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Tourmax

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I had planned an LT1 intake manifold swapfor the L98. I grabbed a used one and had started modifying it:

fr_4149_size880.jpg


But I've kinda lost interest in it. I'll probably still finish it, I'm just not sure if I want to make the "compromises" I need to in order to make it work on the L98.

So I thought I'd do a TPI intake while I decide which way to go. I knew I didn't want to "chop up" the intake currently on the car. I never chop up original parts (if I have a choice), just in case I screw up and ruin them. I usually buy a used part and modify that. That way, if I do screw it up, the car is still drive-able as the original parts are still, well....original.

I've got a couple TPI setups lying around from "the old days", although about all that is usable on them is the upper plenum. The runners are too small and no way to increase thier size. The lower manifolds are all from Camaro's, so the egr ports are in the wrong place. My Vette is an 88, so it has the egr port in the back of the intake, there is no head egr passage in the aluminum 113 vette heads. I want to retain the Egr function, so I needed to get the right lower manifold.

Cruised ebay and scored a Corvette lower intake for 50 bucks:

fr_4226_size880.jpg


Its just a stock piece, but it's a good starting point. Would have been nice if I could have scored an Accel/Edelbrock "Big Mouth" lower, but anywhere I can find one they want ridiculous prices for them. Like close to 1G USD. For 30 year old/obsolete parts?...No thanks. Oh well, I can port out the stocker out just as much, it just means adding lots of weld material to the runners.

The goal is as close to 300 cfm as I can get. That will be a challenge as the OEM TPI maxes out around 220 CFM. But 300 is more flow than the 113 vette heads can use (max out around 260CFM at 0.50 lift IIRC), so the intake won't be the limiting factor. The biggest area that I need to work is the transition from the lower to the head port.

The stock lower has a horrible transition from the intake to the head. GM, for some reason, made the runner almost flat at the end. the roof of hte port needs to be raised to ease the transition. That means welding more material on the top in order to reshape the internal port shape. The diameter of the lower's runners is a problem (it neck down right in the middle and opens again on it's way to the port, horrible for flow characteristics), but at the head transition the air essentially slams into a wall and makes a near 80-ish degree turn. When moving air through a passage, you try to avoid anything over a 45 degree turn or air starts to separate, become turbulent and just generally becomes it's own restriction.

The stock lower measures 1.70 at the runner port, but it "bells" down to 1.40" a few MM in the port, then it has an even tighter pinch point at the halfway point and begins to open up after that. Then the problem is the transition into the head where the turn pretty much forms a wall that the air has to slam into to make it's 80-90 degree turn into the head on it's way to the valve. As delivered, quite frankly, it's a mess.

here's a pic of a reworked TPI lower (Not mine):

MVC-010F.JPG


The blue is a rubber casting of the head port. The front "rod" is laid on an unmodified port roof. You can see how the air exits the manifold and essentially slams into the head passage roof. Not good for flow at all. Of note, that is an edlebrock "hi flow" TPI base. An OEM base is even worse. The second rod is laying on the roof of a reshaped runner. As you can see, the transition is much more manageable. But to get there, you have to grind up well past where the stock manifold roof is. Hense the need to add weld material. The manifold picturedreportedly flowed about 297 CFM once benched. That's as good as a FAST TPI setup, which is serious performance territory for a TPI!

Right now, I still have to wait to buy my TIG so I can add the metal I need to reshape the runners. I could try with my MIG/spool gun, but I'd rather just wait to buy the MIG as the MIG is easy to mess up on a cast piece like this. In a nutshell, I'll be raising the roof of the lower intake runners and reshaping the transition. The rest is just hogging it out as much as I can without blowing through to the adjacent runner, an egr passage or hitting a water jacket. All that is fixable with a TIG should it happen, but I'd rather just not blow through in the first place. Much less hassle.

I'll probably have to look at raising the fuel nozzles as well. They're pretty low on the runner roofs and I believe I'll end up welding higher than the "bungs" in order to reshape the transition area. That's not a big deal though, I'll just spin out some new bungs on the lathe and weld them in where needed. It's great having the tool you need at your fingertips!

