After much excitement and anticipation, I got my camaro back today having had the 305 removed and a freshly rebuilt 350 (.040 over) installed- only to discover LESS power to the wheels. I'm not sure what the problem is, but I think I can say that I definately have less power now then when I had the 305 (b4 it blew up). In addition, it stalled at low idle today in a parking lot. Something is definately out of tune.
My theories:
#1- I know they kept the 305 induction, this produces a '91 350 engine with a TBI system off my original 305. From what I can tell, there never was a combination of 350/TBI for those years, they were all TPI.
#2- Despite running fairly smoothly (at least it sounds smooth), the computer or chip remains that of the original 305 as well, Can someone confirm if all the electronic controls were compatable?
#3- The cam or other timing parts such as a distributor, may not match up.
this engine has remanufactured heads, timing chain, block, new pistons, rings, water pump, thermostat, etc., etc., etc. I p;an to update the Eprom when I get the chance. Any ideas on what's holding back the power in my 350? Thanks for any help! Especially things to look out for (or test)! I was going to get SFC's to deal with the added torque and power, but if this is all I get then forget it! Thanks again!
-Kevin

p.s. So far, I'm hearing that it probably has to do with the computer and TBI- since there was never a 350 TBI, the thing I don't understand is if the chip is incorrect, that it would be close enough to run pretty well anyway but minus some power. How can I get a hybrid computer chip that will properly operate the TBI with 357ci of displacement?!?

 

Dude, it has to be your stock TBI. It is probably choking that motor. They are only good for like 400 cfm.

Get a holley 670 tbi unit. And a new chip couldn't hurt either. Also, are you using the stock manifold? That could be hurting you too.

Are you running the stock exhaust? If so, get rid of that scrap metal from the manifolds back and get headers, high flow cat, and a good cat back exhaust.

That stuff should do the trick. If not, I'd recommend scrapping the tbi altogether and running a carb to pull the full potential out of that motor. Good luck!

 

Fbody's never had a 350 TBI, but trucks did, and other cars did. Our TBI it's self is the same unit that the 350 trucks had. I've always heard that the stock 305 unit, and 305 stock chip should work ok on a 350, this wouldn't be great though. One thing that is definitely needed is a set of bigger injectors, or more fuel pressure.

------------------
1989 Pontiac Firebird Formula LO3 Auto
-180 degree stat
-Hooker Cat-Back
-vinyl security shade, velcro t-top bag
*****Possible summer '01 mods*****
Dual Snorkle, Auburn Posi, Keyless Entry, Wonder Bar from my IROC, 4th gen seats, T/A tail lights

http://www.geocities.com/krt80/

[This message has been edited by Keith5 (edited March 03, 2001).]

 

There was also the 350 TBI Caprice. LO5.

 

I put a 355 in my '91 Camaro with Vortec heads, Crane cam, roller rockers and all kinds of other good stuff. I kept the little stock throttle body too. You need to put 350 injectors, a knock sensor, knock sensor module, and have a prom custom made to work with all the changes in the motor. I boutght most of my stuff for a '91 Caprice 350.

I am still having problems with getting mine totally lined out but it is very close. It is very powerful. Ed Wright (Fast Chips) is making the chip for me and is very helpful.

 

You don't need the big 2" tbi unit for less than 300-350hp IMO. Keep it and either get bigger injectors and/or change your PROM based upon real data from a scan tool. Also, spark curve work is a MUST when you get more serious.

 

Your problems are most likely in the tune. If you increase the demand for fuel and only supply the same ammount of fuel, you will not make more power.

The route I would go if I were you assuming you have a fairly stock cam is to use an ECM from the late 80's - ???? TBI truck, part number 1227747. This ECM will plug directly into your stock harness. The trucks these ECM's came from had TBI 350's.

If you buy the ECM, you will also need an eprom and calpack. The guys at the GM parts counter can help you with this... non-california emissions, standard / automatic tranny, 2wd.... etc.

This will give you a more correct calibration for your motor but not the perfect one. You will also want to play with your fuel pressure and timing to fine tune the combo. If you plan on doing any further mods to the motor, you should consider getting into eprom burning.

One other note. The TBI units for the 350 trucks and 305 cars use the same bore TBI unit but the injectors for the 305 are smaller than those for the 350. You can either bump up your fuel pressure or pick up the correct injectors to compensate for this.

For directions on making your stock fuel pressure regulator adjustable go here ->
https://www.thirdgen.org/newdesign/tech/tbi-afpr.shtml


------------------
1988 T/A,
9" Ford, 3.50 gears, Auburn posi, 700r4 -w- 2100 converter
350 .060 over with forged 1 pc rms crank, and forged TRW pistons, 9.5:1 cr
Factory GM heads Pocket ported, 2.02/1.60 valves, back cut
Lunati roller 219/227, .479/.480, 112 LSA
Holley 700cfm 4bbl on TBI truck 7747 computer and chip by Howell-EFI
Edelbrock Performer EGR intake, Edelbrock TES and 3" cat

 

Just realized I already answered all this stuff for KEVIN (fuel pressure increase to 14+psi and timing advance) on the other forum DIY PROM. c'mon KEVIN. try the stuff before you ask some more, pls...

[This message has been edited by FastBroker (edited March 02, 2001).]

 

On the advice of another member, I posted the msg to the TBI forum as well as the engine/general group- I've gotten different advice on both- all very helpful. I did read the whole adjustable fuel pressure article today and in fact printed it out and plan to perform that mod this weekend, along with some timing adjustment. I'd also like to thank everyone who responded with advice- this is just the kind of help I need from people who really know their stuff. Also, I'd like to encourage people to continue posting to this thread, even if it's just to agree with a previous post from someone, it adds a lot of credibility to someone's post if I can get a second opinion, and a third, and so on. So Thanks again- and keep 'em coming!
-Kevin

 

Check out what I just posted tonight(under THE TBI ANSWER).I think this will be your ticket.Just be careful on how you pick your cam,GO SMALLER THAN WHAT YOU THINK.F-bodies weigh 3000-3300 lbs.,your truck weighs at
least 4100 lbs.THINK TORQUE!!!!
E-mail with questions.

 

Okay- so at this point, using the tech. article I found here on making your fuel pressure adjustable by modifying the TBI regulator- FYI that was a really cool trick, and I'll probably take it one step further one of these days by adding a **** to the base of the regulator so that I can adjust it without removing parts and while the engine is running. It is strange though that tightening the tension on that spring will increase the fuel pressure- I would've expected the opposite (can someone confirm?). Anyway, so I did that, and advanced the timing, and the performance still leaves something to be desired- looks like I need to update the chip next. I didn't have a timing light handy or time to measure the fuel pressure properly, but it should be increased. I think I will take it back to the mechanic and see what he can do... I'll probably print out this thread for him to read, and maybe he'll be able to get it right this time. Let's hope so! Thanks again for the help! Keep any suggestions coming please!
-Kevin
p.s. Sorry if the beginning of this msg is confusing- read that tech article and you'll get it.

 

I am planning on doing this in the future.Let me know how it is going and what you had to do to get it running well.I would really appreiate it.

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