Lean idle. Rich cruise.

[Ironmike]

Well well well. I jetted down the primary from 82 to 77. took a little ride and now cruising at 2600 RPM, level flat ground, I'm now in the 12.4 range. From the 10's. BUT upon brisk acceleration on the primaries only..... BANG! in the 15 range and higher. so take it easy bring it home, and I have a plan.

I COULD jet down a bit further and enlarge the PVRC. After much reading and listening to you guys, I think I need to put restriction in my T slot channels instead. So that's what I'm going to try.

It would be a band aid fix (I think), to have 74 jets up front and 82's in the back. I'm pretty sure these XP's already have brass in that orifice so I will measure it with pin gauges and go down from there. My question is how much? I know what everybody recommends but have no idea where it's at from factory.

Honestly, I hate this carb. Hate that stupid idle air adjustment under the air clear bolt. It's stupid. I talked to Scott at AED yesterday and almost pulled the trigger on a custom dealio. He said they could have one ready in 3 days. determined to fix the one i have. If that's even possible.

 

[Mattax]

LOL. That's the 'idle-eze' method that IIRC Bill Jones came up with and has posted in various places such as Speed-talk.
It's just one of several methods of allowing the primary throttles to be further closed at idle.
The first time I did it we did it the old school way, a hole in each primary throttle plate near the idle port. Then the transfer slot was more the way it should be at idle, but for that engine, it needed smaller IABs. Discovered that trying to leave that evening. So that was also my first lesson in using wire to reduce restrictions. Lots of fun, and sure didn't fully understand it right away, but it worked.

My suggestion is to map out the carb which sounds like you're already planning to do. I don't *think* there is anything inherently better or worse with the XP versus an AED. If you want someone to fixup a carb for your situation, then contact Tuner (if he'll do it) or Mark Whitner, or Thumper (Dominic).

As far as the 15 AFR on the meter, why is that a problem? Was it in 3rd gear? Was it full throttle? Or was it just brief shot from from low rpm in an easy gear? In which case some of what the meter is catching is pump shot (or lack of). Increasing throttle and load the engine will want leaner mixtures. The power valve only opens when the load is too high for the lean mix and needs go richer as load approaches maximum. Somewhere's between 8.5 and 10.5 In Hg will be when you're engine wants to go richer unless its really efficient at part throttle.

Anyway, if I didn't already post so in this thread, focus on the steady state stuff first. After that is good, then the pump shot can be figured out.
Get the idle and off idle pretty decent. When you can get to a track or dyno you can test the WOT jetting PVCR combo. Going smaller with the MAB and reducing the e-holes so there are less and smaller or three and much smaller will be flatter, and worst case, it will get richer near the top rather than leaner.

Yea I know some of what I post contradicts what the magazine writers and marketing guys say. I've learned the hard way they that they don't the principles or the history. I suspect there's a reason Andy didn't go through with the advice that was given to him in that thread. He and all the others in that racket know which side of their bread is buttered. They sell product. Guys like Tuner and Shrinker make race cars go fast and street cars run well.

 

[9secRR]

EDIT: I forgot to mention you need to unlock the distributor and get a GOOD curve in it. You are absolutely KILLING 20-30 HP so fast your head would spin.

You are killing torque below peak and killing power above peak with that locked out distributor. Plus all that timing at peak torque is an engine killer.

Fix that FIRST.

20-30 HP lost by locking out distributor? i would like to see any proof of this as i have a very hard time believing this.
yes my head is spinning

 

[Newbomb Turk]

20-30 HP lost by locking out distributor? i would like to see any proof of this as i have a very hard time believing this.
yes my head is spinning

Pretty sure proof has been posted before.

What kind of proof do you want.

 

[9secRR]

Pretty sure proof has been posted before.

What kind of proof do you want.

show me the proof from your testing? what engines? track times as ET and MPH must have improved.

 

[Newbomb Turk]

show me the proof from your testing? what engines? track times as ET and MPH must have improved.

I have dyno sheets.

 

[9secRR]

just dyno? no track testing?

 

[Newbomb Turk]

just dyno? no track testing?

Of course. It’s not like I’m the only one who knows what locking out a distributor costs.

It’s not a secret.

 

[TT5.9mag]

show me the proof from your testing? what engines? track times as ET and MPH must have improved.

