Iron vs. Aluminum And Their Effects On Handling

[ADiCarlo]

So I thought about posting this in the swap forum, the suspension form and then I thought this might be the best spot.

From what I've read the difference between the Iron block and the Aluminum LS in weight is a total of 80 lbs.

Now with the amount of modifications we do to our cars such as moving the motor back, applying newer designed suspension systems including coil over suspension do you feel that this additional 80 lbs will make a huge difference on the driving characteristics of the car?

Furthermore, what have people done to really help achieve a 50/50 weight distribution in the car beyond moving the battery, to the trunk and moving the motor more center?

-Armand

[214Chevy]

Armand, I don't know a 10th of some of these guys on here do. But, I think the weight issue is more of a concern for the track guys who wants their car to be lighter in terms of achieving faster lap times. For a guy like me who is strictly a recreational/street car guy, 80 lbs or 180 lbs doesn't mean anything to me. So, I think it all boils down to want your intentions are with the car.

[INTMD8]

As you've already touched on, engine position has to be considered when determining how much weight will have an effect.

(Is it all behind the front wheel centerline or is the weight partially leveraged over the front wheel centerline).

Of course lighter is always better and I would say the difference would be at least slightly noticeable to most, especially if you've had some time with the car with an aluminum engine to start.

[ADiCarlo]

Originally Posted by INTMD8

As you've already touched on, engine position has to be considered when determining how much weight will have an effect.

(Is it all behind the front wheel centerline or is the weight partially leveraged over the front wheel centerline).

Of course lighter is always better and I would say the difference would be at least slightly noticeable to most, especially if you've had some time with the car with an aluminum engine to start.

Well let's throw another factor into the equation. The ability to gain a higher output from a iron motor (via turbo and supercharging) to counter react the additional weight. If weight balance can be achieved so it doesn't effect handling how much additional horsepower must a car make to overcome that 80 lbs.

[71RS/SS396]

Originally Posted by ADiCarlo

Well let's throw another factor into the equation. The ability to gain a higher output from a iron motor (via turbo and supercharging) to counter react the additional weight. If weight balance can be achieved so it doesn't effect handling how much additional horsepower must a car make to overcome that 80 lbs.

Is the car going to see a substantial amount of track time? The problem with any boosted combination is managing the incoming air temps, if you don't manage the incoming air temps well the computer will just pull the timing out.

[ccracin]

Originally Posted by ADiCarlo

Well let's throw another factor into the equation. The ability to gain a higher output from a iron motor (via turbo and supercharging) to counter react the additional weight. If weight balance can be achieved so it doesn't effect handling how much additional horsepower must a car make to overcome that 80 lbs.

Armand,
Overcoming extra weight with horsepower is really a drag racing thing. When it comes to most of the builds in the "Pro-Touring" genre handling and braking are key components. The 50/50 weight balance is the target for dynamic balance, meaning when braking and turning. A 50/50 static balance, meaning sitting on a set of scales is not ideal. It is an excellent goal with front engine street cars because this usually takes quite a bit of effort to achieve. But, as I said the main goal in a performance handling situation is to control weight transfer in dive and roll. Therefore if you are dealing with less weight overall, there is less to control. That is really all that springs and shocks do is control how you transfer weight transfer about the the center of gravity in dive (accel. and braking) and roll (turning) situations.

Circle track cars are excellent models to look at for static weight balance versus dynamic. Because they only make left turns, they are setup with static balance to try and achieve that ideal 50/50 balance under sever braking and left turns. Therefore you will see front to rear static balance sometimes 52-54% rear and 46-48% front with 60%+ left side weight bias. Hopefully you see they correlation here.

As with any project it is about compromise. What are the goals, budget, design constraints, builder skill, parts available, etc, etc...... Personally, i think it's always good to go as lite as possible within reason. Especially in the engine bay. That is low hanging fruit. There are not many areas you can address and remove 80#+ in one shot. With today's engine technology, you have to get pretty radical before you have to worry about aluminum blocks.

I hope this helps a bit. I would also suggest buying the book "Chassis Engineering" by Herb Adams. You can usually find it for under $20. After reading it, you will have better understanding of how the components in a chassis work together. This should help you make decisions moving forward.

[ADiCarlo]

Originally Posted by ccracin

Armand,
Overcoming extra weight with horsepower is really a drag racing thing. When it comes to most of the builds in the "Pro-Touring" genre handling and braking are key components. The 50/50 weight balance is the target for dynamic balance, meaning when braking and turning. A 50/50 static balance, meaning sitting on a set of scales is not ideal. It is an excellent goal with front engine street cars because this usually takes quite a bit of effort to achieve. But, as I said the main goal in a performance handling situation is to control weight transfer in dive and roll. Therefore if you are dealing with less weight overall, there is less to control. That is really all that springs and shocks do is control how you transfer weight transfer about the the center of gravity in dive (accel. and braking) and roll (turning) situations.

Circle track cars are excellent models to look at for static weight balance versus dynamic. Because they only make left turns, they are setup with static balance to try and achieve that ideal 50/50 balance under sever braking and left turns. Therefore you will see front to rear static balance sometimes 52-54% rear and 46-48% front with 60%+ left side weight bias. Hopefully you see they correlation here.

As with any project it is about compromise. What are the goals, budget, design constraints, builder skill, parts available, etc, etc...... Personally, i think it's always good to go as lite as possible within reason. Especially in the engine bay. That is low hanging fruit. There are not many areas you can address and remove 80#+ in one shot. With today's engine technology, you have to get pretty radical before you have to worry about aluminum blocks.

I hope this helps a bit. I would also suggest buying the book "Chassis Engineering" by Herb Adams. You can usually find it for under $20. After reading it, you will have better understanding of how the components in a chassis work together. This should help you make decisions moving forward.

Hi Chad - Thank you for the detail explanation. The car is going to be seeing a good amount of track time and is being purpose for it to the best of my abilities and budget.

I was able to pick up a LQ9 block with LS3 heads and a hot cam that had been dyno'd but never installed in a car (it was a motor used for a magazine article) - output was about 520 at the crank.

Now I bought this motor in the first 3 weeks (now approach a year) of owning the car as I was attempting to get parts together as quickly as possible. So, after a year of reading and a few comments on people pushing towards the aluminum motors I feel as if I may have made a mistake.

In an effort to rationalize this and consider all options I started this thread to actually discuss the pros and cons of an iron vs aluminum block when applied to racing and if a gain in HP from being able to apply forced induction can be a more worthwhile quality then being 80 lbs lighter.

" Therefore if you are dealing with less weight overall, there is less to control. That is really all that springs and shocks do is control how you transfer weight transfer about the the center of gravity in dive (accel. and braking) and roll (turning) situations. "

This makes me think that an additional 80lbs can but adjusted for during suspension tuning and that the increase may not be great enough that it can't be overcome if dynamic balance is determined by the shock and spring combo and the ability of these to do the job is set by tuning the spring type, rebound, compression etc.