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 Post subject: Tuning the 436
 Post Posted: Fri Aug 17, 2012 12:34 am 
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When this engine came of the dyno we had found that ran it's best with the jets at 84/94 with a PV in the front. Figuring that the dyno and the race track are 2 different things I figured I would play it safe and step the jets up a couple of sizes and started with 87/97. The 1st test session was a bust as I had a clutch problem after the 1st run and our 1st race was the next day.

That race was at Edgewater and I just left the jets at 87/97. I was struggling to find my shift points with the new motor and to keep from chasing my tail I decided to not change anything with the tune until I had the shifts right. The 3 runs I made at that race had identical 1.17 60' and the 1/4 mile ET ranged from 8.20 to 8.42 with the air changing less than 50'. The slowest run was from short shifting. I had been making the gear changes way too late and made sure I was early on that one. The AFR on those runs was uneven with the right at 14.6 and the left at 15.0. I replaced both the O2 sensors after that race because I found they were older than what I had thought.

I tested at US60 (1/8) the following Friday. The AFR looked better at 14.2/14.6 but I didn't make any tuning changes because I was still working on the shifts which I had down at this point.

The next race was Clay city and before the 1st time run I jetted the rear up to 100 because some of the rear cylinders were a bit warmer than the fronts. This brought the AFRs down to 14.4 and evened the temps some. For the 2nd time run I wanted to step the rears up again but the next size jet I had was a 106. I knew it was a big jump but I figured at least I would see if it made a difference. The AFRs dropped to 13.9. I was in eliminations and didn't want to mess with things so I left it alone and won the race. My ET went from 8.17 on the 1st run to a 8.15 in the final. I was lifting on some of the runs so it should have been a little quicker.

Because on race day we only get 2 time runs I don't mess with things much at the track and I haven't had the chance to make another test and tune until last week. So last Friday Steve met me at the Valley and surprisingly the track was pretty good. Normally the prep is kinda crappy on test nights but not this time. So I made a run to get a baseline and run 5.24 @ 131.57 MPH. I stepped the jets up to 88/110 to see what would happen and it ran 5.26 @ 131.57. The AFR went from 14.2 to 13.8 but because the ET dropped I decided to go the other way and went to 80/102. On that pass it went 5.17 @ 133.6 but the AFR went to 14.5. This is where I figure something is wrong with the AFR and decide to "just give it what it wants". Thinking I have way too much stagger front to rear I drop the rears again to 96. I lost a little ET on that pass with 5.18 @ 133.1 with 15.2 AFR. Still thinking too much stagger but needing a little more fuel I go to 86 in the front and run 5.20 @ 132.6 and AFR at 14.8. Now at this point I'm really wishing I had started without a PV and was jetting square but I know there will only be time for 1 more run. We throw in 83/93 and run my best 1/8 mile pass ever with a 5.16 @ 133.4. I was in a hurry for the last run and turned the logger on too soon so I didn't get a top end AFR for that one but at the top of 2nd gear it looks about the same as the previous run. Now I know the AFR indicates it's way too lean but it runs a lot better and the jetting seems to be a little closer to what's expected. The DA dropped about 500' from the 1st run to the last. I think maybe the location of my O2s are affecting the way they read or maybe the calibration is off.

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 Post subject: Re: Tuning the 436
 Post Posted: Fri Aug 17, 2012 7:41 am 
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Anytime the track need significantly more fuel than on the dyno I suspect some significant turbulence going on in the scoop. Is it sealed? If you don't have one and have room try an air filter setup on it. And one other thing to try is a flute to balance the vent pressures.

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 Post subject: Re: Tuning the 436
 Post Posted: Fri Aug 17, 2012 9:42 am 
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You need an air filter or a flute.. Both are not needed if using one or the other. I have always run a air filter and tried flute with the air filter and made no difference and left it on for the day..Did not hurt anything with it on...

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 Post subject: Re: Tuning the 436
 Post Posted: Fri Aug 17, 2012 10:00 am 
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jmarkaudio wrote:
Anytime the track need significantly more fuel than on the dyno I suspect some significant turbulence going on in the scoop. Is it sealed? If you don't have one and have room try an air filter setup on it. And one other thing to try is a flute to balance the vent pressures.

The scoop is sealed and I have a flute on it. I didn't notice it until I posted this but I ended up 1 jet size smaller all around for the track than what it had off the dyno. I guess the lack of track testing and making small changes without back to back test runs had got me way off course. I think the original plan was to test and go up a couple of numbers then start to drop off to see what it liked. I let the AFR numbers get in my way.

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 Post subject: Re: Tuning the 436
 Post Posted: Fri Aug 17, 2012 10:02 am 
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Quote:
I was in a hurry for the last run and turned the logger on too soon so I didn't get a top end AFR


What do you mean by this?


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 Post subject: Re: Tuning the 436
 Post Posted: Fri Aug 17, 2012 10:15 am 
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Scott Smith wrote:
Quote:
I was in a hurry for the last run and turned the logger on too soon so I didn't get a top end AFR


What do you mean by this?


My guess is that those Computech loggers have a short record time.

I see ppl all the time at the track having someone start the logger from the rear of the car when the driver turns on the first bulb.

That's one thing I do like about the DL-32 as it will record until you stop it, or it runs out of room on the SD card and that would take a while on the 2GB one I use.

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 Post subject: Re: Tuning the 436
 Post Posted: Fri Aug 17, 2012 10:51 am 
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Scott Smith wrote:
Quote:
I was in a hurry for the last run and turned the logger on too soon so I didn't get a top end AFR


What do you mean by this?

I have it set to stop recording 2 seconds after below a set RPM with a minimum of 10 seconds record time. This is because I have a tendency to forget to turn it off after a run. It's a DataPro 45 that uses internal memory (no SD card) and I use this setting to maximize the record time available.

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 Post subject: Re: Tuning the 436
 Post Posted: Fri Aug 17, 2012 3:58 pm 
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#-o I have 7 minuets on mine.. I don't have any help at the track so I use a switch on the overhead to turn on and off..

Also I think your going to use a different jet for 1/8 mile vs 1/4 mile run..

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 Post subject: Re: Tuning the 436
 Post Posted: Mon Sep 24, 2012 5:03 pm 
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Chuck i assume the headers and or o2's are not same as in dyno room. and they read perfect for max power?
i would look to see why the afr was way off to the best mph . look for header/gasket leak or cracked weld .above the o2 .do you have evacuators in collectors? .
was ignition the same and timing ? slight missfires will raise o2 lean as its unused oxy. gets to sensor .
turbulence in scoop is major player as is hood and hot under hood air .
or bracket vega hatchback would need way less jet than a normal carb ...the idle would change when ya lowered the hood .. we tipped the radiator back and ducted the air pan to take air from grill like a vette in front of rad . .had to jet up 5 and picked up a ton upstairs

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 Post subject: Re: Tuning the 436
 Post Posted: Mon Sep 24, 2012 7:50 pm 
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The dyno didn't have O2s, he used EGTs and BSFC. There are no leaks in the headers and the collectors are slip-on but they fit snug. I run a vacuum pump now so the evac tubes are plugged. I didn't touch the timing after it came off the dyno and the carb is sealed to the scoop.

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