600+hp gear ratio and RPM help - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #1 of 7 (permalink) Old 04-10-2016, 12:55 PM Thread Starter
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600+hp gear ratio and RPM help

hello guys,

I am newbie here, so maybe Ill ask some dumb already 100x asked questions - but Iv checked the forums and cant find my answers...
Also please excuse my bad english.

Almost 3 years I am buliding my Mustang 2005, bellow please find very short list of main changes and modifications.
Now i am on 600hp and 810Tq and best 1/4time 11.9 - and I am stuck there...
I think I should have a beter time, but I am not sure.

My main actual question is about gear ratio, tire preasure, shift point and launch RPM.

(My final goal is 1/4 time 10.xx, but its a long way, I know.)
(I still think that I should get more HP from this engine, but I am stuck there aswell)

Ill be glad for any advices, thank you in advance!

**** E N G I N E ****

1.9L TVS VMP Supercharger
66mm Supercharger Pulley
STOCK 3V HEADS (from 2005 4,6 V8 engine)
Manley 3V HP Valvev springs
FORD RACING Throttle Body OEM 60mm GT500 2007-2014
Kooks Headers Long Tube Headers + Kooks Headers X-Pipes (no cat)
Kenne Bell Boost-A-Pump
Kenne Bell Boost-A-Spark
MSD Launch Control


McLeod RST Street Twin Clutch Kits 6912-03
McLeod Aluminum Flywheels 563408


BMR Control Arms, controls, relocation, sway bar, K-member
stock springs
Strange Externally Adjustable Mustang Shocks
Air Lift 1000 Load Assist Rear Spring Kits

*** WHEELS ***

15" Weld Racing Draglite Polished Wheels 90-510354
315/60-15 Mickey Thompson ET Street Radial Tires 3763R

Dyno tested 600 RWHP, 810 troque
Shift point 6000 RPM (limeter 7000 RPM)
Launch RPM 2800
Tire preasure 8 psi

If you check my time slips, yesterday Iv started on 12,4sec and ended on 11.915 sec (1.815 6oft)
(we changed only launch RPM and tire preasure during the day)
but my max speed is still almost exactly 195 km/h - and I dont know why.
I cant improve my 1/4mile time anymore.

I have few questions:

with 600hp and 810Tq, should I still go with 4.1 gear ratio?

I think that 2800 launch RPM is far too low - but with this tires tire preasure I cant go higher
any advice?

generally, I would like to ask you for any advices, how to improve my 1/4 time with this car configuration, or what changes are you recomending.

fi you check the dyna graph, what shift RPM can you recomend?

I am doing something wrong - or I simply cant go faster with 600hp?

Thank you very much for your help!

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post #2 of 7 (permalink) Old 12-29-2016, 06:17 AM
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Re: 600+hp gear ratio and RPM help

Im sorry, but just saw this..maybe over come by events.

2 questions, is it a dynode at the crank 600 or at the rear wheel, or is it a guess?

Big thing, what does car weigh with you in it...then its a simple math problem, weight to HP should equal XX ET as a goal....or weight, Speed, ET equals HP made?

See where that gets you, then you can make your next move, shaving weight is always a good thing. Those Mustangs are HEAVY...

Good example, look at the 700 HP Hellcat, and what it actually runs, don't add up.

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post #3 of 7 (permalink) Old 12-29-2016, 08:39 AM
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Re: 600+hp gear ratio and RPM help

REAL slicks and 5,000 launch rpm would help. You WILL break parts getting to the 10's

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post #4 of 7 (permalink) Old 12-29-2016, 06:53 PM
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Re: 600+hp gear ratio and RPM help

I think you may be a bit over geared, but I think I'd be looking to others with similar combos to be sure. My hunch is that car would be fine with a 3.73.

Typically, "unnaturally" aspirated V-8s don't like a real steep starting line ratio (SLR) and currently you run 13.48:1 (3.38*4.11). That's a serious 1st gear. I generally stay under 12:1 if I can for most combos and like I said, a blower motor often wants less

I work on a car that is also overgeared (but nat aspirated) and we have had some luck with short shifting 1st gear significantly and coming out relatively gentle. Without spending any money, I'd likely start raising your launch to where it spins on a prepped track, and then back off a couple of hundred RPM.

