Question regarding weight distribution and handling

[nucjd19]

Hello everyone again.
I have been scouring the build threads and taking copious notes for my upcoming build. I will be ordering a MK4 Roadster next month ( complete kit, 3 link rear, 17x9 and 17x10.5 wheels, power steering. Already purchased 347 SBF mated to a TKO600 from blue print).
I am very familiar with tracking porsche 911s over the year and driving hard into corners dealing with brake oversteer (snap oversteer). However this car/ rocket it is going to have a completely different handling characteristics than my old 911 ( sold it a few years ago). The rear looks loose on some of the vids I have seen (with a short wheel base and MASSIVE power LOL! ) and weight distribution
...... So my question is... Battery placement. I have been looking at the breeze engine battery kit and was planning on doing that, but would the little bit of extra weight in the rear change handling characteristics making it more neutral? It looks like the engine sits back a bit in the frame which is good and probably negates a lot of any understeer. Also the battery is not a lot of weight but every little bit counts. Finally do you notice a difference in handling with a full tank of gas vs minimal gas in the tank?
As an aside I do not plan on tracking this build. I would just like to have a really nice handling rig to cruise the Appalachian foothills with my wife and therefore this may all be theoretical. Thanks for your expertise in advance :)

[Jeff Kleiner]

Unless you do something out of the ordinary a Windsor engine equipped Mk4 will have 52-53 of it's weight on the rear. Mounting the battery in front obviously shifts that just a bit. As an FYI my aluminum headed Windsor powered roadster with T5, 3 link, PS and full interior weighs 2,180 full of gas. I do a lot of autocross and track days and yes, you can tell a small difference with a full tank vs. say a half but it's not extreme---you feel a passenger a lot more than you do 50-70 pounds of gas. By the way, with the factory spring rates (500F/350R for a 3 link) the roadster will understeer unless you make it loose with the throttle.

Jeff

[GoDadGo]

>..Jeff knows these cars like the backs of his hands.
>..Any advice he gives you will be based on 1st hand experience.
>..Consider getting in line now to have him do your body and paint work.

My car is right at 50/50, but I had to move my engine (SBC) forward 6" to make things fit.
The battery is in the trunk to help offset the driveline move.

[nucjd19]

Thank you guys for the posts. Good to know the overall weight distribution is darn close. It would seem Autocross would definitely expose the weight bias. It is sounding like regular driving would not expose the weight difference, IF there is one unlike GoDadGo :)

[nucjd19]

Jeff. Do you change your spring rates for Autocross vs casual driving? Thanks in advance.

[GoDadGo]

Thank you guys for the posts. Good to know the overall weight distribution is darn close. It would seem Autocross would definitely expose the weight bias. It is sounding like regular driving would not expose the weight difference, IF there is one unlike GoDadGo :)

I finally sold my Beloved C4 which I had for 23 years and that car was driven hard for all 285,000 miles.
https://youtu.be/svZX2BMSDEs

Redbone sports the same transmission, the same rear tires 285's but has 245' up front, instead of the 255's on the C4, with 3.73 gears compared to 3.54.
https://youtu.be/9WEe6-wdNtA

The car handles very well (Better) compared to the Corvette, but the biggest thing that I'm having a hard time dealing with is the power to weight ratio.

I'm at a 1/5 power to weight ratio in Redbone, but was accustomed to about 1/10 ratio in the Beloved C4.

[SJDave]

I do track my car 2-3 times a year with the Shelby Club, I had it aligned by a race shop and corner weighted, Breeze battery box in the front (so much cleaner IMO), 347 with alum heads, TKO 500, IRS....and the car came out ( 45% Front ...55% Rear). With the stock springs it will naturally understeer a bit, but the throttle can bring the rear around pretty quick. All my spins have been too much throttle coming off the APEX. Too much fun to spin the tires I guess! I've been contemplating adding some roll bars to it to limit the roll a bit more and tune the handling a bit more. ..but as shipped it's a pretty capable car. Now that I'm 70 thinking about doing electric power steering, my arm strength gets less each year and having the strength to counter-steer is marginal right now. Other than that, these cars are so much fun on the track! Here's a video of Freddie Hebert in the Black FFR playing follow the leader with me at Sonoma Raceway last year during the Shelby Club Mini Nats, his is a 5.0 L mustang engine FI with 3 link rear.
https://www.youtube.com/watch?v=GV52ObFfWuU&list=FLdydJImO3N_Do3zHeMrW-YA

[Jeff Kleiner]

Jeff. Do you change your spring rates for Autocross vs casual driving? Thanks in advance.

