GT500 vs Boss 302 springs...

[Duane Black]

I know, I know... the race guys are runninf like 600 rate springs anyway...

But I need to replace my front Struts... and was looking at springs...

I currently have Boss 302 springs all around (147f, 181r me thinks) on my car. The gt500 springs list for like, $50-75 each on a couple of sites like Tasca Ford.... but that doesnt mean they even have them.

So, I was curious... we dont have a listed rate on the springs/sway bar page, although @Norm Peterson said they're 260/220?

I'm curious if i shoulf stick with my boss 302 stuff all around, or if gt500 springs are in fact that much stiffer and would help the car point into corners better on factory style struts?

K thx

 

[Mad Hatter]

Why not go for the Ford P springs?? A little lower and stiffer then the Boss springs but perfectly streetable and Ford already worked them out for the track. You really can"t go wrong with them.

You can find them for less then 200 bucks a set.

 

[Duane Black]

Does the roll center, caster/camber (given ive got MM plates), geometry of the ctrl arms, etc, still account for any drastic lowering of the car?

 

[Mad Hatter]

Does the roll center, caster/camber (given ive got MM plates), geometry of the ctrl arms, etc, still account for any drastic lowering of the car?

I would not call the P springs 1 inch drop drastic. But with your camber plates you would be fine, along with your other alignment adjustments.. Remember this is the spring set the Fordd recomendad for our car at the track.

 

[Duane Black]

Ah yes. Also, do those springs require the older strut and/or the gt500 mounts? For that matter, as would a gt500 spring?

 

[Norm Peterson]

The GT500 springs I posted the information for are BMR's rather than Ford's. But they don't seem to be all that much different from some of Ford's performance-oriented springs.

In terms of wheel rate in pure bump, the BMR GT500 springs are within a few lb/in of the rates that Ford used on the S550 GT350R (and just a few lb/in stiffer than the P springs). Lowering with the BMRs is around half an inch up front and an inch at the rear (which you may want to correct). Street ride quality is firm but still good over any reasonable pavement surface.

I wish I knew what Ford had in mind with the P springs, that whole inch of lowering in particular.


Norm

 

[Mad Hatter]

The GT500 springs I posted the information for are BMR's rather than Ford's. But they don't seem to be all that much different from some of Ford's performance-oriented springs.

In terms of wheel rate in pure bump, the BMR GT500 springs are within a few lb/in of the rates that Ford used on the S550 GT350R (and just a few lb/in stiffer than the P springs). Lowering with the BMRs is around half an inch up front and an inch at the rear (which you may want to correct). Street ride quality is firm but still good over any reasonable pavement surface.

I wish I knew what Ford had in mind with the P springs, that whole inch of lowering in particular.


Norm

If I remember right they did lower the car more in the back then the front. I think the fronts are around 0.5 inch as well. It was not a very dramatic drop. But in the end probably not much diference between the two.

 

[drj2k1]

I’ve also found myself in a similar boat after investing in oem style Koni yellows last year and now moving up to CAM-C. I haven’t found an OEM or aftermarket spring that fits what I’m looking to do next season: stockish ride height to keep ground clearance/geometry and avoid epas issue (although Norms bmr gt500 springs are interesting)

Have you considered Ground Control coilover sleeves for the oe style konis? They are ride height adjustable for corner balancing but can also be kept at a stock height. You can order any spring rate you want with them, but you have to be mindful of the limitations of the off the shelf Koni valving. I spoke to Mason at Koni NA a couple months ago and he said the 375-400lb front rates I’m looking to run are within the effective range

not the cheapest option at ~$500 for the front/rear kit, but I’m leaning heavily this way so I can use my konis/their warranty and keep my height & stock geometry

Can always add more spring rate and get the konis “race” valved down the line as well

 

[Grant 302]

P spring are a bit low considering the front geometry impacts.

There are many reasons why I think Norm’s setup would be good for many.

The GT500 springs I posted the information for are BMR's rather than Ford's.

I thought you’ve been pretty clear about that.

