Hi!
Today i am swapping out my 305 for a 350,the 350 its a MAF from 89 and i cant decied if it worth the work of changing harness,i realice that i need to get the painless harness kit and a new ecm to convert over to a speed density computer system.
I have a lot more experience of tbi but nothing whith tpi,how much work is it to swap from tbi to tpi really?
I was told that a stock tpi whith full exhaust and a costum chip can give me my goal of 275-300hp.Today the 305 deliver about 240hp but almoust no low end power and thats sad.
The 305 newer run the way i wanted so i hope that this swap will fill my needs.
Thanks for any replays!!
I have a LT1 cam in the garage to will that be a better choice than the stock tpi cam?

 

Since you know a whole lot more about TBI than TPI, than I would just stick with TBI. But, you're going to need some parts since your swapping in 45 extra cubic inches. You need 350 injectors, a 350 knock sensor, a 350 ESC module, and a 350 PROM.

But, the real question here is, do you burn your own PROMs, or at least send datalogs to someone to burn a PROM for you? I noticed that you had "custom chip" in your sig. No mail-order style PROM is going to even come close to letting that 350 run like it should, especially an L98 (350 TPI).

If I'm not mistaken, I do think that the LT1 cam is a step up from the stock L98 cam, but I am no expert in cam selection.

 

It depends. It's definitely worth swapping to the 350, either way.... but the real question is, how far do you plan on taking it? If you're looking for 500-plus fuel injected horsepower (N/A), then you'll have no choice but to switch to TPI...

Stick with a Mass Air Flow setup if you can, especially if you're just learning TPI. If you're already fluent in burning you're own chips, then by all means, go Speed Density...

Not much, if you have the time. You'll need to swap the intank pump, ECM & harness, sensors & relays, and of course.... the TPI setup itself.

It will.

 

Double Post...

 

OK!
Thanks for all replays.
I am decided to go whith TPI setup,the engine came in today and i really would like to stay whit the tpi setup,i have looked at the tpi painless harness but maybee i dont ned that,i have a complete setut harness from donator car but it is a MAF and i dont have the MAF sensors,but i have seen that they not so expensive on ebay.I alose have the ecm but i dont now if i can use that in my car sence it from a different year.I am already have the tpi fuelpump in tank.
I want the car to be a nice driveble car whit a lot of tourqe.
The 305TBI newer felt that strong.
Anders

 

500-plus horses with TPI...ok. That won't happen.

I saw at the point you're at with the engine it's just a matter of preference now. If you like TBI and want to keep it go ahead, but it will need a decent amount of chip tuning to get it running right. If you can't tune the prom for the new engine, then keep the TPI mass air setup on it and use a stock MAF harness and ecm. That'll run pretty much just like a stock TPI car then.

You can match the power with TBI on that stock engine, but its a matter of if you want to or not. How much work would you do to keep TBI?

 

Yeah okay, why not read between the lines next time.

"If he's looking for 500 plus fuel injected (N/A) HP, then he MUST switch to TPI".... who said anything about achieving those numbers with a 350, using the stock unit?

I'm running a 454 with my 'stock' TPI, and I'm nowhere near 500 Horsepower myself. But the beauty of switching to TPI (for him), is that he now has Miniram, or Stealthram options to look foward to. You don't have too many options with the stock TBI, and the options that you do have with it (N/A), fall victim to emission testing, and a whole lot'a chip tuning. You're lucky if you get 400HP when all is said and done....

I'm even considering an LT1 conversion for my own set up, just to keep it street legal (and the cost is very minimal). You don't have these options with TBI, it's very limited.

 

A factory TPI setup is more for torque than HP. I saw only 25 RWHP and 30 ft/lbs of torque difference switching from a 305 to a 350. Probably not all that noticible in a smaller, lighter car. Towing it makes a huge difference because the 350s powerband is at a lower rpm. My otherwise stock305 was able to pull to 6,000 with a small cam and dual exhaust. My 350 quits pulling at 5,200. I guess it is just individual preference.


I don't know about you'll but it is possible to make 500 hp (NA) with a TBI. Holley makes a 4 injector 900 cfm projection unit. If you can't feed 500 hp with 900 cfm something is wrong with you. I'll make more peak horsepower with a carb any day though.