I run 750# front and 500# rear all the time. It is probably a little hard core for some guys but I stay so busy doing cars for others that I don't have much time for street driving my own so when I get the chance I'm OK with it ;)

This photo of a RH sweeper shows that the it is oversteering slightly as indicated by the rear tire rolling over but with some opposite front steering input holding it in check. I can't stand a car that pushes ;)

https://thefactoryfiveforum.com/attachment.php?attachmentid=134188&d=1514138027

Cheers,
Jeff

134188

[nucjd19]

This data is invaluable guys! Thank you!
SJDave your track video was AWESOME!!!
Thank you for the info on the spring rates.

I am not 100% apposed to tracking it but wanted to really make this street machine rather than a track scalpel. Maybe a dedicated track rig down the road when I get close to retiring.

[rich grsc]

I run 750# front and 500# rear all the time. It is probably a little hard core for some guys but I stay so busy doing cars for others that I don't have much time for street driving my own so when I get the chance I'm OK with it ;)

This photo of a RH sweeper shows that the it is oversteering slightly as indicated by the rear tire rolling over but with some opposite front steering input holding it in check. I can't stand a car that pushes ;)

https://thefactoryfiveforum.com/attachment.php?attachmentid=134188&d=1514138027

Cheers,
Jeff

134188

And that is one of the things wrong with you. :rolleyes: :p

[Avalanche325]

As you noticed, the engine is pretty far back. For good reason. These cars need weight in the rear.

I personally like the battery in the rear. 1 Weight distribution. 2. I have never in 6 years / 25,000+ miles needed to get to it. 3. It keeps it away from heat. 4. I don't want to see it in the engine compartment. The one advantage is a short cable to the starter. Just upgrade the cable from the rear and you're good.

I autocross and track mine. They can be a handful and things happen fast. They like to be dancing on the edge to be quick. But, I also find that the car communicates well. The biggest thing I see people doing to get them in trouble is a full panic lift when the rear is already loose. They reward smooth inputs. I always recommend some autocross events when you get your car built. And please please put appropriate tires on.

I run a 3-link (because of the IRS that was available back then) I run square on my ride height. A lot of guys put 1/2" of rake in. I noticed more rear grip when I took it out. I installed VPM anti-roll bars to adjust the understeer out. Some guys like understeer, not me.

I agree with Jeff that the fuel load doesn't make that much of a difference. I have passengers all the time at autocross, and you can tell, but it's not that drastic since it is not a momentum car.

I agree with GoDadGo. Jeff is who you want for your paint and body.

[nucjd19]

Avalanche325. thanks for the response. I think autocross is in the future just to start getting my head around this machine at the edge. I am little nervous going from a 911 which is so dang counterintuitive to a front engine/ mid engine machine. I have rewired my brain for blipping the throttle in corners to get myself out of trouble and the weight off the front end.

[JohnK]

I do track my car 2-3 times a year with the Shelby Club, I had it aligned by a race shop and corner weighted, Breeze battery box in the front (so much cleaner IMO), 347 with alum heads, TKO 500, IRS....and the car came out ( 45% Front ...55% Rear). With the stock springs it will naturally understeer a bit, but the throttle can bring the rear around pretty quick. All my spins have been too much throttle coming off the APEX. Too much fun to spin the tires I guess! I've been contemplating adding some roll bars to it to limit the roll a bit more and tune the handling a bit more. ..but as shipped it's a pretty capable car. Now that I'm 70 thinking about doing electric power steering, my arm strength gets less each year and having the strength to counter-steer is marginal right now. Other than that, these cars are so much fun on the track! Here's a video of Freddie Hebert in the Black FFR playing follow the leader with me at Sonoma Raceway last year during the Shelby Club Mini Nats, his is a 5.0 L mustang engine FI with 3 link rear.
https://www.youtube.com/watch?v=GV52ObFfWuU&list=FLdydJImO3N_Do3zHeMrW-YA