:)

The fuel rails would be a problem as their fixed dimensions probably won't fit raised nozzles (raising the nozzles pulls them closer together where they meet the rail, which changes their angles) but I'm planning to modify the rails as well. I'll reuse the extruded aluminum rails, but I'm planning a parallel fuel system so I can ditch the connecting pipes between the left and right rail. Each rail will have it's own feed line one one end and each will have it's own return line on the opposite end. That will balance the fuel pressure across both banks and help make tuning more consistent. An adjustable regulator will gather both return lines together and give me an easy spot to adjust the pressures. I might just make my own adjustable regulator so I can put the ports and lines where I want them. All the "extra" fuel rail openings I'll just TIG shut and the 9th injector (IE: cold start injector) will get dumped to make a spot for that rail's return line.

An 89 Vette ECM calibration will do away with the need for the 9th injector (89+ did away with the 9th injector). No big loss, the 9th injector is known to be a trouble point. Not to mention, I don't think you can even buy them anymore unless you can find them aftermarket (IE: GM discontinued). I'm going to have to buy a GPU1 from Moates.net and refine the calibration to get the most out of this setup anyways, so dumping the 9th injector is just going to be part of that. Been a while since I messed with tuning an OBDI car, but it will all come back to me once I get into it again.

For the upper plenum to lower manifold runners, the aftermarket ones are (once again) stupid priced. Assuming you can find them at all that is. So I'll just do what I always seem to have to do when hot rodding an older car and make my own. I have to figure out how large I can go with the stock ported lower (and still have a decent gasket surface), then it will be buy some pre-bent aluminum tube, turn out some flanges and weld it all up. After some of that "math work" that is.

The upper plenum I'm a little tossed up about. I have two options as I see it:

1. A light port and gasket match and call it done, or
2. Full on custom job.

At first thought, I'm thinking option two. Mainly because it will let me increase the plenum volume. As a general rule, you usually want a plenum to hold the CU/IN volume of the engine and the TPI upper plenum is about 50% of that. Only problem is to get more volume (IE make the plenum bigger), the only real direction I can go to steal space is down. I'll have to shorten the runner lengths, which will move the torque curve up in the RPM range. I have to sit down and do some theoretical mathematics to see what lengths will (and won't) work for what i want. I want to keep it lower in the RPM range as this is a street engine, so I want to keep that characteristic TPI "grunt".

To be clear, this isn't intended to be a HP monster. It's meant to be a strong street performer that will shove you back in the seat when you hammer the throttle. TPI is great for that, and it has a good "push" with the throttle as it is. But I want MORE!

;)

I just don't expect to throw down low ET's or big HP numbers on the dyno. This thing is mean to be a bottom end grunter. If it lays down get 300 rwhp, I'll be more than happy. Stop light to stop light though, I'm shooting for a beast!

Of course, I'll also have to look at cam and torque converter specs to go with any improved breathing, but that's just part of the game.

It's also my understanding that while the 113 heads have a nice D shaped exhuast port, GM cheaped out on the exhaust manifolds and went with a square shape that was too small to start with. This, supposedly, results in a large "ledge" that blocks off part of the D shaped port. I'll have to pull off the manifolds and have a look. If they are making a restriction, I'll just reshape the OEM pices to match the exhaust port. That will do until I decide if I want to pop the cash on a set of long tube headers or possibly make my own stainless headers. TIG makes such nice stainless welds....Hmmmm.....Titanium maybe? LOL!

Keep watching this space for more. But not much will happen until I get my TIG welder though. I don't expect that until roughly "black friday sales" in November. Also, full disclosure: I'm only going to be working on this when I feel like it, so posts may be far between and sporadic. But I'll get it done, sooner or later!

:)
 
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turbozig

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Wow, that is one ambitious project! I will be watching this one to see how it turns out.
 

Tourmax

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Wow, that is one ambitious project! I will be watching this one to see how it turns out.
Well, it will be mostly “ass-o-meter” results.

I don’t plan on flow benching the intake, or drag race it or even hit a chassis dyno.

I’m just going to follow the basic porting knowledge I have of what is likely to work and what is not and leave it at that. Likely to have sonewhere between 50-100 hrs into it before done.

And that still doesn’t account for the time “tuning” the ecm....
 
