355 Vortec Tbi Update
#1
Junior Member
Thread Starter
Join Date: Nov 2002
Location: Fayetteville NC
Posts: 89
Likes: 0
Received 0 Likes
on
0 Posts
Car: 87 Iroc
Engine: 350
Transmission: Tremec Tko
Axle/Gears: 3.42
355 Vortec Tbi Update
Well my neighbor went back up to the dyno today to finish up the tune. Numbers still seem low to me though. 203 hp and 310 torque. AF ratio is dead on from idle to 5800. We ended up kicking up the pressure on the holley tbi, the max we could get was 16 psi, which was enough to get the tune down but holley said we could go up to 21. Just to recount the buildup, its a 355 with crane cam 212/218, GM performance tbi intake, gibson headers with true duals, holley 670 throttle body, K&N filter with the aftermarket air tube feeding the filter housing. The truck is a 92 with a 5 speed. Any suggestions on why the numbers might be so low or improvements to be made. The only thing I could think of was valve float or timing retard, but Im sure Jeff would have noticed the timing on the dyno while he was tuning.
Thanks
Thanks
#3
Supreme Member
iTrader: (7)
Join Date: Aug 2005
Location: Ohio, near columbus
Posts: 1,068
Likes: 0
Received 1 Like
on
1 Post
Car: 89 iroc-z
Engine: 305tpi
Transmission: wc-t5
Axle/Gears: 10 bolt 3.08 posi (4 now)
sounds as if you could use more pressure from the buildups i remember recalling.
Your tb is fine, just as good as a 454 tb i beleive (little better if i remember right).
the other guy is right though, you will p[robably need a bigger pump it sounds, a walbro 255 would be nice i'd think.
Your tb is fine, just as good as a 454 tb i beleive (little better if i remember right).
the other guy is right though, you will p[robably need a bigger pump it sounds, a walbro 255 would be nice i'd think.
#4
Junior Member
Thread Starter
Join Date: Nov 2002
Location: Fayetteville NC
Posts: 89
Likes: 0
Received 0 Likes
on
0 Posts
Car: 87 Iroc
Engine: 350
Transmission: Tremec Tko
Axle/Gears: 3.42
The air fuel ratio was dead on between 12.8 and 13.0 for the entire run so I dont think it is a fuel problem, just dont know why I could only get 16 psi out of the regulator?
#5
Member
Join Date: Jul 2005
Location: CNY
Posts: 169
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Camaro RS
Engine: 355 Vortec TBI
Transmission: T56
It's probably because your fuel pump won't generate anymore pressure. It seems most stock tbi pumps tend to max out around 15psi at the throttle body (mine did).
#6
Supreme Member
iTrader: (7)
Join Date: Aug 2005
Location: Ohio, near columbus
Posts: 1,068
Likes: 0
Received 1 Like
on
1 Post
Car: 89 iroc-z
Engine: 305tpi
Transmission: wc-t5
Axle/Gears: 10 bolt 3.08 posi (4 now)
yah what bones said. The higher hp buildup seems to require more fuel pressure is all i know, i remember reading 28 psi on a 300hp 305 so i'll bet you should see pressure somewhere closer to that i'd expect.... could be wrong though.
I'm sure the timing curve could use altered though being that you have a cam swap and other mods which should yeild you a slight gain.
Bigger injecters are a pretty big must too. Although 13 to 1 afr is about the perfect powermaking formula you may not being getting it's full potential with how it's being delivered.
I'm sure the timing curve could use altered though being that you have a cam swap and other mods which should yeild you a slight gain.
Bigger injecters are a pretty big must too. Although 13 to 1 afr is about the perfect powermaking formula you may not being getting it's full potential with how it's being delivered.
