Drag Racing Tech - Why won't it run hard on the backside?

Getting things ready to go back to the track but want to find everything I can to try for better times. My car just doesn't seem to want to run on the back half like I think it should.

Best 1/8: 7.52@91.5mph but has ran some 92mph passes, this I'm happy with
Best 1/4: 11.92@111.03 mph with best MPH of 111.81


I've since swapped from a 28" tall 325/50r15 to a 25.5" 275/50r15 to better suite my 3.42 rear gear. Car feels better on the street and spins a little more on the street. I also added a 85mm MAF to replace the stock one.

Car weighs approx 3750# with me in it

98 ls1
799 heads (shaved .010", rocker boss removed, worked around the intake valve boss, fully sanded intake/exhaust ports)
EPS 230/238 113+2 (eps/lsl lobes)
Fast 90mm with wedges removed from runners, 90mm tb
K&N cone filter with 3" outlet
GM 85mm maf
1 3/4" longtubes, 3" duals (collectors do neck to 2.25" for 2", will be fixing this soon)
4l60e with Yank SS3600, no signs of slip or anything abnormal
12 bolt 3.42 gears

Tune: 12.6 a/f (tried between 12.4-13.0 with no gains), 26* timing, shifts at 6400rpm (tried higher up to 6650rpm with no gain), I need to confirm no vacuum at WOT



Is there anything else at all I can do or check? Is it really asking too much for closer to 115mph?

Since no one else has answered yet, I'm gonna say picking up 20 out the back with your combo is about right. Trying to get in the 25 mph range is gonna need some gas or FI with your engine combo and weight.

Seems pretty normal sounding to me with your mod list.

At 3750, you won't see the mph you're looking for with the power you are likely making..... Get so
E weight out of it, and I bet you start seeing the car pick up a bunch

It takes alot of power to make a 3700 lb car do it on the back half. The power/converter/gear might not be perfect either. I bet the shorter tire will be faster as long as it hooks. Get some gear back in it.

What did it 60'?

I think you should do more on the backed as well my car seems really close to yours. My 60ft is worse than you but I did 7.76@91.2 and 12.02@115.6 with a 1500 something density altitude

When the Formy had the stock engine in it with LS1 intake and LT Headers at 3650 lbs it ran 7.50 and 11.94 with a mid 1.50 something 60 foot. The MPH was about the same as what you posted except I had 3.70 gears and a 26 inch tire. It looks like to me the car is doing correctly. I do believe the smaller tire will help ET but MPH may go down!

I did not see where you posted your 60 foot times what are they?

Good luck on your next outing!

N2

Whats a formy?

Looks about right to me...

I was 11.8X @ 114-115 with 7.5X @ 91-92 660's

Just to compare....

33-3400# approx. w/ driver.

That 28" tire was just too tall for your engine power and gearing. The 26" will work way better but lose a little mph...

Whats a formy?

Cutie name for Formula.:nod:

Thats in the norm

My car is very similar to yours, so I went through my old tickets to find one that was similar in ET. The slowest ticket I could find was from the first trip to the track. Here it is:

1.671 60'
4.802 330'
7.445 1/8 Mile
92.42 MPH 1/8 Mile MPH
9.774 1000'
11.76 1/4 Mile
113.36 1/4 Mile MPH

I was picking up 21 MPH on the back end then. I would imagine my aerodynamic drag coefficient is even worse than yours.

My car:
3725#
6 liter 10.9:1
Ported LS6 heads
2800 converter TH200-4R trans
3.90 gear
28" tire

At the time I ran those numbers, my cam was 222/224 on 112 LSA with 110 ICL and a dual plane carb intake.

Now I have a 226/234 on 110 LSA cam and a single plane carb intake. The last trip to the 1/8th, the car went 7.25 @ 96.5 MPH.

Whats a formy?

This is the Formy or at least that is what the wife calls it when I am not spending money on it! :nod:

With my 325rwhp lt1 setup, I was doing low 7.50's@ 91-91.5mph ran out the back to a low 11.8x@115.5-115.8 on a 1.67-1.69 60' 1200 DA, 3500lb race weight.

I was running a 275/50 m/t drag radial, and a 3.73 in the 10bolt, th350 and an edge Racing 3400rpm converter.

Seems to me like you're 3.42 and 28's were putting you in a bad spot in your power curve past the 1/8th mile mark,
The tire change should help your overall gearing out, and help you in the big end IMO.

I really think your intake setup is killing you. You should make a track only 4" ram air setup that goes to the head light area? The GTO guys and even the RX7 swap guys that run a 90" degree bend CAI usually pick up 15-30 rwhp going to an over the radiator setup, or similar.

