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Still running a holley carb? What jet?


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http://www.bgsoflex.com/auto.html

Forget your rules of thumb such as 1 jet per 2000'. we race at 6000 ft and DA is never that low except in the dead of winter. 65 degrees and around 8000' today. I'm down to 66/77s on my 750HP from a stock set up of 72/84s. Current conditions equate to 72/83s and has never run better! Once you figure out your best set up, this is a great reference.

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Yeah, still running a holley atleast on the 383. The more I think about jetting, power valves, acceletor pump, accelerator cam, secondary springs etc :icon11:... the easier I think it would be to tune with a laptop and wideband, even a narrowband. "Once you figure out your best setup" is the PROBLEM IMO. Not to belittle the calculator or your post at all. It looks like a good resource and I've never even seen a program that actually suggested jet sizes at all. Everyone just says each engine is different even if they're built exactly the same (which is true). I'm just ranting and wishing fuel injection stuff didn't cost as much.

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Yeah, still running a holley atleast on the 383. The more I think about jetting, power valves, acceletor pump, accelerator cam, secondary springs etc :icon11:... the easier I think it would be to tune with a laptop and wideband, even a narrowband. "Once you figure out your best setup" is the PROBLEM IMO. Not to belittle the calculator or your post at all. It looks like a good resource and I've never even seen a program that actually suggested jet sizes at all. Everyone just says each engine is different even if they're built exactly the same (which is true). I'm just ranting and wishing fuel injection stuff didn't cost as much.

 

Part of the "Sport" (bites lip hard) is getting it right. For sea level you can about bolt one on, correct size, out of the box and have it perform well. For a fraction of the price of FI, there's still money to purchassing a basic Innovate wideband for $350 and quit guessing at your jetting, too. Seeing experienced carbureted racers within .02 of their dial in, all weekend long with changing conditions obviously means some have the art down. Its possible to have our DA change from 6000' to over 10,000' DA window in a race day. I don't, lol, but am fianlly having mine run really well. I can leave mine for my home altitude of 4660, and not have to change for racing at 6000. Not until we reach a DA of 8000 will I change 1 jet leaner. Then its only about a 2 minute job. No big deal. Actually if you get it right, there isn't a need to change with every little drop in air pressure, temp etc. especially for everyday driving. I see plenty of frantic posts in the Megasquirt forum to tell me the EFI is not cut and dried. You aren't going to bolt it on and drive away with out a lots of work tuning, trial and error. I don't dispute FI is better for a wide variety of conditions, and for me cost is still the issue. Mine starts year 'round, below freezing above 100, any weather, no choke, only a minute or less warm-up, great throttle response from 1500 up, (244 @ .050, 108 degree .614/.585 cam) gets mid 20mpg. I'll rejet once in the summer80 - 100 degrees, again in the winter can be below 0. Performance-wise I'll bet $$ on a run with anyone with the same engine configuration running EFI.

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  • 1 month later...

Buying an AEM wideband was the best $$ I've spent in a long time. Finally no more guessing if that jet change was too rich or lean, what the WOT is hitting. Was that a lean or rich surge? What I've learned: Take your rules of thumb for running a Holley and throw them in the dumpster. If you are going to live with one of these, the basic set up is usually lacking in many areas. My out of box Holley HP750 ran pig rich 12.5:1 at cruise, regardless of jetting, and had a terrible leaning out 18:1+ at part throttle tip in. Bringing on the PV it would then go to the low 12s. No wonder my eyes always burned. I ran out of time at the track and had made 4mph by going leaner, down to a 79 rear jet, but had no idea how much I should have gone. The 1 jet # / 2000' wasn't even close on my combination. Using this jetting I found I was running 11.6:1 at 2000' lower! Hmmm I remember the BSFC during break in was a low .39-.41. More effecient than I thought? Recently I found best setting to be 68/72 jetting hits a perfect 12.6:1 at wot and a decent 14:1 at cruise. Last year I was hitting low mid 20s mpgs with the 12.5:1...imagine how much better. The overly lean tip in was cured by using some tips found on Innovate's tuning forum..some really smart carb guys there. I had too much rear T-slot exposed which I closed completely, raised front float well beyond level, and reduced primary idle air bleeds by .015. The HP always worked well with the longer duration cam unlike my previous Demon. Readjusted the mixture screws in by almost 1/2 a turn and WOW. It has never responded so well and pulls harder throughout the range. I broke Holley's rules of going past 10 jets, have a wierd 4 jet spread instead of the usual 8-10, and asymetric iabs. The fact a generic carb can be put on a variety of engine configurations and run OK is pretty amazing, but my point is there is a lot you can do to improve. A wideband is the first step and learning what the bleed, emulsion holes, restrictions do would be next. Its easy to hack up a good carb and my settings might melt your new pistons.. so I'm not recommending this to just anyone. Experimenting further I've reduced the idle feed restrctions and found my cam runs very well at idle and cruise with a flat 14.6:1. and can still maintain a 12.6:1 at full throttle. I'm just learning, but with positive results. No more putting up with an unruley carb. Who'da thunk?

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Buying an AEM wideband was the best $$ I've spent in a long time.

 

John, why did you choose AEM over one of the Innovate models?

 

I've been trying to decide what to buy (gas prices seem to make the purchase prudent), but all I've managed to do is confuse myself.

 

I, too, have a Holley-- no laptop tuning at this time.

 

Thanks...

 

 

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John, why did you choose AEM over one of the Innovate models?

 

I've been trying to decide what to buy (gas prices seem to make the purchase prudent), but all I've managed to do is confuse myself.

 

I, too, have a Holley-- no laptop tuning at this time.

 

Thanks...

 

 

<>

 

I wouldn't expect it to pay for itself in gas savings, but beyond the cost it is the frustration of not knowing what's going on. Reading plugs can't tell part throttle or idle, best 1/4 mph tells jetting for wot. What about cruise or pump shot? I've found that less than 1/8th, maybe 1/16 of a turn on the mixture screw can affect the afr by .5, something not detected by ear or a vacuum guage. Dyno time is around 100/hr and doesn't really simulate running down the road, hot air under the hood, changing air flow. I wanted the Innovate, but found the AEM for $244 on ebay. Page3racing sells a lot of them. Strange seller..but unit OK. I have no datalogging like the LM-1, just the gauge, harness, O2 sensor, and bung. Can be used with hyper terminal, wiring for ems. Reads steady enough for to see what's going on w/o data log. Its really cool to see the difference an aircleaner, exhaust insert, underhood temp increase, and weather conditions make. Makes you appreciate FI, but also how complex a carb really is as well.

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Ok so a basic theory question. A properly tuned carb vs. properly tuned FI. Will it be the same or will FI be superior still?

 

Superior in what way? Cold weather starting, flexibility, wot hp? Properly tuned carb can only fit a comparitively narrow range of conditions. FI adjusts. Most situations FI wins.

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