TBI v. TPI
Thread Starter
Registered User
Joined: Dec 2001
Posts: 18
From: Boulder, Colorado
TBI v. TPI
Just the classic question isn't it...
So my daily driver 92 RS w/ 305 and 700R4 is TBI. No mods done to the throttle body. I'm looking for some core comparisions of TBI v TPI - milage, performance, maintance, breakage.
I have about 300 bucks to spend on either TPI setup (found the complete set for about 300) or modify TBI or other.
Thanks!
So my daily driver 92 RS w/ 305 and 700R4 is TBI. No mods done to the throttle body. I'm looking for some core comparisions of TBI v TPI - milage, performance, maintance, breakage.
I have about 300 bucks to spend on either TPI setup (found the complete set for about 300) or modify TBI or other.
Thanks!
Registered User
Joined: May 2003
Posts: 16
From: ocean gate new jersey
TPI is a "batch" fire system (from the factory) which means that each bank of injectors will fire all at the same time. which makes for poor upper rpm performance , however gobs of tq down low . tpi has injectors located in every runner of the intake manifold. However, there are more parts to wear or break
TBI has two injectors placed over the throttle body (carb bowl type unit) indirectly injecting through the intake manifold. This result in less power and imprecise amounts of air and fuel delivered to the cylinders, but there are less parts to wear or break....im not bashing tbi , but im not particularly fond of it either , its good for reliability in my eyes , i mean a stock lo3 does make its max tq at 2400 rpms
i would say start with the tpi system and work from there . get rid of those crap swirl port heads........grab some headers to open it up a bit , these will all compliment your new tpi system
TBI has two injectors placed over the throttle body (carb bowl type unit) indirectly injecting through the intake manifold. This result in less power and imprecise amounts of air and fuel delivered to the cylinders, but there are less parts to wear or break....im not bashing tbi , but im not particularly fond of it either , its good for reliability in my eyes , i mean a stock lo3 does make its max tq at 2400 rpms
i would say start with the tpi system and work from there . get rid of those crap swirl port heads........grab some headers to open it up a bit , these will all compliment your new tpi system
Last edited by jeff87formula; Jun 6, 2003 at 05:50 PM.
Registered User
Joined: Jul 2001
Posts: 80
From: Overland Park, KS
Or you could do an LT1 ('94+) swap if you're too disgusted with the batch fire. 
Or swap in an LT1/LT4 intake. But the main points concerning TBI v. TPI were well covered by jeff87formula. If you basically want reliability, build up the TBI. If you basically want better performance, get TPI. Wiring the TPI *could* be a pain in the ***, so make sure you're well prepared it. Since you only have about $300 to work with, I would stick with the TBI for now and build that up a bit, then once you get some serious money you can get a serious induction system, whether it be TPI, Super Ram, Mini Ram, LT1 swap, etc.
What you could do is buy an Edelbrock Performer (about $100) or Performer RPM aluminum intake manifold for carb'd cars, and get a TBI adapter. Half as much as a TBI manifold and can flow better. That would help it breathe A LOT. Then a set of headers/exhaust and you'll be running well for a while. Then you could put in an LT1 cam if you wanted to and get it running even better. Remember that possibilities are almost endless with engines, so plan out a buildup within your budget and have fun with it!
Or swap in an LT1/LT4 intake. But the main points concerning TBI v. TPI were well covered by jeff87formula. If you basically want reliability, build up the TBI. If you basically want better performance, get TPI. Wiring the TPI *could* be a pain in the ***, so make sure you're well prepared it. Since you only have about $300 to work with, I would stick with the TBI for now and build that up a bit, then once you get some serious money you can get a serious induction system, whether it be TPI, Super Ram, Mini Ram, LT1 swap, etc. What you could do is buy an Edelbrock Performer (about $100) or Performer RPM aluminum intake manifold for carb'd cars, and get a TBI adapter. Half as much as a TBI manifold and can flow better. That would help it breathe A LOT. Then a set of headers/exhaust and you'll be running well for a while. Then you could put in an LT1 cam if you wanted to and get it running even better. Remember that possibilities are almost endless with engines, so plan out a buildup within your budget and have fun with it!
