Made it to 11s but trap might be low, ideas?
02-21-2012, 10:03 AM
#1
Made it to 11s but trap might be low, ideas? I'm fairly pleased but I was hoping for closer to 115mph in good air and at least 113mph.
71 Chevelle, educated weight guess: 3740# with driver
~500ft DA, slight headwind
98 short block
799 heads, bowl work, rocker boss removed, sanding rolled intake/exhaust, stock valve job, hand lapped valves, shaved .010"
EPS 230/238 .600/.615 113+2
Comp 7.4 pushrods (at the high end of preload with almost 2 turns from 0 lash)
Stock rockers
Fast 90mm intake, runner bumps removed and smoothed
Fast 90mm throttle body (stock)
Doug's Chevelle swap long tubes, 1 3/4" to 3"
3" dual exhaust (crappy collector though which neck down to 2 1/4" for an inch)
Powerbond underdrive pulley
GM 41# injectors (from supercharged 3800)
intake tract is a 90* rubber elbow to stock 78mm MAF with a 850cfm cone filter on the other side of the MAF, IAT in the 90* turn post MAF
built 4l60e (alto clutches/steels, transgo hd kit, no yoyo high rpm kit, alto band, beast sunshell, etc)
Yank SS3600
Custom fabbed 56" chromoly 3.5" driveshaft, high speed balanced
GM 12 bolt, no name upgrade axles, Eaton posi-trac, 3.42 gears
15x10 Torque Thrust IIs
325/50r15 MT ET street radials (aired to 12.5# but this lap was a hot lap, likely at 13.5# at time of pass)
For reference: 2011 GT 5.0 6 speed 3.73 gears, no spare, no spoiler, base wheels, stock tires, Ford racing programmer, 94 octane Sunoco fuel went 12.55@113.5mph same day
71 Chevelle, educated weight guess: 3740# with driver
~500ft DA, slight headwind
98 short block
799 heads, bowl work, rocker boss removed, sanding rolled intake/exhaust, stock valve job, hand lapped valves, shaved .010"
EPS 230/238 .600/.615 113+2
Comp 7.4 pushrods (at the high end of preload with almost 2 turns from 0 lash)
Stock rockers
Fast 90mm intake, runner bumps removed and smoothed
Fast 90mm throttle body (stock)
Doug's Chevelle swap long tubes, 1 3/4" to 3"
3" dual exhaust (crappy collector though which neck down to 2 1/4" for an inch)
Powerbond underdrive pulley
GM 41# injectors (from supercharged 3800)
intake tract is a 90* rubber elbow to stock 78mm MAF with a 850cfm cone filter on the other side of the MAF, IAT in the 90* turn post MAF
built 4l60e (alto clutches/steels, transgo hd kit, no yoyo high rpm kit, alto band, beast sunshell, etc)
Yank SS3600
Custom fabbed 56" chromoly 3.5" driveshaft, high speed balanced
GM 12 bolt, no name upgrade axles, Eaton posi-trac, 3.42 gears
15x10 Torque Thrust IIs
325/50r15 MT ET street radials (aired to 12.5# but this lap was a hot lap, likely at 13.5# at time of pass)
For reference: 2011 GT 5.0 6 speed 3.73 gears, no spare, no spoiler, base wheels, stock tires, Ford racing programmer, 94 octane Sunoco fuel went 12.55@113.5mph same day
02-21-2012, 10:05 AM
#2
I've been doing my own tune with EFI live and lc1 wideband. Car drives great and feels strong on the street.
91 octane ethanol free
12.6 afr with 26* timing, car pulled .5* at the top of first on an earlier pass, didn't get to log this one
91 octane ethanol free
12.6 afr with 26* timing, car pulled .5* at the top of first on an earlier pass, didn't get to log this one
02-21-2012, 10:59 AM
#4
MT recommends 12-16# for that size, I was trying to get it to bite on the track which had marginal prep (first day of the season).
I am going to raise pressure back to 14-16# next time, maybe even try up to 18#.
The 1.71 60ft was the only decent one all day, next best was a 1.88
I am going to raise pressure back to 14-16# next time, maybe even try up to 18#.
The 1.71 60ft was the only decent one all day, next best was a 1.88
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02-23-2012, 04:16 PM
#9
True.
Ran through some calculators and it looks like it is making around 400rwhp now. Now bad for an auto with a 12bolt and heavy driveshaft I guess.
Guess I can do some more fine tuning on the pcm, upgrade to 85mm MAF, rig up ram air, and try a 275/50 tire. You fbody guys have it lucky with the lighter weight and better aero for sure.
Ran through some calculators and it looks like it is making around 400rwhp now. Now bad for an auto with a 12bolt and heavy driveshaft I guess.
Guess I can do some more fine tuning on the pcm, upgrade to 85mm MAF, rig up ram air, and try a 275/50 tire. You fbody guys have it lucky with the lighter weight and better aero for sure.