Thanks for all the responses guys. I guess I'm not as far off as I thought.

My 60ft are in the 1.69-1.74 range when it hooks well.

I spent some time over the weekend cutting out the exhaust neck down right behind the collector. It was a 3" slip on made to exit to 2.25" pipe crammed into my 3" exhaust, but the exhaust was at a downward angle so the 2.25" was almost against the 3" inside created a wall where the exhaust could only take a sharp turn down between the gap. (Think of it like sliding a pipe into another bigger pipe at a 45* angle but pushed in past where the smaller pipe slips in.)

The car is noticeably more responsive and smooth during normal driving, WOT there isn't a seat of the pants change but I bet it picked up at least 5hp from this. The exhaust note is more open sounding and the high load low rpm gurgle it had is gone, just sounds smooth and clean.



I will keep toying with ideas for an intake pipe setup without 90* but it won't be easy. It would need a 90* to even get to the headlight area but maybe I could do it with 2 45* spaced apart.

I did talk to a 6.0 nova who went to the 1.8th mile track with me last time. His car is a 6.0 with carb/intake, MSD box, TSP 233/239 cam, 1 3/4" headers to 3" exhaust, TH350 with 3500 converter, 3.73 gears, 26" tire and likely weighs around 3400 or less with him in it. He ran a 7.4@93mph to my 7.6@91mph in the humidity. His car dynoed 380rwhp on a land and sea dyno. He was out launching me but it seemed like I was just barely pulling on the top end. Stupid 1/8th mile tracks haha...

Also to mention when comparing the car to a Fbody, it has the aerodynamic capabilities of a Brick, so those things are working against you, add more power, take away weight, and/or converter fine tuning.

A friend has a 4" inlet cone which is about 3" longer than mine and a 4" to 4" elbow. I ordered some 1/4" reducers to make them fit my MAF. Going to try it out versus my current 3" setup.

I know with the car running at idle (especially cold) there is a very loud hissing sound of air coming from the filter.

I've had one recent experience that may be of interest to you. I tried backing my cam timing up from 108.5 ICL to 110 ICL and the car slowed down a whopping 2+ tenths and 2.5 MPH in the quarter mile. So, I am going to try 107 ICL next. I will let you know how the car reacts. My smaller cam (226/234) is on a 110 LSA though and I have a short runner intake which is also a consideration.

Just did a couple wot pulls for logs.

MAP kpa key on engine off was 97kpa, at WOT it drops to 94kpa at 4k RPM. By the 6350rwhp shift point it was 91kpa.

I think this means I might be able to find a couple HP by going to a 4" intake tract over the current 3" OD pipe and 3" outlet filter. Might need to do a run with no filter in front of the MAF, hopefully its not the 85mm MAF that is the restriction.

The 90* elbow is your restriction...maf will be fine. I'm still using a stock 78mm maf on my car. Been 124.x in the 1/4 - I'd have to dig out a log but I think I'm in the 96 kpa range @ 6600 going through the traps.

The 90* elbow is your restriction...maf will be fine. I'm still using a stock 78mm maf on my car. Been 124.x in the 1/4 - I'd have to dig out a log but I think I'm in the 96 kpa range @ 6600 going through the traps.

That's great news.

I guess I don't fully understand fluid dynamics. Hard to wrap my head around a pipe with 3.5" ID but a 90* smooth bend flowing less than a 3" ID MAF full of stuff in the flow path. Gotta learn some time I suppose.

IF you can I would just SD the car, take the MAF out totally, try putting a filter right off the TB and see what that gets you. May solve all the issues really quick/easy.

^ you heard the man. SD that sucker.

I should be doing that with mine, I just dont have the software or $$ to make that happen but definitly will make your world better, you have no emissions or inspection requirements like I do.

This was the first car I've tuned, so it could surely be possible since I do have EFI live and a wideband...but I am thinking it means there is less room for error in the tune.

I do not know entirely what all is involved in a SD tune but I am not opposed to looking into it. Not like I couldn't switch back just by saving my old tune file and the hard parts.

That's what I would do, look into it.. get a filter that will just bolt on the Tb, and see if you can get it running right. If you can, and can get it right you'll be better off IMO.

Leaves the option of not running anything other then the filter.

It's definately not your maf, I fed a 441ci motor and went mid 9's N/A with an 85mm maf.
Your car is heavy and turning that big-ass converter while pulling all 3700+lbs isn't helping u.
Have you considered a smaller diameter converter? U'd lose the lock up feature but that will give you the biggest improvement I feel.
It would let the motor scream up to where it wants to be rpm-wise and then you'll see something.

