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?

 

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.

 

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?

 

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.

 

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 *** 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.

 

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

 

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.