Do you jet for MPH or ET?

[SUPERSTOCKRACER]

if your looking for horsepower jet for mph. looking for e.t./consistency? I always thought that was a chassis/driver thing, but what do I know,...lol. do whatever you feel the most comfortable with.

Consistency isn't the problem since I run a racepak. By the 2nd time trial I am usually with .02 throughout the day especially when running VP Q16 race fuel
What gets me is a breakout or the unsuspected redlight

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I agree. Jet the car to change with the weather. Density Altitude goes up car slows down, Density Altitude goes down car goes quicker/mph picks up.

The old saying Lean is Mean is true... runs hard but hard on parts...

Yes retarding the timing in high gear will pick up et and mph. We did this in the class cars Stockers and Super Stockers. Hook up a micro switch to the shifter to activate msd retard when you pull it into high gear.

I like this idea As I run a MSD Digital 7 7530T box.
I'm going to play with the retard timing at high gear this year and see how much more
I can gain. Thanks for the advice.

 

[bobtile]

That's against Nendra rules.
Chapter 7
Paragraph 3
Section 12-1.2
No retarded driving allowed in high gear!

 

[dvw]

Jet and timing for mph. If leaning the carb helps ET and hurts MPH or vice versa, you have a fuel curve problem. Advanced timing down low is a crutch, and a dangerous one. Correct timing will give the longest pressure curve pushing down on the piston after TDC. Excessive timing will create a higher but shorter pressure curve. This spike can be momentarily above the fuels threshold against detonation. I think people get way to caught up in jetting for weather. Unless you're in Denver once it's right it'll be very close. Less density altitude=less atmospheric pressure. This pushes less fuel through the jet. The carb is a pressure differential device. Thus it leans accordingly. Is this perfect? no, but very close. You can lean it when the air gets worse but you'll still make less power due to less atmospheric pressure. Less pressure means the engine takes in less air. This translates to less oxygen. Therefore it needs less fuel to maintain the correct mixture. Bottom line. Once your close gaining more than a few hundredths won't happen. If it does your starting tune up is off.
Doug

 

[rapom tsaf]

whats going on between bobtile and ssr?

Bromance

 

[SUPERSTOCKRACER]

Bromance

you think!!:love8:

 

[rapom tsaf]

that's a bad *** black duster in that pic. :icon_jokercolor:

 

[SUPERSTOCKRACER]

that's a bad *** black duster in that pic. :icon_jokercolor:

I fell in love with it :yourock:

 

[SUPERSTOCKRACER]

So I was just thinking, is it better to set your timing for the best ET or MPH?
Seems when you increase timing, and your ET gets better, I lose a bit of MPH
Going from 35 degrees to 32 degrees, I gained over 1.25 mph

 

[Average Joe]

I like the motorized garage stool in the pic!!

 

[SUPERSTOCKRACER]

I like the motorized garage stool in the pic!!

I like camels.

 

[Dako]

I thought most racers chased down the ET?

 

[Budnicks]

I jet for what the engine needs/plugs read & ignition time for ET,
that's what wins races, getting from point a to b the quickest
"{I rarely bracket/handicap raced thou, just heads up stuff & didn't worry about consistency, just best performance, for a given round}
higher MPH is/was HP, or even better weather/air/track prep conditions
or in my case, was usually a product of spinning allot in the 1st 330ft,
running higher RPM out the back door...

we've gone over this...LOL
what car are we talking about ?
I know you know this already,
not trying to be a smart ***, well mostly not

Best of both worlds
is to take out ignition timing on the big end,
jett to see the best plug readings, not hurt the engine,
take timing out after about 660ft
if it's timed instead of RPM actuated,
you could progressively back out timing at track incrementals,
like at the 330ft, then 660ft, then 1000ft, a degree {or 2} each or more if necessary
or after 5000-5500 rpm or so {maybe depending on what your specific combo needs}
maybe in each gear activated by the shifter like Long Roof recommended or even
every gear change drop another degree or so
run your combo were it 60fts & 330ft's well/the best,
IMO the 1st 60ft-330ft is were the biggest changes/improvements in et will be achieved
take out the timing on the big end,
that way you 60ft well & MPH well,
so you can run down people that are out on ya' a couple seconds, like Bobtile

depends on what your specific comb likes
gear, tire size, wheel speed & converter will effect it too
way too many variables

your RacePak should help you determine
where's the best place or RPM to start pulling it back,
where it's dropping off, if you can do some back to back comparison runs,
one with 35*'s the next 34* then 33* then with 32*'s, compare graphs,
preferably with similar weather, sun or cloud cover & track prep conditions
you maybe able to go even more ignition timing like 36*-38*'s
& back it out in more {shorter} incremental,
if that's what your specific engine/car combo likes

what does your engine builder say to do ?
he should know what your combo can or should be able to handle

IMO with a high compression combo
I'd be shutting it down clean, right after the traps
& then reading the plugs after every run,
not idle/cruise around & getting false plug readings after a run
{tow it back to the pits if you have too a couple times, so you get a clean reading}
even running a leak down test to make sure your not hurting something
too lean or detonating the crap out it, just be safe...

I know you must already know all this stuff,
must be testing/messing with us or something...LOL

but what do I know...LOL

good luck, have fun

 

[dvw]

Ever watch how many Pro-Stock cars change jets during the weekend? none. Adding timing for ET while slowing mph may reward you with detonation at the top end, not good. I usually run a change 2-3 times out before declaring it good or bad. I can tell you in my case richer jetting and more timing haven't added more than .05 in ET and maybe .3 mph at the most.
Doug

 

[4406]

I agree. Jet the car to change with the weather. Density Altitude goes up car slows down, Density Altitude goes down car goes quicker/mph picks up.

The old saying Lean is Mean is true... runs hard but hard on parts...

Yes retarding the timing in high gear will pick up et and mph. We did this in the class cars Stockers and Super Stockers. Hook up a micro switch to the shifter to activate msd retard when you pull it into high gear.

This.

Ray

 

[66Satellite47]

Once I got the jet combination figured out & the car ran consistent, good ET/MPH combination, I pretty much left it alone. It took a BIG weather change to matter and for me to project the correct jet change to get that last little bit of improvement was tough. But I was a Bracket 1 guy so it didn't matter that much.

 

[SUPERSTOCKRACER]

Once I got the jet combination figured out & the car ran consistent, good ET/MPH combination, I pretty much left it alone. It took a BIG weather change to matter and for me to project the correct jet change to get that last little bit of improvement was tough. But I was a Bracket 1 guy so it didn't matter that much.

With 2 carbs, on each motor, I have a tune up for Spring and fall which are pretty close and then a summer tune which is usually 3 jet sizes leaner.

 

[66Satellite47]

With 2 carbs, on each motor, I have a tune up for Spring and fall which are pretty close and then a summer tune which is usually 3 jet sizes leaner.

On my tunnel ram 2x4 setups (Wieand w/ 650 DP Holley's, plugged power valves) they stayed pretty close too May through mid Oct. As I recall, I did bump up a couple sizes all around one time at Byron around Nov 1 with temps at barely 50*. It would vary ET & MPH what I considered normal for changing density. But to point, if the setup worked for good ET off the line, I'd adjust to see what MPH did, then compare 60' times until got the balance.

 

[Meep-Meep]

Basic rule of thumb "speed comes from engine. Quickness comes from chassis."

 

[SUPERSTOCKRACER]

Basic rule of thumb "speed comes from engine. Quickness comes from chassis."

I like that saying.

 

[66Satellite47]

I always found that to be true!