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2KforeverC5

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I had planned an LT1 intake manifold swapfor the L98. I grabbed a used one and had started modifying it:

View attachment 32706

But I've kinda lost interest in it. I'll probably still finish it, I'm just not sure if I want to make the "compromises" I need to in order to make it work on the L98.

So I thought I'd do a TPI intake while I decide which way to go. I knew I didn't want to "chop up" the intake currently on the car. I never chop up original parts (if I have a choice), just in case I screw up and ruin them. I usually buy a used part and modify that. That way, if I do screw it up, the car is still drive-able as the original parts are still, well....original.

I've got a couple TPI setups lying around from "the old days", although about all that is usable on them is the upper plenum. The runners are too small and no way to increase thier size. The lower manifolds are all from Camaro's, so the egr ports are in the wrong place. My Vette is an 88, so it has the egr port in the back of the intake, there is no head egr passage in the aluminum 113 vette heads. I want to retain the Egr function, so I needed to get the right lower manifold.

Cruised ebay and scored a Corvette lower intake for 50 bucks:

View attachment 32707

Its just a stock piece, but it's a good starting point. Would have been nice if I could have scored an Accel/Edelbrock "Big Mouth" lower, but anywhere I can find one they want ridiculous prices for them. Like close to 1G USD. For 30 year old/obsolete parts?...No thanks. Oh well, I can port out the stocker out just as much, it just means adding lots of weld material to the runners.

The goal is as close to 300 cfm as I can get. That will be a challenge as the OEM TPI maxes out around 220 CFM. But 300 is more flow than the 113 vette heads can use (max out around 260CFM at 0.50 lift IIRC), so the intake won't be the limiting factor. The biggest area that I need to work is the transition from the lower to the head port.

The stock lower has a horrible transition from the intake to the head. GM, for some reason, made the runner almost flat at the end. the roof of hte port needs to be raised to ease the transition. That means welding more material on the top in order to reshape the internal port shape. The diameter of the lower's runners is a problem (it neck down right in the middle and opens again on it's way to the port, horrible for flow characteristics), but at the head transition the air essentially slams into a wall and makes a near 80-ish degree turn. When moving air through a passage, you try to avoid anything over a 45 degree turn or air starts to separate, become turbulent and just generally becomes it's own restriction.

The stock lower measures 1.70 at the runner port, but it "bells" down to 1.40" a few MM in the port, then it has an even tighter pinch point at the halfway point and begins to open up after that. Then the problem is the transition into the head where the turn pretty much forms a wall that the air has to slam into to make it's 80-90 degree turn into the head on it's way to the valve. As delivered, quite frankly, it's a mess.

here's a pic of a reworked TPI lower (Not mine):

View attachment 32708

The blue is a rubber casting of the head port. The front "rod" is laid on an unmodified port roof. You can see how the air exits the manifold and essentially slams into the head passage roof. Not good for flow at all. Of note, that is an edlebrock "hi flow" TPI base. An OEM base is even worse. The second rod is laying on the roof of a reshaped runner. As you can see, the transition is much more manageable. But to get there, you have to grind up well past where the stock manifold roof is. Hense the need to add weld material. The manifold picturedreportedly flowed about 297 CFM once benched. That's as good as a FAST TPI setup, which is serious performance territory for a TPI!

Right now, I still have to wait to buy my TIG so I can add the metal I need to reshape the runners. I could try with my MIG/spool gun, but I'd rather just wait to buy the MIG as the MIG is easy to mess up on a cast piece like this. In a nutshell, I'll be raising the roof of the lower intake runners and reshaping the transition. The rest is just hogging it out as much as I can without blowing through to the adjacent runner, an egr passage or hitting a water jacket. All that is fixable with a TIG should it happen, but I'd rather just not blow through in the first place. Much less hassle.

I'll probably have to look at raising the fuel nozzles as well. They're pretty low on the runner roofs and I believe I'll end up welding higher than the "bungs" in order to reshape the transition area. That's not a big deal though, I'll just spin out some new bungs on the lathe and weld them in where needed. It's great having the tool you need at your fingertips!

