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Username Post: 1990 Chevy 350 TBI questions        (Topic#198108)
VintageCarryall 
Member
Posts: 1979

Loc: Arizona
Reg: 10-08-06
09-04-08 08:11 PM - Post#1515297    

OK:

Could someone give me a heads-up on what the CFM of a stock TBI as used on a 1990 Chevy 350 C1500 was?

Still pondering on whether to repower a vintage pre emissions control big car.
1994 Dodge Caravan SWB 3.3L V6
1962 Studebaker Lark 4 door 350 Chevy/TH350



 
The_Hunter 
Contributor
Posts: 983
The_Hunter
Loc: Manitoba, Canada
Reg: 02-14-05
09-05-08 08:54 AM - Post#1515535    
    In response to VintageCarryall

Far as I know it's 550 CFM
86 C10 Short Box

Computers are like air conditioners - They can't do their job properly if you open windows.


 
VintageCarryall 
Member
Posts: 1979

Loc: Arizona
Reg: 10-08-06
09-06-08 08:00 AM - Post#1516357    
    In response to The_Hunter

  • The_Hunter Said:
Far as I know it's 550 CFM




Thank you: that may explain why my Suburban does not really seem to want to rev that much under hard acceleration---------it runs out of breath much above ca. 4,000 RPM. Off idle it is fine. I doubt it is exhaust restriction due to the OEM system being almost 3" from the Y pipe through the catalytic converter and muffler.
1994 Dodge Caravan SWB 3.3L V6
1962 Studebaker Lark 4 door 350 Chevy/TH350



 
1983G20Van 
Super Senior Member
Posts: 3223

Loc: Bedford, Texas, USA
Reg: 11-13-02
09-07-08 12:04 PM - Post#1517108    
    In response to VintageCarryall

  • VintageCarryall Said:
  • The_Hunter Said:
Far as I know it's 550 CFM




Thank you: that may explain why my Suburban does not really seem to want to rev that much under hard acceleration---------it runs out of breath much above ca. 4,000 RPM. Off idle it is fine. I doubt it is exhaust restriction due to the OEM system being almost 3" from the Y pipe through the catalytic converter and muffler.



Its the exhaust system (mainly manifolds and cat) and the tiny factory cam. I have run stock TBI units on engines making up to 310 FWHP with no issues at all.

Factory tuning also has a tendency for retarded timing over 4K.

Check your ignition module and if it still has an AC Delco, see if it has 048 or 369 marked into it. The 048 modules have alot of built-in retard. Above 3,800 rpm they will retard the timing 4* and rise to 6* retard by 5,000 rpm. The 369 is a much better module in the fact that it advances the timing 2* over 3,200 rpm and maintains that 2*. There is an 8* difference in advance at the crankshaft between the 048 and 369 modules at 5,000 rpm. That makes an 048 equipped vehicle fall over at a low rpm and the 369 equipped vehicle pull strong up to 5K and beyond.
1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


 
Axelrod 
Senior Member
Posts: 876

Reg: 02-23-04
09-07-08 01:48 PM - Post#1517180    
    In response to 1983G20Van

"Its the exhaust system (mainly manifolds and cat) and the tiny factory cam. I have run stock TBI units on engines making up to 310 FWHP with no issues at all."

What's FWHP? I'm assuming a typo meaning RWHP with the number confirmed by a chassis dyno? If that's the case then you are making well over 300 at the crank, figuring in a % of power train loss. Any tweaking of the stock TBI unit? Do you know what #lb injectors? Sounds like the 369 distributor is the way to go if using a factory unit. What other mods were done to the engine to increase the HP by 100? Thanks.


 
scrambldcj8 
Senior Member
Posts: 1612

Loc: MA
Reg: 04-06-03
09-07-08 04:10 PM - Post#1517235    
    In response to Axelrod

FWHP...flywheel hp

 
1983G20Van 
Super Senior Member
Posts: 3223

Loc: Bedford, Texas, USA
Reg: 11-13-02
09-07-08 04:11 PM - Post#1517236    
    In response to Axelrod

  • Axelrod Said:


What's FWHP? I'm assuming a typo meaning RWHP with the number confirmed by a chassis dyno? If that's the case then you are making well over 300 at the crank, figuring in a % of power train loss. Any tweaking of the stock TBI unit? Do you know what #lb injectors? Sounds like the 369 distributor is the way to go if using a factory unit. What other mods were done to the engine to increase the HP by 100? Thanks.




FWHP = Flywheel Horsepower

275 Rear Wheel Horsepower through a power hogging 700r4 and 3.42 geared 10 bolt along with the 2 piece driveshaft with carrier bearing in between.

The engine was a stock TBI 350 short-block.

