads, I just noticed that all the aftermarket stuff out there (AFR for example) have some heads listed as 'LT1 heads' or 'LT4 heads'... so I figured there was some fundamental difference between them. If it really is just a matter of the extra metal around the sealing surface on the manifold, then thats not such a big deal. I could have some extra metal welded onto my intake and then just have the surface machined flat.

Another little brainstorm I had though too.... I know lots of the 3rdgen guys (those are the cars I cut my teeth on before I got this '97) like to convert the LT1 intake to use on their TPI cars, but could one convert a Gen 1 small block intake to work with an LTx engine?

I don't want to convert a TPI system... I was thinking something more like the Holley Stealth Ram. I know its pretty similar in design to the LT1 manifold, in that its a tunnel-ram style manifold, just a fair bit taller... but just out of curiousity, would that work? Would the longer runners have any benefits?

The HSR might be an alternative to the LT4 manifold for heads that require the LT4 manifold, since they seem to be quite scarce and ungodly expensive...

96m6lt1

this may help you out a bit.some nice info....


http://www.ls1tech.com/forums/lt1-lt...sr-design.html

96capricemgr

In bench racing land everything is better than an LT1 intake. Here in the real world guys spend a LOT and rarely actually improve much of anything. But the pics are cool and they tell everyone about it so gen 1 intake swaps have become somewhat popular, though they usually go to large carbed intakes and convert them to injection.

Skip the AFRs and skip the aftermarket intakes.

You want to go fast, with good reliability and price www.advancedinduction.com

I know that is not the answer you were looking for, but it will be faster and cheaper than the direction you were headed in.

Make great torque, which I assume is your goal.

Injuneer

The LT4 heads are not planed at a different angle than the LT4 heads. Dimensionally, they are IDENTICAL, except for more metal at the top of the runners, to allow the ports to be opened up to match the LT4 heads. The factory did not bother to match the LT4 intake ports to the LT4 head ports.

First 1/2 is correct, but second part is wrong. The ports line up identically, because they are the same dimensions in both intakes. What causes the LT4 intake not to bolt to the LT1 heads is the extra metal at the top of the runners. That metal interferes with the valve cover rail on the LT1 heads. The LT4 heads have the valve cover rail located higher.

Air-Adam

I was just asking about the HSR because I know lots of Gen 1 guys use them on larger aftermarket heads like the 195 and 200cc heads... I was just wondering if it would work inplace of the LT4 manifold on heads that would normally require the LT4 manifold?

I'm just trying to learn the ins and outs of the LTx motors before I decide what to do... port the stock LT1 heads and intake, go aftermarket, etc.. I know the stock LT1 heads can run with the best aftermarket stuff when ported, but I just want to see what more of my options are.

None of the Gen 1 stuff is at all new to me, I've been working with that stuff for many years now, but the LTx stuff is still somewhat new to me. Just wanting to learn what works with what, and why.

<Puck>

There is a guy working on a very promising HSR conversion for LTX's. I believe the user name is GGCP or something.

Looks like a very promising lower cost alternative to a full on single plain conversion.

Air-Adam

Since the intake ports are in the same place between the LT1 and Gen 1, how hard could it really be to convert over an HSR setup? I would think just drilling the relocated intake bolt holes, putting a freeze plug in the distributor hole, and making a block-off plate for the thermostat housing would be all that would really be necessary for a functional LTx HSR conversion... Could cut out the crossover completely, but that wouldn't really be necessary would it?

96capricemgr

Might need a little porting to get the ports to really line up but the other modding they are doing to that manifold is taking some height out so it will clear an f-body hood.

Air-Adam

Clearance isn't a problem for me... mines got the Harwood 3" cowl on it.