Okay i would like to know whats the difference from the TPI 5.0 and the TBI 5.0(besides the type of intake system)does changing to tpi add that much horsepower?

 

Changing to TPI on a stock motor will probably add some power, however TPI (in my mind) is not superior. On my setup I would definetly loose power going to a "stock" TPI setup. That said, When you modify TPI (new runners, new base) its pretty good.

 

i think its safe to say that the tbi heads are garbage too

 

Yeah, I think GM did a lot of what they did to the TBI cars to make the TPI cars look better. TBI came with terrible heads, smaller exhaust, and a smaller cam too I think.

 

can u say peanut cam????

 

Not to mention, the actual timing tables in TPI are much more aggressive than that of TBI.

 

when you say timing tables do you mean that they have i higher timing that you can set on the tpi onlys not on the tbi?

 

which heads would give me more horsepower if you know

the aluminum vortec (ported)


or the Edelbrock Aluminum centerbolt valve cover style(ported)


i know i have to get them milled down but which would be the best.To go with a LT1 cam on the 305.TBI

 

TPI has more timing at low and mid rpms, and a little top end. Just all around more aggressive in stock form.

Theres lots of opions on those cylinder heads. I would probably like the fastburn gm heads over the edelbroke. Just because I've head that regular iron vortec heads will make more power than edelbroke rpm heads. But I'm not aware of any info to back that up. As far a price goes, most will argee that for $300 used iron vortecs are the way to go, they will take almost .500 lift stock, so they just need new springs.

That being said the edelbroke line of alum heads are very good too, they just happen to be expensive.

 

Don't put the fastburns on a 305. The intake runners on those heads are 210cc, which would be great on a high rpm 383. I would not use anything larger than 180cc. I would just get some TPI heads and port them or if you want to spend some money the World product SR torquers are great.

 

Time to get technical *tada*
Believe it or not the LO3(TBI 305) and the LB9(TPI 305) got the same cam grind unless you specified G92 then you got the better cam and more horsepower. If you break it down to the base systems with the same cams the TBI and TPI heads difer only slightly, but its that slightly that gave the TPI more power and therefore the reputation that if you put a TPI on your can you'd get better performance.

The huge hassle of switching from a stock TBI to a stock TPI wouldnt' yeild any results in HP, hell you might loose some. It's much cheaper, and easier just to swap out the stock 400cfm TBI with a higher flowing 670CFM from holley.

 

Forgot the damn heads

Go for the World Products S/R torquer 305 heads, they have excellant flow charactertics and larger valves. They are iron, oh *** I know, but they will bolt right up and with a little pocket porting can flow like vortechs which need a special intake manifold and can run into valve to bore clearance issues if you use anything larger than a mild cam.

They are cheap too, $700/pr new.

 

Holy snit, the stock TBI is only 400 CFM?

That's it I'm getting the holly... It should work for the SBC 400 as well when I get it. The 670 ought to be enough up to around 350hp or so, right?

 

the holley 670 works well with the 330hp 350 H.O. It's debated as to whether or not it will support more power than that. I have a 383 that should be worth over 400hp. I'm going to give the holley 670 a try, get her dynoed and get some times. Then once I have the money and can come up with an external driver, I'm going to go with the holley 900cfm 4bbl tbi. But hopefully, we'll finally be able to put the power issue of the holley 670 to rest. Check my sig for my engine specs.

 

yup, i am going to skip the 670 route, goona run a 454 TB on the 305, and then getting a roots blower and goona run a 900CFM holley. i hope to go 500HP with that combo.

 

CFM flow isn't as big of deal (for making power) that the injectors are. The holley units look good and are a good price, but the rule of thumb applies for making horse power: 1 pph of injector flow will support 2 peak horse power. Holley rates there injectors @ 85 pph. But what they don't tell you is that the flow rating is @ 22 psi. This 85 pph number really means 63 pph at the stock fuel pressure of 12 psi. Now GM rates there injectors at 12 psi so a 90 pph injector (454 tbi) is really a 90 pph injector.


