The 'Dumb Question' Thread

[2012Coyote]

I have a few.

With turbos, will they only build boost under a full load (WOT) or will gradual input into the throttle still spool them? (while staging)

While sitting on the 2 step, will the variance in rpm's be enough to affect the intake pressure and cause the BOVs to pop? I'd like to be able to sit at a set rpm and still have a consistent amount of boost and power coming off the line

What are the advantages/disadvantages of different front tire diameters when at the strip... i.e. r/t, rollout, et, trap?

Thanks in advance.

 

[psfracer]

Since turbos like load, I wonder?

How much does your car weigh? And confirming, 650rwhp?

 

[psfracer]

What are the advantages/disadvantages of different front tire diameters when at the strip... i.e. r/t, rollout, et, trap?

Thanks in advance.

The difference in tire height may or may not be a factor, depending on what kind of tree you race (.400 pro light?/.500 pro light?/Sportsman tree?)

Take two front tires. One is 28 in diameter, one is 26 in diameter. Everything else being equal:

the 26 tall tire will give you faster reaction times, as the car has to move less forward in order to activate the clock.

the 28 tall tire will give you a slower reaction time, as the car needs to move more in order to activate the clock. HOWEVER, because you have this slight "rolling start", your 60' and ET will be less.

Think of it as the same as deep staging vs shallow staging. This is also why if you are going just a tiny bit red, sometimes by airing up your front tires more will slow down your reaction time just enough so you don't go red.

Hell I never had to worry about red lighting on a .400 pro tree, and I can do pretty good on a .500 pro tree even with my 28 tall front tire.

 

[2012Coyote]

How much does your car weigh? And confirming, 650rwhp?

Last year it was 3760 with me in it. The build is in process so I'm not sure the additional weight or power for sure, however my tuner said he will keep it at 600 to the wheels (mustang dyno) even if detuning is needed.

The difference in tire height may or may not be a factor, depending on what kind of tree you race (.400 pro light?/.500 pro light?/Sportsman tree?)

Take two front tires. One is 28 in diameter, one is 26 in diameter. Everything else being equal:

the 26 tall tire will give you faster reaction times, as the car has to move less forward in order to activate the clock.

the 28 tall tire will give you a slower reaction time, as the car needs to move more in order to activate the clock. HOWEVER, because you have this slight "rolling start", your 60' and ET will be less.

Think of it as the same as deep staging vs shallow staging. This is also why if you are going just a tiny bit red, sometimes by airing up your front tires more will slow down your reaction time just enough so you don't go red.

Hell I never had to worry about red lighting on a .400 pro tree, and I can do pretty good on a .500 pro tree even with my 28 tall front tire.

So no affect on trap other than the shallow stage effect, right?

 

[psfracer]

No. But it will affect ET.

I have both shallow staged and deep staged, definitely affected the reaction time and 60 foot / ET, but I saw no difference in MPH.

 

[lindertw]

what data do you all monitor/record to track your progress? I'm putting together a spreadsheet of all my runs, and I'm currently tracking/calculating the following:

- run data from time slip
- weather data from airdensityonline.com
- tire pressure front/rear
- strut/shock settings
- UCA/LCA positions
- race weight w/driver
- calculated RPM for 660 and 1320 [=(mph * final gear ratio * 336)/tire diam]
- 1/8 ET * MPH > 660 indicates spin
- 1/4 ET * MPH > 1320 indicates spin
- back half MPH
- 1/8th to 1/4 ratio = 1.57 [solid estimate of 1/4 performance if I'm running only 1/8th]
- 1320 / MPH = ideal ET

this was an old excel file, it's set up a little differently now:

I plan to load a copy to my tablet and update it after each run while the car is cooling off - with the hopes that it will give me a quick idea of how I'm doing comparatively, and which suspension/tire changes work the best... is there anything else I should keep track of?

 

[Weou09]

I have a few.

With turbos, will they only build boost under a full load (WOT) or will gradual input into the throttle still spool them? (while staging)
I only build 1# while not on the 2 step at 5k rpm, so no they will not build boost with just throttle
While sitting on the 2 step, will the variance in rpm's be enough to affect the intake pressure and cause the BOVs to pop? I'd like to be able to sit at a set rpm and still have a consistent amount of boost and power coming off the line
My car builds 4-5#, only running 6#, while on the 2 step at 6k. The boost gauge doesn't budge the whole way down the track with the 2 step and no lift shift.
Thanks in advance.

Answers in Red.