 

Hi!
The swap is done 8 hr of work,now to the hard bit to get the harness together.
Have any of you done this swap so please replay,do you think i can use the donator harness and ecm if i get a MAF sensor,what about the big harness conector at the fron of the stering wheel,does it match my dashboard?
I am going to run TPI becouse i think it will be easier to get my goal 275-300fwhp.I consider to just pump up the guel a bit and burn a chip,what do you think will be the easiest way to get those extra 40hp?
Thanks !
Anders

 

That's just it though, you have to buy their ECM & harness... and how much does that cost? If you try to implement Holley's throttle body, with the stock TBI ECM (4 injectors, over the stock 2), it's going to be a nightmare trying to burn a chip, especially for someone who doesn't have the experience.

 

Click Here Bro!

 

Ive never been a fan of the stock tpi setup. The SD ecm's, however, where some of the best ecm GM ever made. What id do is get a carb style mpfi intake and use a 7730. SD is more involved, but its also intuitive and is more flexible then the MAF will be (no 255 grams/sec flow limit, no bosch products under the hood). But, the code in the '165 at least is flexible enough to allow the possibility of using a larger MAF with just relatively minor adjustments, provided you know what your doing.

 

Using the 4bbl holley unit on a stock harness shouldn't be that hard to program your own chip around. Just requires you to half all of the duty cycles and make sure you can pump the required fuel of a 4bbl unit. The computer will be wanting to pump a lot of fuel, which is fine, but with two injectors wired up as one, it will have twice the amount of fuel pumping into the TB as it really wants , so you just half it. Then you dont have the constant on duty cycle problem at high rpms that the 2bbl unit has plus, you can supply a crap load more fuel for WOT, by simply adjusting the duty cycles. You just need to keep in mind that whatever you program your chip to pump fuel/wise, the actual fuel is going to be double.

That doesn't sound too difficult to me, if you can do normal fuel adjustments now, you should be able to work around a 4bbl setup just as easily.

 

My point exactly. If holley can drive 8 injectors on 2-4bbl tbis we can run 4 injectors on ours even if it takes some engineering to get the other 2 injectors to drive. I bet all it would take is a power transistor and a current limiter of some kind similar to what the MegaSquirt uses.

 

I was even thinking of using another tbi ecm as a slave to do it. Dump all the stock code and just have teh computer control the injector PW. The main computer then transmits the desired pulsewidth for the second injectors each time through the fuel loop and the slave outputs it to the second set of injectors that it controls.

Although given how rare the good 4 bbl units are, all of this will be nothing more then just a bunch of dreaming. I sure wish those 4bbl where more redily available.

 

ya there are a few on here making their own ecm relay to run 2 more injectors. the 4 bbl holley looks promising but getting 4 injectors is pricey, and you dont need a setup like that unless your looking for 380+hp from a TBI. If thats the case then why spend that kind of money on a wet flow system. You could go mpfi at that point for as much or cheaper.

btw i dont think a TPI system will support 500hp. MPFI will, but TPI is refering to the intake system that came stock on our cars and its quite restrictive.

Also, did he have experience tuning chips? If so, then he can just burn a 730 chip and easily do the swap to speed density by repinning his harness to the new ecm. Those 730 arent too hard to find. I found 2 in one day at a yard and payed $20 for both. Theres a thread currently about repinning that you should check out. And i would take dimented's advice and go SD.

 

Exactly. I was saying, that I'm running a stock TPI system (ported out to the max) on my 454 SBC, with larger injectors.... and I am nowhere near 500HP. I'm not arguing that, in fact, I'd be the first to admit it;

What I am saying, is that switching over to TPI (meaning the ECM & Harness), will allow you a much larger venue to choose from. There are so many systems to swap over to, with not that much prom work needed (as compared to a TBI system), and these system will give you a proven 500HP.

Interesting Comparison

Judging from the thread starters description, he sounds relatively new to chip burning. Asking him to cut/splice/re-map etc.. (although will greatly be to his advantage in the long run), might be a little too soon for him right now.

Plus, will it be worth the hassle, especially if this is his only ride(?)?