Now if you crank the pressure to 15 psi (max pressure a tbi pump can produce) the GM 90# goes to 101 pph (or enough to support 404 hp). The holley 85 # goes to 70 pph (280 hp).

The holley can make power but you need an after market pump and a pressure in the upper 20psi range.

 

that is some good info so what you are saying is that a 454tb works beter with a stock pump? or with lower pressure

 

Somewhat, if your planning on making over 280 hp ( and have a holley 670), you'll need a new pump.

In my mind you'll need a new pump once you get into the 300hp+ range anyway, as the stocker can't flow the volume. But as a pure guess, I would say that the stocker could support 350hp.

 

Yeah, the pressure rating is a major downfall to the delphi injectors that holley uses. The upside is they handle higher fuel pressure better than gm. I'm going with the Walbro 255 pump. I'm changing out the afpr spring to something that will support 30-35 psi, and then make it vacuum referenced to hopefully drop the psi at idle down to around 15. Well, that is my temporary solution at least. I plan on going to the 900cfm tbi for sure, unless some how the 670 ends up supporting some major power. I dunno, my machanic is ragging on me hardcore fore not swapping to a 750 carb......But after the 4bbl tbi is tuned, I'm confident it will out perform any carburator. But yeah, I'm pretty if-e as to the 550cfm(at 1.5") supporting my 383. I think it was just wishful thinking at one point in time. Oh well, we will see.

 

Yeah I think the new holley injectors can handle some decent pressure (30psi+) , they are some guys on this board that have gm injectors running at 22 psi, and they have been doing so for a couple of years, to my knowledge.

It looks like the guys on the diy prom board have figured out how to run dual throttle bodys off one computer.

Then all you have to do is cut up two small block tb's and get em welded together, steal the linkage off an old four barrel carb, and you would have about an 850 cfm, and stock 350 injectors (4 of course) would ssupply well over 400 hp, if needed.

And the cost of this, maybe $100 bucks, and a lot of time.

 

Yeah, I think they're using external drivers to run the extra injectors. It seems much easier than swapping harnesses and computers. Much cheaper too.
I've read a few places that tbi injectors in general can handle some pretty good pressure as well. Their reputation on the subject is only low because of the stock fuel pump imo. I think it just makes tuning a little harder when they're cranked to a higher pressure, that's all.
I've seen the polished version of the 900cfm tbi for a descent price, and it looks to good to turn down. Though your idea sounds pretty cool as well, it would take a lot of work like you said. Unfortuantly, all my extra time is currently being spent polishing these '91 Z-28 rims.....talk about a royal pain in the @$$. But I guess it will be worth the kazillion hours I've put into them......

 

I agree about polishing, it sucks, but the end result is worth it. I've got 6hrs into my 454 tbi, porting and polishing, and I'm still not done. I'm trying to get the bores to a mirror like state.

 

Yeah, I polished up my holley tbi, well the bores and blades at least. That took a while as well, but I achieved the mirror look, and it was well worth it. You'll have to post pics of your 454 when it's done, it sounds like a sweet project.

 

Check it out...
https://www.thirdgen.org/techbb2/sho...hreadid=168041

 

maybe someone can tell me if this is the correct adapter for the stock TBi unti to go to a square bore carb manifold it says it is for the holley projection does that have the same bolt pattern as the stock rochester

http://www.holley.com/HiOctn/ProdLin...FIA/17-45.html

 

Can someone tell me why the the holley 670 is cheaper for the 5.7 than a 5.0? should i just put the 5.7 version on my 5.0? it's something with the injector size i think

 

Astro, I'm just waiting to see how the boards work out for everybody. This seems like a major break-through as I've been wanting dual tbi's for a couple years now.

