Wondering if all those who have swapped from a 305 to a 350 tpi and swapped chips if it made a whole lot of differance. And does anybody know what the differance is between the 305 and 350 chip?

 

The 350s have bigger injectors, 22lb as opposed to 19 lb for the 305, and I am sure that there are other differences. I'm also pretty sure you can't use a 305 PROM in a 350 car, and vice versa.

------------------
1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End with 2.77:1 Gears.

Current Mods: LT4 HOT Cam, Comp Cams 1.52:1 Roller Rocker Arms, Accel High Flow TPI Baseplate, Edelbrock TES 1 5/8" Headers, Catco 3" High-Flow Catalytic Converter, Hooker 3" Aerochamber Cat-Back System, Transgo Shift Kit, Performance Resource Chip, Accel Ignition, K&N Filters, Jet TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET: 14.32 @ 97.7mph
(corrected for elevation)

 

a freind of mine put in a 355 tpi in his 305 tpi iroc.and he has been using the stock chip for over a year now.and it runs pretty good.it would run alot better if he had the 350 chip in it though.

------------------
1991 banditt2 #130 of 600
Project 350 TPI Banditt II
http://www.street-dawg-racing.cityslide.com
http://discussion-board.com/GreaterC...dyAssociation/
http://www.cincyspeed.com/

 

Thats what I'm kinda wondering how much differance will it make. Right now I'm running a 350 with 22lb injectors with the 305 chip. Havn't really run into any problems, just wondering how much of a differance there is between the proms.

 

Just the injector constant is what you need to worry about.

Theres some other minor differences, and the timing table is different, but right now its compensating for a lean condition since the injectors arent as big as the ecm thinks. A bump in fuel pressure can fix that for now. Its probably a change of about 10-12psi off the top of my head, see if you cant find the formula to calculate fuel flow based on pressure on this board somewhere, its out there.

 

Sure you can, I used my stock 305 5-speed prom in my 350 5-speed car with the ZZ4 heads and cam for quite a while, about 6 months. But I can tell you it wasnt optimized for the setup, it just was able to control it.


------------------
1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

Hey kevin91z, did you notice any differances when you did switch to a 350 chip? Thats what I'm looking for since I'm currently running a 305 chip and havn't had any drivability issues.

 

It really depends on which EFI system you have as to whether there is a difference betwen 350 and 305 eproms.

On SD cars, the eprom needs to know the displacement of the engine and the injector size to calculate the injector pulse widths. On SD cars, the 305s have an injector size of 15% less than 350s, but it also has 15% less displacement. Effectively, they kind of "negate" each other, so there isn't a great difference between the two on an SD car, provided they have the same transmission (ie. automatic to automatic).

On MAF cars, the MAF measures air flow, so there is no need for a MAF eprom to know the actual displacement of the engine and no constant is available on the MAF eproms for engine displacement. The only constant you have is the "Injector Size". So, because the injectors are 15% smaller on a 305, using a 305 MAF eprom will cause the car to run 15% leaner if installed on a 350 car.

So, based on the above, SD cars are less affected by using 305 eproms in 350 cars than MAF cars are. You will need to adjust the injector pulse width on a 305 MAF eprom to get the mixture right.

On last note: Most of the stock eproms from GM tend to be overly rich, so the 305 MAF eprom MAY actually get you closer to your proper mixture IF installed on a 350. Ideally, you should have the eprom "customized" to your engine to get optimum results.

 

PS: This does not take into account for the different knock sensors and the ESC circuitry differences between a 305 and 350.

 

Hey thanks thats what I was looking for. I should have mentioned that I have a maf motor. I would like to get into prom burning, it looks like a lot of fun and I probably would but this is something that converted into my jeep so I'm looking for good drivability, and i have too many other projects going. I was surpised to see the 15% differance, that is quite a bit. One thing that I have noticed is that I do get a code 43(I can't remember if that is the right one, esc code anyhow) and I do have the 350 knock sensor. I'm hoping that once I do switch proms that it will clear this up. Do you have any advice on what prom to get? What I'm thinking is getting the stock prom right from gm. I can get it for 40 bucks shipped to me. I would like to avoid the vats setup for sure and have even thought of maybe a corvette prom. Anyhow thanks for the info and any advice on picking out a prom would help me a bunch. later ken