 

[psfracer]

what data do you all monitor/record to track your progress? I'm putting together a spreadsheet of all my runs, and I'm currently tracking/calculating the following:

- run data from time slip
- weather data from airdensityonline.com
- tire pressure front/rear
- strut/shock settings
- UCA/LCA positions
- race weight w/driver
- calculated RPM for 660 and 1320 [=(mph * final gear ratio * 336)/tire diam]
- 1/8 ET * MPH > 660 indicates spin
- 1/4 ET * MPH > 1320 indicates spin
- back half MPH
- 1/8th to 1/4 ratio = 1.57 [solid estimate of 1/4 performance if I'm running only 1/8th]
- 1320 / MPH = ideal ET

this was an old excel file, it's set up a little differently now:

I plan to load a copy to my tablet and update it after each run while the car is cooling off - with the hopes that it will give me a quick idea of how I'm doing comparatively, and which suspension/tire changes work the best... is there anything else I should keep track of?

What about shift rpm? And for me, one of the largest factors was engine water temp. Too hot and the top end would definitely drop off. It looks like since you are N/A, IATs wouldn't be much of a factor, but when you throw on the blower I would definitely add that to.

 

[lindertw]

What about shift rpm? And for me, one of the largest factors was engine water temp. Too hot and the top end would definitely drop off. It looks like since you are N/A, IATs wouldn't be much of a factor, but when you throw on the blower I would definitely add that to.

at present, I don't know what my shift points or water temps are. I hope to rig up my SCT and laptop/tablet at some point and log that info. I picked up an OBDII extension cable so I can just have that gear in the passenger seat.

I do have an old scangauge that I can use to monitor water temps, guess I could use that in the interim.

 

[lindertw]

rear tire question...

I'm currently running M/T ET street bias ply rears (26.5" tall), and using this calculator: rpm = (mph x final gear ratio x 336)/tire diameter I'm crossing the stripe at 5500-5600 rpm. What are the pros/cons to running a shorter rear tire? I found M&H makes a 15" slick that's 24.5" tall.

If my math is right, the effective gear ratio would be closer to 4.53 and should have me crossing the stripe at 6000-6200 rpm. Dyno graph here, if that helps...

 

[JEWC_Motorsports]

What gear do you cross the trap in?

 

[psfracer]

A shorter diameter tire has a smaller contact patch, and will spin easier vs an equal tire of larger diameter.

What you need is more power ……

 

[lindertw]

What gear do you cross the trap in?

- cross the stripe in 4th gear (stock 3650 5spd manual trans)
- 4.10 gears
- M/T ET street (p/n 3743) 26x11.5-17LT rear tire

What you need is more power ……

lol, I know right? I'm just trying to make my miniscule 300rwhp work as hard as it can.

A shorter diameter tire has a smaller contact patch, and will spin easier vs an equal tire of larger diameter.

nerd mode time... I was thinking about your contact patch comment on the way home from work today, and tried a low tech way to measure my OEM Pirelli. I slid sheets of paper front/back/sides until they touched the tire and taped them down - presumably what's left is the contact patch.

it measures approx 5-5/16" x 7.5", or just under 40 sq-in.

When it warms up I'll put my M/T ET streets on and remeasure. I also contacted a guy that I know is running Hoosier 16" drag radials (24.9" diameter) to see if he would measure his contact patch for me. The 15" M&H specs looks like it might fall somewhere in between my OEM Pirelli and the M/T ET street.

 

[cm581978]

My mods are in my sig, but I'm going to a track rental in 3 weeks and want to at least beat my personal best of 13.8, before the 4:10s went in. I'll be running on street tires, but what do I want to launch and shift at?

 

[psfracer]

When it warms up I'll put my M/T ET streets on and remeasure. I also contacted a guy that I know is running Hoosier 16" drag radials (24.9" diameter) to see if he would measure his contact patch for me. The 15" M&H specs looks like it might fall somewhere in between my OEM Pirelli and the M/T ET street.

Another factor you need to consider is air pressure. The less air pressure the larger the contact patch. So, for your experiment to work you would have maintain the same air pressure. This is why you lower air pressure in slicks or DRs, to increase the size of the contact patch.

 

[irishpwr46]

street tires, you want to take off like youre on the street. they arent going to hook. especially in new jersey in late october

 

[cm581978]

But if I run a set of Mickey Thompsons, what rpm can I launch at?

 

[irishpwr46]

thats gonna be a trial and error thing. try launching around 2500 rpms at first and see how it feels. if it bogs, drop to 2k.

 

[stkjock]

But if I run a set of Mickey Thompsons, what rpm can I launch at?

Which MTs? Model, size, construction....

 

[cm581978]

I'll need to ask Frankie, since there his

Which MTs? Model, size, construction....