The 5.7 holley is cheaper simply because they sell more of them than the 5.0 (cheaper to make the injectors, I guess)

 

Astro, DO you have pics of a "home-made" 4 barrel tbi, if so could you email me ... ryanhart@shaw.ca thanks

 

No, it is not the correst adapter. The one holley makes is for the 2" bores, not the 1 11/16" of the stock tbi. Turbo City sells the adapter you are looking for.
Hmmm....it must be based on demand like Low said. I know when I bought mine through Auto Zone, the 5.0 version(502-5) was $20 cheaper than the 5.7version(502-6). I think it was around $280. Before you decide to go with either, be prepared for chip tuning, or else you will run way rich especially with the 350 version w/ 65pph injectors. I was running the 57pph injectors (5.0 version), and it took a while to get the chip correct.

The driver board does sound like a break through. I tried to get in the group order, but was to late. There should still be interest so hopefully there will be a second order. I would really like to keep fuel injection without having to spend a couple of thousand dollars.

 

R90

Yeah if the boards go good, I would like get in on the second order.

 

oh yeah, here is something I found kind of interesting about the holley (delphi) injectors. They are rated at 21psi. I had the 57pph on my holley 670. However, I was running stock fuel pressure of 11psi which equates to 41.25pph. The stock ones are rated at 40pph. The wierd thing was that I ran really, really rich after the tbi swap and prior to tuning. My BLMs were on average of 112. So this leads me to believe that maybe the injectors are underated. Anyways, just thought it was interesting.

 

LowC1500... That's some good info up there...thanks. I've got a mild 355, and I'm running stock 350 TBI, FPR, and fuel pump. I was thinking of going to 65PPH injectors and a VAFPR...you think I'll need a new fuel pump too? (or did I misread something). Once that's done, I guess I'm going to have to either learn how to burn my own chips (which I haven't a clue about) or find someone locally who can help out, right? I want to get my hardware nailed down first, then move into tuning it right.

 

Dmax,

How mild is you engine, if your going for say 260 hp, the 65 pph injectors would probably work pretty good. With your fuel pressure cranked to say 14 psi, with a vac refference on the reg this pressure would probably come dowm to 12 or 11 psi. So in other woulds a vac ref lets you maintian stock pressure at idle, matching your stock chip config (which is what motors need as they don't make any more power, so roughly the same amount of fuel is needed). Then at high rpm, the injectors will flow more (giving the motor more gas to feed more hp).

A vac ref regulator can, and does work well for people. That being said I consider it a band-aid fix. Tuning is the real fix. I run a vac ref (along with tuning) because my injectors would have to create too small of a pulse width at idle and the motor would run like crap.

 

Heres a site to calc new injector flow rates for different fuel pressure.

http://www.csgnetwork.com/fiflowcalc.html

 

Yeah, that's what I used to calculate my flow. The formula written out looks like this: (New Flow Rating)=(Old Flow Rating)*(Squareroot (new pressure/old pressure))
The wierd thing about my situation was that I had the 57pph injectors rated at 57pph at 21 psi. I was running them at 11psi which equates to 41.25pph. I never had any problems with running rich with the stock 40pph injectors, and an extra 1.25pph isn't going to make much of a difference. But I ran incrredibly rich with the delphi injectors. Who knows....I'm hoping that holley under rates them, as it will mean I will need less fuel pressure to my 85pph injectors

 

can someone send me the link i need to look at that turbo city TBI adapter

 

LowC1500...thanks for the reply. I grew up on carbuerators, so all this fi and electronics gets a little involved. You think there's a better choice than 65# injectors? I'd guess the engine is making around 260, maybe 280 HP at the crank (Dyno2000 charts it out at 310, but who knows how accurate that is. I'd like to get it there though if I can). The hardware specs are in my sig. It runs good now, but I'm sure there's room for improvement. Thanks for any suggestions.
Red92Bird....try www.turbocity.com

 

Dmax,

The 65#'s would be nice fit. If you were to get into tuning a 454 tbi with 80 #'s would be better. I ran a 14.17s 1/4 with the stock 350 tbi and 55 # injectors last summer. Using a "cheesy" online time calculator, it came out that for how heavy my truck is it had 360 hp. Seems high for those injectors. So in other words the stock TBi can make power. Some guys have said in the past, only go with the 454/670 tbi if your making over 300 hp. SO would be at a crossroads with your motor.