alright guys i want to swap from my blown 305 TBI to a 350 HO....i assume i need a new harness and computer but what else is involved? will i need to swap the harness and computer if i keep the TBI setup? anything will help....thanks guys

 

If you keep your TBI setup you do not need to change computers or harnesses. You will be limited to about 350 flywheel HP if you get the truck TBI setup (bigger bore and fuel injectors). It's actually not a bad swap. Do the 350 first then figure out what to do with your POS fuel injection later.

Ben

 

Thanks Ben. Any idea what kind of power i would be getting to the wheels with a 700R4 and stock rear end? Im not too educated on gearing. Thanks again.
Steve

 

i think that it is said that between the engine and the wheels u lose 15 or 20% of power due to frictionie transmission, driveshaft, rear end. i think that is right.

 

Your correct. Usually %15 for mauals and %20 for automatics.
That's 280hp to the wheels. The cool thing though is if you build the motor right you can got over 300 TQ at a dcesent rpm. I had the setup for a while, you can run it on a stock bottom end too cause your not revving it over 5000rpms anyway.

Ben

 

i was hoping i was right.

 

I am working on a TBI engine that will push 500HP at the flywheel and its a pretty cheap. If you wan't messege me on AIM from my profile or e-mail me and I can help you out with what ever you need.

 

Thanks guys. My next question is about the transmission....I eventually want to put a t56 in but will not have the money for a while and i still want to drive the car.....will the 700r4 be ok for a while? its got about 130K on it...OUCH....but it would only have to last me a few months.....what do u think?

 

If your not putting huge numbers on it...it will be fine. Its in good working order I presume?

 

yea it was in decent shape before i took it out....it had a bit of a hard shift but no slipping or anything like that....seemed pretty strong

 

I agree with crrllmich, your 700r4 will be fine as long as you dont abuse it. They put em in the TPI350 3rg gens and they held up okay.

crrllmich - What kind of injectors set-up are you using? I had the truck tbi unit on my motor and I dyno'd it. I was making 342 hp at 5200 rpms and my inj duty cycle was 85%, A/F ratio was 12.8:1. That's with 2 80lb injectors or whatever they are. I think I did the math and with stock fuel pressure and this injectors set-up you can't supply more than 360hp with 80% duty cycle. Did you up the fuel pressure? Run an aftermarket TBI unit? Run dual tbi units?

 

Its a single double 52MM unit with a raise. Dual 90 Pound injectors. I am still trying to work out all the fuel pressure issues. I just posted about working out all that with the stainless steal lines.

 

GM 5235231 Part Number

There 90 Pound Injectors as just 13PSI See GM seems to be hiding the good stuff hehe.

Up the pressure to about 30 PSI and all hell lets loose.


I am trying to find a link to the 90 pounders.

 

http://www.fiveomotorsport.com/Injector_SetsTPI.asp

 

Link posted below will verify what I'm saying here.

There is a formula that will allow you to figure out what the max HP a set of injectors can produce.

HP = ([INJECTOR SIZE (LB/HR) X DUTY CYCLE] / BSFC)
X (# OF INJECTORS)

TBI injector size - 90 LB/Hr

Duty Cycle - Time injector is on. Your injectors shouldn't be ran at more than 80% but will be generous and say 90%.

BSFC - This is basically how effecient you engine is. Most well maintained lightly modded engines run around .50 - .55. If you have a full race motor professionally tuned it's .40 - .45. Again we'll be generous and say you have a perfectly tuned motor with a BSFC of .40.

TBI has 2 injectors

90 (lb/Hr) x .90 (Duty Cycle) / .40 = 202.5

202.5 x 2 injectors = 405 hp

So the most a TBI unit can produce is 405 hp and that's in race trim with over-worked injectors.
If you increase the fuel pressure you change the 90 lb/hr inj rating. This will add some horsepower but your injectors have to work much harder and will wear out much faster. How much pressure can the stock tbi fuel pump supply anyway? I know I had to change mine when I went to a 40 psi system.

You don't by chance have a dyno sheet for 500hp tbi motor do you?

 

http://www.edelbrock.com/automotive/...ct/tech_2.html

 

I said I am building it and trying to get that much power at the crank and 450 at the wheels. Fuel is the issue I am working on now lol. And from what I heard from the begining fuel would be my issue. The 7.4L Injectors working ranges up to 40PSI with no problems from what I hear. I am looking for the solution to this but I do not think it is impossible and instead of giving up like most TBI owner I wish to atleast try.

 

I used a simlular formula to come up with needing basicaly 125 Pound injectors.

Power: 500HP
BSFC: .40
Number of Injectors: 2
Injection Duty Cycle: .80

Flow Rate: 125Lb/Hr

Now even if I lower my expectations and drop some upgrades and stay with the standard rating of a fastburn at 430HP at the crank. I would be looking at about 105LB/Hr. Now heres the problem I am trying to solve. You didn't have to me lol. I am pretty sure I said I was working on the fuel system. What about custom fuel rails or something along those lines? Whats your opinion on that matter?

 

http://store.summitracing.com/partde...=KeywordSearch

Would that solve the fuel problem?

I would have to replace the CPU with a later truck model but I was going to anyway.

 

Sorry, I hear about a lot of 400+hp tbi motors and I have yet to see one.
I had tbi and I bought the manifold you showed in the link, well the 4 barrel version anyway. It's a great manifold, I don't know if you can gut your tbi unit and use it, I had to buy the throttle body they sell for it. It was $600, it comes with IAC, a TPS sensor, and flows over 1000 cfm. The whole system cost me $2000 w/o TB it be more like $1400. Not a cheap way to do fuel inj but it works damn well.