#7
Supreme Member
iTrader: (1)
Join Date: Jun 2002
Location: Chicago, IL
Posts: 1,843
Likes: 0
Received 2 Likes
on
2 Posts
Car: 91 Camaro RS Convertible
Engine: 305 TBI
Transmission: 5-Speed
Axle/Gears: 3.42
The pressure either pegged because your pump can't go any higher or because the spring in your regulator bottomed out. But if your A/F ration is dead on all the way up based on a wideband O2 I'm assuming right? then it doesn't matter if your pressure is maxed out.
How much timing are you running in it? What's full advance at open throttle and when does it all come in?
How much timing are you running in it? What's full advance at open throttle and when does it all come in?
Trending Topics
#8
Supreme Member
iTrader: (4)
there has to be something seriously wrong there. 203 rwhp; figure 10% parasitic loss with a manual trans give 223 crankshaft hp. I'm pretty sure a stock 350 tbi truck made that.
There's no way that combination should make less than 250 rwhp. It sounds like the heads and intake weren't swapped; all you have is a mild cam, exhaust and throttle body, but, tuned properly, those mods should be worth 30-40hp over stock.
It can't befuel pressure. If it was lean, the a/f ratio would be off. You didn't say anything about timing .... have you done anything with the chip? Too little timing could account for the low hp. If the cam was installed a couple of degrees advanced or retarded, you'd never see it until you did some datalogging.
There's no way that combination should make less than 250 rwhp. It sounds like the heads and intake weren't swapped; all you have is a mild cam, exhaust and throttle body, but, tuned properly, those mods should be worth 30-40hp over stock.
It can't befuel pressure. If it was lean, the a/f ratio would be off. You didn't say anything about timing .... have you done anything with the chip? Too little timing could account for the low hp. If the cam was installed a couple of degrees advanced or retarded, you'd never see it until you did some datalogging.
#9
Junior Member
Thread Starter
Join Date: Nov 2002
Location: Fayetteville NC
Posts: 89
Likes: 0
Received 0 Likes
on
0 Posts
Car: 87 Iroc
Engine: 350
Transmission: Tremec Tko
Axle/Gears: 3.42
A/F ratio is dead on, truck has been on the dyno 4 times now and the timing curve seems to be almost perfect. Around here we consider Jeff at Carolina Auto Masters to know his stuff so I dont think its in the tune.
#10
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,119
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
What does your timing look like @ WOT? Vortecs are fastburn heads. Too much timing and you will be killing power. Have you tried going to a higher octane fuel and then running it. Knock retard will kill power.
This is a 4th gear pull right?
Have you tried experimenting from 12.8-13.0:1? If this ratio is from after the cat, you will be off. Have a bung installed in the exhaust immediately after the header and install the wideband there, if it is not already there.
Something is still wrong though, I had a stock L03 305 that made 181 RWHP/268 ft/lbs after headers, exhaust, ultimate TBI mods, and a custom chip rework.
This is a 4th gear pull right?
Have you tried experimenting from 12.8-13.0:1? If this ratio is from after the cat, you will be off. Have a bung installed in the exhaust immediately after the header and install the wideband there, if it is not already there.
Something is still wrong though, I had a stock L03 305 that made 181 RWHP/268 ft/lbs after headers, exhaust, ultimate TBI mods, and a custom chip rework.
#11
Junior Member
Thread Starter
Join Date: Nov 2002
Location: Fayetteville NC
Posts: 89
Likes: 0
Received 0 Likes
on
0 Posts
Car: 87 Iroc
Engine: 350
Transmission: Tremec Tko
Axle/Gears: 3.42
Played with timing and he tuned for max power on 93 octane. Im still thinking valve float or a fuel pressure issue, although as I stated before the A/F ratio was dead on across the board. Truck runs great, still have some driveability issues to work out with timing down low (surging) but other than that definitely pleased with the results. Still looking for ideas though. Also remember not all dynos will read the same so maybe this one is low (dynojet).