02-27-2012, 10:26 AM
#12
On my logs from previous runs that day, the 1-2 shift occurred at 6600rpm and the 2-3 hit at 6500rpm. But in the video it almost sounds like the 2-3 came early (maybe due to a different MPH due to hooking better? IIRC I always have to tune the 2-3 shift by MPH, not RPM).
Thanks for the input.
02-28-2012, 08:23 AM
#15
I just ordered the 7.35" pushrods.
Not sure about the converter slip, I will add it into my log PID selection for the track. If the pushrods come in by Saturday (and hopefully my MAF harness too) I will be going back to the track Sunday.
Changes to try so far:
shorter pushrods
more tire pressure
85mm MAF
double check 2-3 shift rpm is correct
re-route air ducting to pull air from under the bumper vs engine bay
Not sure about the converter slip, I will add it into my log PID selection for the track. If the pushrods come in by Saturday (and hopefully my MAF harness too) I will be going back to the track Sunday.
Changes to try so far:
shorter pushrods
more tire pressure
85mm MAF
double check 2-3 shift rpm is correct
re-route air ducting to pull air from under the bumper vs engine bay
02-28-2012, 04:24 PM
#16
Check out the converter slip calculator, all you need to know is finish line mph, rpm and your rear gear ratio + tire size. http://www.tciauto.com/tc/racing-calculators/
03-05-2012, 02:04 PM
#17
Went back to the track and ran 11.92@111mph with a 1.69 60ft. 7.52@91.8mph in the 1/8th. I did trap 112 mph on a different run.
According to that and the best data I can get from my runs it looks like 12-14% slip. [3.42 gear, 28" tire, 1:1 gear ratio, 5200rpm (as seen on tach) and slip showed 111mph so I added 1-2mph since the track uses an average]
I must have measured pushrod length wrong, car ran and sounded horrid with the 7.35" so I put the 7.4" back in. It takes a little bit over 1 3/4 turns from zero lash to 22 ft/lbs.
I couldn't get the rubber/filter to install the 85mm MAF.
According to that and the best data I can get from my runs it looks like 12-14% slip. [3.42 gear, 28" tire, 1:1 gear ratio, 5200rpm (as seen on tach) and slip showed 111mph so I added 1-2mph since the track uses an average]
I must have measured pushrod length wrong, car ran and sounded horrid with the 7.35" so I put the 7.4" back in. It takes a little bit over 1 3/4 turns from zero lash to 22 ft/lbs.
I couldn't get the rubber/filter to install the 85mm MAF.
Last edited by thunderstruck507; 03-05-2012 at 02:50 PM.
03-05-2012, 02:57 PM
#18
I think you could benefit from getting the converter tightened up a bit. Shovel's are not much of an aerodynamic car so they won't have the same 1/8th to 1/4 mph as a fbody.
On checking your pushrod length:
Roll your cam over until you're on the base circle.
Hand tighten your rocker arm until all play is removed and contact is just made with push rod.
Now count the number of turns it takes to fully tighten the rocker.
Threads are 1.25mm pitch or .049". Take the number of turns and multiply by .049".
This will be the amount of preload on your current length push rods.
1 3/4 turns would be .085" preload.
On checking your pushrod length:
Roll your cam over until you're on the base circle.
Hand tighten your rocker arm until all play is removed and contact is just made with push rod.
Now count the number of turns it takes to fully tighten the rocker.
Threads are 1.25mm pitch or .049". Take the number of turns and multiply by .049".
This will be the amount of preload on your current length push rods.
1 3/4 turns would be .085" preload.
03-05-2012, 03:08 PM
#19
Thanks!
Is there a sure fire way to be sure all the slip is in the converter and not in the trans clutches? It doesn't have that many miles on it since the upgrade rebuild but you never know. Everything feels solid and it even feels like it pulls good on the highway up to 130mph.
Guess I will focus on getting the new MAF on and iron out the tune 100%. Thinking of richening it up just a tad to see if it might like another degree of timing more than the more aggressive a/f ratio.
BTW DA at the track at the time of my best was 1340ft.
Is there a sure fire way to be sure all the slip is in the converter and not in the trans clutches? It doesn't have that many miles on it since the upgrade rebuild but you never know. Everything feels solid and it even feels like it pulls good on the highway up to 130mph.
Guess I will focus on getting the new MAF on and iron out the tune 100%. Thinking of richening it up just a tad to see if it might like another degree of timing more than the more aggressive a/f ratio.
BTW DA at the track at the time of my best was 1340ft.
03-05-2012, 03:25 PM
#20
The ET/MPH ratio is the nature of the beast for a 1971 car with big 28" tires. Any HP gains you can find will show up in both MPH and ET, so the ratio will likely end up the same.
FYI, I lost 3 MPH when I changed from 26's to 28's (totally different car, but still drag racing).
Al
FYI, I lost 3 MPH when I changed from 26's to 28's (totally different car, but still drag racing).
Al