Marmz

Hi all, I just started gathering the parts for swapping out the TPI for an LT1 setup on my '91. I know there's plenty of people who've done this before, I've done a ton of research. There seem to be more people sharing failure stories than success stories, but hopefully there are people successfully running this setup who can offer some guidance.

I think I'm aware of most of the potential pitfalls with the conversion and I think I have the tools to deal with most of them. I'm keeping the stock large cap HEI. I've already started to fab up a plate to help locate the distributor hole accurately and am aware that I'll need a 1/4" thick and 5* spacer for it to sit properly. I also know about the EGR boss clearance issues, remote thermostat, etc etc.

For the record the manifold is off of a '92-'93 vette, I purchased it before I knew that the fuel rail setup is no good for the conversion. I've already ditched the fuel rails as they were corroded on the inside so I didnt want to use/modify them either way. I'm most likely going to pick up a set of later style fuel rails that I'll modify for AN fittings and braided lines. Other than the fuel rail situation, the '92-'93 manifold will still work for the conversion, correct?

Anyways my main concerns lie with the coolant setup and the manifold gaskets I'll need. From what I've read it's easier to tap the rear of the manifold for the coolant lines in order to avoid clearance issues with the TB and TB cables (I'll be using the TPI TB). However I'm not sure what manifold gasket I should be using that will work properly for the modified rear coolant passages. I think that the Felpro 1204 is the proper one to use (for the L98 bolt hole placement) but I cant get a straight answer on whether or not this gasket has the rear coolant "restrictor" holes I keep reading about, and I'm not sure whether or not I need them for the modified rear coolant passages. Can anyone shine some light here?

I'm building this car for track use (HPDE and time trails) and will be upgrading the rest of the cooling system as well (better radiator, new hoses, higher flow WP, deleting the heater core and AC, etc). Needless to say that I want a bulletproof cooling system that will withstand the higher RPM's without blowing out a gasket and grenading my whole engine.

I'm open to all opinions/input here positive or negative, as of now I want to keep moving forward with the conversion but will consider people's opinions if they dont think it's a good setup for a road course car. Right now all I have is the manifold which I got for a reasonable price, so it's not too late for me to go in a different direction if need be. Thanks!

cv67

Should bolt up the same as the later intakes
1204 is fine outside your bolt holes which is an easy fix
Not clear on the question of the rear coolant passages
Dont think you need a blockoff plate the gasket should do it long as it seals. Bet felpro makes one with and without.

Marmz

Thanks for the reply, good to know it will bolt up the same as the later intakes. I know that the 1204 has no provision for the rear heat crossover so you're probably right about not needing the EGR block off plates, but I'll probably cover them up anyways for a clean look.

My main concern is definitely the rear coolant passages, I don't want to cause a lack of proper cooling on the rear cylinders. Maybe I should contact felpro directly and see...

ANTI VENOM

What's wrong with the 92-93 rails? I wasn't aware that any corvette rails and fuel lines would fit with a standard dist. in the rear. The camaro/impala seems to work but but the fuel lines on the drivers side.

Marmz

There are two fuel crossover lines in the rear of the 92-93 rails and no front crossover, which means the rails are longer in the rear, which means that the rear crossover lines will probably hit the large cap dist. Also, and I haven't found this info anywhere actually, but the 92-93 rails are also different internally; they have a internal tube that carries the fuel to the front of the rails first where it then dumps into the main rail body to feed the injectors. That internal tube was no good for modifying the rails for AN fittings, but the specific rails I bought were corroded internally anyways so I returned them to the seller and kept the manifold. You're right about using f-body rails that have the fuel enter the rear of the rails which will be much better for modifying, so I'm going to go with those.

