weight % front to rear

I have a blowen 540 bbc in a 2000 lbs altered, and i was just wondering what the weight percentage should be front to back. We started the year with the blowen combo, (injected last year) and it was pickin the front so hard it wasn't drivable. We added 40 lbs to the front, lowered the wheelie bar and pulled some motor out of it. That worked great for 1 weekend on a division prepped track. Now all I do is spin or shake at the hit. Any way we are making a rear end change for next year and want to see if we can get rid of the 40 lbs. More weight = harder on parts and slower. Just lookin to see what other people run. Thanks. Chuck.

 

What wheelbase?

 

couple very important questions to start with:
1- clutch? glide? lenco-drive? bruno? if applicable what converter?
2-how are you leaving? 2-step? pneumatic throttle controller? flat foot/swapping feet?
3-how far out is the motor?
4-how tall is the tire?
5-first gear ratio/number of gears?
6-rear gear with the injected combo? rear gear with blown combo?
7-and wheelbase like mentioned above

probably a step in the right direction

not necessarily true when you are talking weight on the front end of an altered... the old adage 'lighter is faster' is all relative with an altered. they have a 'sweet spot' if you will. and it revolves around the balance between front-to-rear/leave style/gear/engine set-back

 

Sorry, left out some important info. It's 125 wb. glide w/4000 stall converter (10.5 in). leaving on trans brake with a 2 step. tried everything from 3000 to 4000. Had 4.30 gear w/ injected motor, now 4.10. Broke my last 8 3/4 chrylser and going to a MW full floater as we speak. Planning on 4.10 in it also. Tranny was in car, but beleive 1.80 low, but not sure. We had 33 in tire but with the rear end change will be going to a 34.5. I havn't even started tuning on the motor. It is really safe right now. Has run several 7.30 with a peddal or 2 at the hit to get it moving. I know that there is a bunch of changes, but tryn to get it close for first outing. not sure of engine placement. will check tonight and post. Thanks

 

The back motor plate is 63 inches from rear end centerline. Any help would be great. As I said, I'm changing the rear end and can move some weight around, if needed, at the same time. Thanks Chuck.

 

just gonna throw my suggestions out there as if i you brought me in to consult and i was trying to get you a-to-b for an early outing with the new combo

disclaimer: this is the internet and racing combined (help us baby jesus)... if you ask 20 guys for their opinion you are gonna get about 45 answers... proceed with caution

63 out from the rear is gonna make the car a bit more aggressive so it'll probably like a bit more weight on the nose than some others and as the power goes up... usually so does the nose weight required

as for gear ratio i'd err on the side of a higher gear versus a lower gear... it's been my experience that in a blown altered usually 'less is more'. so i'd suggest a 3.89/3.90 in the rear end especially with a 1.80 first gear glide deal and a converter that multiplies all that blown torque

i would definitely agree with going to a 34.5 vs the 33 tire to help knock the gear down a bit more

as for your converter... is that the 'advertised' stall speed? if it stalled at 4000 with your injected motor i would almost guarantee you it is NOT the stall speed that happens with your blown combo

on a blown/converter combo i would also strongly suggest you add a pneumatic throttle controller with an adjustment valve to control blade opening speed as the transbrake is released... in my mind... this becomes your 'clutch'

also where is your fuel cell?? up front?? how many gallons??

so here is the set up i would take to the track:

-34.5 tires 6.5# (just a starting point)
-3.90 gear
-mild tune up
-rev motor at the stage to just a couple hundred rpm below where the converter starts to tug the motor back
-if you have a throttle controller use a fairly mild blade opening speed (really hard to describe in a chat forum)
-wheelie bar height is all relative to length/cross-bracing/flexibility/attachment point/etc... i have a 6-1/2' wheelie bar attached to the rear-end and i set mine on level ground using about a 2-1/2" block under the wheel
-assuming your cell is up front i'd fill it FULL (ballast)
-add as much weight to the front end as you can... if you can put 100# on it... do it

then i'd go shoot the thing down the track*... and change one thing at a time. that being the weight. i'd drop 20# off the nose at time and keep making runs

*don't fight it! if the thing doesn't run clean to 60 or 100ft... shut it off. bring it back make adjustments and try again

hope that makes some sense to you... i'm just going off of things that have worked on my blown altered combos. i've had a blown alky chevy/converter/glide combo, a blown 90% nitro chevy/converter/glide combo and i'm currently working with/driving a blown hemi/converter/lencodrive combo

your original question was about weight percentage front-to-back... and i wouldn't worry about a specific number and/or comparing it to someone else's set up

feel free to ask any follow up questions or tell me i'm crazy lol

 

Love the disclaimer. and I agree completly.

Converter was changed for the blower motor. 4000 is close to the acual stall, but motor is still really soft. I cant run the pneumatic throttle because im trying to make legal for 7.0 Pro heritage stuff.

fuel cell is getting changed to 8 gallon. It is up front at the front wheel center line.

Thanks for the imput. and ya you probabally are crazy, isn't that the fun in driving an altered!!!!

 

Hey Will, I'm currently running a 7al-2 box with HVC coil with crank trigger. So I don't have any timing retards on it. I run Top Dragster, Super Pro (at local tracks) but want to be legal for 7.0 Pro at the heritage stuff. I could run a retard in everything but the 7.0 Pro. I don't think it is legal there. I have a MSD 12 sitting on the shelf, just lookin for the cash for the front drive stuff.

I do like the idea of leaving fatter. I do have a high speed now (no pump loop), but it doesn't come in untill 80 lbs fuel pressure. But,could I put another bypass in that came in earlier and run a fatter stage-launch to get the car moving?

The tune up has lots left in it. We have the timing at 32 and a really fat fuel system. Thats whats pissin me off. I want to get the car workin, so I can see what it really has......or what going to break.....
Thanks for the imput. Chuck

 

with the automatic as some have already said and i have run that combo and back then there wasnt any way to knock timing out and the car nasty leaving wheels up i never knew witch way it was going to go i went to a 4.10 gear it was like nite and day difference but it was set on kill every pass knowing what i know now that is not always mean it will be the fastest way with the automatic several thing will make i drivable and fast timing retard controller then you can ramp it back once it gets going or slow the blower down a little taller gear timing retard is what most are doing good luck

 

Reviving this thread and getting back to the original topic...I weighed the Nitro Madness car (Altered) this weekend...and here are the results with 180 Lb driver - includes fuel, oil & wheelie bar just as it would stage:
Front = 1053 (46.68%)
Rear = 1203 (53.32%)
Total = 2256

The engine is 65" out.....

Seems a little heavy to me so I'm gonna work on a weight reduction program (for the car) over the winter....
We have 35 lbs. in the front weight bar that can probably be reduced substantially or completely (added a 14-71 Kobelco SM this year = +25 lbs over a standard 14-71?)....

Maybe swap for a Ti or Aluminum 6.3 Lenco Drive Bell Housing....and move a few other small items to redistribute the weight...

I know that every car weight is part of the tuning...so there is no absolute rule.....but does 55% rear and 45% front seem like a number to shoot for? The Funny Cars are probably a little different.....what are some percentage numbers that have worked well with Altereds?

 

Thanks for the input. My altered was 58% rear and 42% front before adding the 40 lbs in the nose. I think thats too agressive for an PG car. Im with you on shooting for a 55 - 45 split, then have some movable weight for different track conditions. My car was 2020 lbs with the 40 in the nose and me in it after the pass. I can't lose much anywhere with out spending big bucks, but I think that I can move some stuff around to get a better %.