Tire height RMP will I have to shift into 4th? Help

[gtkurt]

Currently I do not have to shift into 4th gear in the quarter mile.
I am adding the Whipple,Stainless Works no cats,Accufab,2 Boost a pumps,52lb injectors,and a spec clutch. 23lb of boost on 109 unleaded.
I believe this will add around 200 RWHP to my current 572RWHP.
My question is if I go with a 29.5 inch tall tire and run to 7000rpm will I have to shift?
I have been running the Nitto drag radial it is 28.78 inches tall and I go through the traps at about 6300 to 6400rpm. That is shifting at 6500 rpm.

I hope one of the math geniuses in the forum can help me with this question.
It is way beyond me! Thanks Kurt

 

[TEXAS GT]

I don't know about shifting but I think you'll see more than 200 rwhp out of the setup you're talking about. I got 215 rwhp out of just the Whipple and tune.

You're gonna love that Whipple!

 

[gtkurt]

I don't know about shifting but I think you'll see more than 200 rwhp out of the setup you're talking about. I got 215 rwhp out of just the Whipple and tune.

You're gonna love that Whipple!

Who did your dyno? I keep hearing different results?

 

[dbk]

You're going to be very close. I'm not sure on the math though.

My recommendation? Shift it early into 4th. You've got the power to pull big mph as long as you make the 3-4 quick. The mod motor isn't big on spinning high rpms as it is, and with 700+ on tap I'm not sure how beneficial ringing out a couple hundred RPMs will be over just blasting into 4th.

 

[TEXAS GT]

Who did your dyno? I keep hearing different results?

Jason Heffner when he installed it. My car baselined at 518 rwhp and ended at 732 uncorrected rwhp. Accufab x-pipe, 93 0ctane tune, 19 lbs boost,Accufab throttle body.

I did 190 mph at the Texas Mile last weekend against a Hennessey 700 GT that was turning 185 and a Heffner Twin Turbo GT that did a 192 but he had a lot of room left I believe. Stock GTs have been tested by the magazines at 171 mph. You should be able to do well over 190 in the mile with the setup you're talking about.

 

[californiacuda]

Your question about gear shifting, if it simply relates to max rpm, would solely depend on mph at 1/4 mark. If your wondering about quickest et, than it does get more complicated. Shift time, best power band, etc. A good tool for max et is a device that measures G force. A driving strategy that produces the highest G force equals quickest time.

 

[gtkurt]

You're going to be very close. I'm not sure on the math though.

My recommendation? Shift it early into 4th. You've got the power to pull big mph as long as you make the 3-4 quick. The mod motor isn't big on spinning high rpms as it is, and with 700+ on tap I'm not sure how beneficial ringing out a couple hundred RPMs will be over just blasting into 4th.

DBK,
John at Accufab told me in his recent 100 or so dyno tests the 5.4 kept making more and more power until 7500rpm then it has valve float problems.
That surprised me but he seems like a incredibly reliable source. I guess I will have to see what the torque curve is like at high rpm.
It seems to me it would be better if I did not have to shift but I really have nothing to back that up except saving the shift time/wheel spin.
Thanks for your in put. Kurt

 

[gtkurt]

Your question about gear shifting, if it simply relates to max rpm, would solely depend on mph at 1/4 mark. If your wondering about quickest et, than it does get more complicated. Shift time, best power band, etc. A good tool for max et is a device that measures G force. A driving strategy that produces the highest G force equals quickest time.

Cuda,
Is there a max speed for third gear with the parameters I had described?
If so what is it? I think I should be some where around 140 mph in the 1/4 mile. Thanks Kurt

 

[gtkurt]

Jason Hefner when he installed it. My car baselined at 518 rwhp and ended at 732 uncorrected rwhp. Accufab x-pipe, 93 0ctane tune, 19 lbs boost,Accufab throttle body.

I did 190 mph at the Texas Mile last weekend against a Hennessey 700 GT that was turning 185 and a Heffner Twin Turbo GT that did a 192 but he had a lot of room left I believe. Stock GTs have been tested by the magazines at 171 mph. You should be able to do well over 190 in the mile with the setup you're talking about.

That is awesome you ran in the Texas mile. I would love to make it next year.
Why do you think Jason is giving you uncorrected numbers? Thanks for the info. Kurt

 

[dbk]

DBK,
John at Accufab told me in his recent 100 or so dyno tests the 5.4 kept making more and more power until 7500rpm then it has valve float problems.
That surprised me but he seems like a incredibly reliable source. I guess I will have to see what the torque curve is like at high rpm.
It seems to me it would be better if I did not have to shift but I really have nothing to back that up except saving the shift time/wheel spin.
Thanks for your in put. Kurt

Yeah, it'll still make power up there, but it comes at a price. I discussed it with a couple GT engineers and they said consistently spinning a GT engine above 7000 to a limit of about 7400 is where you'll run into problems with the engine. Obviously I doubt you'll be hanging out at 7300rpms, but it's definitely putting you closer to throwing a rod than 6800 long term...

 

[californiacuda]

There is a book called Auto Math Handbook by John Lawlor. I looked in the book and there was an equation that I think helps.

MPH = rpm X tire diameter / gear ratio X final drive ratio X 336 . If we plug in the numbers from previous post.

MPH = 7000 X 29.5 / 1.23(3rd gear) X 3.364 X 336, so Max speed for 3rd gear would be 148 mph. So, I think the answer to your question is, as long as you don't gove over 148 mph, then you won't have to shift.

If you need more or that didn't help just post, I have the book handy now.

