The figure I have seen used a lot is about 1 tenth quicker for every 100 pounds dropped in weight. Is there some general figure that works the same for MPH. eg, In my old car I was running 13.4s @ 104mph & in my new car it will have the same engine , converter , Turbo 400 instead of 350 & 3.73s instead of 3.55s & will weigh between 900 - 1000 pounds less. So is there something that says every 100 pounds you drop you gain a certain amount of MPH.

It's not a linear progression. Losing 100# from a 1000# car will have a more significant effect than losing 100# from a 4000# car. If you look at it like that, each increment of weight you lose is more important than the last increment.

Id say at least a second, what body style is the new car? aerodynamics come into play too. Most Chevelles like a Parisienne have the aerodynamics of a brick.

i don't know the rule but i do know that i had my 496 in a 3750 pound 66 olds 442 and it ran 6.50's in the 8th.i bought my vega thinking if i put the motor in it it would run 5.50's since it only way's 2680.....well i have not go to the 5.50's on motor yet.the best it's ran is 5.77 at 120. so i droped over 1000 pounds but did not lose 1 tenth per 100 pounds....but i do have a diff tran's and gear....went from a 400 to a powerglide and from 4.56 to 4.86

The new car is a 68 Firebird running my 406 exactly the same as it came out of my Parisienne. The Parisienne was running a 3000 stall , Turbo 350 & 3.55 open centre 12 bolt & street tyres when it run the times it did. I am hoping that the Firebird will run into the low 12's somewhere between 110 - 115mph with the lower weight , 3.73's , slicks & more aerodynamic body style. It will be a few months off yet before it is finished though. Do you guys think this is possible.

He is wondering about MPH, not E.T.

The new car is a 68 Firebird running my 406 exactly the same as it came out of my Parisienne. The Parisienne was running a 3000 stall , Turbo 350 & 3.55 open centre 12 bolt & street tyres when it run the times it did. I am hoping that the Firebird will run into the low 12's somewhere between 110 - 115mph with the lower weight , 3.73's , slicks & more aerodynamic body style. It will be a few months off yet before it is finished though. Do you guys think this is possible. The transmission will hurt you. A 400 Turbo is .11 slower than a 350 Turbo and unless you gut the Firebird it is only going to be about 3100-3200 lbs. What is the weight of the car you now run? A posi track rear end is worth a couple of tenths and a Firebird bites pretty good with Cal Tracs on other traction bars installed. You need way more gear than 3.73's. Something along the lines of 4.33 or 4.56 would make a lot of difference. Mid twelves at about 107-109 MPH would be more like it. Find out what the exact weight of your present car is and get back to us so we can make an accurate prediction.

i don't know the rule but i do know that i had my 496 in a 3750 pound 66 olds 442 and it ran 6.50's in the 8th.i bought my vega thinking if i put the motor in it it would run 5.50's since it only way's 2680.....well i have not go to the 5.50's on motor yet.the best it's ran is 5.77 at 120. so i droped over 1000 pounds but did not lose 1 tenth per 100 pounds....but i do have a diff tran's and gear....went from a 400 to a powerglide and from 4.56 to 4.86 Not meaning to hijack this thread but what did you do with the 442? You can P.M. me if you like.

I don't think you'll pick up 10 MPH going from a A body to an F body

The weight of my old car was a little over 4400 pounds. This is going to be a very streetable car so I will not be putting any more diff gearing in it than 3.73.

In your performance range, going from 4400# to 3400#, everything else remaining the same, you should pick up 9-10 mph.

I agree with Roger, in a 11-12 second car in the 3000-4000 range, 100 lbs could be .1 and 1 mph.

This is what the combination was that I had in my Parisienne & the times that it ran. I have also put down the changes I have made for the new car , what do you guys reckon it will run & what sort of power do you think the motor is making ?

1967 Parisienne ( 4400 pounds )
406 standard stroke crank with 5.7" rods
TRW flat tops total 9.85:1 comp
Dart Sportsman 2's with 2.02 & 1.6 valves & some port work
Solid cam 495 lift at valve , 110 lobe separation , 238 @ 50 , 268 advertised , intake opens @ 28 & closes @ 60 , exhaust opens @ 68 & closes @ 20.
Performer RPM intake with 1" open spacer
830 double pumper Holley
1.75" 4 into 1 extractors / headers into a 3" collector into a 2.5" x pipe into 2.5" straight through mufflers
2200 converter
Turbo 350 with a hard shift
3.55 open centre 12 bolt
Koni street shocks all round ( set hard )
275 / 60 / 15 BF Goodrich street tyres
2.069 60 foot
5.706 330 foot
8.669 660 foot @ 82.64mph
1000 foot 11.239s
13.409s @ 103.98mph

New car is a 68 Firebird ( not sure on the weight yet , should be lighter than standard as it will now have a small block but I am thinking around the 3200 - 3300 pound mark )
Engine is exactly the same as before
Has a 3000 stall in it
Turbo 400 instead of the 350
Will have a pair of 2.5" Hooker Aero Chambers on it
3.73 Posi Lock
Will also have a set of Koni street shocks
Running a 26" x 8" slick

Once I have run the car in a few months I will get back onto this post to let you all know how it went.

This is what the combination was that I had in my Parisienne & the times that it ran. I have also put down the changes I have made for the new car , what do you guys reckon it will run & what sort of power do you think the motor is making ?

1967 Parisienne ( 4400 pounds )
406 standard stroke crank with 5.7" rods
TRW flat tops total 9.85:1 comp
Dart Sportsman 2's with 2.02 & 1.6 valves & some port work
Solid cam 495 lift at valve , 110 lobe separation , 238 @ 50 , 268 advertised , intake opens @ 28 & closes @ 60 , exhaust opens @ 68 & closes @ 20.
Performer RPM intake with 1" open spacer
830 double pumper Holley
1.75" 4 into 1 extractors / headers into a 3" collector into a 2.5" x pipe into 2.5" straight through mufflers
2200 converter
Turbo 350 with a hard shift
3.55 open centre 12 bolt
Koni street shocks all round ( set hard )
275 / 60 / 15 BF Goodrich street tyres
2.069 60 foot
5.706 330 foot
8.669 660 foot @ 82.64mph
1000 foot 11.239s
13.409s @ 103.98mph

New car is a 68 Firebird ( not sure on the weight yet , should be lighter than standard as it will now have a small block but I am thinking around the 3200 - 3300 pound mark )
Engine is exactly the same as before
Has a 3000 stall in it
Turbo 400 instead of the 350
Will have a pair of 2.5" Hooker Aero Chambers on it
3.73 Posi Lock
Will also have a set of Koni street shocks
Running a 26" x 8" slick

Once I have run the car in a few months I will get back onto this post to let you all know how it went. Is the big car like a '67 Impala? Just wondering how it got so heavy with such a light engine, sounds kinda screwy if it was an "A" body, like a Chevelle or GTO.

It is like an Impala. It is the car in my Username picture on the left. 4 door pillarless tank. 1965 Kgs with a full tank of fuel with no driver.

I say you will pick up 8 - 10 mph, and shave more than 1 sec off your et, likely to a 12.0 - 12.2 as long as you can make it hook. A higher stall would drop you into the 11's.