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Previous owner installed the GM Performance LT4 Hot Cam Kit including upgraded valve springs and 1.6 Roller rockers, as well as long tube headers and a tune from PCM of NC
Car has original 113 heads I am pretty sure..
This seems like a really good candidate for a converted LT1 intake manifold swap, or a miniram. I found another thread on the forum where someone got 310rwhp on a dyno with an L98 with converted LT1 intake, cam swap, and aftermarket aluminum heads and 1.5 roller rockers.
I would be pretty happy with 300rwhp
Does that seem reasonable for a 1991 L98 with 113 heads, LT4 Hot Cam Kit with 1.6 Roller rockers, long tube headers, a decent tune, and either a miniram or converted LT1 intake?
I know LT1 intake manifold conversions have sorta fallen out of favor with the availability of the miniram, but I am really trying to keep things on a budget.
Has anyone done the conversion more recently? Any tips or pointers?
Machining the 0.250" thick shim spacer with 5 degree slant isn't too bad, but I am worried about how to locate the center of the distributor hole.
Most conversions seem to involve lopping of the EGR portion of the intake to run the large cap distributor. This then requires welding to seal the plenum area back up, right?
If running a small cap, a remote ignition coil needs to be mounted and associated wiring harness to adapter the large cap TPI harness to the small cap and remote coil?
I have seen coolant inlets/outlets put on the front or back of the manifold. Thoughts on what is best for cooling performance?
What about the throttle cable bracket?
Thanks to @Tunedport90 I found an already converted LT1 manifold for sale. The owner claims it was mounted to LT1 heads. He did not do the conversion himself. This means I would still need to drill and clearance mounting bolt holes in the converted LT1 manifold in order for it to bolt to my 113 L98 heads? The coolant inlet/outlet are at the front of the manifold. Thoughts on that?
The current owners also claims no shim/spacer with 5 degree angle on their manifold. Is it possible someone built up or welded up the distributor mounting boss surface at the rear of the manifold then machined it to the right angle? The owner claims to have used a small cap distributor with the setup, and no shim or spacer...
Obviously custom fuel lines need to be run... 1991 TPI I believe sends fuel send and return up the front of the motor. Perhaps that can be shifted to the rear since the LT1 fuel rail ports and pressure regulator are rear mounted?
Thanks for any input!
Last edited by yakmastermax; 03-29-2023 at 06:05 PM.
was hoping the intake was completed, good start and nice throttle body.
fragola and earls makes saginaw to an6 and I think click on or push on adapter for lt1
What throttle body does he have on there?
Here are some pics
Why couldn't I just reuse my 91 TPI throttle body?
Thanks, I was literally just looking at that wiring adapter. Says 85-86 TPI large cap but I assume it works with 85-91 TPI large cap?
I don't mind a little splicing and soldering though.
Can a budget 87-92 Chevy small cap work?
The MSD 8366 is expensive...
Remote coil suggestions and mount ideas?
He claims the front driver side coolant inlet/outlet doesn't interfere with the throttle cable.
Thoughts on the lack of distributor shim spacer? He claims no issues or leaks.
The throttle body is a Accel/lingenfelter 58 mm with 85-88 linkage probable worth $400 alone. Might want to use yours since I think throttle cable will fit. The adapter to hei external coil would work on 85-91 Vette. Just have to connect your tach and coil power to the new pigtail the icm part is plug and play. A tbi truck or tpi with melonized gear distributor would work. Not sure if there’s room to make an external coil fit on rear intake bolt holes on passenger side. Might search older threads for pictures of swap.
Items to address with Lt1 converted intake
Drilling bolt bosses for 113 heads to match (if not buying one converted already)
Distributor
Fuel lines
Throttle linkage
Coolant lines with thermostat
I'm sure there is more I am forgetting. I pulled mine off and it went to the scrap yard. Got tired of the leaks and other things going on.
Since this is going to be more of a track toy from what I gather, my suggestion with this new car. Get it sorted before doing any modifications. Ideally you would focus on suspension fixes and stripping weight out and having fun on track. Shaving 100-150lbs will make for a lively L98 with the mods that are already done.
