: increasing top speed?



cadillacdeville
03-26-06, 12:38 AM
I've heard that the top speed of a 77-79 cadillac 425 is around 112 MPH now I'm getting ready to swap out my 425 with a 69 472 which its speedo gose to 120 I'm just wondering if by doing this swap will I increase my top speed?

Night Wolf
03-26-06, 01:27 AM
My '79 reached 112mph according to my GPS, it was up a slight incline, the worst part was the severly bald and off-balance tires... stuff was shaking pretty bad....

There are no speed limiters on the cars, so the limiting factor is what it should be - engine power. Aerodynamics surely don't help at all.

The 472 will definitly have more power, and thus more speed.... if you hop up the 472 before you swap it in, she'll go faster... Keep in mind though, its a big block pushing a barn door..... it's going to take alot of power to move a box at speeds much higher then the 120-130 region. I personally have no desire to go that fast anyway.... atleast in a box Caddy :).

davesdeville
03-26-06, 03:52 AM
Yeah, provided you have the gearing (which you do if you have 2.28s) so you're not RPM limited, more power will increase top speed.

I've done some mildly in-depth top speed calculations... I figure 500hp in my 75 (when I airbag it, lowered about 4") would get it to do just over 150 (assuming a coefficent of drag around .57 - which is the Cd of a Hummer H2; I have no real idea what the Cd of a 75 Deville would be.)

sizanjdf
03-26-06, 06:55 PM
What is the fastest most of you have had your cars??? Ive had my 74 limo w/ 472 at a cruising speed of 107 without a problem. I thought I was actually doing around 90-95, but a buddy of mine on his motorcycle following me was like WTF... I was doing 120 plus and was barely catching up. he said I was at 107 not 95 like i thought

Night Wolf
03-26-06, 07:42 PM
all my cars stop around 110

The '79 ran out of power around 112

the '89 Oldmsobile also ran out of power at 113.... never did hit the speed limiter on that car...

the '93 Coupe hits the speed limiter at 112mph.

N0DIH
03-27-06, 12:53 AM
Do the speedo's go past 100?

Reason I ask is my 80 Turbo T/A shows 80 with a few ticks past it, but actually hits a hard stop (the trip odometer reset shaft) and stops @ 84 mph. So you could be going much faster, but the speedo won't be reading it all.


all my cars stop around 110

The '79 ran out of power around 112

the '89 Oldmsobile also ran out of power at 113.... never did hit the speed limiter on that car...

the '93 Coupe hits the speed limiter at 112mph.

Fleet
03-27-06, 03:01 AM
The listed top speed for a 1978 Coupe de Ville, as tested by Car & Driver, was 108 mph. 0-60 mph was 10.6 seconds.

davesdeville
03-27-06, 05:31 AM
I had my 78 Fleetwood around 115 (calculated using a stopwatch and mile markers.) The 75 didn't mind doing 100+ for 60 miles, dunno what the actual top speed was since that little peg was in the way. And of course about 153 in the ETC...

Night Wolf
03-27-06, 06:49 AM
Do the speedo's go past 100?

Reason I ask is my 80 Turbo T/A shows 80 with a few ticks past it, but actually hits a hard stop (the trip odometer reset shaft) and stops @ 84 mph. So you could be going much faster, but the speedo won't be reading it all.

Speedo only goes to 85....

but all 3 of those speeds are GPS verified... that was one of the first things I did when I got the Garmin GPS :).

N0DIH
03-27-06, 04:40 PM
Ahh, ok. I have a 160 mph speedo and 8000 rpm tach in there now out of a 1973 455 T/A....

I have had it up to 135 and still pulling.... I didn't have a front sway bar then, so I wasn't too fond of doing that....

ShadowLvr400
04-04-06, 12:44 PM
My Fleetwood's been just over 120. I want to figure out the vibration in the driveline first before I try faster.

N0DIH
04-04-06, 01:06 PM
Just had my PW up to 132 yesterday, running E85 too... Sweet......

I don't think the little ricer Acura that wanted to go fast liked the idea that a 5000# barge was chasing him and accelerating on him.....

Car did well at those speeds, was comfortable at them, was surprised it was stable as it was.