But they don't seem to be all that much different from some of Ford's performance-oriented springs.

by the published specs, maybe. But I suspect they aren’t as ‘progressive’ or dual-rate design as the FRPP stuff. Do you have any pics of the BMR springs handy?

BMR Handling SP072 (1.5" drop w/GT500)(~0.5"F/~1"R on GT) 260 lb/in front (linear), 220 lb/in rear (dual-rate)

I think it difficult to get away from dual rate in the rear. I think more people should consider this spring set.

 

[Duane Black]

Isnt a 1.5 drop on the bmr pretty aggressive compared to the P spring, with no other effective adjustment ti the front end geometry?

 

[Grant 302]

Isnt a 1.5 drop on the bmr pretty aggressive compared to the P spring, with no other effective adjustment ti the front end geometry?

(~0.5"F/~1"R on GT)

^ That’s based on @Norm Peterson ’s measurements.

For a V6, it certainly won’t be as much drop as it would with the GT500 engine...

 

[Duane Black]

@Norm Peterson , is this your spring?

SP066R-SD - ***SCRATCH & DENT*** - Lowering Springs, Front, 1.5" Drop, Handling, GT | 2005 - 2014 Mustang | Lowering Springs | BMR Suspension - High Performance Suspension & Chassis

2005 - 2014 Mustang Lowering Springs SP066R-SD - ***SCRATCH & DENT*** - Lowering Springs, Front, 1.5

m.bmrsuspension.com

 

[Norm Peterson]

@Norm Peterson , is this your spring?

SP066R-SD - ***SCRATCH & DENT*** - Lowering Springs, Front, 1.5" Drop, Handling, GT | 2005 - 2014 Mustang | Lowering Springs | BMR Suspension - High Performance Suspension & Chassis

2005 - 2014 Mustang Lowering Springs SP066R-SD - ***SCRATCH & DENT*** - Lowering Springs, Front, 1.5

m.bmrsuspension.com

No. That's the 'Handling Spring' for the 'regular' GT. The GT500 handling springs are SP073 (front) and SP074 (rear). They used to be available together as SP072.


Norm

 

[Norm Peterson]

Isnt a 1.5 drop on the bmr pretty aggressive compared to the P spring, with no other effective adjustment ti the front end geometry?

Keep in mind that the GT500 springs are wound for the heavier car. Like you'd expect, the biggest difference from the 1.5" claimed for the GT500 would happen up front where the bulk of the GT500's extra weight is located.


Norm

 

[Duane Black]

Ah yes, found it. I think i would need the older style strut and strut mount to make it work.

 

[Norm Peterson]

But I suspect they aren’t as ‘progressive’ or dual-rate design as the FRPP stuff. Do you have any pics of the BMR springs handy?

BMR Handling SP072 (1.5" drop w/GT500)(~0.5"F/~1"R on GT) 260 lb/in front (linear), 220 lb/in rear (dual-rate)

I think it difficult to get away from dual rate in the rear. I think more people should consider this spring set.

The BMR rear springs are dual-rate, but are solidly into the firm rate region (closely spaced coils all touching) at static ride height. I never tried to see how far into rebound that continued to be the case.

Front springs - BMR's pictures (I'll see if I can dig up a snapshot of mine as installed, but no promises).




Rear springs




Norm

 

[Norm Peterson]

Ahhh, found one. Taken at full droop. The close-spaced coils have opened up (they're way up at the upper spring seat so you might have to squint a bit).




Norm

 

[302 Hi Pro]

I’m not a suspension engineer so I let Ford Performance do that leg work.

I went with the Ford Racing Boss 302 ‘T’ springs. Excellent stance. They lower the front end a bit less than 1/2”. Once you go more than 1/2”, it alters the front end factory spec geometry.

My only tweet to that was adjustable camber plates to get a wee bit more neg. camber.

 

[Duane Black]

Those T springs sound like a viable option tbh....

 

[Grant 302]

Those T springs sound like a viable option tbh....

Those will lower the front about the same as P springs.

The thing that most forget is that stock Boss front end geometry is already ~1/2” lower than a stock GT.

The T set uses the K rear springs.