 

It all really depends on how much work and how much money he wants to spend. TPI has a lot of options, sure, but it also means it's a huge money sink and not getting it right on the first try means spending a lot of money. There are so many pieces to a TPI system that need to be balanced and done correctly that, sure, it may be more advanced than TBI, but it can hardly be stated to be cheaper or easier to tune. He has experience tuning his TBI already as he has said, so it might not be a big leap to get around tuning a 4bbl tbi unit, and the physical wiring of the 4bbl tbi I'm almost sure would be trivial to setup in a 2bbl way (2 injectors made to look like 1). This saves a lot of time and money and removes some of the serious limitations of TBI, especially in the top end. Plus, you get to use intake manifolds from carb setups too, so there are still lots of options and choices.

There's obviously no right or wrong way here and there is no clear obvious choice since depending on the circumstances, both look like pretty good choices. If i already had a setup for chip tuning on my TBI, i would go with the 4bbl unit and continue on the upgrades to the heads and so on to handle more hp. If i was able to get a hold of a tpi setup off a donor car though, that would be different.

 

Edelbrock makes an intake for 2 four barrels on a chevy V8. You could take a pair of TBI-square bore carb adapters and put twin stock type TBIs on them. That would give you twice the air and twice the fuel. You could take and piggyback two ecms so that they both get the same signals from the sensor but control the TBIs seperately. One ECM would control one IAC and two injectors. The other would control everything else. I know it would be a little different for chip tuning but probably different in the end.

 

The thread wasn't really about trying to make TBI better than stock. Also, why go for such an insane type of "cross fire injection" scenario when 4bbl tbi units exist already. The object was to look for the choice that had the least amount of work and the least amount of expensives for the biggest amount of gain, syncing up 2 ecu's and 2 tb's is the opposite direction.

This thread has probably run it's course. The thread originator has already made his choice.

 

Yeah, a lot of people considered this in the past.... the concept is nice!

Wouldn't it be easier to just lie to the one ECM, and splice in two newer injectors with the stock leads, as well as splicing into the stock TPS & IAC, then do the prom work?

 

Hi!
I have been in contackt whith "THE MAN" in TBI/TPI chip engineer here in sweden,he has worked whith my car before and he nows what he taking about, he toled me to skip tbi and go for tpi without any question.He will costumbilt my stock tbi harness to tpi MAP whith a new 730 ecm and a custom chip.
He had worked a lot whith both tbi and tpi and he sas that i will be pleased whith the tpi setup and the hp goal 275 will not be hard to get.
I will get back to you whith the results
Thanks!!

 

You can't just splice into it and run 4 injectors. The injector drivers won't have enough power to run all 4 injectors, that's the problem. YOu'd need to run another injector driver board. There was a guy on the DIY-Prom board that was making the boards for a while but I don't think there are any left. Might want to search around the Prom board if anybody is interested.

edit: We posted at the same time. I think that guy has the right idea, a 730 is a good ECM to work with and I think speed density is the way to go. You'll be happy with that.

 

Very interesting. Although I'm not running TBI, I'm honestly very curious to hear about his results. I think I will check it out, thanks!

 

From what I read about the 4 injectors TBI setups was that they were a bear to tune correctly. Which makes sense considering that even big injectored 2 barrel setups get fussy. The problem lies in the fueling strategy that GM uses. The switching from synch to asynch makes things messy. Way too deep of discussion to get into here and quite frankly I don't completly understand it yet. Rbob really knows what he's doing when it comes to TBI and luckily he's mentioned releasing his "ultimate TBI code" with the new speed readers that are due out this spring. It's supposed to fix alot of the fueling problems and make the big injector/ multilple injector setups much easier to tune.

 

Its possible to run a 4 bbl tbi on anything. The trick is to make sure that you only have two injectors running at low loads/idle to make sure you ahve reasonable PWs. That would take some work with a stock ecm.

 

Plus with a two TBI setup you have 4 throttle bores opening up at the same time. Part throttle and off idle I could see that being a big problem with all that air coming in at once. Then you're looking at fabbing up some kind of progressive linkage. Although with a 4bbl unit, I think some of them already do have progressive linkages so two bores act like secondaries.

 

correct on the 4 bbls...i believe holley's is progressive.

2 ecms wont really work and having 1 ecm do the job of running 4 injectors wont work either, there are heat issues and others which show the limits of the circuitry. Check out that thread about secondary driver boards. The guys name is "427" something. I cant quite remember. He showed how to go with a setup such that you can run 4 injectors without buying an aftermarket ecm like C950. Very good stuff.

I think the thread starter went with speed density so i guess advice on either system doesnt really matter anymore.