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Lowering GT350R ...is it worth it? (Eibach, FP and BMR)

Driveway Demons

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Front is 1.55hz and rear is 1.2hz at 565lbs and 1.4hz at 765lbs. Personally I do not like when the front frequency is higher than the rear on a non aero car.



Doesn't look like I can get one that is not the steeda spring that will fit the stock spring cups for the rear. I will have to go with an aftermarket coilover and use a 24k swift spring which ends up being 1344lbs (still less than 2.0hz) so it will work for me.
Does it cause problems or what makes it bad? I am thinking of putting the steeda rear springs. They said only 3/8” is required to get into the dual 1280 lb/in which means almost all the time. I wonder how that would feel with the ford front springs.

What do think the difference would be between the four different setups below.

1.
front fp springs and rear fp springs (0.78” drop all around)

2. front linear fp springs 250 lb/in and steeda rear Dual rate 800/1280 lb/in (0.78” front drop 0.5” drop rear)

3. fp linear front spring 250 lb/in and BMR rear spring 980lb/in (0.78” front and 0.55” rear)

4. steeda front dual 220/350 and steeda rear 800/1280 (0.5” drop all around)

I also find it weird that ford performance didn't include new bump stops or ask to cut the stock ones. I wonder if I am hitting them more often now.....
 
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Niz55

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Front is 1.55hz and rear is 1.2hz at 565lbs and 1.4hz at 765lbs. Personally I do not like when the front frequency is higher than the rear on a non aero car.



Doesn't look like I can get one that is not the steeda spring that will fit the stock spring cups for the rear. I will have to go with an aftermarket coilover and use a 24k swift spring which ends up being 1344lbs (still less than 2.0hz) so it will work for me.
I don't think you will find any rear springs over 980lbs.
 

ShatterPoints

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Does it cause problems or what makes it bad? I am thinking of putting the steeda rear springs. They said only 3/8” is required to get into the dual 1280 lb/in which means almost all the time. I wonder how that would feel with the ford front springs.

What do think the difference would be between the four different setups below.

1.
front fp springs and rear fp springs (0.78” drop all around)

2. front linear fp springs 250 lb/in and steeda rear Dual rate 800/1280 lb/in (0.78” front drop 0.5” drop rear)

3. fp linear front spring 250 lb/in and BMR rear spring 980lb/in (0.78” front and 0.55” rear)

4. steeda front dual 220/350 and steeda rear 800/1280 (0.5” drop all around)

I also find it weird that ford performance didn't include new bump stops or ask to cut the stock ones. I wonder if I am hitting them more often now.....
Few things to address here. Your car as it accelerates and decelerates, turns, and hits bumps will pitch, heave, and yaw. All of this motion is transmitted through the chassis and to you. Similar to how you experience NVH. When the front frequency is higher than the rear, the car will pitch in response to bumps from a steady state and it will stay that way in roll as well. When the rear has a higher frequency it allows the chassis to settle evenly before it goes into bounce (basically the car evenly front to rear bounces up and down, vs in pitch the car teeter totters like a see saw). This results in a more comfortable ride and when setup correctly does not sacrifice a large amount of performance. When the front frequencies need to be higher, or when you would want the car to pitch is when you have a large amount of aerodynamic grip, or if one particular end of the car has more aero than the other. Aero is pitch sensitive, say for instance the nose of the car pitches upward, this moves the aero balance forward since it is reducing the rear's efficiency. This will cause the car to become imbalanced for how you may have it setup. So in that case you would want to be mindful of the car's pitch. There are plenty of race engineers whom use flat ride and plenty who do not. Both strategies will yield winning results and ultimately the driver mod is the biggest variable.

Since I daily drive my car I want the comfort and performance, and flat ride is how I achieve that. Ford seems to agree since the gt350 has flat ride with the OEM springs.

1. FP rear springs to me are too soft.

2. Seems like the 2nd best setup tied with #4 below.

3. FP/BMR springs would be my first choice if you want a similar to stock ride.

4. steeda's springs are very close to what I want personally however I want to keep the OEM ride height if I can. For you this may be the best option since you do want to lower your car.

You are hitting your bump stops. ALL vehicles with bump stops use them all the time. They are and integral part of your suspension. Some race engineers do not use them and tune their shocks accordingly. I prefer them and I have cut or swapped them to a smaller and softer material in the past. They are an excellent, cheap way to soften the ride you feel.

This article I feel shines the light on why dampers now are rebound biased (jack the car down onto the bump stops). It is a tuning strategy to use them as a timing device that you can tune for with predictable results. It is one, valid way of doing things, but not the end-all-be-all
https://bluetoad.com/publication/?m=&l=1&i=470289&view=articleBrowser&article_id=2991492



I don't think you will find any rear springs over 980lbs.
As far as springs which fit the stock location, only the steeda spring comes close with their 800/1280 dual rate. If I go coilover then swift 24k springs will be what I have to go with in the rear. I have asked the guys at vorshlag and they will sell a magnaride delete kit for the gt350. Its like $400 but ¯\_(ツ)_/¯
 

ShatterPoints

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Back with an update for the route I am going. I found a vendor who sells magneride delete kits as well as they will custom valve a set of shocks for me.

I will be relocating the rear spring for a true coilover, this will mean the spring and shock motion ratio will be the same. The front does not change since they are struts to begin with. The rear shock MR is 0.77, so I will be using 450lbs springs front and 750lbs springs rear. I can make a separate thread discussing the valving I will be targeting for damping if anyone is interested.
 

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