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optimum AFR for power
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Author:  74 firebird461 [ Sun Nov 11, 2012 9:58 am ]
Post subject:  Re: optimum AFR for power

Well Looks like i am getting to do a chassis dyno on my car this coming thursday or friday :). Whats the best way to do a plug chop? Just warm car up first then put a new plug in and kill it after the run? Its by the hr so I probably won't get to do much tuning which is fine . I am more concerned about my torque and power curve, and what the plug looks like with my current 94 square jetting,Also will 1 run show enough color to tell me the jetting? I also took out the .063 IAB and put some .061's in to help out on the top,like shrinker suggested to try. Not going to try any timing, cause evrytimne i tried that at the track it slows down, so i will be leaving it at 28 total.

Author:  shrinker [ Sun Nov 11, 2012 5:14 pm ]
Post subject:  Re: optimum AFR for power

Do what you said for a plug read, but one pull probably wont be enough. Check it after the first run. Just do a few runs then check it. Figure out which is the weakest cylinder and tune to that. Dont be too concerned if the plug is only slightly coloring, its the piston you have to look at. the plug only shows the start of the burn but if youv'e got a tan on the piston it should be OK. If the dyno shop is any good it will have a gas bench, use it. Going down to a .061" IAB is only a temporary measure, if it likes that it will like a larger IFR even better or a T-slot mod. An IFR at .061" is getting close to not enough air flow through the circuit for good atomization exiting the t-slot.

Author:  jmarkaudio [ Sun Nov 11, 2012 6:52 pm ]
Post subject:  Re: optimum AFR for power

Moroso 62348 magnifying light, works good for plugs without cutting them.

Author:  74 firebird461 [ Sun Nov 11, 2012 8:51 pm ]
Post subject:  Re: optimum AFR for power

shrinker wrote:
Do what you said for a plug read, but one pull probably wont be enough. Check it after the first run. Just do a few runs then check it. Figure out which is the weakest cylinder and tune to that. Dont be too concerned if the plug is only slightly coloring, its the piston you have to look at. the plug only shows the start of the burn but if youv'e got a tan on the piston it should be OK. If the dyno shop is any good it will have a gas bench, use it. Going down to a .061" IAB is only a temporary measure, if it likes that it will like a larger IFR even better or a T-slot mod. An IFR at .061" is getting close to not enough air flow through the circuit for good atomization exiting the t-slot.



So If it helps richen it up on top by trying the .061 iab, then I should try a tad bigger IFR,Or maybe a tad bigger TSJ then? I got them at .067 now

Author:  shrinker [ Sun Nov 11, 2012 9:41 pm ]
Post subject:  Re: optimum AFR for power

Yeah thats it. Its all stuff you do at the race track. Race track is different to the dyno. You know your car goes down the rtrack successfully its not blowing up so dont be too worried about the dyno stuff, just get your numbers and be gone. If there is a glaring anomaly well then deal with it but you will find whats best on the track is not best on the dyno for little changes. It makes stuff all difference unless your way off with your track tune. My preference in tuning is to use an engine dyno only if the builder want it I prefer the chassis dyno because I can feel whats happening, then its tune it in the shed and go to the track.

Author:  74 firebird461 [ Wed Nov 14, 2012 12:19 pm ]
Post subject:  Re: optimum AFR for power

Well dyno fell thru, first he told me 125 hr, now today its 200 min just to get the car set up etc, then 125 hr, forget that, plus they use two sensors and my car is only set up for one, they would charge me to add another one in the other pipe, and that would count towards the time bs, and labor ! find a different place in the spring

Author:  74 firebird461 [ Mon Nov 19, 2012 1:04 pm ]
Post subject:  Re: optimum AFR for power

So lets say my idle jet is .036 now, should I just increase it to .037 then, is .001 enough to make a difference? One other thing I have my plates adjusted so I have a square in back on the transfer slot, but the front its covered, if I adjust the idle up to open that up to a square it idles too high, anyway to fix that, and still have a square on both sides , and keep my idle right?

Author:  Beretta [ Mon Nov 19, 2012 5:58 pm ]
Post subject:  Re: optimum AFR for power

You need to read the sticky about tuning a T-slot

Author:  nomad [ Mon Nov 19, 2012 8:16 pm ]
Post subject:  Re: optimum AFR for power

Here you are.

viewtopic.php?f=6&t=3811

Author:  blown55409 [ Tue Nov 20, 2012 12:13 am ]
Post subject:  Re: optimum AFR for power

74 firebird461 wrote:
So lets say my idle jet is .036 now, should I just increase it to .037 then, is .001 enough to make a difference? One other thing I have my plates adjusted so I have a square in back on the transfer slot, but the front its covered, if I adjust the idle up to open that up to a square it idles too high, anyway to fix that, and still have a square on both sides , and keep my idle right?


Have you tried it the other way around? With the front square and the rear closed off. Do you need the rear TS flowing at idle? I suppose you could lower the slot to close the blades but harder to undo that mod.

Author:  74 firebird461 [ Tue Nov 20, 2012 7:26 am ]
Post subject:  Re: optimum AFR for power

blown55409 wrote:
74 firebird461 wrote:
So lets say my idle jet is .036 now, should I just increase it to .037 then, is .001 enough to make a difference? One other thing I have my plates adjusted so I have a square in back on the transfer slot, but the front its covered, if I adjust the idle up to open that up to a square it idles too high, anyway to fix that, and still have a square on both sides , and keep my idle right?


Have you tried it the other way around? With the front square and the rear closed off. Do you need the rear TS flowing at idle? I suppose you could lower the slot to close the blades but harder to undo that mod.



I have not,but being its a 4 corner idle I figured its best to have both front and back the same.

Author:  shrinker [ Tue Nov 20, 2012 4:09 pm ]
Post subject:  Re: optimum AFR for power

Every time I've seen a primary idle only setup the rear cylinders don't function correctly at low flow rates. If the cam has exhaust reversion at idle there is always a build up of ex gas at the rear of the plenum. 4 corner idle helps alleviate the issue by allowing the rear cylinder the correct AFR. And in order to get the fuel from the rear you need the barrels open so that way there is fresher air in the rear of the plenum.

Author:  74 firebird461 [ Tue Nov 20, 2012 4:55 pm ]
Post subject:  Re: optimum AFR for power

That makes sense, kinda why i always did it that way being it had four corner may as well use it! I read that TS Thread, but not really understanding what ken is talking about with filing the throttle blade at a 45? I would rather do that then lengthen the slot if i could. It does run better to with the .061's I put in for the IAB. Thinking if i get the front slot right it will help it at idle, its a tad lean now, and when coming to a stop it spikes to like 17 after letting off the gas when slowing down, then settles at 15 or so at idle.I would guess its from not getting enough gas off that front slot being its closed off?

Author:  shrinker [ Tue Nov 20, 2012 9:53 pm ]
Post subject:  Re: optimum AFR for power

You file the bottom side of the throttle blade and make it thinner that way it makes the T-slot more exposure without actually touching it. Some stock Holleys even come like that with machined blades. It alters the ratio of t-slot to air as the blade moves through small angles but its probably not an observable change.

Author:  74 firebird461 [ Tue Nov 20, 2012 10:26 pm ]
Post subject:  Re: optimum AFR for power

Ah okay I understand now, I just couldn't visualize it when i read it ,lol..

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