Registered User
Joined: Jul 2001
Posts: 550
From: Calgary, Alberta, Republic of Western Canada
Or you could actually put that $300 to good use and scrap fuel injection altogether. Instead buy a QJet carb and Edelbrock Performer and kick the asses of both TPI and TBI cars, while saving thousands of $$$ in fi repair bills.
Just a thought
Just a thought
Registered User
Joined: Apr 2000
Posts: 1,677
From: T-town
Originally posted by Nitromethane
Weiand roots blowers are pretty simple n they're for carbs.
Weiand roots blowers are pretty simple n they're for carbs.
...or you could get the little 144cid with a low-profile air cleaner and fit it under a small cowl. The only major downside is that you can't run it through an intercooler.....you just have to deal with the high intake temperatures.
Registered User
Joined: Nov 2001
Posts: 44
From: FL NY
I own and modded both.
Some good info and some BS
In there a few pages is my link to 1/4 mile times vs Mods.
First off when you say complete TPI set up, do you mean the whole car for $300? It's a pretty involved swap. And you will double or triple that $300 price if you don't have the whole car to pick from.
Ex.
high pressure fuel pump ~$120, wiring harness, ECM, possibly VATS(depending on yr), MAF sensor is ~$150+ by itself, throttle and tranny cables, I'm sure there are many more, but I've never done the swap to find out.
Anyways, the stock TBI heads are the limiting factor for HP IMO.
Running the same cam (stock L98), both T5s, close gears (3.42 vs 3.73s), same headers, SLP chip vs. custom tuning, etc.
The TPI 305 ran a best of 14.6 @ 96 mph and the TBI 305 (untouched TBI) has run a best of 14.48 @ 96.28 mph.
The TBI car even ran 14.7s @ 93 mph with a peanut cam and just a few bolt ons made 178 rwhp and 271 rwtq.
The TBI car has always got better MPG, pretty similar though.
IMO the TPI system stock won't help at all (maybe a small increase in mid-range torque), except make your car less reliable, more costly to fix, and a major PITA to work on (i.e. try to remove valve covers on a TPI). I think the 20 hp difference between the TBI and TPI (autos, peanut cam) is the much bigger exhaust the TPI's came with and better timing curves.
The advantages that TPI has is 8 injectors vs 2, Meaning after getting rid of the TPI system and moving on to Mini-ram/LT1 or super-ram you will be able to fuel as much HP as you want.
ex. 8 x 40lbs inj. = twice the fuel of 2 80 lbs inj.
The TPI system will be easier to find a supercharger kit for since the TBI, a kit has to be modified from a truck or TPI kit.
The TPI system looks a lot cooler. (Kinda like stickers adding HP lol)
My opinion bottom line. If you plan on making this car run mid 13s or faster at some point (won't happen with stock heads NA) or if you plan of running a 350 or bigger engine later then maybe the TPI system will be the right choice, but as a $300 mod, then it's probably the worse $$$ vs hp mod you can make.
Get some headers with a 3" y-pipe and 3" cat and 3" cat-back.
Headers and 3" cat gained me .6 sec and 5 mph in the 1/4 (almost as good as N2O).
In there a few pages is my link to 1/4 mile times vs Mods.
First off when you say complete TPI set up, do you mean the whole car for $300? It's a pretty involved swap. And you will double or triple that $300 price if you don't have the whole car to pick from.
Ex.
high pressure fuel pump ~$120, wiring harness, ECM, possibly VATS(depending on yr), MAF sensor is ~$150+ by itself, throttle and tranny cables, I'm sure there are many more, but I've never done the swap to find out.
Anyways, the stock TBI heads are the limiting factor for HP IMO.
Running the same cam (stock L98), both T5s, close gears (3.42 vs 3.73s), same headers, SLP chip vs. custom tuning, etc.
The TPI 305 ran a best of 14.6 @ 96 mph and the TBI 305 (untouched TBI) has run a best of 14.48 @ 96.28 mph.
The TBI car even ran 14.7s @ 93 mph with a peanut cam and just a few bolt ons made 178 rwhp and 271 rwtq.
The TBI car has always got better MPG, pretty similar though.
