350 TBI tows 5000/6000lbs

[gmc406]

Grind/shave your throttle shafts down. That’ll open up the air flow as well

[econo racer]

I have not read the whole thread but have you tried a holley tbi and a tbi spacer?

[donforeman]

No, its a low rpm tow vehicle. I really don't want to get too carried away. I use 2000 rpm to 3500 rpm the most. I should probably hook the vacuum sensor up again on the dyno. I did it before when I first got the van and the restriction at WOT was not as bad as people make it out to be to 4000 rpm. Of course I cant explain the jump in the graph when the air cleaner spacer is removed today either. Its a larger increase at lower rpm so I am not sure its a CFM issue.

[Carnut1]

No, its a low rpm tow vehicle. I really don't want to get too carried away. I use 2000 rpm to 3500 rpm the most. I should probably hook the vacuum sensor up again on the dyno. I did it before when I first got the van and the restriction at WOT was not as bad as people make it out to be to 4000 rpm. Of course I cant explain the jump in the graph when the air cleaner spacer is removed today either. Its a larger increase at lower rpm so I am not sure its a CFM issue.

Tbi is a funny system. They can run well and can make good power for what they are. There is an oversized 2" throttle body from Holley I have used that feeds about 670 cfm, stocker is about 500 cfm. I run a 4 barrel Holley projection system from the 90's laptop tunable on a 355 ci work truck, 900 cfm. Tip in on a big throttle body can aggrivate the guys with lights on the roofs. For your application do some grinder work on the stocker without touching the sealing surfaces of the butterfly. The spacer may help depending on plenum design. Thanks, Charlie

[donforeman]

Thank you for the tips. I have a Bridgeport so knocking down the lip of the throttle body is not a problem. I did cut away the center divider on the GMPP adapter manifold a bit. Just matched the cutout in the factory gasket to the replacement manifold. Its only a small cut made to duplicate what was on the early factory tbi manifolds. Even my 1995 Chevy tbi manifold had the two plenums joined from the factory, it was just lower and done with a passage. I looked at the GMPP manifold and decided if GM went to all that trouble with the factory manifolds there was probably a reason. So far I am happy with the 40hp and 50 ft lbs increase without moving the rpm range of the engine. Really without changing a lot, I am probably close to done.

[cardo0]

Congrats on getting the little mouse to tow. Thats a lot of hard work you have invested now. So I had to look over the thread and I don't see what you are using for exhuast. I would suggest some small tube 1 5/8" long tube headers (as long a tube as you can find) would help with VE. A cheap cross over H or X pipe too. Many times used headers for different model cars will fit but you won't know until you try them while used headers are on Craigs List all the time. They almost give used headers away at swapmeets.

Good luck and thx for sharing. It's been interesting.

[donforeman]

Thank you for the advise. The exhaust is at the top of page 10 viewtopic.php?f=1&t=53477&start=135
Just manifolds that I took the air pump lugs out of with a mill and the 2" to 3" exhaust system.

[cardo0]

Stock manifolds would be the next item for improvement. While I'm sure you know some can flow better than others they just don't give you any exhaust flow scavenging. Something worth considering on a budget exhaust system are the little block hugger manifolds as you will find them on eBay in SS for much less than $200. They don't have a collector so they won't have that amplifying effect but on a tow vehicle I doubt it would be significant. And I recall many C4 corvette manifolds were in effect a tubular block hugger manifold.

Sometimes I think budget builds can be as much fun as any when you get to swap parts for pocket change.

[levisnteeshirt]

I'm doing something similar ,,I ordered a pair of the vortec hybrid EQ heads , the HT383 cam ,, speed pro LT1 style flat tops with the metric ring stack , eagle 3.48 replacement crank , SIR 5.7s , .015 head gasket ,, I may open the intake port divider up ,

[midnightbluS10]

Sheesh, I don't know what software you are using and it doesn't matter. The left side is percentage tps. You are about to kill that trans. There are many balances needed in auto trans electronic functions. I hope you have fixed the upshift/downshift stuff too. I hope I am not sounding too brash. The transmission tuning can take as much or more tuning as the engine. Just warning that it all has to work together and you can't change one table at a time. All of these tables work together and I see it all the time where "tuners" don't know you have to make all of the tables work together and they kill stuff.

