TPI vs. LT1 vs. Carb
Thread Starter
Member
Joined: Apr 2000
Posts: 213
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From: Ok, USA
TPI vs. LT1 vs. Carb
Well guys I am looking at getting a new motor in my car in the next 6 or so months. I have been debating whether or not I want to go with my orginal TPI setup but just go with a 350 or go with an LT1 or a Carb.
I know the LT1's run stronger out of the box than a L98 but the L98's do have a lot of potential. However, the one big thing about the L98's is there inconsistancy that they had from the factory. I know this due partly because of GM's lack of quality control however, I have seen guys that have a lot of mods like, cold air, pullies, exhaust, ignition and Edelbrock baseplate and runners only running high 13's and a friend of mine just put in a chip and an exhuast and runs 13.8's with his L98. If I do a rebuild on a TPI 350 what could I expect with SLP headers, exhaust, a decent cam and hopefully an edelbrock intake. I have 3.42's and a 700 R4 with a stage 1 shift kit and Corvette Servo.
Then I could get a low mileage (60k or less) LT1. This would get me mid to high 13's with headers exhaust and chip. However the swap may cost significantly more especially for the wiring and all that computer crap. It would be different but with 60k miles or so I would be looking at a rebuild within about 80k or so.
Then there is the ever present Carb question. I can get good gas mileage with a carb if I drive halfway sane and also that would be different for my car as well. Carb motors can be modded easily and run really really hard. I know a guy that is in the low 13's like 13.2's with his 305 carbed motor!!!
What are your opinions and pro's and con's. Feel free to e mail me if you would like. IROCZSS@AOL.COM
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
I know the LT1's run stronger out of the box than a L98 but the L98's do have a lot of potential. However, the one big thing about the L98's is there inconsistancy that they had from the factory. I know this due partly because of GM's lack of quality control however, I have seen guys that have a lot of mods like, cold air, pullies, exhaust, ignition and Edelbrock baseplate and runners only running high 13's and a friend of mine just put in a chip and an exhuast and runs 13.8's with his L98. If I do a rebuild on a TPI 350 what could I expect with SLP headers, exhaust, a decent cam and hopefully an edelbrock intake. I have 3.42's and a 700 R4 with a stage 1 shift kit and Corvette Servo.
Then I could get a low mileage (60k or less) LT1. This would get me mid to high 13's with headers exhaust and chip. However the swap may cost significantly more especially for the wiring and all that computer crap. It would be different but with 60k miles or so I would be looking at a rebuild within about 80k or so.
Then there is the ever present Carb question. I can get good gas mileage with a carb if I drive halfway sane and also that would be different for my car as well. Carb motors can be modded easily and run really really hard. I know a guy that is in the low 13's like 13.2's with his 305 carbed motor!!!
What are your opinions and pro's and con's. Feel free to e mail me if you would like. IROCZSS@AOL.COM
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
Member
Joined: Jul 1999
Posts: 130
Likes: 0
From: Ct
Well, since I've looked into the same options you have (and you can check my sig to find out which one I went with) I know your dilemms. I can say right now that putting a 350 under your existing TPI system is going to be the easiest option and least expensive for you to do. The LT1 would be cooler for the "that's not supposed to be there" factor, and it can take up to 12:1 compression because of the reverse-flow cooling on the street.
Tell me what kind of performance you're looking to get out of the swap and I can give you several different LT1 and L98 build-ups depending on what you're looking for.
Well, lets just use generalities and say that you're going to keep the bottom end stock. If that's the case, go out and get yourself some AFR 190s, an emissions-friendly cam, a full exhaust, some TPI goodies like big mouth manifold and siamesed runners and/or TB, and a custom chip. Depending on the cam, you could have one nasty L98 on your hands. If you're looking for a LOT of power, say through nitrous or a blower then I would suggest beefing up the bottom end, especially if you mix nitrous or a blower with that head/cam combo idea.
LT1 - stock bottom end but add forged pistons and up the compression a click to 11 or 11.25:1 and put a nitrous kit on the car. OR swap the pistons but go to lower compression ratio like 9.25 - 9.75 and get a low to medium boost blower.
