Drag Racing Tech - 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.

http://img.photobucket.com/albums/v477/thunderstruck507/Chevelle/20120220141723_00001.jpg

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

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

why so low on air pressure?

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'm guessing the headwind had something to do with it.

Lower ETs win races not MPH

True but I was expecting better gains in ET too.

Looks good to me. Don't forget you're hauling 3700#'s.

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.

You got the cool factor on us tho'. Nice ride

Only questionable from what I read is the lifter preload and if it's hanging valves at high rpm. I'm guessing shift points are at 6600 rpm ?

Only questionable from what I read is the lifter preload and if it's hanging valves at high rpm. I'm guessing shift points are at 6600 rpm ?

Yeah I need to go buy a torque wrench so I can measure and order shorter pushrods.

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.

Just measured and it looks like I'm running ~.125 preload cold (let the engine run just 30-40 seconds to make sure the lifters weren't leaked down).

I think I'm going to try to back that down with some 7.375" pushrods.

Any idea on what % of converter slip you have? Seems to run hard to the 1/8th and fall off. I'd step down to some 7.35" pushrods.

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

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/

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.

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.

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.

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

Holy crap. I figured they would cut some but I guess less than a tenth and a mph.

I was already planning on going back to a 26" tire anyway. I just got a killer deal on these since I got both for $200 with only 3 passes on them.

I didnt lose much ET at all, it was mostly just MPH from the gearing change.

Al

May not be he whole thing but....

15x10 Torque Thrust IIs325/50r15 MT ET street radials (aired to 12.5# but this lap was a hot lap, likely at 13.5# at time of pass)

Drag radials when aired to a comparible PSI to a Bias PLy slick should put down a faster MPH but being that you have a heavier rim, and the PSI is LOW those are contributing factors. If you can't launch with a higher PSI, then you may need to do some work on suspension so that the tires can hold more and thus have a better MPH on the back half. Heavier rims running off the axles effect HP and hence MPH so put something lighter on there, you will see a difference.

Being that its a 4L60e car you should not need that low of PSI in the tire and the converter seems a little tight and given the race weight 3.73 to a 4.10 would really turn up the wick on the N/A runs. Just depends on how much you want to get into it.

Last to mention, Areodynamics and Drag co-effiecent. Your not a 4th Gen Firebird or a lighter C5, your pushing air and thats going to effect the back half mph too.

Was about to ask why you're running 28's with 3.42's, can't beat $200 for new tires though. You should come run at ozark raceway park with us some time, several guys from here run there.

I was running lower pressure based on MT website recommendations. I went back to the track Sunday and ran 17# and the car was more consistent on the burnout and launch. Didn't seem to affect MPH but it did let me get 3 decent 60fts.

1.69
1.70
1.71

Then the track got messy from all the street cars and I never got another clean pass.

It also looked like the pcm was short shifting the 2-3 at 6200-6300. I forgot to compensate the tune for the 28" tires since I run 26" on the street. I need to work out a track tune and a street tune to account for the difference.

Consistancy is important, but further upping the pressure to the point where 60 foot is negativly effected is a good plan to see HOW MUCH you can run before it detracts from the results.

If the car likes low 20's and puts up 1-2 MPH due to the harder tire and cuts the same 60 foot, there is room to work here.

Shift RPM affects my MPH more than my ET. That cam should like being shifted around 6600-6800 RPM.

Did you degree that cam when you installed it? 111 degree centerline on your combo seems late to me. I bet it would run better at 109 ICL.

The cam was designed by Geoff for my combo and he said it would peak before my desired 6500rpm shift point but carry on to 6800rpm if I wanted to. I had set the pcm to shift higher by RPM, but it acts like the tire size threw off the MPH and the pcm was shifting off of that for the 2-3 instead.

The cam was installed dot to dot, I can't remove my oil pan with the engine in the car and wouldn't be able to remove the oil pump pickup without doing that. Since there was no way the engine was coming out during the cam/head swap I didn't see the point dropping money on the tools I would have needed and the adjustable timing set to properly degree the cam since I couldn't have changed it anyway.

In fact I had a huge "oh shit" moment when I dropped a cam gear bolt and it bounced into the small passenger corner of the pan and rolled along the pickup tube into the pan. 1 in a million shot. I had to spend 10 minutes with a magnet to drag it over the the driver side and then use a magnet on a flexible rod to fish it out between the block and the pan lip.

Do you plan to run your car NA and never plan on using nitros? Then If you went from the (YANK)SS3600 to a (YANK)PT4000 like I'm running you wouldn't see as much rpm drop between gears. That would help out your trap speed alot.

I've toyed with the thought of a 50-75 shot but no immediate plans to buy or install a kit.

