Built a 355, and put on a bunch of aftermarket mods on (check the sig), well its running rich and I have the AFPR (adj. fuel regulator) turned down all the way, but it is still pushing around 48lbs static and about 44 lbs ideling. It is running pretty rich which is causing the catalitic converter to run extremely hot and get a really nice oarnge glow.... I know some of this is because I removed the smog stuff which pumped oxygen into the cat... so Im replacing the cat with a straight pipe! But is there anyway to TURN DOWN the fuel pressure a little????? Thanks a bunch

 

I also have 24 lb LT1 injectors..................

 

Didn't see anything about a Prom change...............that is where you're gonna really get the tuning needed. Which prom is the motor running, a 305, a 350? Either way the 24 lb injectors are going to let it run richer than 'stock'.

Do you have a scanner? What are the BLM and Integrator numbers saying............

 

Yeah I the original 305 prom.... is there a difference in the 350 and 305 prom.... also can I use a stock 350 prom in my car since I have a 5 speed??? (IE 5 speeds and 350's didnt mix together from the factory)........ I really hate shelling out $$$$ for a custom prom when a month later Im gonna have more mods.... then ill just have to get another made!!!

 

Yep, the 305 prom is assuming you have 19 lf/hr injectors, the 350 prom will assume you have 22 lb/hr injectors. It's definitely worth a try putting the 350 chip in, but I don't think you can run an 'auto' chip in a 'stick' car..................others will chime in I'm sure.

 

Looks like its time to start burning proms for yourself. Read trax's article to get you started https://www.thirdgen.org/newdesign/tech/promintro.shtml

 

How much do you have to know about motors to program your own proms?

 

It still amazes me how topics like this can come up.

"Lots of mods, Now running Rich!!!"

Of course you're running rich. Your PROM is programmed for 19lb/hr injectors and you are running 24lb/hr injectors. That's 25% more fuel. Ouch. Check out the article I wrote on programming your own PROMs. Its in the tech section.

Tim

 

what trax said, Its time to bite the bullet and actually learn something

If you Plan to keep modding, especially.

 

I was under the impression that the 305 and 350 had the same
fuel and spark tables. I ordered a prom from Howell and they sent
me a one lebeled for a 305. When I called them to get a 350 prom
they told me they were actually the same and not to worry about
it.

 

The 305 vs 350 debate is on the prom is useless. I've used both, and there absolutly is no difference.

Your problem is as follows:

1) Your running 48lbs of fuel pressure on big injectors. Why?
2) Your running too much fuel for a motor that cannot breath.

Your running stock throtte body and runners, right? You'll run rich -- been there..

Whats your o2 reading? (voltage)

I'm running a 355 with similar heads, and 48lbs of pressure makes
everyones eyes water in my shop. And I have a big shop.


Everyone has good intentions with their advice here, but I think the prom story is beaten to death. Spending gobs of money to burn proms on an obsolete and pretty much useless DFI setup doesn't make sense to me. Spending the money on a better, more programmable setup (such as Accel's DFI) seems to be the better option. You can spend the next 6 months programming chips just to find out the computer still doesn't like more than 350hp.

Now 90 people are gonna attack my post, saying they're running 350 on their Stock TPI electronics. Not realizing the same motor
with a better electronic setup, or even a carb would probably produce 50hp more.


Anyway, put 19lbs injectors back in for now, until you can flow more air. Else you'll scortch yoru cyls' and you'll be .040 over by July.

-- Joe

 

Edited for reasons of insanity. I did not say 500hp on $500 I said
400hp which is not that easy to do anymore because prices have
gone up in the last 25 years.

 

You last two guys aren't serious are you? "400 hp in the olden days!!" Ha. "My car without headers will spank alot of a**." "These computer only like to make 350 HP" Give me a break!

For my own personal reading enjoyment "your" does not equal "you are."

 

This thread is beyond a joke

no difference between a 305 and 350 prom? pfft


500hp with $500 on a 350? pfft

Thanks for the laughs

 

400hp for $500.00?

1) Stock 350 2 bolt motor
2) ported 2.02/1.60 chevy heads
3) 750 holley
3) 150shot nitrous

I don't know about you guys, but with the exception of the nitrous kit, obtainable used, I've got about 3 sets of each of the
above listed parts on shelfs at my shop. Gimme a break.