You said you were working on a CHEAP TBI system that would allow 500HP. Just haven't seen one yet.
I think your best bet if you want tbi is this...

http://store.summitracing.com/defaul...=egnsearch.asp

You can get their kit without the computer for less than $1000.

Now, if you wanna really keep things cheap, here what ya gotta do. The 95 lb/hr injector rating is at 15psi, there is a formula on the edelbrock website but basically if you can up the psi to 40psi you will change the rating to closer to 125 lb/hr for the same injector. I've been told that their aren't any tbi injectors that can take 40psi, but I was never convinced of that. Maybe you can find one that can.
One other problem though. Carb and TBI systems always make the center cylinders run richer than the outer cylinders. If you up the pressure to 40 psi I don't know that you won't make this problem alot worse. Either way, no way your getting .40 bsfc with tbi.
I've been though most of this already and decided it was best to go tp an MPFI system. If you wanna try to get TBI work best of luck and keep us posted. Sorry for the BS but until I see a dyno sheet for 450 rwhp tbi car I'm gonna keep waving the flag.
If you got any other q's I can help with, I'd be glad to help.

 

Well keep in touch and maybe we can pull it off. I spoke with edelbrock today and found out that I can use the stock CPU aloung with the wireing harness. They said I need to use atleast a 670CFM big block TB and all you do is just remove the injector system. I can get a 750CFM unit pretty cheap on eBay so that should work fine. Also they said they will trade me for the 45 Pound injectors for just 40$. Sounds good to me. Think of it this way:

8 45LB injectors 400$+
Vortec Intake Manifold w/ EGR Provisions 400$ + (With 2" bore)

Sounds like a reasonable price amount to me. If I have to pay 200$ more then I planed to anyway and it will feed the system even up to 575HP with the injector formula you gave me and pay for itself it gas. Sounds damn good to me. Plus it will still appear pretty stock.

 

Here refer to this thread to help if you would.

https://www.thirdgen.org/techbb2/sho...hreadid=318399

 

Okay, there ya go. Read the whole post.
Seems to me your options are...

1. Use a stock 454 tbi system, get a aftermarket external FPR and fuel pump. Crank the psi to 30 and deal with the major PITA of tuning.

OR

2. Switch to a MPFI system and spend more money and get a lot more streetable HP.

I like the MPFI but it really depends on what kind of budget you have for car mods.

 

lol thanks guys. i think i will just spend more money and take the easy way out....thanks again

 

Goin MPFI? I think you'll be happier. You know which system your goin with? Just curious.

Ben

 

I will probably just go with TPI for now. Do you know if there are any complete kits out there with harness, ecm, and all?

 

New or Used?

 

preferably new but something tells me that i will pay out the a$$ for that....so im sure used would be fine as long as its in good shape....any idea on a price range?

 

75$ to 150$ For one that works just fine. Check out the classifieds on the forum they areon there all the time.

 

TPI makes torque for days and as you noticed, is pretty cheap. Good choice.
New would be expensive and their aren't a lot of reasons for it. You can polish or powdercoat just about anything for less than new would cost. A recomendation though, if you don't buy new injectors, test the old ones and then have them cleaned and check em again. A bad injector really screws up your tuning efforts and it's hard on a new motor. If you buy a used system usually the only parts you would have to worry about are the inj or a sensor and your ecu will tell you all about the latter.

 

thanks alot ben youve been a huge help in decision making. just one more question. when i swap the harness what all gets changed? the wiring in the entire car or does the engine have a seperate harness? as you can see i know nothing about how the wiring works. thanks again i appreciate it.

 

Your gonna need a different harness for the TPI. When you go to buy it try to pick it up with it.

Also gonna need the TPI computer.

 

If your switching from TBI...
You will need to buy a new computer, I'm pretty sure it's the 7730 computer you need. They are $50 used.
You don't need to buy a new harness, your TBI harness can be re-pinned to control 8 injectors. However you have to find someone who knows how to do it. I don't know where you located but I know a couple people in Socal that can do it. Otherwise you might be better of swapping harnesses. It's a lot of work IMO though.
There is one harness for the engine bay but it goes to everything, A/C, lights, cruise control, brakes, every connection on the engine.

If you have your motor out anyway it's not that hard to switch harnesses I guess. Really depends on if you can find someone good with automotive electronics. I've done the entire swap so any snags you run into let me know. 350TPI rocks compared to TBI305. Got a guy in our club running high 12's with mild but well built TPI motor. He avgs over 20 mpg with a T56 tranny (6speed).

 

So i wouldnt have to tear apart the wiring from front to back including interior and all? Only from firewall and forward? Thats a relief if im understanding right. Wow this seems to be a little cheeper than i expected. Where can i pick up a computer, classifieds as well? Thanks alot guys.

 

The wiring harness you would need to change goes from the computer which is under the passenger side dash to the engine compartment. If you remove the pass. side kick panel You will see a fat bunch of wires going outside the car through the sheet metal. Go back to the engine bay and look in the back passenger side, you'll see the same harness, it then goes all over the place.
So yes, firewall forward. Classifieds are good, junkyards work, you can also get them on this site all the time. I've bought 2 from here and they were both good. Try to find someone KNOWS there comp is good. One of the biggest advantages of TPI is the cost. I also know a mechanic who has been playing with TPI for over 10 years so he got cheap TPI down to a science.