Say you lock the distributor at 33 degrees. Set your timing at idle, about 1000 rpm. Run it forever there, until you learn about slew rate and that 33 degrees at 7400 is more like 27 degrees. There’s an easy 15-20hp loss maybe more. If you lock it out, set the timing at your MAX rpm. When you do that, at idle it’ll show more than than 33 degrees, And through peak torque you’ll be on the verge of rattling unless you have a lot of converter and a light car.

 

[9secRR]

Say you lock the distributor at 33 degrees. Set your timing at idle, about 1000 rpm. Run it forever there, until you learn about slew rate and that 33 degrees at 7400 is more like 27 degrees. There’s an easy 15-20hp loss maybe more. If you lock it out, set the timing at your MAX rpm.

i want to see time slips that prove this? if it's 20-30 HP more HP, the ET and MPH will change.

 

[Newbomb Turk]

i want to see time slips that prove this? if it's 20-30 HP more HP, the ET and MPH will change.

Then you won’t get the proof you want.

My question to you is why would locking out a distributor make more power?

Most everyone knows that ICE’s want a curve.

 

[fishmens67]

i want to see time slips that prove this?

Time slips prove nothing.

 

[9secRR]

Then you won’t get the proof you want.

My question to you is why would locking out a distributor make more power?

Most everyone knows that ICE’s want a curve.

what engines did you dyno test this theory? stock, mild, all out race engines?

Say you lock the distributor at 33 degrees. Set your timing at idle, about 1000 rpm. Run it forever there, until you learn about slew rate and that 33 degrees at 7400 is more like 27 degrees. There’s an easy 15-20hp loss maybe more. If you lock it out, set the timing at your MAX rpm. When you do that, at idle it’ll show more than than 33 degrees, And through peak torque you’ll be on the verge of rattling unless you have a lot of converter and a light car.

i do have a lot of converter and my car is light.

 

[9secRR]

Time slips prove nothing.

ok thanks for your knowledge

 

[Newbomb Turk]

what engines did you dyno test this theory? stock, mild, all out race engines?

i do have a lot of converter and my car is light. i have mine locked out at 37*.

What?

lol it’s not a ******* theory.

It works for ANY internal combustion engines.

I absolutely guarantee you that your engine doesn’t have a clue it’s a race engine.

Bet all you have and a lot of what you don’t have that 37 degrees of timing at peak torque is EASILY killing 20-30 HP. If it was 35-40 I wouldn’t be surprised.

Of course, that assumes you actually have 37 at peak torque. You probably have less than that and unless you set the timing at max RPM you don’t have 37 there either.

I’m going to assume you want proof of that too…

 

[Mattax]

@9secRR.
See the links in post #44.
I think those will answer your question.

 

[AndyF]

LOL. That's the 'idle-eze' method that IIRC Bill Jones came up with and has posted in various places such as Speed-talk.
It's just one of several methods of allowing the primary throttles to be further closed at idle.
The first time I did it we did it the old school way, a hole in each primary throttle plate near the idle port. Then the transfer slot was more the way it should be at idle, but for that engine, it needed smaller IABs. Discovered that trying to leave that evening. So that was also my first lesson in using wire to reduce restrictions. Lots of fun, and sure didn't fully understand it right away, but it worked.

My suggestion is to map out the carb which sounds like you're already planning to do. I don't *think* there is anything inherently better or worse with the XP versus an AED. If you want someone to fixup a carb for your situation, then contact Tuner (if he'll do it) or Mark Whitner, or Thumper (Dominic).

As far as the 15 AFR on the meter, why is that a problem? Was it in 3rd gear? Was it full throttle? Or was it just brief shot from from low rpm in an easy gear? In which case some of what the meter is catching is pump shot (or lack of). Increasing throttle and load the engine will want leaner mixtures. The power valve only opens when the load is too high for the lean mix and needs go richer as load approaches maximum. Somewhere's between 8.5 and 10.5 In Hg will be when you're engine wants to go richer unless its really efficient at part throttle.

Anyway, if I didn't already post so in this thread, focus on the steady state stuff first. After that is good, then the pump shot can be figured out.
Get the idle and off idle pretty decent. When you can get to a track or dyno you can test the WOT jetting PVCR combo. Going smaller with the MAB and reducing the e-holes so there are less and smaller or three and much smaller will be flatter, and worst case, it will get richer near the top rather than leaner.

