'14 GT Automatic - drag racing results from a few simple mods

[psfracer]

Bob doesn't have 630rwhp if he is only running 119mph. Something is terribly wrong.

As far as gearing, you could run some steeper gears if you were N/A and running a tall tire, but if I had the 5.0 with a power adder and an auto, I would just stick with the stock rear gearing due to the 4.17 first gear.

A friend of mine had a KB on a 5.0, running high 9s, went from 3.15s to 3.73s, no difference at all. But, that was with a power adder and over 750+rwhp, with a 28 tall tire.

 

[Five Oh Brian]

Bob's Procharged '12 GT AT put down 630 rwhp on two different dyno's here locally. Car was trapping 124 mph at that time. It's down to 118-119 trap speeds now and the DA hasn't really changed, so something else is going on. Boost leak? Spark blowout? I'm not sure and I'm trying to sort out my own car.

Just got my bent 1-pc driveshaft out of my car and the factory 2-pc is back in now. I installed a BMR rear tunnel brace and d/s loop to keep NHRA compliant tonight now that I'm back to the 2-pc d/s. PITA to install in my driveway on jackstands! I should have done it on a lift. I'll be hitting our local tracks this week to see how much the 2-pc d/s slows me down vs the 1-pc. Then I'll decide what to do about the bent 1-pc.

 

[TimMcc]

Sucks about the driveshaft! Interested to see et/mph difference with the stocker.

 

[psfracer]

oh crap, how did you know it was bent? Vibration I assume? Who's driveshaft was it? was it 3.5 diameter or 4.0 diameter?

 

[Five Oh Brian]

oh crap, how did you know it was bent? Vibration I assume? Who's driveshaft was it? was it 3.5 diameter or 4.0 diameter?

It was a Shaftmaster 3.5" that went in the car last summer. Vibration started a couple months ago - could feel it at 65+ mph. I had our shop investigate and found it bent near the back end of it. I've never run over anything to actually hit it, so I'm really baffled as to how it bent. I've made about 100 passes down the 1/4 mile with it, but it was supposed to be able to handle nearly 4000 lb ft of torque. I have not contacted Shaftmaster yet, but am curious to see what they say.

 

[Five Oh Brian]

Sucks about the driveshaft! Interested to see et/mph difference with the stocker.

So many people say it's about a tenth or two tenths in ET. I'm really hoping it's not that much. I had the 1-pc installed at the same time as my Circle-D converter and my ET's dropped 6 tenths, so I didn't isolate the improvement of the 1-pc at that time. I guess I can isolate its effect now.

 

[cbracoupe]

GREAT post! Really dig the averages and mod build up!

 

[Five Oh Brian]

GREAT post! Really dig the averages and mod build up!

Thank you. I always love sharing info with others on what works and what doesn't. This site has been very helpful in guiding me to pick the correct mods for my goals.

 

[Five Oh Brian]

Made it out racing Friday finally to see the effects of going back to the stock 2-piece driveshaft vs the 1-piece. However, it was 90-93 degrees, humid, and a 2200' DA versus the typical sea level to 300' DA we normally have. And, I ran a full tank of gas instead of the 1/4 to 1/2 tank that I normally race with, so between the 2-pc, DA, and extra weight, I was figuring on 12.20's to 12.30's at around 111-112 mph.

I made four passes: 12.12, 12.15, 12.18, and 12.20. Each was 115+ mph trap speeds, which was surprisingly faster than I expected. Using the dragtimes.com DA calculator, these runs would have been in the 11.80's at 117+ at sea level DA's, so I don't think the 2-piece driveshaft is slowing me down much, if anything at all.

Just need to make some passes on a nice cool day with DA's near sea level to really compare. I dislike drag racing in the middle of summer when it's so dang hot!

 

[MachRan]

I really thought the lighter driveshaft would be worth a tenth or two.

 

[Five Oh Brian]

I really thought the lighter driveshaft would be worth a tenth or two.

Me too, which I why I spent a lot of money to buy one. Now I'm questioning whether that money was wisely spent or not.

 

[JEWC_Motorsports]

Brian id say yes. I dont have a converter but I do have a dss driveshaft that I just installed. The car def feels better and imo revs faster.

 

[Mystickeith50]

It's worth more than a tenth....it's worth the cost inflicted when the stock one breaks in half and leaves you stranded or with ripped off exhaust lol.

 

[Five Oh Brian]

It's worth more than a tenth....it's worth the cost inflicted when the stock one breaks in half and leaves you stranded or with ripped off exhaust lol.

I made a few hundred passes down the 1/4 mile on sticky tires in my supercharged '07 GT and '11 Brembo GT with the stock 2-pc d/s's with no failures. For me, the 1-pc went in my '14 GT solely because I was chasing 1-2 tenths improvement in the 1/4 mile. The extra strength is just frosting on the cake.

I've heard people say 1-pc d/s's are worth 1 or 2 tenths, while others have said no gains. I'll reserve my final judgment for a day at the track with the same DA that I ran my 11.78 and 11.80's.

 

[Five Oh Brian]

So, a little update on the effects of switching back to the factory 2-pc driveshaft. With the 1-pc, car went a best of 11.78 with a bunch of 11.8's. With the 2-pc back in - and no other changes - I've only been able to make one race day so far. The weather was horrible - 95 degrees, crazy high humidity, and DA well over 2000'. Timeslips were in the 12.10's @ 115+ all day in bad weather. Corrected for DA, those times would have been 11.80's all day, just like it ran with the 1-pc driveshaft.

I'll be racing again this Friday and the weather should be more reasonable (75 degrees with DA under 1000' most likely).

 

[rcm90]

The weather was horrible - 95 degrees, crazy high humidity, and DA well over 2000'.

I wish that was bad air up here!

 

[vinylinterior89]

I really like how you broke down each mod and the results! Thanks for that info. How do you like daily driving with that converter? Is there any neg effects from it like lower mpgs or anything? Also how is the odor from the O/R x pipe?

 

[Five Oh Brian]

I really like how you broke down each mod and the results! Thanks for that info. How do you like daily driving with that converter? Is there any neg effects from it like lower mpgs or anything? Also how is the odor from the O/R x pipe?

I love the converter - makes driving the car so much funner every day! Fuel economy dropped a couple miles per gallon, but worth it to me.

No weird odor from the off road pipe. It's no different than driving a car from the 1960's before catalytic converters were required.

 

[Unreal]

I'm going out Friday after 1 piece shaft and swapping from 3.73 to 3.31s. Best before was 12.2@115. Hoping for 12.0-12.1s before I do the convertor and suspension.

 

[Grabber Blue 5.0]

I'm going out Friday after 1 piece shaft and swapping from 3.73 to 3.31s. Best before was 12.2@115. Hoping for 12.0-12.1s before I do the convertor and suspension.

What size tire do you run?