An efi engine is dumb, it only knows what you tell it. It can make some adjustments just like the transient logic in the trans controller. Fuel and spark allowed adjustments are not near how you can kill a trans.

No you dont sound brash, you sound, uneducated. I showed you a table of the tunerproRT converter lockup points and you started off about shift points being wrong? You cant see the shift points. Skip the lecture about working together when you haven't seen the rest of the tune. I have a chassis dyno business and see bad tunes all the time, so thats a fact but I show you one part and you get all of that out of it? Dont get me wrong positive criticism is good, but you started off on a tangent that you have no clue on.

He was only going by what you've written. You talked about adjusting shift points pages ago. He never said anything about the chart you posted being shift point related. You did. He just said that what you've done to that table will kill your trans.

Then he says he hopes you fixed the shift stuff, too. In addition to that table. You're so worried that he's critiquing you that you aren't even comprehending what he said. I would suggest that you go back through your posts in this thread so you can remember what you've written before you jump somebody's ass for giving advice about something you think you haven't even talked about.

Maybe try to break up the whole "walls of text", also. It's hell to read. Would you want to read a book with no paragraph breaks?

[donforeman]

He was only going by what you've written. You talked about adjusting shift points pages ago. He never said anything about the chart you posted being shift point related. You did. He just said that what you've done to that table will kill your trans.

Then he says he hopes you fixed the shift stuff, too. In addition to that table. You're so worried that he's critiquing you that you aren't even comprehending what he said. I would suggest that you go back through your posts in this thread so you can remember what you've written before you jump somebody's ass for giving advice about something you think you haven't even talked about.

Maybe try to break up the whole "walls of text", also. It's hell to read. Would you want to read a book with no paragraph breaks?

Besides just being argumentative, you lack a basic understanding of how the converter lock functions in the G30s $0D and how it relates to the tune. Even with the stock tune the converter is always UNLOCKED during a shift. So treating them as one is incorrect, because if there is a shift going on your converter is unlocked period unless you uncheck the flag, and I did not. FYI I was lucky enough to have a person who actually worked in GM trans calibration help explain things even before I started making changes. I have not blown up anything towing close to 10000 lbs of van, dyno and trailer.

If you have trouble reading, that's your problem, no one else has a problem with paragraphs.

[levisnteeshirt]

I found the melonized distributor gear doesn't fit well on the TBI distributor shaft so I used a HEI and paralleled the trigger signal to the TBI ignition module with all its normal connections except the white wire from the coil pigtail has to be grounded ,, I also found a bent pushrod so still checked why that occurred

[donforeman]

The project ended today, but in a good way. I learned a lot. I wanted to thank everyone for the input, even those who I disagreed with. I very much appreciate the guidance. A startup company decided they wanted delivery vehicle with some character. It is actually going to get wrapped and lowered. Its not my style but I am glad its going to a good home and I got paid well for my project.

The vortec style heads(just don't buy Jegs home brand) and the ramjet cam were great for the money with towing. No problems pulling 5000 lbs at all power wise, within reason. It will never pull like a diesel. It was the wide gear spacing of the 4l60e that had me wishing for a 4l80e. 3rd some times was too high and 2nd was a long way down ratio wise. First was way too low also for the 350 with more torque. It did it but it was not ideal. The trans is still in great shape so I could not see ripping it out, so I just decided to move on. The new head. cam combo will run on a stock 95 tbi computer, but I will not recommend it. Easily 30% in results with a custom tune, plus there would be some very lean areas with the factory calibration. Not hard and its a learning process.

I wanted to restate some of the information I received from a trans calibrator (Billy) that worked for GM, just because its info I had not received anywhere else. The 4l60e has a low volume front pump compared to the 4l80e and locking the converter too soon can cause starvation of the 3-4 clutch pack because it changes the oil flow through the transmission. This is one reason GM waits so long to lock it up with factory calibrations at high load. With the 4.11 gears instead of the 3.26, it did not turn out to be a problem if done with care. Locking the converter at the very top of 2nd was also a suggestion from the same person. That's why you see the weird numbers in the bottom of 2nd gear column a few pages back that looks like its a mistake, it was not and works great.