But there are a lot of hidden costs in going with an LT1. The swap itself can be expensive and is definitely very time consuming. At the very basics, if you do a 350 swap under your TPI all you're really changing might be the injectors and the chip, everything else will bolt up. If you're concerned with $$ overflow I'd suggest putting a 350 on your existing TPI. Then with whatever you have as extra beyond the different injectors and the chip program you can dump into headers, heads, cam, TPI parts, etc. I'd do the heads/cam first in the order on that list since it will be a pain in the *** to go back and change later - it's just a lot easier to do when the engine's out of the car. Then you can go back and get headers and what have you.
Hope this helps!
And should you opt for the LT1 swap let me know, I can give you all the info you need. I will be posting a tech article on it in a few weeks before the holidays.
------------------
1991 RS LT1
every imaginable bolt-on, ungodly LT1 355, and 12 pounds of intercooled boost on it's way in '01
2000 C5 Coupe
black/black 6-spd, optional polished rims, first run 13.056 @ 109.52 stock
"So what DOES the back of a Mustang look like?"
Tell me what kind of performance you're looking to get out of the swap and I can give you several different LT1 and L98 build-ups depending on what you're looking for.
Well, lets just use generalities and say that you're going to keep the bottom end stock. If that's the case, go out and get yourself some AFR 190s, an emissions-friendly cam, a full exhaust, some TPI goodies like big mouth manifold and siamesed runners and/or TB, and a custom chip. Depending on the cam, you could have one nasty L98 on your hands. If you're looking for a LOT of power, say through nitrous or a blower then I would suggest beefing up the bottom end, especially if you mix nitrous or a blower with that head/cam combo idea.
LT1 - stock bottom end but add forged pistons and up the compression a click to 11 or 11.25:1 and put a nitrous kit on the car. OR swap the pistons but go to lower compression ratio like 9.25 - 9.75 and get a low to medium boost blower.
But there are a lot of hidden costs in going with an LT1. The swap itself can be expensive and is definitely very time consuming. At the very basics, if you do a 350 swap under your TPI all you're really changing might be the injectors and the chip, everything else will bolt up. If you're concerned with $$ overflow I'd suggest putting a 350 on your existing TPI. Then with whatever you have as extra beyond the different injectors and the chip program you can dump into headers, heads, cam, TPI parts, etc. I'd do the heads/cam first in the order on that list since it will be a pain in the *** to go back and change later - it's just a lot easier to do when the engine's out of the car. Then you can go back and get headers and what have you.
Hope this helps!
And should you opt for the LT1 swap let me know, I can give you all the info you need. I will be posting a tech article on it in a few weeks before the holidays.
------------------
1991 RS LT1
every imaginable bolt-on, ungodly LT1 355, and 12 pounds of intercooled boost on it's way in '01
2000 C5 Coupe
black/black 6-spd, optional polished rims, first run 13.056 @ 109.52 stock
"So what DOES the back of a Mustang look like?"
Thread Starter
Member
Joined: Apr 2000
Posts: 213
Likes: 0
From: Ok, USA
Well my original goal was a high 12 second car which I had all the info I needed. However, cash might be a little bit tight because this school thing is very expensive. I was thinking a 350 with possibly an edelbrock intake and runners, and airfoil, a decent cam so I can rev to about 5500 or 6000 effeciently, headers, y-pipe, exhaust custom chip and I should be low 13's quite easily from what I hear. What about the carb option?
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
Thread Starter
Member
Joined: Apr 2000
Posts: 213
Likes: 0
From: Ok, USA
Hey guys come on now help me out a little bit.
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
Moderator
Joined: Jan 2000
Posts: 19,660
Likes: 311
IM,
Just for argument's sake, the major power differences between the L98 and LT1 are the result of higher compression, better head flow, better cam profiles, better induction system, and better balance.
The reverse-flow cooling on the SBCII engines allows the higher compression on pump gas. You can get similar results by lowering your coolant temperature to effectively cool the heads better.
Modifying the L98 heads can improve flow, and decent aftermarket heads not only increase flows but can reduce temperatures more if they are aluminum castings - double benefit.
The cam swap is almost a given. As a matter of fact, I have a used-but-nice LT1 cam sitting in a box around here somewhere, since the "better" factory cam in the LT1 just wasn't good enough. (GM always seems to keep the cam profiles mild and tries improving flow everywhere else.)
Balance is easy to attain if you just take your time with your build, and spend the few dollars necessary to do the job right.
In effect, you can make a "standard" SBC very similar in function to an LT1/4 without pumping the coolant backward. You can also convert an LT1/4 to a standard distributor and carburetor with the right manifold, but you'll still have the reverse coolant pump.
