To anyone out there running the 670 Holley unit: I'm looking to get more out of my TBI. It currently runs 13.6's in the 1/4 mile with a stock 350 TBI unit sitting on top of the motor. (No ultimate TBI mods) Estimated 330-340hp. What will i realistically see from swapping my stock 350 TBI unit to the 670cfm Holley unit? Also, what do the stock 350 TBI units flow in terms of cfm? Thanks.

I am interested inhearing your complete setup. as far as heads, cam, compression, chip (or tuning). that's a pretty good time

Well, with proper tuning for the added cfm, the 670 will make for a HUGE topend power gain. I just got mine about 2 weeks ago, got rid of the stock and it made an crazy deference on a 90 gmc truck that is very out of tune. It pulls hard enough that i'm scared that i'm going to break something like the rearend or something. by the way, if you are like me, get the 89 model of holley tbi because my truck is a 90, but has the flat style tps connector. the 90-95 670 tbi's have the round style like the lt1. Plus the 89 tbi is 439$ and the 90-95 is 504$ Dont ask why i dont know, but the 89 one came with everything i needed to mount it.

Vortec heads
GMPP Aluminum intake
55lb injectors
Comp cam .425/.440 with a 112 lsa
Not too sure on compression guessing around the 9-10 range (cant remember..)
Tune by TBI Chips
B&M 2300 converter
B&M Shift kit
3.42 posi 4th gen rear
Edelbrock shortys to a flowmaster

Why in the world would you run 55# 305 injectors on that engine? I hope you are running the high pressure regulator and atleast a TPI pump. Hole'd pistons are never fun.

If i am correct, the stock injectors in a 305 are 40lb. 55lb's came in the 350's.

GM injector application and size

4.3 = 46#
5.0 = 55#
5.7 = 61# on non police/vortec models

I had the holley TB on my 305 in my T/A. It ran decent but ran very rich as i never tuned it. Only drove the car for a short time before i parked it for winter with the holley on it but it pulled very good in the high end but low end seemed the same as stock. I have it for sale now if your looking to buy one. Let me know.

5.0 = 40#
5.7 = 55#
5.7 = 61# for police interceptor

Reference: http://www.thirdgen.org/techboard/di...ctor-info.html (TBI Injector Info)

WRONG, WRONG, WRONG....That list was from a time when we barely even knew the injectors had a color code to them.

5.0 = 55#

5.7 = 61#

5.7 = 65# for the Square Body Caprice 9C1

5.7 = 68# for the Round Body Caprice

So be it, the car still runs like a top. Stock fuel pump and reg.

and it is very likely running lean.. I have seen a ZZ4 swapped into a 1995 truck, running a Hypertech chip, that the guy thought was running like a top (and it DID at part-throttle) run so lean that it melted the pistons out of it. In my pre-wideband days, I took the tops off of some pistons on a TBI build as well..

This is the correct chart..

http://www.turbocity.com/default.php?cPath=16_30

61# running at 12 psi is enough fuel for only 240ish flywheel HP. Your engine should be making ATLEAST 300 flywheel horsepower. See the problem. Just trying to save you alot of grief.

EDIT- FWIW I know all too well myself. I melted 3 pistons on a long highway pull, near WOT in my Van. The piston looks like that because it melted the aluminum away and deposited it all over it and the chamber.

what injector size/fuel pressure would you recommend for my setup?

If you are making 330 HP you need 90#/hr worth of fuel per injector. Which means you need the ability to tune for the increased fue delivery at lower rpms and part-throttle.

and what do you mean by that. increased fp and a new tune? or variable regulator?

VAFPR allows better control of idle quality. When you significantly increase the fuel pressure to adequately fuel WOT with large injectors the ECU attempts to reduce the pulse width at idle causing issues. Some will say car has better all around drivability as well with VAFPR. Unfortunately it requires swapping ECU to one that will support a vacuum based reference to BPC.

Say the fuel pressure is bumped up from ~12psi to ~18 psi. Will this increase cause idling issues? Or are you talking significant fuel pressure increases?

It takes 28.5 psi of fuel pressure to get 61#/hr injectors to flow 90#/hr.

At .45 BSFC and 85% duty cycle that is good for 341 HP.

RBob.

RBob,

Will I still be pressing my luck if I do the following:

50mm Bored TBI
50mm bored GMPP manifold
afpr
255 fuel pump

Thanks.

i am very interested in getting my tbi running at least 50 more horse than stock, without losing too much mpg's cuz its a d.d. how would i adjust the regulator, where is it? ive been in and out of third gens, had 4 of them, and dont know where they are. lol. some simple tuning to add a couple horse would be nice

fuel pressure reg is on bottom of injector pod behind injectors....

http://z28boy.cz28.com/main.htm see TBI tech-TBI info

Not if you also increase the fuel pressure to 30 psi. But it will be a bear to get tuned on a stock ECM.

Note that with the 255 LPH fuel pump you won't be able to set the fuel pressure lower then say 18 to 22 psi. I don't know the exact pressure value, hence the range. What happens is that the TBI unit & FPR become a restriction to the fuel flow. Which back pressures the system.

RBob.

Thanks for all of the info guys. You're really helping me out here. RBob again, by bumping up the fuel pressure and using a 50mm throttle body, what gains can you see coming out of this?

Just thought I would pass this one back to you. This should be the 30 PSI GM Marine VAFPR regulator.. If not its the normal 18 psi one. But based on the time frame and the application, it should be the 30 PSI unit.

http://cgi.ebay.com/ebaymotors/Boat-...1%7C240%3A1318

how would i tune it to make higher psi at the injectors

Well you would need to be able to program the chip to dial back the fuel at part throttle.