Really not wanting to lose the lock up or do anything to slaughter the drivability of the car. Might do some 3.73 gears in the future.

I see where you are coming from but without the fuel economy and being pleasant to drive around town and on the highway while still running half decent at the track it would kind of defeat the purpose of the ls1/efi swap.

I would consider having the converter rebuilt as a 4k when it goes in to be freshened up.

Any new track time or tests?

I Had had a new best MPH on Saturday. 118 with 95.5 in the 1/8th. It seems my car picks up 22.5 mph on the back half typically now. On the nitrous it picks up a little over 25.

I just went over the weekend, last time they will be open for the year and the car is finally in a better spot!

Trapped a best of 115 mph and consistent 114 mph all day.

Changes:

upped timing to 27.5*
5 gallons of 94 octane mixed with 14 gallons Shell 91 (had 3/4 tank by the time I was at the track) to insure no burst knock was possible at all
12.7:1 AFR with the tune on pure 91, didn't read what the 94 did to it if anything
upped the shifts/rev limit, shifts at 6750rpm
1100-1400ft DA, slight tailwind
installed smaller orifice PCV valve and an oil catch can to reduce oil in intake
cool air so IAT were reading 68-74* which I think helped a lot


Car ran new best everything but 60ft (crappy track prep):

1.7155 60ft (rolling into throttle a bit) (previous best 1.68)
7.50@93.05 mph 1/8th
11.7916@113.95 mph 1/4

That pass the car kissed the rev limit on the 1-2 so an adjustment of rev limit there should help some more. I honestly think the car just wants to rev further than I am, but I can't advance the cam without pulling the engine so I'm stuck with it for now. Overall I'm pleased. I bet if I shifted it at 6850 or higher it would pick up more. I finally found graphs of similar cams and they seem to peak at 6500-6600 but carry flat to 6800-6900 before falling off slowly.

Looks good. All those little things add up. It is really looking good in the 1/8th.

Post up a few timeslips.

http://img.photobucket.com/albums/v477/thunderstruck507/20121121111636_00001.jpg

the scanner at work doesn't like to scan the yellow ones for some reason

On the first timeslip, you picked up 21.5 on the back half. That is better than before right? Weren't you at 20 on the back half before?

Also, do you have a switch to manually turn off your cooling fan? I pick up about a 1/2 MPH if I do that.

I have a dual Ford Windstar fan system: 1 fan set up on an auto on setup but it has stopped working so I was just running the bigger fan which is on a switch. Didn't try turning it off. I'll keep it in mind next time.

Also, do you have a switch to manually turn off your cooling fan? I pick up about a 1/2 MPH if I do that.

Really?

Really?

Yep. Give it is a shot.

I will have to try that. I used to run both of them during a pass. I figured the cooler air under the hood would offset the pull on the alternator.

Fwiw it's not uncommon to see guys turn off every unneeded electrical load possible, makes the alt have a lower load, which decreases drag, and without an alt it keeps the ign. Voltage higher for the run as well... I know people that will even shut the water pump and fans off as they stage the car, and flip them back on after going thru the traps. I don't suggest it but its a more common practice then you'd think.

Sorry Im late to the party on the MAF stuff. As a basically self made beginning tuner (like you), who used mine and close buddies as guinea pigs while learning to tune, I can tell you do NOT be afraid of a SD tune. Now, I'm not saying that you'll gain anything but what I am saying is don't be afraid to give it a try. My (and others) drive-ability is exactly like stock. Throttle response and smooth running are all there. You wouldn't know its a SD tune by riding in it. If you need any help setting it up let me know.

Well, I got some good news and bad news over the weekend when I weighed the car.

With a basically full tank (within 1-2 gallons) and an empty trunk with my drag wheels out back it came in at 3500lbs even on a CAT certified truck scale.

This puts my race weight at about 3600-3620 since I usually leave the tank fairly full to be certain I don't encounter fuel starvation late in the day. So good news is the car is lighter than I thought by around 120+ lbs. The bad news is that makes me not be able to help wondering if the car should be making a little more power that I haven't been able to find.

Any thoughts?

Well, I got some good news and bad news over the weekend when I weighed the car.

With a basically full tank (within 1-2 gallons) and an empty trunk with my drag wheels out back it came in at 3500lbs even on a CAT certified truck scale.

This puts my race weight at about 3600-3620 since I usually leave the tank fairly full to be certain I don't encounter fuel starvation late in the day. So good news is the car is lighter than I thought by around 120+ lbs. The bad news is that makes me not be able to help wondering if the car should be making a little more power that I haven't been able to find.

Any thoughts?

Damn you are light! I should have you drive my car.