How much do you think we paid to make a 200hp motor go 11 seconds? not what I spent on my firebird, I can tell you that.

I'm not gonna get into a debate over the limitations of
the ecm, prom swaps, blah. Burning proms is a waste of time.
You spend 3 months of learning, 3 months of tuning, to shave off
3 tenths? How much money is your time worth??

-- Joe

 

400hp for $500.00?

1) 1970 350 2 bolt motor (not included in price)
2) ported 2.02/1.60 chevy heads $100/150 (swap meet)
3) 750 holley $35/50 (swap meet)
3) Chevy 1st design racing cam $135 (new back then)
4) Single plane manifold $25/50 (swap meet)
5) cheap a$$ headers with only turbos bolted on them ($100 new)
6) HEI distributor $20/25 (swap meet)
7) and old jet in the oil pump $0 (for the old timers)
8) Vega converter to slap in the stock 350 $20 (junk yard)

The look on the guys face you just blew away, priceless!

Hold on MaMa we goin' for a ride!

 

So anesthes, why did you build a TPI when you could save so much money on a 400 HP carb set up? Oh, and the stock TB flows 750 cfm or more so I have heard.

Old schoolers grow up!

 

The stock throttle body flows just under 650cfm, 685 w/airfiol.
A 52mm body flows 785cfm, 825 w/airfoil.

 

Why? Because I wanted to try something new.

Injection is nicer, no doubt about that. But you pay.

And the "old schoolers grow up" comment is kinda lame, considering I'm promoting advanced DFI over gm TPI.

Your 500.00 challange was to Swapmaster, which I agreed with was more than dooable. Carbs go just as fast (usually) for cheaper, thats life. Although the overall efficiency per CI is better with injection, I don't feel GM TPI is comperable to other DFI systems.

Example, 450HP Honda vtec. Theres about 200 of those at the track every year.

-- Joe

 

Stock 48MM flows 783CFM without an airfoil. Thats not the problem. Its the rest of the silly system, including the 400CFM maf..

-- Joe

 

I was under the impression that the GM tpi system is much more powerful than accel DFI. I am not sure if there is a new system accel has that is better. There probably is, it is very just expensive. (or the other companies for that matter. I believe your comments about the limitations of the GM computer systems are unfounded and absurd (maybe the maf systems solely b/c of the small sensor. I am not sure how you say it is poor when many cars go over 120mph NA in the quarter with this system. Maybe somewhat complex to learn initially, though. Also, you mentioned earlier that the stock TB was an imposed limit. Since we agree on flow numbers we can both agree it (TB) is not a limit until a very very fast car.


You think burning a prom is worth 3 tenths?? It scares that you have your own shop. I hope it is for personal projects.

 

The GM TPI system is a basic emmisions based fuel injection system. It produces extra horsepower soley on the fact that its more efficient than a vacume based carburated system.

Accel makes a few products that are very nice.

I can't see gaining more than a few tenths on the stock TPI system by prom burning.. Every person who has claimed they can get more out of it, never has explained why. Frankly adjusting spark tables is great, but I think I'd buy an aftermarket timing master control box for that. (which is programmable).

The size of the MAF truely does not matter, its the limitation of an
8 bit storage address in the ECM that creates a problem. -127 to
127 of total possible counters for incoming air metering. It uses this to calculate 1 - 255 grams. At a natural atmospheric pressure of sea level, thats a absolute max of 540 CFM. So even after we take out those silly screens, thats all the computer knows about.

SO then we move on to our fuel pulses. Since you have absolutely no idea how much air you have after 540 CFM, you have to guess*.

Lemme guess, speed density is the answer? Well yeah, of course, so those of us who are lucky enough to have a 91-92
can burn slighty better proms, but we have to deal with the stupid VE tables that were neevr really meant to be messed with.

We can program shift points better right? Cept for those of us that can drive a stick.

Then you find that your tinkering with the fuel pressur regulator anyway, cuz you can never get those pulses where you want them.

How fast does the O2 sensor detect change? Faster if you get a heated one, but then we have the limitation of how often O2 is referenced, which is not exactly every cycle.

