350 TBI tows 5000/6000lbs

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donforeman
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Re: 350 TBI tows 5000/6000lbs

Post by donforeman » Sat Feb 09, 2019 6:38 pm

Stock manifolds with the air boss plugs milled out. Even though the air bosses were undrilled they blocked off a lot of the upper port. One is OEM the other is Dorman. Dorman has bigger passages. I did a budget 409 exhaust, no cat but a big and quiet Jones SS muffler. I used pie cuts out of straight 409 tube from Summit, mostly welding practice and I need more of that.
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cardo0
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Re: 350 TBI tows 5000/6000lbs

Post by cardo0 » Sat Feb 09, 2019 6:44 pm

That's a lot of good useful info and thx for sharing. What I see is your making 30ft-lbs more torque at over a 1000rpm less than your previous peak torque. But now your fighting knock and the cheapest cure for that is make it richer. Gonna need a wideband for that but I imagine a wet flow system would like 12.something for A/F though your in the high 12's already. And you can still run the engine way richer but it uses a lot more fuel and power begins to taper off. Won't hurt to try though.

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Re: 350 TBI tows 5000/6000lbs

Post by Old School » Sat Feb 09, 2019 10:09 pm

How does your fuel economy compare before and after?

donforeman
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Re: 350 TBI tows 5000/6000lbs

Post by donforeman » Sat Feb 09, 2019 10:42 pm

I cant really say mileage as most of my road trips for the last few weeks have included a lot of WOT to get readings in the different data cells, that really is not good for mileage. It took a lot of work to get the fuel table close. Its very close now but I think there is a little more left. There are some areas part throttle where the vacuum is actually really good, better than the stock combo. So I think that should mean better mileage when tuned properly and I am not towing. I have a wideband on both the dyno and on the van. The one on the van just logs data so you can compare it to the block learn in the gm ecm. I will say that it would be very easy to mess up the mileage following some of the advice on Power Enrichment given on the internet. Some of the stuff like AE was increased about 15% just on the advice of some forum members past experience. Once the tune is a little closer I will gradually try to take some of those changes out and see what happens. The software is not perfect, there are glitches and obvious mistakes that makes some readings not make sense. I figure the theory of making as few changes as possible is the best as some stuff is just a mystery that no one can explain. In $OD in tunerpro and some android data loggers, any retard of the total timing will log 23000 degrees advance or more. I burned a -5 chip to test with fixed timing and my OTC scan tool reads -9 degrees which is a lot closer than 23000! There are some very smart people that have tried to help me out, one use to work in the electronic department for GM. He was the one that said even the aftermarket scan tools like OTC have mistakes in data as GM never released the code to the public. So its a wild guess working in reverse. He said he had checked some of the transmission pressures against known good code he had and said changing some of those could result in the code being corrupt at times. So needless to say I did not touch any trans pressure settings on the chip.

gmc406
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Re: 350 TBI tows 5000/6000lbs

Post by gmc406 » Sun Feb 10, 2019 10:43 am

Talk to this guy


http://westersgarage.eidnet.ca/index2.html

His name is Lyndon. He may help you for the most part, but like any good tuner......I don’t think he’ll give away secrets.

He also tuned my 89 Camaro with a 420sbc that’s run off a TBI computer. It’s a lot of fun on the street, and runs perfect.

donforeman
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Re: 350 TBI tows 5000/6000lbs

Post by donforeman » Sun Feb 10, 2019 11:55 am

Thanks for the advice, its been a learning curve! I really don't want to bother anyone that doesn't volunteer information. I use to have a repair shop and it use to bug me people calling on the phone asking to borrow manuals, tools etc. So I will not do that to anyone else uninvited. I am not stuck yet, it's a process. The fuel map is pretty good so far. Verifiable with the wideband data. So time to switch gears and look at the spark timing. I tried to short cut it by using the 1995 LT spark table as that was recommended, I took it back out because of spark retard in a few areas and use the base vortec timing table for a late 90s vortec truck that has no retard anywhere in testing. Somewhere in between is probably the best compromise, but its snowing outside so I am not dragging out the chassis dyno today.

In $OD in TunerPro there is a a lot of files put together by mostly free labor and some files don't play well with others, even though to the new person, there is no real info on this. The A217 adx file does not account for any initial advance if its set. There is an easy way to add the initial advance (if any) into the data log file (adx), but it has to be done manually. While the 251 xdf (the one that converts what you type in to change the chip) does try to account for that, even though its not done in the file. That's the first stage. Once you get to that point, The logged data still will not exactly match the timing table. I think a few things could be happening. Either mistakes in the code that interprets what the computer is seeing. That is most likely! It also looks like on fast decel, the data is just too slow. What may start at one cell, ends up recorded in another as the rpm rapidly drops from WOT. I am not sure on the last one, but I think something like this may be going on. I try to remember to do throttle movements slowly as the logger seems to record more accurately.

In the TBI computers there is a field defined as spark latency correction. That's what I want to look at next. Different ignition modules require different settings in order for the computer to get close to what it's programmed spark wise. I guess age and other factors can change that requirement too. So the third gen camaro site has a few threads on how to check that and that's the plan. It really has been a struggle to find the nuggets of info, compared to the wrong info that gets parroted so often.

One big tip I got that may help others is the tbi computers have a idle spark over speed and under speed advance/retard tables at least on the 94/95 years. When I put in mild roller cam in the timing would be constantly advancing and retarding by a lot even just sitting there in neutral. Neutering those table advance and retard numbers when the idle was fairly close to the ideal speed, even with my baby cam, helped. I did leave some timing adjustment when the speed was greatly out of whack. Now the idle speed is stable, like stock, and the timing is not bouncing up and down like a yo yo on the data logger. That, raising the hot idle speed in gear to 600 rpm and fuel mixture adjustments where all I did to get a factory idle again. Larger cams will probably require more work, but for my small one it was done in less than 15 minutes of changes.

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