At the track I can't go 11.5 or they will ban me until I get a roll bar (not happening). So if I did it would be a small shot at the track and maybe a larger one if something else were going down from a roll.

Just an update.

I got the 85mm MAF installed (removed stock screen and put one of the Saxon PC screens with larger mesh in), also installed a much larger air filter with a built in velocity stack. Car shows a 2-3 kPa vacuum at peak WOT which if I understand correctly is pretty fair for no ram air.

Retuned the car WOT for the maf changes, 12.6 air/fuel. Also added a degree and half of timing and pulled a degree from where the car hits on a WOT stab so it doesn't get KR on a launch.

Raised shift rpm to 6700rpm, saw a new best peak MAF reading of 49.7 lbs/min on a log run so the car seems to like the extra revs.

Went to a 275/50r15 ET street on a 15x8.5" aluminum slot wheel

new trans fluid and filter



These changes didn't seem to make any difference in the heat, car was running low 12s at 109-110mph in mid 2000 da. I tried to go back the other night now that it was cool (~1700 da) but I unknowingly got bad gas so I was down to 105mph and went home to find out what was wrong. (didn't have my laptop to see that it was pulling over 10* timing)

I am going to try to make it back to the track in the next week or two. Looking for some other budget ideas worth trying.

Keep at it, it'll get better.

I hope so, I'm running out of ideas and I don't get much in the way of ls1 cars to compare to at our track so I'm left looking on here and I seem to be way out in left field compared to where I think the car should be for the mods.

I can't imagine it being anything too serious since the car has been running and getting the snot beat out of it for years, I would expect a major problem to have caused serious damage by now.

We might be having a local forum dyno day soon on a Land and Sea dyno (which I gather is more like a Mustang and less like a Dynojet) so I could get a graph for the new heads/cam and see if anything looks funny.

It's just hard to believe 100-200lbs and possibly the aero of the car cut .4-.5 and 4-5mph from what a comparable fbody would run. Maybe I should do some research on GTOs, they seem like they would be more comparable for weight and body shape...

Here is a GTO with very similar mods but I have a Fast intake and mildly ported 799 heads on him but he is a manual. I would really hope the intake and head work would about even out the trans difference. His 1/8th is about the same but similar to an fbody the 1/4 is in the 115mph range:

"Nice and cool tonight. 800-1000' DA.

Spare/jack/skid plate removed.
EPS 230/238 .600/.615 112+2
Vararam, ported TB, stock IM.
Full catless exhaust with PS longtubes.
Monster 3 and McLeod short throw.
Nitto 555R's"

http://www.ls1gto.com/forums/attachment.php?attachmentid=155983&d=1348117374

Late model GTO or early model conversion?

Late model, I know it's still not a perfect example.

Here's to hoping I get a clean pass before winter hits...maybe the higher shift points and timing will help a tad. I can also do another tune that is leaner up top (12.8-13.0) and see if it responds better but I've read when you often end up getting e10 fuel the engines can make better power at closer to 12.4 so I compromised on 12.6 since I doubt there is more than a few HP difference between that range.

Mine runs best right at 13:1 area. I am going to the track tonight to test the results of several changes. But, we run year round down here.

When are you going back out?

Probably in November when the track stops running Friday night and starts doing Sunday afternoon.

Too hard to get off work Friday, drive 2+ hours in traffic, race until midnight, then drive 2hours home. Our temps here just started getting nice and cool, might be able to get some 300-800 DA if I'm lucky.

Thinking of richening it up just a tad to see if it might like another degree of timing.

While you are experimenting at the track, try going the other way. Last night when I was at the track I picked up MPH by pulling some timing and leaning it out.

I leaned it out one jet size which netted about .25 on an AFR point and picked up MPH. I also pulled 1 degree and picked up MPH. Earlier in the night I tried more timing at 29 and lost MPH.

Between the two, I picked up 1 full MPH and those were really small adjustments.

Yeah, I am going to play with it a little more next time I go. I found I didn't have to richen it to get it to take more timing, just had to go to the cells that were getting hit from a wot punch or downshift and pulled 1.5* out of them so it didn't get KR on the hit.

I'm going to try leaning it out to closer to 13:1 and go a few degrees each way to see what it likes. Right now it's at 27.5*, up from the previous 26*.

updates?? i', running 12.0 n/a and trapping 113 on my full weight t/a, would like to know what works for you o.p

12.0 at 113 is just right. The MPH may even be a touch on the high side for an automatic.

Back in the day, I remember running a 12.09@112.47 on a manual trans turbo Talon.

Al

I would say you have a great mph considering the weight of your car. I have a 4th gen fbody that has ran 12.11 @110 I have a cam only (torquerv2) 232/234 .595 .598 112 with a yank 4000 and 4.10's. I also run a 275/50/15 mt drag radial. Hope this helps with your comparison.