#12
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,119
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Originally posted by likeistoleit
Played with timing and he tuned for max power on 93 octane. Im still thinking valve float or a fuel pressure issue, although as I stated before the A/F ratio was dead on across the board. Truck runs great, still have some driveability issues to work out with timing down low (surging) but other than that definitely pleased with the results. Still looking for ideas though. Also remember not all dynos will read the same so maybe this one is low (dynojet).
Played with timing and he tuned for max power on 93 octane. Im still thinking valve float or a fuel pressure issue, although as I stated before the A/F ratio was dead on across the board. Truck runs great, still have some driveability issues to work out with timing down low (surging) but other than that definitely pleased with the results. Still looking for ideas though. Also remember not all dynos will read the same so maybe this one is low (dynojet).
#13
Junior Member
Thread Starter
Join Date: Nov 2002
Location: Fayetteville NC
Posts: 89
Likes: 0
Received 0 Likes
on
0 Posts
Car: 87 Iroc
Engine: 350
Transmission: Tremec Tko
Axle/Gears: 3.42
Well I thought I had checked for all the simple stuff, your reply reminded me that there was not a heat source for the thermactor with the headers now. Pulled the air cleaner to find that it was froze (rusted) closed. He drove the truck after I removed it and said it drove like a totally different truck. Now to install the rockers and get it back on the dyno, since Im sure the A/F will be off now that it is actually getting air. Do you guys recommend the open air element?
Thanks
Thanks
#14
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,119
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Originally Posted by likeistoleit
Well I thought I had checked for all the simple stuff, your reply reminded me that there was not a heat source for the thermactor with the headers now. Pulled the air cleaner to find that it was froze (rusted) closed. He drove the truck after I removed it and said it drove like a totally different truck. Now to install the rockers and get it back on the dyno, since Im sure the A/F will be off now that it is actually getting air. Do you guys recommend the open air element?
Thanks
Thanks
An Open Element air cleaner will look better, sound better, allow for alot more airflow.
#15
Supreme Member
iTrader: (1)
Join Date: Jun 2002
Location: Chicago, IL
Posts: 1,843
Likes: 0
Received 2 Likes
on
2 Posts
Car: 91 Camaro RS Convertible
Engine: 305 TBI
Transmission: 5-Speed
Axle/Gears: 3.42
That's a good sign then that it made that much power through that thermac, man. My guess now, is that you're going to run real lean and probably run out of fuel up top. Now you may need that new fuel pump and upped fuel pressure. You'll see though at the next dyno trip for sure what's going on now with the fuel. Glad it was something easy like that though!
#17
Member
Join Date: Jul 2006
Posts: 161
Likes: 0
Received 0 Likes
on
0 Posts
Car: 92 & 93 caprice 9c1's
Engine: L05's
Transmission: 4L60's
Axle/Gears: 3.42's one G80, one open
Re: 355 Vortec Tbi Update
What is the auto thermac? Is that like a thing that draws warm air off the exhaust untill it heats up?
I too am interested in an update.
I too am interested in an update.
#19
Junior Member
Join Date: May 2011
Location: Port Orchard, WA
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 RS Camaro
Engine: 5.7 Vortec V8
Transmission: 700R4
Axle/Gears: 86 Iroc Rear POSI
Re: 355 Vortec Tbi Update
Well I thought I had checked for all the simple stuff, your reply reminded me that there was not a heat source for the thermactor with the headers now. Pulled the air cleaner to find that it was froze (rusted) closed. He drove the truck after I removed it and said it drove like a totally different truck. Now to install the rockers and get it back on the dyno, since Im sure the A/F will be off now that it is actually getting air. Do you guys recommend the open air element?
Thanks
Thanks
Well I know its been several years... but man, I read the whole discussion and you left us all hanging...? LOL.. I think we are all dying to know what the Dyno read?
Thread
Thread Starter
Forum
Replies
Last Post
Billy Decker
Engine/Drivetrain/Suspension Wanted
0
09-04-2015 03:46 PM