99 L29 454 build

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Supercharged111

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Well I'm on the 8th or 9th tune and it is still pinging hard at 1800 when towing and moderate 30-40% throttle. I emailed BB a log of the current tune along with a log from the previous tune and I see no difference. Both show 6-7 deg KR at 1800 rpm and 20-40% throttle. Tuner replied and said we need to go back to the very first spark table, which gave only 5-7 deg additional cruise timing over the WOT curve. So I just sent the following email. I will send the box back up again, but I just don't understand why the cruise timing can't drop off more aggressively toward the WOT curve as throttle and map goes up and vac goes down.


"Ok I will send it back, so do whatever it takes.

I was definitely wrong about the wot timing curve and I apologize for that. For part throttle conditions I requested more timing at real light throttle cruise; say 1800-2k and 60-65 mph on flat ground with no load and high mani vacuum. (forgive me for still thinking it terms of vacuum). And it did in fact get better milage at that condition when timing there was 30+ rather than low 20's. I know now that this engine needs only about 16 deg at 1800-2k and WOT. I just wonder why can't the cruise timing drop off more aggressively as throttle goes up? At only 1800 rpm, 30% throttle will result in pretty low mani pressure, so the timing should drop pretty close to the wot number. Is it not possible or not easy to have the timing drop by 15 deg or more when it goes from max vac to minimum? I have seen those 3d spark tables and I would not want to try to set each of those numbers by hand."

Maybe he doesn't want to either? That really is the secret sauce that makes these so much nicer to drive. Sure more WOT timing can wake them up, but using less throttle to loaf along is something you can enjoy on a drive anywhere.
 

Scottm

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Super tht's exactly right, I went from 10.5 to 12 mpg highway when I had them boost the cruise timing from 20-25 to 30-35 deg. It just doesnt drop off enough when it goes into heavier part throttle.

L31, how much timing over the wot curve do you add at cruise? I need to drive around with a vacuum gauge to get some numbers. I expect vac to be in the range of 13-15 inches at 60-70 mph cruise. I think that should add 15 degrees timing over base. It's true the engine needs a lot less timing at wot than I expected, but it does run better with the current high level of cruise timing.
 

L31MaxExpress

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Super tht's exactly right, I went from 10.5 to 12 mpg highway when I had them boost the cruise timing from 20-25 to 30-35 deg. It just doesnt drop off enough when it goes into heavier part throttle.

L31, how much timing over the wot curve do you add at cruise? I need to drive around with a vacuum gauge to get some numbers. I expect vac to be in the range of 13-15 inches at 60-70 mph cruise. I think that should add 15 degrees timing over base. It's true the engine needs a lot less timing at wot than I expected, but it does run better with the current high level of cruise timing.
I tune it to what it wants at any given point. There is no set number. Some engines will want as much as 20-25* more timing at cruise than WOT. My 383 wants more than I can physically give it at cruise due to the 42-43* limitation of the distributor. I have tested it with the CMR set to +6* and given it 48* and still wants more. My old 350 with coil near plug wanted 52* at cruise and yet on 29* (31* over 5,200 rpm) at WOT.
 

L31MaxExpress

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Here is a GM timing map, IIRC LS6.

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Here are a few screenshots of my 97 run by a P59. The values will not match, but the dynamic air, dyn cyl/air for short is where the timing value is pulled from.

At 783 rpm and 0.23 gm/cyl it would be pulling from the interpolated value of 4 cells in the timing map. 600 rpm/0.20 airmass, 600 rpm/0.24 air mass, 800 rpm/0.20 air mass and 800 rpm/0.24 air mass. The values placed in all 4 cells contribute to the final number.

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Light throttle cruise at speed. This one would be pulling from the 4 table values corresponding with 2,200 and 2,400 rpm and 0.24 and 0.28 air mass.
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TIpping into it a bit at a bit less rpm. Values would be essentially coming from the 2 cells at 2,000 and 2,200 at 0.36 air mass.
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Slam the pedal down into a 2nd gear kickdown. Timing value would essentially be from the 4,400 and 4,800 rpm at 0.92 air mass values. If the engine was turning exactly 4,600 rpm at exactly 0.920 air mass the 4,400 and 4,800 rpm values would be averaged for the 4,600 rpm value.
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Scottm

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Great! What software is that? It went from 41.5 deg at 7% tps and 54.0 map, to 28.5 deg at 100% tps and 94 map. That's the 14-15 deg range I think it needs between low map/ low throttle and high map/wot throttle. So how do you set all those cells? Is BB blowing me off because it's a lot of work?
 

L31MaxExpress

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Great! What software is that? It went from 41.5 deg at 7% tps and 54.0 map, to 28.5 deg at 100% tps and 94 map. That's the 14-15 deg range I think it needs between low map/ low throttle and high map/wot throttle. So how do you set all those cells? Is BB blowing me off because it's a lot of work?
HP Tuners

Not sure what the issue there is. I never got along with the guy in a forum we both frequented years ago.
 

L31MaxExpress

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I tune real-time a few times I have done some tuning on the dyno and more importantly on the street. When I street tune, I have someone else drive and make changes real time. In real-time you can change 1 cell, any group of cells or the whole map. You can add timing or fuel in say the VE table by pressing the + key and subtract by the - key. I never get too hung up on the actual value in the table. The engine lets me know what it wants. I add timing until the engine stops responding to it or spark knocks, then back off 2-3 degrees. If I am cruising say 70 mph on flat road, I add timing until the MAP and TPS required is as low as possible or I run into knock retard. Rinse and repeat at various speeds and in multiple gears. I have a tuning loop that I like that is about 200 miles round trip, the mid point is a nice small town with a great little homestyle restaraunt to eat lunch at. It is right off the interstate and a rural country road. The route has a mix of everything from 75 mph interstate to 55 mph winding, hilly back roads and numerous small town squares. To get even more of the table, I will hitch a trailer to it once I get it running well solo. I also do a lot of datalogging on longer roadtrips. When I went to Ohio numerous years ago, I played with the tuning quite a bit especially in the long rolling grades in Kentucky.

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Scottm

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L31, does the 8.1L table ramp up timing at low map like we are talking about? Add 15 to 20 deg at cruise? BB said they could go to the 8.1 table but never did.
 

Scottm

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I have sent it up to BB for the tenth and last time. I could have bought HP by now. I can't imagine they don't know how to make a lot of cruise timing drop off fast, so it must mean they are just too lazy to change all the cells.
 
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