Yea I know some of what I post contradicts what the magazine writers and marketing guys say. I've learned the hard way they that they don't the principles or the history. I suspect there's a reason Andy didn't go through with the advice that was given to him in that thread. He and all the others in that racket know which side of their bread is buttered. They sell product. Guys like Tuner and Shrinker make race cars go fast and street cars run well.

That thread was 2016 and I switched to EFI in 2017. Holley made a ton of changes to the emulsion circuits of the newer carbs but never explained it. It wasn't just Holley though since other carb vendors like QF did the same thing. Even the tuners like Braswell made big changes. I never did find anyone who would tell me what the theory behind the changes was. Tuner and Mark both felt the bigger holes in the emulsion jets were counterproductive.

Mark was a big help to me in those days. He had a carb flow bench and could measure booster depression and stuff like that so his recommendations came from data. Most of the other carb "gurus" that I talked to did a lot of hand waving.

We still run a lot of carbs on the dyno these days since roughly half of the customers are still carb while the others have switched to EFI. The Holley XP carbs tend to work great for drag racing, but sometimes they just don't work. Had an 1150 three circuit on the dyno the other day and it was a mess. Swapped on a 1050 two circuit and picked up 150 hp. Both carbs were new and there was no visible problem with the 1150. Just didn't work for some unknown reason.

Back then I was doing a lot of dyno testing with my own dyno "mules" for magazine articles as well as the engine book. I had two 470 pump gas engines and a 514 race gas engine. The engines ranged from 700 to 900 hp. I probably tested a dozen brand new carbs during that timeframe. The two best carbs were a 1050 Dominator two circuit, and a 4150 flange 1050 QF with annular boosters. Both of those carbs worked just perfect on anything. The 1050 AN worked great from around 550 to 750 hp, and then the 1050 two circuit was great from 700 up to 900 hp. I kept both of those carbs and sold or gave away the other ones.

One thing I learned is that some new carbs just don't work. And typically nobody can figure out why they don't work. There aren't any obvious reasons, all of the jets are the same size, same with emulsion and air bleeds and all of that. I have a feeling that it is something hidden, maybe internal to the booster or something like that. I don't have the equipment to find it or fix it so I just tell people to return the carb to Summit and get another one.

 

[TT5.9mag]

i do have a lot of converter and my car is light.

And it’s likely not predominantly a street car. But you can do the drag strip test yourself easy enough. Don’t change a single thing between two runs EXCEPT the way you set the timing. Set the timing at idle on the first run and set it just below the rev limiter on the second run and let us know what happens.

 

[9secRR]

And it’s likely not predominantly a street car. But you can do the drag strip test yourself easy enough. Don’t change a single thing between two runs EXCEPT the way you set the timing. Set the timing at idle on the first run and set it just below the rev limiter on the second run and let us know what happens.

i will do this and see what happens.

 

[Mattax]

Even Tuner has said at times to lock a distributor - when in some situations its the easiest path to get the results wanted. I can totally respect that. Sometimes its the practical thing to do. But if you can build even a small advance into the distributor it should help find more power.

 

[Newbomb Turk]

Even Tuner has said at times to lock a distributor - when in some situations its the easiest path to get the results wanted. I can totally respect that. Sometimes its the practical thing to do. But if you can build even a small advance into the distributor it should help find more power.

That’s true. So does William Baldwin. I usually start with the distributor locked out and then tune from there. I have a 3 stage retard on the desk I use so I can change the timing and see the results.

A bracket car maybe, maybe I might lock out. Maybe.

But to do it so you are not beating the engine to death around peak torque means you will hurt peak power even worse.

You can really get in the weeds trying to make a locked out distributor to not kill a bunch of torque while trying to make the most peak power you can.

I know if everything goes right (it never does) it takes me about an hour or so to figure out what the curve should look like. And probably another two hours at least to put that curve in the distributor.

It would be near impossible to do it at the track unless you had it all sorted out on the dyno first. It would be really easy if you had two distributors with one locked out and then at the track you could just swap them.

But sorting out the curve in the car?? That’s a tough one.