And my final dislike for burning proms, is just that -- burning proms. Drive car, collect data, park car, burn prom, install prom, drive car.. Ehh no.. How much do you pay for dyno time?

The LT1 system is better, I'll give you that. And the Vortec systems are nice too. Both systems utilizing optical ignition timing, MAF and MAP sensors, 16 bit computers, flashable rom, etc.

The Jap kids are using Accel and similar real-time programmable DFI setups. Thats where I'm going.

The personal attack on owning a shop is kinda lame. I didn't attack you, or even call you a backyard mechanic. In fact I think the car in your sig is fairly impressive, and if I saw it at the track I'd check it out. We're all on the same team here, its about having fun. I respect your opinions even tho I don't agree with them.

I own a race shop, which I run on nights and weekends. My family has owned garages for many, many years. However, I am an engineer by trade, and currently reside as an Operating System developer. So I can safely say I have the qualifications to judge who's very-basic-barely-calculating-based-on-input ECM is better.

-- Joe

 

Anesthes, where did you get that flow number for a 48mm TB, It is a lot higher than I have seen in the past. Also, I agree, I don't see the benifit in burning PROMS.

 

I burn proms to let the computer know how I want it to control the motor.

Also, a 5 speed prom will work in an auto car, slapped my SLP 91 305 5 speed prom into a friends 91 383 A4 Trans Am and drove around the block, actually ran better than the chip she had in her car. Torque Converter probably won't lock up since the prom is for a 5 speed, but it does work, and it should work the other way as well, A4 prom in a 5 speed car.

 

HI,

The flow numbers I got were done at a flowbench by some buddies at MIT a few years ago. Although I've seen a few different people claim different numbers.

Remember its not like Carbs since all we're flowing is air.

I'm running an auto prom right now in my 5 spd car and it seems to work Ok.

Without running off the charts on this one, My point was simply that I feel buying an aftermarket programmable computer is
a better idea than investing in burning proms. Unless your selling proms to people, which I think is a mistake..

To the original topic, have you made any beneficial changes or are you still running rich?

 

Other than the Part Number, right?

You should look at their tables etc. and repeat what you just said. Oh wait, at that point, you would know better, huh?

Sure. I've heard the same about the computer controlled Q-jets. But, those people were wrong. Just like you are here.


Emissions based. What kind of a misnomer is that? They programmed in some things like diverter valve. So what? it still has tables for spark & fuel that can be hacked. The GM TPI system is a busload more powerful than what the Holley TBI is setup to do. And other earlier aftermarket systems.


It wasn't that it hasn't been explained {on this board and elsewhere numerous times}, it's that you didn't understand the explanation.

Would you rather have spark advanced based on TPS and temp and other signals, or would you prefer a monocapable advance box that does things based on RPM only? Your choice to run the less advanced (no pun intended) system. This is one of the reasons why you'll get the "grow up, olde timer" statement.

The size of the MAF truely does not matter, its the limitation of an
8 bit storage address in the ECM that creates a problem. -127 to
127 of total possible counters for incoming air metering. It uses this to calculate 1 - 255 grams. At a natural atmospheric pressure of sea level, thats a absolute max of 540 CFM. So even after we take out those silly screens, thats all the computer knows about.

Things can still be run off the O2. While this isn't as ideal as a fully functioning MAF setup that sees all air, it works. GN's have a similar MAF reading limitation (unless running a translator)

Lemme guess, speed density is the answer? Well yeah, of course, so those of us who are lucky enough to have a 91-92
can burn slighty better proms, but we have to deal with the stupid VE tables that were neevr really meant to be messed with.[/b][/quote]

Common misconception here. Just because an Edelbrock pro-flow setup is more easily "messed with" doesn't mean that the GM tables aren't meant to be messed with. If they weren't meant to be messed with, they wouldn't have made richer PROM's on export cars, different ones for 350 cars vs. 305's, etc.


[quote]We can program shift points better right?[/quote[

Not with the ECM we can't. This is a 3rd gen board. Not a 94-up 4th gen board.

Nope. Heated is for cold start emissions so as to get into closed loop quicker. Grow up, Olde Timer.

How much do you save by burning your own PROM's?

Me too, But there are gains to be had.