Making the system run at higher pressure is easy. Just need the GM high pressure regulator, TPI pump in the tank, and replace the little piece of fuel hose between the pump and sending unit.

Hey Rbob would a pro using a dyno be able to tune a stock ecm with engine mods to have around 350 fwhp?

Great thread guys

There are really too many variables for me to answer this. A lot has to do with the displacement and the cam used to get the 350 fwhp. The wider the LDA/LSA on the cam the easier it will be to tune. The larger the displacement, the milder the build will be. This also makes it easier to tune.

The biggest issue with the '8746 & '7747 ECMs is that the VE tables don't have enough resolution. This can lead to surging issues that can not be tuned out.

Although most of the time a dyno tune only consists of WOT. This isn't hard to tune in. It is the driveability and the ability to idle that are the issue.

RBob.

ok then how bout 131 block .010 over, heads vortec stock, lt4 hotcam 9.7 to one compression and if I have clearance 1.6 ratio rockers, manifold theres a few in this forum i have an eye on, also tbi would be bored to 2 inch and cop injectors and of course press reg and tpi pump.

in an 88 iroc with the stock ecm

looks interesting...

I dont think many of us on these boards have used a "pro" to tune our engines. Some have paid for a chip. tbichip.com. I would think the ecomonics of it might be prohibitive. Correct me if I am wrong but a speed density aka SD is a bit more difficult to tune. That adds to more time on the dyno and time is $$$ a we know. Certainly some of us have done WOT runs to see what we have but not expressidly to do a tune. MAF cars I believe are considerably less difficult. If fact there is an advertiser in Chev Hi Perf that says their system tunes itself! Now if you move to Corvette Forun aka CF you have a different economics and some of those cars are higher value so the time on dyno and cost is proportionately less. Besides DIY is a rewarding experience.

Thanks for that I am trying to weigh the pros and cons of tuning myself or having some one else do it. As for some one else doing the $$$ is not an issue for me. But like you have just said if i do the tuning myself it would be a good experience. I may back off on some of the hp expections to have an easier time to tune if i do it myself. Also in consideration is time I dont want to be tuning for a year man I travel for a living and with 3 kids.....

Thanks for the input guys

I purchased one of these Holley units for my 88 iroc, and I have it on a Edelbrock Rpm intake manifold pre 87. I have a 1" carb spacer also. I can see a very big difference in the injectors and the amount of fuel they spit out. Now I see people talking about these units. So is there anything else I should know about this unit? Or do any other mods to the car for her? I see everyone talking about AFPR's.... Should I be putting one on the car? Are they recommended with this unit? Also is the stock fuel pump good enough?? Let me know what you guys think I should do. Thanks.

Stock fuel pump is only good to 13 psi and if aged maybe wont hold 13 at WOT. The Aero VAFPR or GM for that matter allows one to run high fuel pressure yet maintain idle control. W/O VAFPR the high fuel pressure causes ECU to cut fuel to maintain A/F and pulse width gets too low(<1.00) and causes havoc with idle quality(surging). It is said the VAFPR also allows better throttle response off idle as well. Vehicle just runs better ion and off throttle. The ECU you run needs to be able to change BPC as VAC changes. Not sure if the later GM ECU's (TPI) will do that? I believe they use a VAFPR so prob so. EBL does. dynamicefi.com.

Well I will be getting my ECU flashed, or a TBI chip put in by TBIchips.com
Now what is a VAFPR?? is that a Vacuum AFPR??? If so how come We need a Vacuum AFPR? and not a Normal one??

Now I just put in a stock fuel pump becuase the old one was shot. I guess I shall be going in there to replace the fuel sending unit, because my gas gauge does not work. So When I go in there I guess Ill go get a 255 walbro???

Well thanx for the info/.

Be warned Wal 255 may be too much. Wal 190 is available. VAFPR reduces the flow under VAC. I idle 63 VAC or 37 MAP. WOT my FP is 23.5 lbs. VAFPR pulls it down to 13.5-14.0 lbs FP. VAFPR is variable fuel .....

Now I believe it also works reverse under boost. IOW 0 VAC-100 MAP is WOT so 125-150 MAP under boost it increases FP assuming FP pumpwill allow. Someone correct me on that if WRONG.

Soooo I guess I will be looking for a VAFPR?? For my car and a nice Wal 190 FP??

Now what else will I have to do? Any other setups or modds needed? SInce I have done some mods to my car?

Also does any1 know where to get lines to replace the stock fuel lines and those hard lines?? Id like to run sum Braided hose if possible.

I used a TPI pump. Not sure if Wal 190 is superior. Cost?

I used synthetic pust fit EFI hose and filttings from Aeroquip. I believe Earls and summit sells similar. Real easy to use. heat up end in hot water and push it on barbed fitting. Slick. Reusable and easy to cut with utility knife to size.

have any pics of your fuel line/reg setup?

This was taken day of install.

Pic is small can you get bigger?

Vafpr is the same as a AFPR??? or whats the difference??

I believe it is the same. That is all I have,

so what kind of afpr should i be looking for with my setup. search in the tbi thread i made a posting with my car, and all i did so far.

Aeromotive is best and most costly. Check EBay. Several users bought VAFPR there. Turbo City offers one as does Holley. I recall Extreme EFI Xtreme? has one too. I thought GM offerred one too for TBI and I bought one years back <$50. gmpartsdirect.com rockauto.com. Might be Marine application only currently.

Looking to put this wiht my holley projection soo what do you prefer?

Easy. Aeromotive. #13301 $120.00 Summit

little on the pricey side 127.95 any other companies make 1 for TBI setup?

Do you have the Holley TBI unit? The FPR on those should already be adjustable, and from the top side. Not sure if a AFPR set up for a GM TBI unit would bolt on either.

RBob.