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MG MGB GT V8 Factory Originals Technical - Springs Revisited

Alright, thanks for your help so far gentlemen. I have decided to use the idea of starting with 12" springs and clipping them down to the right height. I know that the 305 v8 weighs around 550 lbs, so my question is; What rate springs should i be buying to support the weight, and also provide comfort without too much bounce? In the contest beetween comfort vs. performance, i want to err a bit on the side of comfort, as the car is not being driven for competition or anything like that. Any input would be greatly appreciated. Alan.
Alan Raddatz

Also, if the above questions cannot be answered, what is the spring rate of an original cb spring? What is the id and od? Thanks
Alan Raddatz

Alan,

Have you considered Hoyle NG/Hawk Front suspension as adjustable. As designed for kit cars with various engines up front may be suitable.

Details are on Doug Jacksons site mgbmga.
Also try mgb-stuff for spring rates.

I use about 550 springs with 4.6Rover V8 which gives a firm road ride.

Paul
Paul

Alan,

The spring rates for the chrome bumper BGT's were:
4 cyl: F:100 lbs/inch, R: 105 lbs/in
8 cyl: F:102 lbs/inch, R: 115 lbs/in
Published in Autocar, 16/Aug/ 1973 quoting factory figures according to the text.

Sorry cannot help with coil dimensions.

Cheers, Pete, Queensland, Australia.
Peter Thomas

Alright, thanks for the responses so far. My question now is, since the 305 weighs approximately 200 lbs more than the rover v8, does that mean i should get 750 lb springs for a comparable ride to Paul's car? I'm sure that i'm wrong about this assumption, so im hoping that one of the experts will set me straight. Thanks again. Alan.
Alan Raddatz

You're making assumptions and we would be compounding it if we make recommendations.

You really need to have the before and after weight distribution front to rear before making intelligent changes. Not all of the 200 lbs (presumable an assumption) will be on the front axle. Since there are two springs there, each carries a proportionate amount - depending also on anti-sway bar rate for front and rear, etc.

Is the ride the way you want with the nose of the car too low, or what?

Lots to consider here.

Wayne
Wayne Pearson

Yous assumption would be true enough if your car was a Morgan three wheeler. Each spring doesn't have to be beefed up to support the additional 200 pounds and the rear springs are also sharing some of the burden. Notice that in the Autocar specs cited the V8 had heavier springs than the four, even though it was lighter. Of the top of my head, anything over about 625 would be too much for a street car.
George B.

The ride with the nose too low is not how i want it, it bounces around a lot. I know that shocks would help that, but im not looking at that option for now. But, irregardless, the front end does have too much travel for sure. Also, the rear suspension is still quite stiff and has not sagged, so i need not worry about that.
Also, im running with a 4 speed auto, which i believe is not as long as a manual 5 speed would be, so i believe that most of the weight is sitting on the front springs.
Would i be able to use 550-600 rate springs, but just use longer ones than with a rover? Thanks once more
Alan.
Alan Raddatz

Moss (uk) Had a list of uprated and lowered front and rear sprigs in their special tuning catalogue, it can be downloaded from their site mossint.co.uk. I used uprated lowered springs on my conversion, with their uprated shocks the ride is just right, not too hard, not too soft.

Mike
Michael barnfather

You cant't have too much spring travel unless you are constantly hitting the rebound rubbers. Bounce is controlled by the shocks, not the springs. Maybe you need more compliant springs in the rear, as lowering the rear will raise the front by an almost equal amount.
George B.

Lowering the rear is not an option, as i only have a few inches of exhaust clearance as it is. As for the bounce, it is quite substantial. If i decided on 550 or 600 rate springs, would a 12" 550 rate spring clipped down to 10" or any length for that matter still be a 550 rate, or does it depend on the length.
Alan Raddatz

It would be logical to use springs the same length as the original springs if you are changing the rate. Longer than stock springs would likely cause spring bind. Shortening the springs by itself increases the overall spring rate.
George B.

Alright, so that opens the door for 2 more question. What length are the original springs, and what spring rate should i be using? if 550 works for a rover, i doubt the same spring would be any good for the 305
Alan Raddatz

Just remember, improbable as it may sound, that when you cut a coil spring, the spring rate increases, it does not stay the same. If you are planning to cut a spring, start with a lesser rate than your final goal, so when cut, you will be somewhere in the ball park. Sorry, I cannot provide a formula for predicting the rate change. I do know that when I cut 1 coil from a set of rubber springs, the ride was noticably stiffer, although not to the point of being unpleasant.
Jim Stuart

Alan,
I am not sure what stage the conversion is so this may not be possible yet.

What I would do is get the 305 installed and have the car 4 corner weighed to determine the exact weight on each wheel.Ant decent race car preparation place can do this for you at nominal cost.

With this as your starting point you can then determine spring rates, travel, shock rates, sprung to unsprung mass ratios and so on.

The installation need only to be enough to determine the on the road weight so the engine need to be in the final position, g'box in place, radiator in place and so on.
Solid bar can replace the springs and shocks for the weighing.

Good luck, Pete
Peter Thomas

The car is done, save for the springs. I have driven it off and on for the last month, but cant really take it on anything but nice roads so far, partly because of springs, and also because it doesnt have an overdrive transmition yet. Does anyone know how long the original chrome bumper springs are? It would save me a large amount of hastle if you could let me know. Thanks
Alan Raddatz

Look at http://www.mgb-stuff.org.uk and click on 'Spanners' and 'Ride Height' for spring specs, including free and loaded heights of fronts.
Paul Hunt

Alan

I use 8inch 600lb springs on front which gives 13.5 inches between centre of wheel and chrome strip, with uprated levers.

Paul
Paul

This thread was discussed between 05/06/2002 and 09/06/2002

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