Cobra Weight Distribution....

JimP · #1 (**permalink**) 10-04-2002, 05:22 AM

I'm looking into all my engine options. Wondering what the weight distribution is with a Small (Iron) block Ford (305/351). I'm wondering if putting an Aluminum block engine would make the handling better or would it be too light? I thought I had read somwhere that with the IRON block the weight distribution was 50/50 front to rear, but I can't find that information anywhere. So would adding an aluminum block make the front too light? Is anyone using an LS1/LS6 engine in their Cobra? That is consideribly lighter than a stock 305/351 Iron block.

Thanks,

Jim

Ron61 · #2 (**permalink**) 10-04-2002, 06:31 AM

Jim,

I have an iron block 351 in mine and I have my weight at 51/49. The weight can be adjusted by using the coilovers and also when you put the motor in by setting it a little back or forward. I used scalesand set my coilovers for this because I like just a little more weight up front to plant the front end when going into a corner. Some of the BB guys here are setting theirs at 50/50 but they don't drive them hard into corners.

Ron61
Ron Widener

dscott · #3 (**permalink**) 10-04-2002, 07:17 AM

Jim, The car was originally designed around the 302. It gave a 50/50. With the 351 it does come in at 51/49. I agree with Ron on how the weight is for cornering.
Don

JimP · #4 (**permalink**) 10-04-2002, 07:59 AM

Now I'm confused... I understand moving the engine more to the front or moving it to the rear would affect weight distribution, but how are you affecting it with the coilovers? Also, how is it possible that a BB could still have a neutral weight distribution when it was a few hundered pounds more? Is it placed that much further aft?

Ron61 · #5 (**permalink**) 10-04-2002, 08:08 AM

Jim,

Using the coilovers and scales you can shift weight just as the Winston Cup cars do. When you change the height of the ride, you are compressing the springs which is like adding more spring rate. We have played with the changes and a friend of mine who races has a FFR Daytona Coupe and I think he wound up setting his at 53/47 for the track here. If you are going to drag race then some of the drag guys will have to chim in and help you with the weight transfers and settings as I don't know a thing about them. But the reason for the old jack bars and now the coilovers is to be able to shift weight from track to track and when trying different tires or setups. I am not good at all at explaining things and I am sure some of the others can make everything a lot clearer than I do.

Ron61
Ron Widener

scottj · #6 (**permalink**) 10-04-2002, 08:34 AM

With the aluminum small block in my car it had 56% rear with 10 gallons of fuel. It was tighter on corner entry and need more rear brake bias. Then you had to pick up the throttle early to transfer weight to the rear and stop the pendulum effect caused by the high rear %. The high rear % had better forward drive off the corner though.

With the iron small block it has 53% rear, gets in and through the middle easier but has less drive off. Its easier to drive but not as fun.

You can't change front/rear and left/right % by adjusting coilovers. You have to move/add weight to do that.

Coilover adjustments can affect corner %, but they can't move the center of gravity.

Scott

Ron61 · #7 (**permalink**) 10-04-2002, 08:51 AM

Scott,

Thanks for clearing that up. I know Rich added lead weight when he had his car on the scales and they did adjust the coilovers. I knew you couldn't change center of gravity by coilovers but just can't explain things like most people. Spring weight changes for handling are what I was trying to say and as usual I got it wrong. I agree with you about the more weight in the back the harder youy can come off the corner and they set Rich's car up with a little more weight in back because of his 660 lbs. torque. I like the 51/49 on mine as I can set the rebound to hold the nose planted and still come off the corners at a decent speed with good tires. But I don't have the horsepower and torque a lot of you guys do either so I can get away with a little more.

Ron61
Ron Widener

Jack21 · #8 (**permalink**) 10-05-2002, 11:02 AM

According to some of the data in the Ford documentation, the 351W iron block weighs 195#. The aluminum SVO 351W block weighs 120#. A lot of $$$ to save 75#.

The real savings, and performance gain is in the use of aftermarket aluminum heads. An aluminum headed 351W (or 393W) is lighter than an all iron 302. This is enhanced further with aluminum intake, aluminum water pump, and aluminum steering rack (Flaming River manual, or '79-up OEM Ford power) instead of iron MII. So, you're still maintaining your ~50/50 weight distribution.

The coil overs allow you to easily adjust front ride height that you can't do with the OEM spring setup.

Trying to move the engine forward or back, at least with a CR, is an exercise in futility. Put the battery in the trunk instead.

Remember also, that the 351W mounts 3/4" - 1" lower than the 302. Use 351W specific motor mounts. And, you have to drop the trans a like amount or the engine will tilt forward, and the sidepipes will not be parallel to the body.