Items to address with Lt1 converted intake
Drilling bolt bosses for 113 heads to match (if not buying one converted already)
Distributor
Fuel lines
Throttle linkage
Coolant lines with thermostat
I'm sure there is more I am forgetting. I pulled mine off and it went to the scrap yard. Got tired of the leaks and other things going on.
Since this is going to be more of a track toy from what I gather, my suggestion with this new car. Get it sorted before doing any modifications. Ideally you would focus on suspension fixes and stripping weight out and having fun on track. Shaving 100-150lbs will make for a lively L98 with the mods that are already done.
Im with Chump on this one.
In the meantime, you can set a bunch of auto searches for miniram and/or Superram that may come up.
Your new toy was probably one of the best buys in recent history and id get the platform solid like chump suggests and then grab z51 springs or coils.
I know u r thinking u may as well swap intakes while u address the china wall leaks but i wouldnt worry bout it. Get the platform ripping and grab a great deal on the miniram or superram when it comes across you.
Yeah you nailed me. My thought was if I'm pulling the TPI intake manifold to reseal the rear china wall in the event that the oil pressure sender isn't the main leak, then I might as well put something better one.
But yeah I don't plan on swapping the intake manifold until I've got more of the poor running figured out.
BUT the owner of this converted LT1 intake manifold DID confirm that it has the correct shim spacer with angle in the rear for the distributor. He claims it is bolted to LT1 heads, but in the pics they are perimeter valve cover bolt heads. Aftermarket LT1 heads?
Will the coolant inlets/outlets at the front of the manifold work okay with my 1991 113 heads?
Should something like that work? I would prefer to spend a little bit more to get something higher quality, but spending $300-$400 for an MSD unit is out of the question. At that point I will try my hand at chopping off the EGR stuff and making my large cap work.
I've never done a cam swap or headgaskets, but the owner previous to the previous owner said that after the cam kit swap and headgaskets the car was running well, and I believe him. So something went south between then and now. Can a cracked brake booster cause a vacuum leak that both kills brake performance and makes the car run poorly?
Last edited by yakmastermax; 03-23-2023 at 10:21 AM.
I did some more research and my understanding of the factory TPI cooling system is that coolant is pumped into the block from the water pump. This coolant then goes from the block into the heads. Looking at a normal TPI intake manifold base, as well as the intake manifold base to head gaskets, there appears to be a coolant passage in the intake manifold base at both the front AND rear of the TPI Intake manifold base, allowing coolant to pass/equalize between the heads at both the front and rear. The coolant exits the heads however at the FRONT of the motor into the front coolant passage in the TPI base, then goes to the thermostat housing and then back to the radiator.
An LT1 intake manifold does not have any coolant provisions at all. I have seen documentation on multiple LT1 to L98 intake manifold conversions, and most seem to install either a pair of coolant outlets either at the front of the manifold or at the rear.
It seems to me that to best recreate the conditions of coolant flow of a factory TPI system in a converted setup, the pair of coolant outlets should be put at the FRONT of the converted intake manifold, BUT that additionally there ought to be some sort of passage (section of hose) placed at the rear of the manifold so that coolant can cross over and equalize between the heads at the rear of the manifold. So outlet/inlets should be put at the rear of the converted LT1 manifold as well as the front, except at the rear it is just a simple section of hose acting as a connecting passage?
Also are there any performances benefits to running a small cap remote coil distributor over a large cap HEI? I was reading that remote coils can do larger voltages than the in cap, but that maybe small cap has "cross talk" between the leads at high RPM?
Last edited by yakmastermax; 03-23-2023 at 10:27 AM.
You might try unplugging the booster line and then pinching it off or put a bolt in the line temporarily to seal from vacuum leaks. It can cause high idle . Stalling and yes poor brakes.
I try to stay away from the cheap distributors . I had one years ago dead icm out of the box and there replacement icm only lasted a month or so.
https://www.thirdgen.org/forums/engine-drivetrain-suspension-parts/783988-msd-distributor-8366-efi.html
or a stock distributor from a early tbi truck from the junkyard.