If you can get a repeatable launch, then start shifting 1st early. I'd say if you are shifting at 5800 now, shift 1-2 at 5000 and see what happens on the time slip. Then go up or down from there, if it's quicker, try lower, slower, try higher, but you have to get the launch stable first. One variable at a time

Then I'd likely shift at 5800-6000 for the remaining gears. I normally say 400 rpm over the peak as a starting point, but with your flat curve and so much torque, I think stopping at 5800-ish is a good start until you get launch and 1-2 down, also setting a shift light at 5800 will likely get you 6000. Then after you get it repeatable, play around from there.

With a big torque car though and a lot of gear, you'd be amazed how coming out a little more gentle and shifting early can help, 2nd gear really ends up traveling down the track if you have an engine with a lot of torque. Seems counter-intuitive, but 1st gets so short it actually slows you down to let it rev

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post #5 of 7 (permalink) Old 01-07-2017, 12:29 PM
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Re: 600+hp gear ratio and RPM help

4.10s are too much for your car. 3.55s or even 3.27s are much better suited to your setup. Or you could use a 28inch tall tire to counter the gearing if your in love with them. Not to mention a 28 inch tall slick or DR will help your 60ft times immeasurably.

I've been there and done this with my 2003 Cobra. Had 4.10s when I was making around 500whp and they were perfect. Found 3.55s were great through 6-700whp for the weight of the car. Now that I'm 850whp+ I've switched to 3.27s.

Did I read the tire size right? 315-60-15? So, you're running an approximately 30 inch tire?
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Last edited by garbonzo1991gt; 01-07-2017 at 12:33 PM.
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post #6 of 7 (permalink) Old 01-22-2017, 09:51 AM
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Re: 600+hp gear ratio and RPM help

Also, Looking at your time slips that you posted... Your 60fts and kph at the big end are all over the map. Consistency is the name of the game and you should keep a log book for every run you make. Every little change you make (I.E Tire pressure, launch rpm, temperature, humidity etc.) should be logged and you can start to see where you can improve or what needs to change. The combo you have now should be well into the 11 second range consistently. Especially with all that torque.

I think your tire pressure is too low as well. Try starting at 15-18psi and working your way up or down to see if your 60ft times improve.

Last edited by garbonzo1991gt; 01-22-2017 at 09:54 AM.
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post #7 of 7 (permalink) Old 01-22-2017, 12:05 PM
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Re: 600+hp gear ratio and RPM help

Your MPH in the traps (finish line) indicate your engine tuning. Dyno tuning is excellent to get a base tune on it, but racing is dynamic, and final tuning should be done on the track. I notice your Lambda2 on the dyno sheets is rather high at high RPM, and while it's better than too low for HP, any change in fuel or run pressures can drop your power. I also have no idea what your ignition timing is like, and at top-end is critical, yet many tuners are very conservative for the base tune. Both AFR and timing should be tweaked under track conditions, using the fuel in the tank (which may be different than what was used on the dyno). Fuel composition is critical in maintaining or improving the tune.

Watch your MPH for changes as you tune for best speed. Once you find good numbers (minimum timing that makes best MPH, repeat for fuel), repeat the process at half-track. I think you will find your best improvements in the final tuning. Find your best shift RPM in the same way, shifting at (example) 5500 and compare your ET and MPH at timing points down the track. Having said all that, it has to launch well to go anywhere, so tuning your chassis and tires would follow. I did a write-up covering much of that, but can't find it now, or it's gone. Here is a short snip about tire heat, chassis and tuning until I can find the old posts: Burnout


[EDIT] PS: Your gear should be selected to give RPM a couple hundred above shift PRM as you cross the finish in 4th gear. If that makes 1st gear too short, then do it for 3rd gear. The balance is a good gear for launch and crossing the finish at the right RPM. Many broad-torque cars like yours actually go quicker with 3 gears than 4. Also, don't forget to stay on the throttle until you clear the timing lights after the finish line to get good numbers for tuning and diagnostics.

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Last edited by PSIG; 01-22-2017 at 12:15 PM.
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