My guesses:

1. Tune is off
2. Driveline loss - slipping trans or convertor
3. Engine - maybe do a compression/leakdown test.

something doesn't add up.

I don't think his MPH is that far off. He is going 93 in the 1/8th. His 60' should be better though. I would think that Yank 3600 should produce some low 1.6s. But his rear suspension is all jacked up and that is not helping his drag coefficient on the big end either.

93 in the 1/8 is good - it's the 20mph on the back half......it's just not pulling like it should. He should be seeing 22-23mph in the back half with his mods.

It's like his car takes off slow - goes like hell - then falls off. Imo the slip doesn't add up.

I weigh 135-140lbs, but I was trying to account for the fuel too. I usually fill up and then drive to the track.

The car has gone a best 60ft of 1.68 just barely slipping out of the hole. At another track my best were all 1.72-1.74 dead hooking...almost felt like it was bogging a little. Both of those were on a 325/50 MT.

The car definitely runs hard in the 1/8th, I'm happy with it there. Could it just be too little gear or converter? I went from a 325/50 (28") to a 275/50 (25.5") with no changes.

Speedtigger's car seems to do fine with the smaller converter and he even has a less steep first gear with the 200r4, but he also has the 3.90 rear gear which helps.



As far as the tune, I really don't know what else I could do. It's based off a base tune and I fine tuned the VE, PE, and MAF tables from there. It won't take any more timing down low or it gets KR. I'm up to 27.5* up top so I doubt there is much left there either. A/F is set to high 12s.

The trans has no signs of slipping at WOT, it was built with all the components a sponsor would use in a stage 2 build (good clutches, band, bunch of trans go parts like the "no yo yo kit", etc) and the fluid and filter were recently changed again. I have actually changed the fluid at least partially 4 times since it was built a couple years ago just to keep it fresh and clean.

I don't know how I would check the converter, but nothing feels strange. The converter was built for a ls1 GTO so I'm not sure if Yank builds those to order and factors in things like the weight of the vehicle and such. It's pretty tight but around 35-40% throttle will quickly hit 3500rpm on my tach.

I have not done a compression check since the new heads and cam went on. With stock heads and a 230/224 cam they were all between 190-205.

Back then the car ran consistent 89-90mph traps in the 1/8th and 109-110mph in the 1/4. It dynoed 370rwhp with a partial tune before the drive shaft/trans grenaded. Fixed the trans (added 3.5" chromoly drive shaft) and went back on a different day and it dynoed 350rwhp but ran .2 faster in the 1/8th after the tune was finished.

The heavy driveshaft, 12 bolt, and aero of the car are all hindering factors but I'm just not sure they should eat up that much. I do appreciate the help guys. I can try to do a compression check soon if I find a gauge.

http://www.tciauto.com/tc/racing-calculators

use the converter slip calculator to see where you are at.

I don't think you have a compression problem or anything serious at all. If you did, the car would not run as strong as it does in the 1/8th.

It might be worth it to call Yank and tell them your 60' and MPH concerns and just see what they think about it.

http://www.tciauto.com/tc/racing-calculators

use the converter slip calculator to see where you are at.

I have intended to do that before and forgot. I think EFI live is actually capable of calculating that for me even if I log the correct data, so I will try to do a log WOT tonight if I can and see if I can get that calculation or at least log the data needed to input into the calculator you posted.


Based on several 1/8th to 1/4 calculators, my ET match dead on.

Don't get me wrong - I'm not knocking you. Just trying to give you different things to look at. I'm all about squeezing every last ounce out of every combo.

Similar combos in fbodys would easily run 116-118mph - do you think there is 3/5mph of aerodynamic loss at this level? I don't - but I could be wrong.

Have you logged voltage on a run?

Don't get me wrong - I'm not knocking you. Just trying to give you different things to look at. I'm all about squeezing every last ounce out of every combo.

Similar combos in fbodys would easily run 116-118mph - do you think there is 3/5mph of aerodynamic loss at this level? I don't - but I could be wrong.

Have you logged voltage on a run?

I am not taking any offense what so ever. That is exactly what I am doing: trying to squeeze every last safe reliable bit of power for max et/trap gain on this combo. I am out of mods to throw at it aside from high dollar cylinder heads and there aren't really good places to lose much weight without destroying it as a street car.

I don't know how much aero loss there is for sure...I know you can watch the rain shoot almost directly up off the headlight areas so it's not good but I agree with you I find it hard to believe it's eating up more than a couple mph at my level...on a higher mph car I'm sure it gets much worse quickly. The engine might very well just be making all it's going to make. I'm just trying to be sure of that.

I will see if any of my logs have voltage and if not I will get that too.