:)

The fuel rails would be a problem as their fixed dimensions probably won't fit raised nozzles (raising the nozzles pulls them closer together where they meet the rail, which changes their angles) but I'm planning to modify the rails as well. I'll reuse the extruded aluminum rails, but I'm planning a parallel fuel system so I can ditch the connecting pipes between the left and right rail. Each rail will have it's own feed line one one end and each will have it's own return line on the opposite end. That will balance the fuel pressure across both banks and help make tuning more consistent. An adjustable regulator will gather both return lines together and give me an easy spot to adjust the pressures. I might just make my own adjustable regulator so I can put the ports and lines where I want them. All the "extra" fuel rail openings I'll just TIG shut and the 9th injector (IE: cold start injector) will get dumped to make a spot for that rail's return line.

An 89 Vette ECM calibration will do away with the need for the 9th injector (89+ did away with the 9th injector). No big loss, the 9th injector is known to be a trouble point. Not to mention, I don't think you can even buy them anymore unless you can find them aftermarket (IE: GM discontinued). I'm going to have to buy a GPU1 from Moates.net and refine the calibration to get the most out of this setup anyways, so dumping the 9th injector is just going to be part of that. Been a while since I messed with tuning an OBDI car, but it will all come back to me once I get into it again.

For the upper plenum to lower manifold runners, the aftermarket ones are (once again) stupid priced. Assuming you can find them at all that is. So I'll just do what I always seem to have to do when hot rodding an older car and make my own. I have to figure out how large I can go with the stock ported lower (and still have a decent gasket surface), then it will be buy some pre-bent aluminum tube, turn out some flanges and weld it all up. After some of that "math work" that is.

The upper plenum I'm a little tossed up about. I have two options as I see it:

1. A light port and gasket match and call it done, or
2. Full on custom job.

At first thought, I'm thinking option two. Mainly because it will let me increase the plenum volume. As a general rule, you usually want a plenum to hold the CU/IN volume of the engine and the TPI upper plenum is about 50% of that. Only problem is to get more volume (IE make the plenum bigger), the only real direction I can go to steal space is down. I'll have to shorten the runner lengths, which will move the torque curve up in the RPM range. I have to sit down and do some theoretical mathematics to see what lengths will (and won't) work for what i want. I want to keep it lower in the RPM range as this is a street engine, so I want to keep that characteristic TPI "grunt".

To be clear, this isn't intended to be a HP monster. It's meant to be a strong street performer that will shove you back in the seat when you hammer the throttle. TPI is great for that, and it has a good "push" with the throttle as it is. But I want MORE!

;)

I just don't expect to throw down low ET's or big HP numbers on the dyno. This thing is mean to be a bottom end grunter. If it lays down get 300 rwhp, I'll be more than happy. Stop light to stop light though, I'm shooting for a beast!

Of course, I'll also have to look at cam and torque converter specs to go with any improved breathing, but that's just part of the game.

It's also my understanding that while the 113 heads have a nice D shaped exhuast port, GM cheaped out on the exhaust manifolds and went with a square shape that was too small to start with. This, supposedly, results in a large "ledge" that blocks off part of the D shaped port. I'll have to pull off the manifolds and have a look. If they are making a restriction, I'll just reshape the OEM pices to match the exhaust port. That will do until I decide if I want to pop the cash on a set of long tube headers or possibly make my own stainless headers. TIG makes such nice stainless welds....Hmmmm.....Titanium maybe? LOL!

Keep watching this space for more. But not much will happen until I get my TIG welder though. I don't expect that until roughly "black friday sales" in November. Also, full disclosure: I'm only going to be working on this when I feel like it, so posts may be far between and sporadic. But I'll get it done, sooner or later!

:)
Will be following your BIG project ahead. Very interesting. 😳🤓😎
 

Tourmax

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project shelved for the near future. No idea when will revisit.

Moving on to a "big mouth TPI" project.

Basically, reworking a stock lower, larger runner tubes (same length) and lager plenum. 52mm AS&M LT1 TB. Blowerworks 3" MAF and custom bin to run it. Bunch of other small tweeks. Plan is not to move power delivery RPM range (runner length determines that), just to make more in that range. BIgger tubes, more air, more fuel, more HP and torque. Still will be fairly lopo, shooting for around 300 RWHP, maybe a little more if I can get it.
 

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