IMO the TPI system stock won't help at all (maybe a small increase in mid-range torque), except make your car less reliable, more costly to fix, and a major PITA to work on (i.e. try to remove valve covers on a TPI). I think the 20 hp difference between the TBI and TPI (autos, peanut cam) is the much bigger exhaust the TPI's came with and better timing curves.
The advantages that TPI has is 8 injectors vs 2, Meaning after getting rid of the TPI system and moving on to Mini-ram/LT1 or super-ram you will be able to fuel as much HP as you want.
ex. 8 x 40lbs inj. = twice the fuel of 2 80 lbs inj.
The TPI system will be easier to find a supercharger kit for since the TBI, a kit has to be modified from a truck or TPI kit.
The TPI system looks a lot cooler. (Kinda like stickers adding HP lol)
My opinion bottom line. If you plan on making this car run mid 13s or faster at some point (won't happen with stock heads NA) or if you plan of running a 350 or bigger engine later then maybe the TPI system will be the right choice, but as a $300 mod, then it's probably the worse $$$ vs hp mod you can make.
Get some headers with a 3" y-pipe and 3" cat and 3" cat-back.
Headers and 3" cat gained me .6 sec and 5 mph in the 1/4 (almost as good as N2O).
Registered User
Joined: Jul 2000
Posts: 1,880
From: Norfolk, VA. USA
I've done the carb to TPI swap a couple of years ago.
It was an involved swap, re-doing fuel lines, wiring up the car, programming the chips (I chose to convert from an 87 MAF setup to a 90-92 Speed Density setup to elimanate the MAF and run the SLP Dual CAI intake).
I had about $1000 or so in the TPI swap.
Looked really nice when it was done too.
this is the Carb setup,
http://www.transamws6.com/pics/transam/Edelbrock.jpg
And here was the TPI,
http://www.transamws6.com/pics/transam/engine.jpg
And here is a video of it after I got the exhaust put on,
http://www.transamws6.com/video/ZepherWS6.mpg
It was an involved swap, re-doing fuel lines, wiring up the car, programming the chips (I chose to convert from an 87 MAF setup to a 90-92 Speed Density setup to elimanate the MAF and run the SLP Dual CAI intake).
I had about $1000 or so in the TPI swap.
Looked really nice when it was done too.
this is the Carb setup,
http://www.transamws6.com/pics/transam/Edelbrock.jpg
And here was the TPI,
http://www.transamws6.com/pics/transam/engine.jpg
And here is a video of it after I got the exhaust put on,
http://www.transamws6.com/video/ZepherWS6.mpg
Registered User
Joined: Jan 2002
Posts: 90
From: SANDIEGO, CA,92123
Originally posted by TheGreatJ
Not to mention easier to install, and very cool lookin. They aren't quite as efficient, but you make up for that by intimidating people when you pull up with the big shiny 8-71 sticking out the hood sucking up air.....
...or you could get the little 144cid with a low-profile air cleaner and fit it under a small cowl. The only major downside is that you can't run it through an intercooler.....you just have to deal with the high intake temperatures.
Not to mention easier to install, and very cool lookin. They aren't quite as efficient, but you make up for that by intimidating people when you pull up with the big shiny 8-71 sticking out the hood sucking up air.....
...or you could get the little 144cid with a low-profile air cleaner and fit it under a small cowl. The only major downside is that you can't run it through an intercooler.....you just have to deal with the high intake temperatures.
Registered User
Joined: Jul 2000
Posts: 305
From: South Louisiana
Originally posted by jeff87formula
TPI is a "batch" fire system (from the factory) which means that each bank of injectors will fire all at the same time. which makes for poor upper rpm performance , however gobs of tq down low .
TPI is a "batch" fire system (from the factory) which means that each bank of injectors will fire all at the same time. which makes for poor upper rpm performance , however gobs of tq down low .
I was always told that the runner design was the reason for lack luster High end RPM and HUGE amounts of torque.
Someone clarify this for me please....I have owned a TPI for 10 years and I am now finding out I was taught wrong....I thought that was the reason for the superrams, minirams, stealthrams, siamesed runners, big mouth runners, etc. etc....TO GIVE YOU MORE HP IN THE HIGHER RPM BANDS!! Could all of these manufactures be wrong???
Clarify please
Later