My observation of similar combos is 2 to 3 MPH difference between our bricks and F-bodys for mid-eleven second cars in the 1/4.

In looking at Thunder's last time slips, I really don't think there is a problem with his MPH. If you put his best MPH together with a his best ET, you have a car running 11.70s at nearly 115. That is good MPH for his aerodynamics. Get him some good D/A and a nice clean pass and he is 11.50s or 60s at 116. I think his car is making the numbers it should. I just think the car owes him some low 1.6 60' times.

http://img.photobucket.com/albums/v477/thunderstruck507/20121121111636_00001.jpg

You might very well be right. I could be chasing a white dragon on the backside when I should just be more worried about why the car can't go at least 1.65 60ft, especially considering the lower weight than I thought I was working with.

You might very well be right. I could be chasing a white dragon on the backside when I should just be more worried about why the car can't go at least 1.65 60ft, especially considering the lower weight than I thought I was working with.

I know I have said this before, but get some correct offset back rims to get the wheels under the car and ass down. That will fix your suspension geometry. Make sure you have at least a 1" rear sway bar or an anti-roll bar and firm shocks.

When I run the nitrous, my car needs an anti-roll bar or an air bag, but on the motor it works great as it is.

Just for comparison, this was a slip for an ls1 camaro with heads and cam, 6 speed car in the left lane. He was running BFG drag radials.

http://images1.snapfish.com/232323232%7Ffp438%3Enu%3D3254%3E2%3C6%3E%3B%3B7%3E WSNRCG%3D323336995%3B44%3Anu0mrj

This was my slip on the same day with just a lid, loudmouth catback, SS3800 converter and nitto 555rs in the right lane.

http://images1.snapfish.com/232323232%7Ffp438%3Enu%3D3254%3E2%3C6%3E%3B%3B7%3E WSNRCG%3D3233369962%3B2%3Anu0mrj

I know I have said this before, but get some correct offset back rims to get the wheels under the car and ass down. That will fix your suspension geometry. Make sure you have at least a 1" rear sway bar or an anti-roll bar and firm shocks.

When I run the nitrous, my car needs an anti-roll bar or an air bag, but on the motor it works great as it is.

I run KYB Gas-A-Just shocks which are pretty firm compared to stock type stuff, springs are Hotchkis and are decently heavier rate than stock SS f41 suspension springs. Stock SS rear sway bar which I believe is 1" diameter.

I know what you mean about the suspension work, but if it's dead hooking and not running any quicker in the 60ft and I do have my pinion angle correct...shouldn't the issue be elsewhere? (not that the suspension wouldn't be wise, but would it really help anything if the car is hooking?)

I run KYB Gas-A-Just shocks which are pretty firm compared to stock type stuff, springs are Hotchkis and are decently heavier rate than stock SS f41 suspension springs. Stock SS rear sway bar which I believe is 1" diameter.

I know what you mean about the suspension work, but if it's dead hooking and not running any quicker in the 60ft and I do have my pinion angle correct...shouldn't the issue be elsewhere? (not that the suspension wouldn't be wise, but would it really help anything if the car is hooking?)

I was under the impression traction was hit or miss based on another thread you had. But with that said, there is a small amount of time that can be picked up in the suspension even if the car is hooking. It is to do with efficiency and chassis load. But, I only know it is possible. I don't has all the answers. The super stock guys do though and maybe a good chassis shop.

The traction problem seems to be related more to prep on test n tune day than anything, although I'm sure if the suspension was set up better it would be less hit or miss.

But I have run the car at a different 1/8th mile strip which had prep so good I didn't even need a burnout and it was sticking like glue. I tried several launch rpm methods there while the gettin was good and they all resulted in the same ~1.74 60ft that day.

Man. I don't get it. My Circle 2b is only about 2800 to 3000 stall yet I have had 60' times as low as 1.64. I would have to think you should be able to best my 60' times. Your intake has much better low end torque characteristics than my Victor Jr. My cam is a bit smaller and has more advance though. That helps me a bit.

with a 325 on the back, in an A-body with your power you should be able to hook on dirt. You need to work on your suspension get those shitty KYBs off there and get the ass down some.
Also i think your converter is the culprit here, I have witnessed a number of yank SS converters under perform, I had a SS3400 and it was complete garbage much like this, picked up 3mph changing it
Also for reference, this is my timeslip, stock 346, heads cam, 4.10s 295/65 M/t stock trans and a PTC 3800 1.8STR.
3400# 1 3/4 headers, 3" full exhaust and LS1 intake, stock throttle body
http://i214.photobucket.com/albums/cc192/Grrh77/CAM00205.jpg