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Author
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Topic: ET better but MPH slower
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Tom G
Gearhead Posts: 734
From: Bethlehem, Pa USA
Registered: Nov 2001
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posted 11-10-2004 09:17 AM
   
Last weekend at Maple Grove which was very crowded BTW. Over 350 cars. We got the 67 to ET faster but Mph down from last year same time of year and temp. last year [email protected] this year [email protected] 60's are now down from 2.2s to 1.94 Changes made from last year are 4.11 spool to a 3.89 equaloc and a switch to 255/50/16 BFG drag radials. I am leaning towards subframe connectors to stiffen the chassis and some drag shocks in the front for some weight transfer. battery is also going in the trunk. launches have been from 3k-3500rpm spins alot if burnout sucks or equaloc doesn't cooperate. I can use some suggestions for winter project.------------------
67 Mustang F/B 302 GT-40X FMS engine RPM Air Gap 600 Holley ceramic coated headers T5, cable clutch Flows X Pipe 3.89 9". Clearwater Aqua GT Clone Vintage40 series 16X8 225 front 255/50 rear drag radials 13.30 on 255/50/16 BFG Drag radials
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Moneymaker
Administrator Posts: 26813
From: Lyons, IL, USA
Registered: May 99
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posted 11-10-2004 09:45 AM
How was the wind?
If the wind was not a factor, then the car did not like the gear change.
The ET and 60 foot pick up was due to the spool to posi unit swap.
Slower, heavy cars get killed with a spool.
Too much initial drag to overcome.
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Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,& '04
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
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Tom G
Gearhead Posts: 734
From: Bethlehem, Pa USA
Registered: Nov 2001
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posted 11-10-2004 12:12 PM
quote:
Originally posted by Moneymaker:
How was the wind?
If the wind was not a factor, then the car did not like the gear change.
The ET and 60 foot pick up was due to the spool to posi unit swap.
Slower, heavy cars get killed with a spool.
Too much initial drag to overcome.
It was windy but maybe I'm wrong but that's why i ask you what to do about 60ft times which is where I think most improvement in ET can come from? Car only weighs 2920 with 3/4 tank of fuel and folddown rear seat installed. I tried bumping the timeing up 3-4 degrees and the car slowed down 3 tenths and MPH down to 100. Advice please????
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67 Mustang F/B 302 GT-40X FMS engine RPM Air Gap 600 Holley ceramic coated headers T5, cable clutch Flows X Pipe 3.89 9". Clearwater Aqua GT Clone Vintage40 series 16X8 225 front 255/50 rear drag radials 13.30 on 255/50/16 BFG Drag radials
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Fastymz
Moderator Posts: 20708
From: Reno Nv USA M&M#1240
Registered: Apr 2001
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posted 11-10-2004 12:14 PM
Tom, maybe the new gears are pushing you out of your peak power range ?
Also that 600 seems alittle small for the higher RPM's too.
Just my opinion  ------------------
SCOOP oddly obsessed with big scoops on little Mustangs 65 coupe,351w,C4,Big Boss 429 hood scoop,8" 3.40 TracLoc. My Pics
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Tom G
Gearhead Posts: 734
From: Bethlehem, Pa USA
Registered: Nov 2001
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posted 11-10-2004 12:24 PM
quote:
Originally posted by Fastymz:
Tom, maybe the new gears are pushing you out of your peak power range ?
Also that 600 seems alittle small for the higher RPM's too.
Just my opinion
I think your right about killing the powerband. Between the gears from 4.11 to 3.89 and a taller tire 205/70/14 to a 255/50/16 killed my off the line HP Car doesn't seem to bog bu a higher launch rpm 3700 or up just blows away the BFG's tach goes right to 6500 then you have to shift which kills the motor in the first 100 feet.
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67 Mustang F/B 302 GT-40X FMS engine RPM Air Gap 600 Holley ceramic coated headers T5, cable clutch Flows X Pipe 3.89 9". Clearwater Aqua GT Clone Vintage40 series 16X8 225 front 255/50 rear drag radials 13.25 @ 103mph on 255/50/16 BFG Drag radials
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Moneymaker
Administrator Posts: 26813
From: Lyons, IL, USA
Registered: May 99
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posted 11-10-2004 12:25 PM
In "good air" you retard the timing.------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,& '04
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
IP: Logged |
Tom G
Gearhead Posts: 734
From: Bethlehem, Pa USA
Registered: Nov 2001
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posted 11-10-2004 12:31 PM
quote:
Originally posted by Moneymaker:
In "good air" you retard the timing.
OOPS! 
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Fastymz
Moderator Posts: 20708
From: Reno Nv USA M&M#1240
Registered: Apr 2001
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posted 11-10-2004 12:40 PM
Tom, the 4:11's and shorter tires would helpt the car off the line. Did you change the RPM you shift at too, and did your RPM's change across the line too ?
I'm just taking guess, the real race guys know what their talking about.------------------
SCOOP oddly obsessed with big scoops on little Mustangs 65 coupe,351w,C4,Big Boss 429 hood scoop,8" 3.40 TracLoc. My Pics
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Tom G
Gearhead Posts: 734
From: Bethlehem, Pa USA
Registered: Nov 2001
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posted 11-10-2004 12:43 PM
quote:
Originally posted by Fastymz:
Tom, the 4:11's and shorter tires would helpt the car off the line. Did you change the RPM you shift at too, and did your RPM's change across the line too ?
I'm just taking guess, the real race guys know what their talking about.
Last year with the 4.11's it was turning 6k plus thru the lights in 4th gear now it is 55-5700 in 4th
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Ryan Wilke
Gearhead Posts: 2289
From: Stanton, Michigan 49707
Registered: Oct 2000
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posted 11-10-2004 08:09 PM
[/b][/QUOTE]
I think your right about killing the powerband. Between the gears from 4.11 to 3.89 and a taller tire 205/70/14 to a 255/50/16 killed my off the line HP Car doesn't seem to bog bu a higher launch rpm 3700 or up just blows away the BFG's tach goes right to 6500 then you have to shift which kills the motor in the first 100 feet. [/B][/QUOTE]The height of a tire (using math, rather than a measure tape), is figured via: Width x Aspect Ratio = Section Height x 2 = Combined Section Height + Wheel Diameter = Tire Diameter. So your previous 205/70/14 tire was:
205mm x .70 = 143.5mm
143.5mm x 2 = 287mm
14" x 25.4mm/inch = 355.6mm
287mm + 355.6mm = 642.6mm or 25.3" tall. However, your 255/50/16 tire is:
255mm x .50 = 127.5mm
127.5mm x 2 = 255mm
16" x 25.4mm/" = 406.4mm
406.4 + 255mm = 661.4mm or 26.04" tall. Then using the race calculator (located in M&Ms, "Tech Articles"), with the 4.11 gears, 25.3" tall tire and a trap speed of 105.5mph, your rpm across the stripe would have been 5764 rpms. However, now with your 3.89 gears, 26.04" tall tire and trap speed of 103.4mph, your rpm across the stripe is 5195 rpms. A drop of about 570 rpms.... or about 10%. Your taller 3.89 gears are only about 5% taller than your old 4.11 rear gears. But at speed, the tire diameter change affected your trap rpm by nearly 10%. So - although the taller tire probably "looks better" on the car, they hurt your total performance combination much more than the gear change. GOOD LUCK!
Ryan
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