formula5

This is an 85 305 ecm + prom.I am trying to learn enough about burning proms before I go buy the stuff to do it.My pee brain is understanding there is some kind of map for the advance rate and pulse width.The 305 prom would have a spark advance map similar to a vac advance dist having heavy weights an springs.The pulse width would be on the conservitive side.I have read the articles about burning proms a couple of times so I have a general understanding.The computer works fine without any codes.But I would just like to know if i give it full throttle there won't be a detonation problem.What should the initial timing be set at?(now it's at 6btdc).

TRAXION

The main problem that you will encounter is maxing out the MAF since the ECM will only register 255g/s. You can still try to use the '85 ECM but it will be tough. You'll have to lower the PE threshhold so that the car can get the fueling that it needs once the MAF is pegged. However, this is a kludge that works ... but doesn't work that well. Furthermore, the '85 ECM is terrible. The 85 MAFs are rediculously expensive to replace and the 85 EFI system is terrible.

I know that you will hate to hear this but the best solution for a 400SB is the speed density ECM (730). You could swap to this ECM for the price of a brand new '85 MAF.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

formula5

I would'nt mind changing over to the speed density system.Would'nt I have to change the harness too or pins?But your saying that under full throttle the ecm will read too high mas gr/sec.Is it possible to erase the flag for the ses.Andor put a resistor or something in line from the mas to the ecm to get the voltage to drop.It would'nt max out past 255 and then adjust the pe threshold.I just finish the 400 tpi setup(from the lg4) and would rather burn a chip than swap the harness.I'm just on a budget and would only get the speed density system if it's in one of the local boneyards.I could get it for $50 "if" I can find one.What is the difference between the obd 1 and 2 mas(other than physical shape)?And would the speed density have problems w/extensive mods?

TRAXION

This topic has been covered several times (255g/s limit of the '85 ECM and the 165) and I wouldn't be doing justice to those posts by going over it again. However, in short, I am not referring to the SES .... the car will just be pulling in more air than what the ECM can register. Fact is - the MAF can flow more than 255g/s ... its just that the 8-bit value in the ECM cannot be more than 255. The end result is that your car (being a 400SB) may peg the ECM 255 limit at a relatively low RPM. As mentioned, you do have an option. That option is to set the enable for Power Enrichment (PE) lower such that the PE Fuel vs RPM table is utilized. This is the only table (that I am aware of) that will allow you to add extra fuel ABOVE AND BEYOND the fuel calculated via the MAF. For example ... if your 400SB pegs the 255 limit at 4000rpms then there is no way that your car can supply more fuel than what has been calculated for that 255 value. Thus, if you need to add more fuel then the only way to do it is via the PE tables. So, you may have to lower the PE threshhold in order to get into PE sooner. Chances are ... if you are pegging the 255 limit at 4000rpms then you probably SHOULD be in PE mode (unless you are running 4.10 gears with a TH350 tranny ). This kludge would probably work for you. However, from this explanation you can see that this is a huge problem for supercharged cars where the owners don't want to run an FMU. The 255 limit gets pegged at like 2000-3000rpms with those cars (depending on displacement).

In any case ... keep in mind that since you are using the '85 ECM that the MAF is more expensive and would probably cover your swap to a 730. Check out Mike Davis' site. He did a conversion from an '85 ECM to a 165 ECM and then to a 730 ECM.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

formula5

Thanks for the exellent response and patience.I will buy the stuff to do my own prom soon.I just scanned my ecm and at 3650 the mas reads 113gr/sec.The engine is fresh so I can't redline it.But where at in the rpms do you think it'll max the mas at?One more thing,how can someone get a 1000 cfm tb,383ci and the likes and not max the mas?Thanks again!

hectorsn

Some people may be OK with a 383, 1000 cfm tb and a MAF and some people may be maxing it out. Just because you have a 1000 cfm tb doesn't mean you are flowing 1000 cfm. Once you get the car running all out see what the scanner reports. If you see 250 gps, make the change. It boils down to this: if you're serious about your engine you have to be serious about what you have controlling it. Most folks put a lot of time and money into their engines but then want to skimp on some other part of the drivetrain or engine management. A good analogy would be to have a monster engine and have the stock 7.5 rear. You could replace the rear every time it blows up but wouldn't replacing it with something that can handle the power make more sense? Besides, unlike a rear end upgrade, a MAF to MAP conversion isn't all that expensive.

formula5

I did state the harness would be cheap if I could find it.Besides right now it has a stock cam,heads,tb.Would it be called skimping if I saved a few hundred buck and do my own chip.This is stage one for me right now.If you could see my engine you would know I'm serious.Thats the reason i'm talking to you folks now.It's nice to know you guys will help when I burn a chip!

GregWestphal

iTrader: (1)

With the stock heads and cam on a 400, you probably won't max out the MAF, so I wouldn't worry about it until you've build up the engine. It'll be a good safe start tuning the engine in this configuration since you don't have to make too many changes, but you should probably upgrade to either the '165 or the '730 before anything else, then learn how to change things and how they affect the way the engine runs. I did the same with my old 305, and now have a built-up 355 to tune up, and it's a lot easier now.

------------------
Greg Westphal
'87 IROC 355TPI/A4

Jim85IROC

iTrader: (2)

I'm currently running a fairly healthy 355 with my original 85 ECM and 305 PROM. IT SUCKS! Don't even consider this swap until you put a new computer in, and I'd suggest doing that first and getting it running well with the 305 to eliminate the computer as a potential problem after the swap. My 355 IROC is a PIG. I ran a 16.1 with it at the strip, which is worse than the stock 305 could do. It's got good low throttle response, but at WOT it's a useless pig. I'm in the process of collecting all of the hardware to swap to a 165 ECM (86-69 style) but if you're going to be doing that motor, you want to eliminate all potential problem sources possible. If you do a computer swap at the same time as the engine swap, it's just one more parameter that could cause potential problems and it could take forever to track them down. By doing the swap ahead of time, you can get the 305 running good with the new compuer, and that will completely eliminate any associated problems, and when you put the 400 in, all you'll need to do is screw with new PROMs.

------------------

The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
Custom Thirdgen Subwoofer Enclosures
"I didn't know a bored out Ford could go so slow" -Shenandoah

leirch

Jim,
Have you considered going to the 730 ecm? Its a little more work to tune but you won't be maxing out the MAF sensor. Which if your 350 is even a little mild it may do. The stock 350 almost maxes it out. I'm just trying to save you a little time, even though I didn't go through the aggrevation of the 870-->165 swap and started with the 165. I can tell you its about a waste given the sensor that can malfunction and the price to replace all of them.

Brendan