As for the induction system, the stock TPI is great for torque from 1,500 to 4,500 RPM, where it dutifully falls on its face. It is possible to improve flows with the TPI system to sustain torque at higher RPMs, but it isn't cheap or easy. A Mini-Ram on a Gen I engine is effectively a functional clone of the LT1 induction system.
The LT1 induction system uses the same theory as the Mini-Ram, essentially de-tuning the runners to avoid resonance at most RPM ranges. This helps make good torque through a wider RPM range. The stock LT1 plunum will only fit on LT1 engines, and LT4 intakes on LT4 engines.
A carburetor/intake can be tuned to support the same kind of torque at the lower end of the range, but it requires dilligence and a bit of skill. A carburetor will have a much easier time supporting torque at higher RPMs, since the intake runners are usually shorter and the fuel atomization at high air velocities isn't a significant problem. The big knock on carbs is the variability you can experience. It can be tough to keep a carb tuned correctly for all conditions, whereas an injection system is a little more automatic. A carburator manifold can be found for either the Gen I SBC, LT1, or LT4 engines.
For peak torque numbers, an injection system is hard to beat. For peak horsepower totals, the carburetor is the easiest way to get big numbers.
Decide what you want your car to do first, then decide what fuel system you will use. Once you do that, the rest will fall into place.
If you install a LT1 complete, you'll have a lot of wiring and modifying to do. You'd either have to get a 1993 PCM and use your standard distributor, or rewire for the Opti-Spark unit on the '94+ LT1 PCM. Then there's the radiator, expansion tank, front cover, accessories... I've seen it done many ways. I recently looked at a '37 Chevy coupe with an LT1 neatly tucked in, new PCM and all. It can be done if you really want to.
If you use your TPI, the wiring will be easier but the induction modifications will make up for all of that. The cost of a decent system will be fairly high.
If you decide to use a carburetor on whatever engine, the ECM will be essentially a paper weight from the fuel system's perspective. Emissions tests may be harder to pass, but the engine options would be unlimited.
Once the fuel system choice is made, you can move on to the appropriate engine, since the intake may determine what heads you can use, and the heads might determine what engine family you use.
Sorry about the length, but you left the door wide open.
------------------
Later,
Vader
------------------
"Make Me Bad"
Adobe Acrobat Reader 4.0
Just for argument's sake, the major power differences between the L98 and LT1 are the result of higher compression, better head flow, better cam profiles, better induction system, and better balance.
The reverse-flow cooling on the SBCII engines allows the higher compression on pump gas. You can get similar results by lowering your coolant temperature to effectively cool the heads better.
Modifying the L98 heads can improve flow, and decent aftermarket heads not only increase flows but can reduce temperatures more if they are aluminum castings - double benefit.
The cam swap is almost a given. As a matter of fact, I have a used-but-nice LT1 cam sitting in a box around here somewhere, since the "better" factory cam in the LT1 just wasn't good enough. (GM always seems to keep the cam profiles mild and tries improving flow everywhere else.)
Balance is easy to attain if you just take your time with your build, and spend the few dollars necessary to do the job right.
In effect, you can make a "standard" SBC very similar in function to an LT1/4 without pumping the coolant backward. You can also convert an LT1/4 to a standard distributor and carburetor with the right manifold, but you'll still have the reverse coolant pump.
As for the induction system, the stock TPI is great for torque from 1,500 to 4,500 RPM, where it dutifully falls on its face. It is possible to improve flows with the TPI system to sustain torque at higher RPMs, but it isn't cheap or easy. A Mini-Ram on a Gen I engine is effectively a functional clone of the LT1 induction system.
The LT1 induction system uses the same theory as the Mini-Ram, essentially de-tuning the runners to avoid resonance at most RPM ranges. This helps make good torque through a wider RPM range. The stock LT1 plunum will only fit on LT1 engines, and LT4 intakes on LT4 engines.
A carburetor/intake can be tuned to support the same kind of torque at the lower end of the range, but it requires dilligence and a bit of skill. A carburetor will have a much easier time supporting torque at higher RPMs, since the intake runners are usually shorter and the fuel atomization at high air velocities isn't a significant problem. The big knock on carbs is the variability you can experience. It can be tough to keep a carb tuned correctly for all conditions, whereas an injection system is a little more automatic. A carburator manifold can be found for either the Gen I SBC, LT1, or LT4 engines.