Couldn't one use the 92-96 but preferably 94-96 fuel lines from an LT1 corvette that run under the car from the fuel filter then up to the fittings on the rail to avoid custom fuel lines? It looks like 92-96 LT1 send and return fuel lines coming off the rail shoot out towards the passenger side then there is that pair of quick disconnects, then the stainless braided factory line section goes down to the fuel filter under the car.
Anyone know if a small cap distributor conversion would clear with the use of those factory fuel line components? A conversion of a standard LT1 car to a small cap distributor setup should answer that clearance question.
Will the LT1 fuel lines that go from the quick disconnects above the passenger valve cover then down to the fuel filter bolt to the 1991 L98 fuel filter and return line sections down under the car?
The factory LT1 fuel pressure regulator ought to provide the right PSI to run the LT1 injectors even with the L98 ECU controlling everything?
94-96 LT1 fuel line:
93LT1 fuel line connections at filter side:
96 LT1 fuel line connections at filter side:
88-91 L98 fuel line connections at fuel filter:
Last edited by yakmastermax; 03-24-2023 at 10:48 AM.
Looking for small cap distributor suggestions. The smaller the better. Hoping for something that is 85-92 TPI Camaro compatible, or is otherwise GM compatible such that I can use one of those large cap to small cap adapter harnesses.
Looking for small cap distributor suggestions. The smaller the better. Hoping for something that is 85-92 TPI Camaro compatible, or is otherwise GM compatible such that I can use one of those large cap to small cap adapter harnesses.
I used a Duralast Gold small cap dizzy and auxiliary coil for my Mini Ram swap. I can get the part numbers. It’s worked well and has plenty of clearance.
In all reality is that Duralast distributor any different than this one that is nearly a third the price?
These all sorta look like Chinese clones out of the same factory no?
A guy on third gen talked about replacing the cap, rotor, and ignition control module electronics internal to the distributor with AC Delco parts. One could do that with one of the cheap $50 Chinese distributors and be into it total for around $150
Or should I find a used GM on ebay or at a parts yard?
I haven't figured it out for sure but with one of these GM Camaro/truck small cap distributors, the LT1 intake manifold rear EGR provision chambers don't need to be lopped off right? What about fitment with the 94-96 LT1 fuel rail inlets/outlets and the fuel pressure regulator?
Should I expect to be able to use the GM LT1 fuel pressure regulator?
I am going to tune the chip, so can't I just adjust injector duty cycle to compensate for any difference in injector flow rate and fuel rail pressure?
For a distributor that cheap is question icm quality and reliability. For adjusting fueling I’d set tune flow rate, injectors offsets. Datalog and adjust ve accordingly. Not sure the answers to your other questions.
I used a Duralast Gold small cap dizzy and auxiliary coil for my Mini Ram swap. I can get the part numbers. It’s worked well and has plenty of clearance.
I went to the bone yard and got a small cap from a later Chev truck. $22. I like $22.
That’s works, just have to make sure it’s a skinny mounting hold down. I think 91 or 92 trucks used the large hold down and hole could be larger.
tbi trucks is non melonized gear
Last edited by Tunedport90; 03-29-2023 at 03:44 PM.
Right now I think what I want to try to do is use the LT1 fuel lines that go from the fuel filter up to the fuel rail in order to get fuel from my 91 L98 fuel filter and return up to the converted LT1 intake manifold fuel rails.
I am looking at a parts car tha lt the seller is calling a 1994 Corvette. Here is a pic of the motor. Curiously the fuel rail inlet and outlet lines are on the DRIVERS side as opposed to the passenger side. My understanding is that all 92-96 vette LT1 had the fuel inlet/outlet on tbe passenger side and the lines routed down to the fuel filter near the passenger footwell.
On the other hand, LT1 camaros I do believe had tbe fuel inlet/outlet on the drivers said. Also note the valve covers look like camaro LT1 valve covers?
Perhaps this was a camaro LT1 motor that was swapped in?
03-22-2023, 06:53 PM
1991 L98 LT4 Hot Cam KIT, LT1 Intake Conversion Swap, Miniram
