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Discussion Starter #1
I've been noticing that when I launch at 3000 rpm; the car spins in first then bogs when I hit second. This is on an old back road with 315/17 drag radials at 28psi.
400rwhp 347
3.73 gears
Peak power is at 5800
Probably a 3500-3600 lb car with me in it.
I'm a complete amatuer curious as to why this happens.
Too much tire?
 

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At what rpm does it hit 2nd gear at?
 

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Discussion Starter #3

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And what is the rpm when it hits 2nd gear? It is not 6k rpm Lol.
 

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Discussion Starter #5
And what is the rpm when it hits 2nd gear? It is not 6k rpm Lol.
That's all the info I have until I drive it again. I knew what you meant. I'll datalog it.
 

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Discussion Starter #7
What’s the engine combo? You sure it’s making 400rwhp?
Why do I always get asked that? Lol.
The car has been dyno'd countless times. Even on a 105° day it made 389rwhp on a Mustang dyno.
10:1 347
AFR 185 Renegades
Custom cam 230/238 @ .050
Systemax ll ported and matched by Ed Curtis
1-3/4" shorties into full 2.5" exhaust with H pipe and straight through mufflers
.041" quench
1.6 RR's set at 1/2 turn past 0
180ish cold cranking compression
T5
 

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That bog is odd. I’m in the same neighborhood as you hp wise and my car usually spins a little when I shift second. Have you tried power shifting or spinning it higher in 1st?
 

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Discussion Starter #9
That bog is odd. I’m in the same neighborhood as you hp wise and my car usually spins a little when I shift second. Have you tried power shifting or spinning it higher in 1st?
My son's Fox does the same thing now that he has installed drag radials. I think the hot roads in Phoenix really make the tires grab. Does that make sense? The rears do break loose on the 1-2 shift occasionally.
I'm pretty careful as far as high rpm launches due to having a T5. My rev limiter is set at 6200 and it happens quick with the 3.35 first gear.
 

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Discussion Starter #10
And what is the rpm when it hits 2nd gear? It is not 6k rpm Lol.
I finally logged this. It looks like I shift at nearly 6400 and rpm's drop to 2300 before climbing again. Being that my rev limiter is set to 6200; I'm overshooting that by a bit before shifting. I guess I need to readjust my shift light to trigger earlier. I'm not shifting like grandma either. I don't power shift due to having a T5.
Engine makes peak hp in the 5800-5900 range.
 

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I am not buying what you are selling. There is no way you are dropping 4k rpm on a shift. It would be the widest ratio trans in the world. Lol. If an auto, then it is going from first to third on the shift....missing 2nd gear completely. It is the only reasonable explanation.
 

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Discussion Starter #12
I am not buying what you are selling. There is no way you are dropping 4k rpm on a shift. It would be the widest ratio trans in the world. Lol. If an auto, then it is going from first to third on the shift....missing 2nd gear completely. It is the only reasonable explanation.
No missed gears. I watched the rpm's on the datalog. It was just pointed out to me that the inj PW was cutting fuel.
I'm still in the tuning stage with forced open loop so who knows.
 

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Discussion Starter #13
I'm having a hard time reading my logs in BE. It looks like I get back on the gas after the 1-2 shift at 4600ish. Sound better?
 

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Your problem is that it's still spinning when you shift to 2nd. Your engine may be spinning 6400, but since you don't have enough power to spin in 2nd, the tires hook after the shift and pulls rpm down to match actual ground speed. If the tires were hooked before the shift, 6400 would drop to around 3800 after the shift due to the ratio change from 3.35 to 1.99.

Grant
 

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Discussion Starter #15
Your problem is that it's still spinning when you shift to 2nd. Your engine may be spinning 6400, but since you don't have enough power to spin in 2nd, the tires hook after the shift and pulls rpm down to match actual ground speed. If the tires were hooked before the shift, 6400 would drop to around 3800 after the shift due to the ratio change from 3.35 to 1.99.

Grant
Correct. Tires are spinning in first, but can't when I hit second. Being in Phoenix; there is no problem getting heat in the tires and they want to bite. A 315 tire has a big footprint which probably doesn't help.
 

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What are trans ratios? What are you rev limited to? I almost see a 2800rpm drop from 1st to 2nd which almost drops me out of the peak power range causing a slight bog. Maybe this is the long version to what saleen is saying, but what I’ve learned to overcome is to shift as high as possible to keep the boost and peak power from dropping off so much.
 

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I did a datalog recently to record rpm and wheel speed. A shift around 6500rpm put me in second gear at 3200, which when I overlayed that to my dyno graph, showed a significant drop in power. Only way for me to remedy is to shift at 7k.
 

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Discussion Starter #18
What are trans ratios? What are you rev limited to? I almost see a 2800rpm drop from 1st to 2nd which almost drops me out of the peak power range causing a slight bog. Maybe this is the long version to what saleen is saying, but what I’ve learned to overcome is to shift as high as possible to keep the boost and peak power from dropping off so much.
See post #9.
 

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Discussion Starter #19
I did a datalog recently to record rpm and wheel speed. A shift around 6500rpm put me in second gear at 3200, which when I overlayed that to my dyno graph, showed a significant drop in power. Only way for me to remedy is to shift at 7k.
I hear what you're saying. I just never thought I'd have to shift that high for an engine that makes peak power closer to 5800. I'm curious where you racers would shift for my combo. I realize the track and proper suspension changes a lot of variables.
 

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Your problem is that it's still spinning when you shift to 2nd. Your engine may be spinning 6400, but since you don't have enough power to spin in 2nd, the tires hook after the shift and pulls rpm down to match actual ground speed. If the tires were hooked before the shift, 6400 would drop to around 3800 after the shift due to the ratio change from 3.35 to 1.99.

Grant
this...

easy way to fix this is to ride the clutch out more. keep the RPM up so to speak
 
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