 

[gtkurt]

There is a book called Auto Math Handbook by John Lalo. I looked in the book and there was an equation that I think helps.

MPH = rpm X tire diameter / gear ratio X final drive ratio X 336 . If we plug in the numbers from previous post.

MPH = 7000 X 29.5 / 1.23(RD gear) X 3.364 X 336, so Max speed for RD gear would be 148 mph. So, I think the answer to your question is, as long as you don't give over 148 mph, then you won't have to shift.

If you need more or that didn't help just post, I have the book handy now.

californiacuda,
Thank you very much for the info. I don't think there is any chance of me going over 148 mph in the 1/4 mile. Now I am really glad I ordered the 29.5 M&H's. I think they might work well for your application as well. Mine should be here 04/06/07 I will be sure to let you know if they fit. Thanks again Kurt

P.S. When do you think your car will be on the road? I am very impressed with your project!

 

[californiacuda]

Engine is assembled and ready to go back in, so I think we'll be running soon.
Did you get special rims made for the M&H tires? Could you run more boost with the 109 octane? Do you run your car on a 1/4 mile track? Thanks

 

[gtkurt]

Engine is assembled and ready to go back in, so I think we'll be running soon.
Did you get special rims made for the M&H tires? Could you run more boost with the 109 octane? Do you run your car on a 1/4 mile track? Thanks

CCW Wheels made my rims I have the only set with 18 inch Micky Thompson skinnys they have made for the Ford GT.
I am going to run 109 octane with 23lb of boost. I was going to run nitrous as well but your friend John at Accufab was nice enuf to talk me out of that.
I do run 1/4 so far bone stock with a kenne bell mail order tune and nitto drag radials 11.42 @ 129.78 is my best. 60ft 1.74
My Spec clutch did not come with a throw out bearing so I wont get to race until next friday.

New mods are Whipple w/23lb pulley.109 octane tune,Accufab T-Body,Stainless Works headers w/no cats no muffler, 2 kenne bell boost a pumps, 52lb injectors, Spec clutch, trans axle cooler,Diablo Mafia,Sct Live Wire tuner,and CCW Wheels w/M&H 390/40R17 drag radials.
I am hoping to run a low 10 second pass mabe with a great 60ft a 9.99
Kurt:thumbsup

 

[californiacuda]

Sounds like your mods are right on. Hope you are the 1st to break into the 9's. Get some videos so we all can all enjoy. The tires seem like they would be a little too wide to fit in the wheel well, do you have to jack the rear end up a wee bit so they don't rub? If you would want to post some pics, very fun to see.

I understand the reason for your original question about shifting. When rapidly accelerating, shift time can eat up precious moments.

I recently talked to a successful drag race guy who used to work with GM drag race team. He was using an Xtrac road racing dog box transmission with a shift interrupter. He would bump the shifter, the engine would cut for a micro second and the car would shift with no clutch. An expensive setup, but very fast and effective. They would run 200mph with a 2L Cobalt engine. Sorry for going on, I just thought it was interesting and relates to shift time.

 

[gtkurt]

Sounds like your mods are right on. Hope you are the 1st to break into the 9's. Get some videos so we all can all enjoy. The tires seem like they would be a little too wide to fit in the wheel well, do you have to jack the rear end up a wee bit so they don't rub? If you would want to post some pics, very fun to see.

I understand the reason for your original question about shifting. When rapidly accelerating, shift time can eat up precious moments.

I recently talked to a successful drag race guy who used to work with GM drag race team. He was using an Xtrac road racing dog box transmission with a shift interrupter. He would bump the shifter, the engine would cut for a micro second and the car would shift with no clutch. An expensive setup, but very fast and effective. They would run 200mph with a 2L Cobalt engine. Sorry for going on, I just thought it was interesting and relates to shift time.

I have not received my 390/40R17's yet hopefully 04/06/07 red label over night of course. I did get the 325/40R17's seeing how much room I had left over and a lot of measuring and talking with John at M&H is what makes me think they will fit. Honestly I did not think much about the height. The stock tire and my Nitto drag radials are almost 29 inches and these are 29.5. It seems like there is enough gap between the tire and the well to allow for a 1/2 inch I hope. The clam shell is off right now so I cant check the width up top.
I looked up some old posts and found where Tony ran Joe's car with nitrous he went through the traps at 144.5 in third gear at 7000RPM. They used the Nitto at that time ( a shorter tire) so I think your calculations are going to be right on. Thank again for the help. I will post pictures and video of my set up ASAP. Kurt
P.S. I may have to change my TRBOKLR name now that I have a friend with a turboed GT. That was for my Supra and Honda friends.:lol

 

[gtkurt]

Tires not in at M&H yet. I might see them Saturday.:frown

 

[Jason Watt]

keep us posted... Any pics of those rears??

 

[Fast Freddy]

Currently I do not have to shift into 4th gear in the quarter mile.
I am adding the Whipple,Stainless Works no cats,Accufab,2 Boost a pumps,52lb injectors,and a spec clutch. 23lb of boost on 109 unleaded.
I believe this will add around 200 RWHP to my current 572RWHP.
My question is if I go with a 29.5 inch tall tire and run to 7000rpm will I have to shift?
I have been running the Nitto drag radial it is 28.78 inches tall and I go through the traps at about 6300 to 6400rpm. That is shifting at 6500 rpm.

I hope one of the math geniuses in the forum can help me with this question.
It is way beyond me! Thanks Kurt

i am in arizona to. who put the supercharger on for you and who did the tune?