 

[9secRR]

That’s true. So does William Baldwin. I usually start with the distributor locked out and then tune from there. I have a 3 stage retard on the desk I use so I can change the timing and see the results.

A bracket car maybe, maybe I might lock out. Maybe.

But to do it so you are not beating the engine to death around peak torque means you will hurt peak power even worse.

You can really get in the weeds trying to make a locked out distributor to not kill a bunch of torque while trying to make the most peak power you can.

I know if everything goes right (it never does) it takes me about an hour or so to figure out what the curve should look like. And probably another two hours at least to put that curve in the distributor.

It would be near impossible to do it at the track unless you had it all sorted out on the dyno first. It would be really easy if you had two distributors with one locked out and then at the track you could just swap them.

But sorting out the curve in the car?? That’s a tough one.

my car is a bracket car with a loose converter. The rpm window is narrow, I leave at 5800 and shift at 7000. I have no dyno to try just track time. Only have 1 distributor also.

 

[Mattax]

That thread was 2016 and I switched to EFI in 2017. Holley made a ton of changes to the emulsion circuits of the newer carbs but never explained it. It wasn't just Holley though since other carb vendors like QF did the same thing. Even the tuners like Braswell made big changes. I never did find anyone who would tell me what the theory behind the changes was. Tuner and Mark both felt the bigger holes in the emulsion jets were counterproductive.

Mark was a big help to me in those days. He had a carb flow bench and could measure booster depression and stuff like that so his recommendations came from data. Most of the other carb "gurus" that I talked to did a lot of hand waving.

We still run a lot of carbs on the dyno these days since roughly half of the customers are still carb while the others have switched to EFI. The Holley XP carbs tend to work great for drag racing, but sometimes they just don't work. Had an 1150 three circuit on the dyno the other day and it was a mess. Swapped on a 1050 two circuit and picked up 150 hp. Both carbs were new and there was no visible problem with the 1150. Just didn't work for some unknown reason.

Back then I was doing a lot of dyno testing with my own dyno "mules" for magazine articles as well as the engine book. I had two 470 pump gas engines and a 514 race gas engine. The engines ranged from 700 to 900 hp. I probably tested a dozen brand new carbs during that timeframe. The two best carbs were a 1050 Dominator two circuit, and a 4150 flange 1050 QF with annular boosters. Both of those carbs worked just perfect on anything. The 1050 AN worked great from around 550 to 750 hp, and then the 1050 two circuit was great from 700 up to 900 hp. I kept both of those carbs and sold or gave away the other ones.

One thing I learned is that some new carbs just don't work. And typically nobody can figure out why they don't work. There aren't any obvious reasons, all of the jets are the same size, same with emulsion and air bleeds and all of that. I have a feeling that it is something hidden, maybe internal to the booster or something like that. I don't have the equipment to find it or fix it so I just tell people to return the carb to Summit and get another one.

I beleive you that no one at the company's could, or were willing, to say why they were following this fad. Techniques that Brasswell used for specific race cars can not be applied broadly. Somehow that got missed by some the folks who wanted to sell us on the newest latest and greatest. I'd say Barry Grant probably did as much as anyone in promoting a new and improved 4150 type carb. To his credit he had some good ideas, including having different flavors more closely setup to the then current engines hot rodders were building.

Tuner and Mark didn't feel the bigger emulsion holes were counterproductive, they knew it. Tuner explained it in post #2. Mark explained it here.

 

[Newbomb Turk]

my car is a bracket car with a loose converter. The rpm window is narrow, I leave at 5800 and shift at 7000. I have no dyno to try just track time. Only have 1 distributor also.

Where is the timing at 5800 and at 7000?

You probably need 2 degrees more at 7000 than you do at 5800.

Are you foot breaking or on the trans brake?

Damn. I had one more question and I forgot it. If I think of it it I’ll ask.

 

[Mattax]

Well since this topic has wandered all over the place, for those interested in a deep dive with Shrinker, and Klaus came across this one while looking for a different thread. It does touch on timing for a race car. Also Klaus's explanation for rich - lean changes between gears better answers a question I've had.

read-only-Please Evaluate my run data

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Here's an archived thread where Mark W suggests a slow short advance and Bill Jones mentions idle-eze

read-only-Drill Butterfies??

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