For peak torque numbers, an injection system is hard to beat. For peak horsepower totals, the carburetor is the easiest way to get big numbers.
Decide what you want your car to do first, then decide what fuel system you will use. Once you do that, the rest will fall into place.
If you install a LT1 complete, you'll have a lot of wiring and modifying to do. You'd either have to get a 1993 PCM and use your standard distributor, or rewire for the Opti-Spark unit on the '94+ LT1 PCM. Then there's the radiator, expansion tank, front cover, accessories... I've seen it done many ways. I recently looked at a '37 Chevy coupe with an LT1 neatly tucked in, new PCM and all. It can be done if you really want to.
If you use your TPI, the wiring will be easier but the induction modifications will make up for all of that. The cost of a decent system will be fairly high.
If you decide to use a carburetor on whatever engine, the ECM will be essentially a paper weight from the fuel system's perspective. Emissions tests may be harder to pass, but the engine options would be unlimited.
Once the fuel system choice is made, you can move on to the appropriate engine, since the intake may determine what heads you can use, and the heads might determine what engine family you use.
Sorry about the length, but you left the door wide open.
------------------
Later,
Vader
------------------
"Make Me Bad"
Adobe Acrobat Reader 4.0
Thread Starter
Member
Joined: Apr 2000
Posts: 213
Likes: 0
From: Ok, USA
It's cool Vader thanks for the info. I am leaning toward the fuel injected end of the spectrum and I would like to get an edelbrock intake and runners for my TPI allowing it to breath better. A good cam will also be needed. However, there is still that question of whether or not to go with the LT1. For the price of the LT1 I could get a pretty hefty L98 with some good mods, however, even with the Edelbrock intake and runners I would only be able to rev to about 5500 rpm right???
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
Member
Joined: Jul 1999
Posts: 130
Likes: 0
From: Ct
Well, knowing that you're going into school let me give you some advice - don't build the car until you're out. Too many friends (myself included) have done this, blown the motor or something else and just been totally screwed for bills and minus one operational car.
I would say gear the car, get a higher torque convertor, headers and full exhaust, then swap a 350 under your TPI and cam it. You'll need a new chip with that. Then if you've still got money get the parts for the intake and either work your existing heads, get aluminum corvette L98 heads and work them, or get a set of aftermarket heads. Since money is a question and you're in school I definitely suggest avoiding the LT1 swap. It's more pain (expense) than it's worth for only marginally better performance on a stock for stock comparison. So since a 350 will bolt right up to your car, the accessories, TPI, etc - that would seem the way to go for you.
------------------
1991 RS LT1
every imaginable bolt-on, ungodly LT1 355, and 12 pounds of intercooled boost on it's way in '01
2000 C5 Coupe
black/black 6-spd, optional polished rims, first run 13.056 @ 109.52 stock
"So what DOES the back of a Mustang look like?"
I would say gear the car, get a higher torque convertor, headers and full exhaust, then swap a 350 under your TPI and cam it. You'll need a new chip with that. Then if you've still got money get the parts for the intake and either work your existing heads, get aluminum corvette L98 heads and work them, or get a set of aftermarket heads. Since money is a question and you're in school I definitely suggest avoiding the LT1 swap. It's more pain (expense) than it's worth for only marginally better performance on a stock for stock comparison. So since a 350 will bolt right up to your car, the accessories, TPI, etc - that would seem the way to go for you.
------------------
1991 RS LT1
every imaginable bolt-on, ungodly LT1 355, and 12 pounds of intercooled boost on it's way in '01
2000 C5 Coupe
black/black 6-spd, optional polished rims, first run 13.056 @ 109.52 stock
"So what DOES the back of a Mustang look like?"
Trending Topics
Thread Starter
Member
Joined: Apr 2000
Posts: 213
Likes: 0
From: Ok, USA
I wouldn't be doing anything to this motor if I didn't have to because I am in school. However, it is going to go out here probably in about 6-8 months and if I am going to rebuild I am going to do it right.
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph
"Speed kills, wanna live forever, drive a Ford."
Member
Joined: Jul 1999
Posts: 130
Likes: 0
From: Ct
That's cool. I just didn't want to tell you something and then have you end up in over your head with expenses. Either way, the LT1 is still the more expensive, time consuming, and difficult swap - so unless you're dead set on it just put in a hopped up 350 - I think you said it that you could put all the money from an LT1 swap into modding the 350 you'd use and beat any LT1s all day. Go for it.
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