Background: My car has a Vigilante 3600 converter, 4.30 gears and 29” slicks. Earlier this year I was getting 1.51 60fts, although, I’ve had some 1.50s and 1.48s in the past. In typical air at our local track my car was running 11.10s at 120 MPH. Recently my 60fts have been in the high 1.50s (1.57s-1.59s) and also somewhat inconsistent. So, I decided it is time to make some changes and adjustments to my car to improve the weight transfer on the launch in hopes of getting consistent 1.50, 60ft times.

With all the weight reduction, the back of the car appeared to be too high (2 ½”+ gap, slick to wheel well). So the first change was to replace the rear springs and reduce rear the static ride-height by about 1 ½”. I also changed the pinion angle from 3 to 2 degrees.

Next was to lighten the front end with a new tube K-Member and A-Arms (-60 to 70 pounds). Also, the front QA1 coil-overs were reset to “0” and adjusted down ½” on the front ride-height.

Here are the track results following the changes, which are somewhat puzzling. The DA at the track was around 4000 and most car's 60ft times were off about .05 to .07 and ¼ mile ETs 2 tenths slow (at a minimum), along with a few MPH slow at the trap.

With all the changes my 60ft times were unimproved at 1.57s, but very consistent now. Everyone said the weight-transfer looked good with the car (lifting the left front about 9”). My ¼ mile ETs were 11.35s, typical for the air conditions (2 tenths slow due to air).

Now here’s the kicker. All my trap MPHs are now over 123+ MPH, with the last run at 124+! “WOW!” Also, in bad air and everyone else was way down on MPH due to the air.

So, where did all that trap MPH come from? Did reducing the ride-height by 1 ½” add 3 to 4 MPH?

WD

 

i was going to take a stab at it but its over my head. Sorry bud, best of luck.

 

Re-check your pinion angle, first. It may have been somewhat "bound" and your "new angle" is freeing this up.

Did you get your convertor restalled for the new race weight? It doesn't sound like it.

If you re-did your front shock settings maybe the car is recovering better after the launch and the front is "porposing" less and scrubbing less forward momentum?

I'm curious, what rear springs did you swap to?

 

The pinion angle was checked with a high-tech digital instrument. So, I'm sure the pinion angle was correct previously (-3 degrees) and currently at -2. I don't think 1 degree could make that much difference.

The car weight without driver is now down to 3240 and I don't think the converter would be a major issue. It seems to be working well flashing it off the line.

I've had two different sets of rear springs in the car the past two weeks. The ones in the car now are Eibach Drag Packs that have been cut-down and reworked by a spring shop locally. I goal was to reduce the rear ride-height by 1-1/2".

WD

 

Maybe the car being lower, not getting air under it so it helping a little.

1 degree could free up quite a bit but I would guess maybe .5 mph or so.

The wt. sure helps alot too. for better MPH.

Where does your converter flash?

Its odd the 60' didn't improve, is it possible you think its lifting too much?

Mine was pulling up hard, but when I got it just barely pulling them the 60' picked up 2 tenths

 

One of my friends watched me leave every round and said it looked good. Only lifting about 9 inches at the most and that it looked very controlled (according to him). Also, I didn’t feel a hard bounce as it came down.

The recent weight reduction was only the K-member and A-Arms (maybe 70 pounds at most off the front).

Again, with my changes I was expecting better 60fts along with an ET improvement. The huge trap MPH increase is a really big surprise. It can't be a fluke either; I had three 123+ MPH in a row and then one 124. And other racers were below their typical trap MPH with the air conditions.

WD

 

The trap speed could be an effect of lowering the the ride height. The height of the long nose while going thru the traps can sometimes trip the sensor rather than the tire.
We had a couple of years at or local track where one lane showed about 3 mph faster than the other with the 60' and et being the same. Figured that it had to be that the sensor 60' from the end was tripping on the tire like it's supposed and the final sensor was tripping on the body to showing that the car covered that 60' faster and that's how mph is calculated.

 

The easiest and least high tech way to measure pinion angle, angle finder on face of cylinder head write that number down, angle finder on rear cover write that number down and subtract the 2 numbers. I know you know this but others may want to know. I still can see a full mph from this especially if the driveshaft is a touch too long and you didn't realize it.

70-100 lbs can change things up quite a bit with a tight convertor like you have don't under estimate loosing this weight. I can see you not picking up much sixty foot because the convertor is not working as hard if that make sense. Maybe try another technique for leaving. I can also see the mph increasing some because the convertor will be more efficient in getting the slippage taken care of quicker.

I just noticed you said on your first post you said your cars 60' were getting inconsistant, I would pull it out and have it re-done especially since you bracket race. You could have a sprag going bad or bent fins or ???? I'd be willing to bet that this is your issue.

What does "reworking" mean when you had them cut them down? How does this spring rate compare to your last pair? I wouldn't discount this as part of the reason why your cars sixty foot didn't pick up. The last time I tested rear springs they all had the same ride height, however they definately didn't produce the same 60'

 

Unless his car rode with the height of an old gasser or there is an extreme dip in the track the beams are higher at the end of a track than at the 60' clocks, IHRA/NHRA made this adjustment x years ago. His ET would increase to correct???

 

Yes, the down-track photo-electric cell beams and center-track reflector cones are at 6 inches above the track surface. Therefore, the beams often trip on the car body down-track, rather than the tires. Additionally, 4th Gen F-Bodies often have an issue with the front air-dam (spoiler) tripping the down-track timing beams “intermittently” due to the like-of cross-sectional area. However, my car has a fix installed to prevent that anomaly from occurring and ensure my times are consistent.

Check-out this photo and the black-tab in the center of my air-dam (I've thought of everything). Also, I couldn’t find anything in the NHRA rulebook that said the tab was illegal. Additionally, I had the same trap MPH in both lanes, so that indicates there wasn’t a glitch with the timing beams and cones (a track-lane issue).

WD

 

My Vig 3600 is only a few months old and has a minimal number of runs on it. From all indications it appears to be working well and flashing to its rated stall. While my 60ft times were not great this past weekend, they were very consistent. And, most people at the track also had slow 60fts.

In two weeks I'll be racing at another track (which has just been resurfaced by Penhall) and that will give me a good compairson to the times at the local track(60fts, ET and MPH).

I also plan to adjust the front QA1s down another 1/2 inch and see if that adds even more MPH.

WD

 

If they become inconsistant at this new track then I'd say you have a convertor issue. Age of a convertor has nothing to do with its state of health, we've broken convertors in a weekend after installed.

Your car should be a solid consistant low 1.5 to high 1.4 sixty footer no matter what the air/track/whatever. I wouldn't settle for anything less even if it comes with a few mph.

Put a metric or a turbo 350 and a good convertor behind that beast, you'll be a low 10 second player for sure.

 

I have a question if you don't mind. Have your rpms at the finish line changed at all?

 

No, I can't see any real change in trap RPM (6580 RPM). And, it always has been completely "maxed-out" on RPM at the stripe w/ the 4.30 gears.

WD

 

Never mind then. I new I was shooting blanks as usual, and you confirmed it. Good luck and hope you figure it out.