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Discussion Starter · #1 ·
Finally, after almost 3 yrs. of having my motor in the truck, I'm taking it to the dyno.  I'll have it on there for an hour and have a tail pipe sniffer for A/F metering. I know the sensor in the headers is better, but my headers don't have a bung.  I wanted to get some advice on what type of adjustments to do while on the dyno.  I'll have no limit to the number of pulls for an hour.  Hopefully, I can get some video(If I'm not too busy wrenching) and put it up for y'all to see.
Oh, here's the engine specs.;

'89 model roller 360 bored .030
Speed Pro hypereutectic coated skirt pistons
Mild head work(ports opened, bowl blended)
9.5:1 comp.
Comp Cams .538/.534 lift 230/240 dur. @ .050
Comp roller rockers 1.5 ratio
Speed Demon 575 on top of Eddy dual plane gasket matched
MP windage tray
MSD 6AL ignition with MSD 8mm wires
Electric fan

Any and all comments/suggestions welcome!
 

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You have a tiny carb and a big cam.  For the dyno run, I would find a 750 carb.  It would be good for at least 50 HP.  If you don't believe me then swap carbs during the dyno testing and see what the difference is.
 

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big camshaft bet it sounds nice. I`m thinking 350-380hp and 390-420 tq at the crank. A bigger carb like 650-750 carb
 

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Discussion Starter · #4 ·
chrysler300le said:
You have a tiny carb and a big cam.
10-4 on the carb size. The story on that is that while in the building process of the motor I got excited and purchased the carb to go with the original cam I picked. Then my machinist tells me that he would like to see a bigger cam in there, he talked me into it. So I'd already paid $450 for the Demon and was cutting it close on the budget anyway. I do think I have a bit of a lean condition on the top end, but for street driving, it's fine. I'd like to pick up a used Holley 750 for cheap just to try it out, but I think that Holleys use a different thread pitch on their inlets ???. I'd have to get new adapters I think. Anyhow, we never have all the issues worked out on our projects, do we? Thanks for the reply!
 

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Maximum torque usually occurs around 13.2:1 AFR. A slight bit of carbon monoxide, no hydrocarbons, no oxygen in exhaust. (at WOT peak torque rpm)

Power should be a smooth line and not have jagged ripples or spikes. Those irregularities can be from air, spark fuel. Yes, air as in secondaries improperly timed, timing advance rate and spring bounce can cause some irregularities. Having a good fuel supply is obviously paramount. Preferably somewhere around 5psi but with jets/needle seat that can provide sufficient flow. Small jets+higher psi can equal erratic power as the needle/seat rapidly bounces open and closed, actually causing the engine to run leaner with more pressure. Like trying to fill a bucket with a firehose, w/o overfilling it. They have seen the bowls actually sucked dry and under vacuum by having psi too high. Counter intuitive, I understand.

Air flow is power, but that is not really adjustable in a dyno setting, so when squeezing out power on dyno, timing=power. AFR just adjusted to allow you to run enough timing. Usually varies between 12.7-13.2 on this type of application.

So basically, timing, timing, timing....and enough fuel to run that timing w/o knock. (which may also show as jagged lines in the curve)
 

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Discussion Starter · #8 ·
Joe!  You da man!  Seriously, thanks for all the info!  So, what I gleaned from that was that I should concentrate on getting the correct timing setting to work with the AFR that I've got(determined by jet size in carb).  I didn't plan on changing jets, because mine take a bit more time to get to than a quick change bowl on a Holley.  Basically my goal is to get a good baseline and then see if I can improve it any while I'm there and then I'll have the data so that next time at the dyno, I'll know where I started.
 

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Mopowa said:
Joe! You da man! Seriously, thanks for all the info! So, what I gleaned from that was that I should concentrate on getting the correct timing setting to work with the AFR that I've got(determined by jet size in carb). I didn't plan on changing jets, because mine take a bit more time to get to than a quick change bowl on a Holley. Basically my goal is to get a good baseline and then see if I can improve it any while I'm there and then I'll have the data so that next time at the dyno, I'll know where I started.
Except if you're running excessively lean or rich it will seriously hinder your performance too. So as long as you are close...
 

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I agree. On several various practice applications, I lost a bit of power down in the 12-12.5:1 range. A bit over 13:1 and it would ping like crazy.

Having good control of your temperature allows you to run more timing. In the morning when I started, I scored big on the dyno with the addition of timing. Never found much in the name of hp with air fuel that was already within range. +2 here, -4 there. By mid afternoon, power was way down and tunes had to be scaled way back. Not so much because of ambient air, but at 215*+ it was just no longer safe to run so aggressive a curve. Others have various results greater than this, but generally speaking fuel is not nearly as important to fine tune as us gear heads would like to believe. (hence the reason carbs are suitable for all out WOT power) With timing I instantly saw almost 20hp with minor advance adjustment.

Provided your curve is within reason you can just creep the timing up until it pings or fails to crank when hot, but what if you have a nasty spike some where? No matter what you do, you aren't going to use the distributor to tune around a 15:1 @ WOT.  ;D
 

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Discussion Starter · #11 ·
Good stuff, man... real good stuff.  Thanks again for the info!  {beer}
 
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