Also another note, I noticed that the gasket surface of my manifold has some gouges in it in a few spots. They're not huge but they are noticeable. I know that's no bueno for sealing, but is it as serious a deal as say gouges on a head gasket surface? Will I need to get the surfaces machined or can I still get a good seal with the proper gaskets and rtv? I'll post a pic in a bit.

bjankuski

I did this conversion about 5 years ago and this is my opinion and this is what I did. I added the coolant lines to the front of the intake by milling off the bolt mounts that were on the front of the intake and then tapping the intake for fitting that ran the water lines out to a remote T-stat. I did this because I did not like the idea of reversing the coolant flow through the head by pulling out the water from the back. I was concerned that the head gaskets would have been designed to equalize flow through the head and block with water being pulled from the front, if I reversed this I was concerned about creating hot spots around some cylinders (#3, #5). I also milled the intake for the large cap distributor but be warned it takes a lot of milling and welding after you are done to seal the EGR passages back up, since they will be exposed to atmosphere. As far as road racing this it should be fine as long as you keep the coolant flowing as designed by GM. When it comes to the distributor spacer I milled in my distributor hole on the required angle and then added in a spacer that was flat and then bolted it into place at the correct distance from the intake. It worked well since the manifold was milled on an angle that matched the distributor so the spacer did not have to be machined on an angle.

I have some pictures of my set-up if you need them.

Marmz

Good insight on the coolant flow, I thought the front bolts mounts would be a good spot for the coolant lines too. What sized fitting/hose did you use?

What gasket did you use? 1204?

Unfortunately I don't have easy access to a mill and I'm trying to avoid machining costs if I can. That said I'm not welding to avoid warping the piece so I'm going to use JB weld liberally.

cv67

Put up pics of it

Theres always a light dust coat of spray paint on the surface then take a longboard to it to ck flatness. Dont get too carried away with rough grit
Its a little old school but will tell you what you want to know

blackozvet

this is how i set up my remote thermostat from the front of my single plane, using a Moroso unit and -10 lines, the Moroso piece sits on top of the water pump.
Im not running a thermostat in it however, it doesnt seem to want to open, but the car cools fine otherwise.

cv67

Hey oz how do you like that thermostat housing?
Does it use an oring?
Have a cast alum piece they all seem to deform and leak once you snug them down even after excluding the oring making them flat and using a gasket.

Marmz

That's a good idea with the long board sander, I should pick one of those up anyways. Here's a few pics of the gouges I was talking about. They're not overly deep, but I'm more worried about where they're located.



Not deep at all, but long gouge here on the front of the piece.



These are the two worst ones in terms of depth. Notice the long gash on top and the shorter wider gash near the bolt hole. This is at the rear of the piece.



Notice the gash connecting the bottom of the two ports. Again not super deep, but this location worries me the most for gasket sealing.

What do you guys think, am I better off having the surfaces machined? I know only a tiny bit can be taken off, but I want to avoid fitment issues obviously.

Drool! That's a very cool setup, I like looking at all the custom single plane setups around here.

I also didnt know that Moroso piece existed, it seems like a very clean way to integrate the remote thermostat. How's the quality of the piece? I know Moroso stuff can be hit or miss.

Also, what WP are you running? I made the call that electric WP's wouldnt be the best choice for consistent high RPM road racing unless I got the most expensive highest flowing pump, so I'm looking at a more budget friendly Stewart Stage 3 WP.

blackozvet

Drool! That's a very cool setup, I like looking at all the custom single plane setups around here.
I also didnt know that Moroso piece existed, it seems like a very clean way to integrate the remote thermostat. How's the quality of the piece? I know Moroso stuff can be hit or miss.
Also, what WP are you running? I made the call that electric WP's wouldnt be the best choice for consistent high RPM road racing unless I got the most expensive highest flowing pump, so I'm looking at a more budget friendly Stewart Stage 3 WP.

The moroso unit is machined from billet, so its pretty strong, I used 2 x -12 O ring fittings (going down to -10 for the hose fitting) and the water neck is an O ring 360 degree swivel, there has not been a hint of leaking so far, the moroso unit is good value at $70. you can use either an o ring neck or a flat gasket neck with it.
I was a bit dubious about the O ring water neck sealing, but its a pretty solid piece and there is no flex. there is a big price difference in those water necks, maybe the more expensive ones are better ?

Im running the GM C4 water pump, with a wet and dry polish, I did have another pump in there (some generic brand) but the GM pump cools better at slower speed.

cv67

Thx sure its worth the extra dough

Dont think that gash would cause an issue touch of sealant and youre good making sure its straight, why not