1.)Ported 14022601 305 HO Truck heads (1.94/1.60 valves, 53 cc chambers)
2.)Production GM Corvette LT4 roller cam 203/208 @ .050, .446/.459" lift, 115* LSA
3.)Stock GM 350 TBI intake (elongated 4 center bolts) and TBI unit (stock 61# injectors @ 14 psi fuel pressure)
4.)Doug Thorley Tri-Y headers
5.)2 1/4" into single 3" exhaust, high flow cat, and flowmaster muffler
6.)6299 ECM with DIY Chip Tuning

The 369# is a number that is stamped/painted into the top of the ignition control module. You don't have to swap the whole distributer just the module.
1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


 
Axelrod 
Senior Member
Posts: 876

Reg: 02-23-04
09-08-08 05:58 PM - Post#1518064    
    In response to 1983G20Van

FWHP = Flywheel Horsepower ....How could that have eluded me. I'm thinking at the crank, not flywheel and since the F is right below R on the Qwerty Keyboard....you get the idea. Thanks for the addtional info. I have a few follow up questions if you don't mind. I've collected a bunch of parts and one of these days I'm going to build mine.

Why 305 heads? Do you know what CR you ended up with? I have a fresh set of pocket ported and polished cast iron L98's, can't remember the cc's offhand but for a truck motor I think I'd build mine for a 9.-9.5 CR.

What year block? Mine's a '93 350 and I haven't taken it down so I don't know if it's roller compatable. I do have the "RV" flat tappet cam, if I decide to go that route and the heads are already set up for flat tappet.

I have an Edlebrock TBI replacement manifold to replace the stock one. What do you mean by elongated center bolts. Weren't all the GM TBI manifolds staggered center bolts? Not sure the specs on my injectors. I'll likely follow CFM Tech's recommended tweaks for the GM TBI.

Tri-Y's and a high flow cat, yes.

Not sure what my ECM model I have. I will have to have a chip custom programmed, or buy one in the can. I don't know the first thing about tuning.

I'd stroke it to a 383 if I was certain the TBI would support it. It's so darn dependable as is, I've hesitated even touching it. I would like some addtional TQ and HP without losing MPG and reliability, if that is possible. Assuming normal driving, at least after the intial novelty wears off.

 
VintageCarryall 
Member
Posts: 1979

Loc: Arizona
Reg: 10-08-06
09-10-08 08:29 PM - Post#1519785    
    In response to Axelrod

That is one huge reason that I like TBI-----------it is flat bulletproof.
1994 Dodge Caravan SWB 3.3L V6
1962 Studebaker Lark 4 door 350 Chevy/TH350



 
1983G20Van 
Super Senior Member
Posts: 3223

Loc: Bedford, Texas, USA
Reg: 11-13-02
09-27-08 08:57 AM - Post#1530533    
    In response to Axelrod

  • Axelrod Said:
I have a few follow up questions if you don't mind. I've collected a bunch of parts and one of these days I'm going to build mine.

Why 305 heads? Do you know what CR you ended up with? I have a fresh set of pocket ported and polished cast iron L98's, can't remember the cc's offhand but for a truck motor I think I'd build mine for a 9.-9.5 CR.

What year block? Mine's a '93 350 and I haven't taken it down so I don't know if it's roller compatable. I do have the "RV" flat tappet cam, if I decide to go that route and the heads are already set up for flat tappet.

I have an Edlebrock TBI replacement manifold to replace the stock one. What do you mean by elongated center bolts. Weren't all the GM TBI manifolds staggered center bolts? Not sure the specs on my injectors. I'll likely follow CFM Tech's recommended tweaks for the GM TBI.

Not sure what my ECM model I have. I will have to have a chip custom programmed, or buy one in the can. I don't know the first thing about tuning.

I'd stroke it to a 383 if I was certain the TBI would support it. It's so darn dependable as is, I've hesitated even touching it. I would like some addtional TQ and HP without losing MPG and reliability, if that is possible. Assuming normal driving, at least after the intial novelty wears off.



Sorry, I guess I missed this post.

I used 305 heads because they were already ported up and running great on my 305 that I pulled them off of. I replaced the 305 with the 350 when it spun a rod bearing while running about 6,500 rpm! I wanted the additional flow and the 10.5:1 compression that came with the 53cc chambers. With a .016" compressed head gasket and stock 12cc dished pistons, .025" in the hole, I came out at 10.5:1 compression. Running the proper .040-.045" quench, I had NO problem with detonation on 93 octane.

Your cast-iron L98 heads have 64cc chamber.

You will not know if your block is compatible for a roller until you tear it apart. Some need the provisions drilled and tapped, some are already ready to go, yet others lack provisions and can never be stock roller equipped.

All the TBI engines were staggered center bolts but I was running 1983 era Truck/Van HO 305 heads with the conventional bolt angle.

To get the ECM #, you need to pull it from behind the glove box. All of the TBI ecms for trucks have been hacked and can be re-programmed.

383s are definately nice and I would build one in a heart-beat.

TBI can and will feed a 383 or even a 400. The factory feed a 454 with them.

http://www.youtube.com/watch?v=M6hL8aku4-8
1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


 
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