Hey Dave. Where did you have your car aligned and corner-weighted? There's a place here in Los Gatos (BR Racing) that I was going to take mine to (when that time comes) for alignment, corner weighting, and ride height but I have no first-hand experience with them. They just happen to be close by.

I've got stock springs in mine with front and rear sway bars and the Koni double-adjustable shocks. I also have the battery in the front in a Breeze box. Any sense for how that will balance out and handle with a coyote, TKO600 and IRS?

[RoadRacer]

I'm a big fan of corner weights - made a big difference when I was tracking my car. But I was on a shoestring so I bought something very similar to this (https://www.ebay.com/itm/ADA-Corner-Weight-Gauge-0-450kgs-Inset-Race-Rally-Motorsport-Chassis-Setup-/303124199508) (they come in many sizes/weights) that are certainly cheaper than the full scales setup. And certainly less accurate, doing one corner at a time. But it's within reach of most people, or get together with local car club, etc.

[SJDave]

Hey Dave. Where did you have your car aligned and corner-weighted? There's a place here in Los Gatos (BR Racing) that I was going to take mine to (when that time comes) for alignment, corner weighting, and ride height but I have no first-hand experience with them. They just happen to be close by.

I've got stock springs in mine with front and rear sway bars and the Koni double-adjustable shocks. I also have the battery in the front in a Breeze box. Any sense for how that will balance out and handle with a coyote, TKO600 and IRS?

Hey John,

I took it to BTM Motorwerks in Campbell on Bascom, their owner races and I trust him and his guys with anything. They did alot of work on my BMW M3 over the last 5 years, that was my primary track car. Brad McClure the owner is a great person and races BMW's among other things, so he takes a close interest in customer cars in terms of setup and handling. It was $375 for both. They also fixed my rear end toe in when this did this, so it was very reasonable.

Kevin Heneghan has that exact setup except no sway bars...yet....and his car handles very well. I think the weight distribution will shift slightly forward as the Coyote is further forward in the chassis. But I'm no expert on getting the most out of these cars....Now a 2005 BMW M3 I know quite a bit!

[GTBradley]

I did my weights back in April and did not include myself in them, for which I would add 170 lbs. Half tank gas:
Front 1090 and rear 1187 for a weight balance front to back of 48% - 52% and total 2277 lbs

FWIW, I have the Gen2 Coyote (which is a lightweight motor at 445 pounds) and the forward battery mod. The advantage of the forward battery to me was the weight savings from shorter and smaller gauge power cables and lower CG as the battery is at the same level as the frame rails. I hear the lower CG is helpful, but haven't done anything on the track or autocross yet.

My personal experience on mountain roads is, the car is very stable and predictable even without anti-sway bars. On a hard transition from left to right, or a sudden turn in I can detect some body roll but not much. The only thing that I'm concerned with is the amount of power application as you can kick the back out at will, but even that is starting to feel predictable and fun. I was new to this type of car and learned pretty early on that you may not realize you are pushing it so hard as it feels so capable, but you are and therefore are closer to the edge than you think.

[CraigS]

One way to have a combination car is get the QA1 double adjustable shocks from Breeze. In < 5 min you can go from AX setup to street setup. I have always run a lot of front spring up to 800# and the ride is fine. Since you are sitting so close to the rear wheels the rear springs have much more effect on ride. So I keep them maxed at 350.

[nucjd19]

Thank you GTBradley and CraigS! I have ordered the base shocks from FFR on my kit with the game plan to upgrade to the QA1 in the long run. You must have read my mind LOL!