G'day..couple of questions:

I've ran my car again last weekend to get a time before the NOS kit goes on next week. I got a best time of 14.40 at 96 mph.

I run 2.73 10 bolt posi rear end and get very little wheel spin, but shift into 3rd gear only 2 secs before the finish line...I thought the car had a 3.42 diff and checked this coz my 60 mph revs were very low,but someone has changed it at some stage.

Q 1) will changing to a 3.42 improve my ET?
Q 2) or Would I be better getting my converter uprated to a 2200 rpm stall rather than changing the diff ratio, bearing in mind the NOS getting installed.

 

1. Yes
2. Yes

I would say if money permits do both.

 

i think the gears would be a good thing to change first, 2.73's are great highway gears but seem to be hurting you in the 1/4 mile.

what kinda 60 foots do you run?

 

Get gears and a converter and you should have no problem getting into the 13's.

 

Thanx for replies,

Mdformula350: With stock cam it ran pretty consistant 2.05 @ 60. Once I changed the cam, last week it ran 2.18's on 4 runs probably due to the cam profile?

Thing is, since puttin the world heads and XE cam in it has alot more seat of the pants grunt, yet my times prior to heads/cam/afpr were only .25 slower.

Me thinks you guys are right!

 

Why do you have World products heads on there when you live in New Zealand? You could probably pick up a set of Pro Toplines for alot cheaper considering they're made there.

 

Probably because they're crack prone, and he wanted a better head.

 

I shift to third at 58mph.



Get the 3.42's!

 

I shift into third at around 96 mph. What does that have to do with it?

If you're getting into high gear at or around the 1/8 mile then you should be crossing the finish line at or around the red line in high gear. The best gearing/tire size should have you hitting the red line just before the finish line. Since that's the end of the race, there's no need to go faster since a drag race is an accelleration contest not a top speed contest.

When I used to have a 383 with 3.27 gears I was shifting at 6700 rpm and crossing the finish line around 5500 rpm. The car really started to pull around the 1000 foot mark. Cars that ran a similar ET to me got off the line quicker but I ran them down at the end with big mph. Better gearing for that old combination would have been 3.90.

Since most street cars are not going to change tires or gears to go to the track you need to decide what's going to work best. When designed properly you should first install the tallest tires you can into the wheel wells. Stock tires are only 26" tall. 28" will fit and give a bigger contact patch on the ground from front to rear. After you decide on the tires, calculate what gears will work best with the. 26" tires and 3.73 gears will work out to be similar to 28" tires and 4.10 gears for total rpm range. The difference is that the 28" tires won't slip as much and the 4.10 gears will increase to torque multiplication factor to the wheels to get you off the line quicker.

 

Yeah if you aren't worried about sacrificing some highway gas mileage (and you wouldn;t be sacrificing much), you should get a set of 3.23's or 3.42s... those would make the desireable difference in off the line acceleration you're looking for. They'll also allow you to see third way earlier, therefore they'll elminate that upshift that is interrupting your acceleration right before the traps

 

it has to do with the fact that he's running 14's and you're running.....what.....10's? with an altogether different transmission. i cant think of too many 14 second cars that ARENT going to benefit from swapping from 2.77 to 3.42. you said it yourself he's wanting to cross the finish in high gear at peak power. he's not doing that by just having shifted into third.

 

Word. I think before you do anything you should go back to the track and hold 2nd gear across the traps... you know - just to see what you're sacrificing with the upshift.

 

Lads..thanx heaps for all the replies!!! Friggin awesome...

No can do to holding in 2nd and crossing the line..I'm redlining and need to change.

Stephen: You're right, its got to do with RPM and thats what I'm referring to re my very short time in top gear..a rear gear change is the order of the day, I'll do that before I do the stall.

Cruz'n: Pro topline heads would have been ok and flow better than the world heads I have, problemo was that they don't do a 58cc head off the shelf which the 305 needs...next motor if I do one with have them on, I'm a KIWI so I gotta support the local manufacturer!!!

But I think what I should do FIRST off is stick the NOS on and see how that effects things, I'm thinkin that I'll get into 3rd gear alot earlier with a 100 shot goin in. See then what RPM I'm goin over the line at in 3rd and choosing my diff ration based on that level of acceleration.... what yu reckon?

 

For sure. I'm supporting them. Just a long wait for the boat to arrive.

And as for prone to cracking, thats a new one to me. Can anyone confirm this or is it a pile of

 

yes nos will make u shift into 3rd alot sooner.u might get closer to redline in 3rd gear depending how much of a shot.u might break your drivetrain if u use too much nos ,giving u a better reason to switch the rearend.

 

Stop encouraging me!!!