Help picking out spring rates? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 7 Old 07-23-2016, 08:11 AM Thread Starter
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Help picking out spring rates?

Hopefully this is the right section for this....

I'm trying to find out what rate springs to get for my car and hoping some people on here can help me make that decision.... I'm going to be stuffing an iron Dart block 427ci motor under my hood (9.5 deck) of my 1993 Cobra. So I'm sure the additional weight over a stock block 302 is going to have to be factored into the decision. I'll of course end up going with a fiberglass hood so that should help shed some pounds off the front as well.

I'm going to be ordering a MM entire front K-member kit with coil overs, so that's what I'll need the right springs for. I've heard nothing but great things about MM's products, but I've never had such a wait just to give a company money. I'm hoping I can find someone who can recommend a spring rate so I can get these parts ordered already. I got an email from Jack a week ago but haven't heard back yet and just want to get going on ordering this stuff. I'm sure he's just busy at this time....

Currently the car is on Steeda competition springs and Tokico Illumina shocks, stock 1993 Cobra sway bars.

I was thinking about doing MM's TA and PHB setup in the rear as money allowed but am now leaning towards putting an 03/04 Cobra IRS in the back of the car when money allowed. Not sure how much this might affect the front spring choice, but if it does, I would assume IRS will be the rear suspension.

I may be trying out some auto-x events in the future, but the majority of use for the car is going to be street driven (biggest reason for going MM instead of one of the other k-member companies with lighter k-members). I just want my 1993 to handle much better so I can still have fun with it instead of trading it in for something newer.

Any suggestions?


1993 Cobra #235. Stage 2+ TFS TW heads from TEA, Stage 1 TFS cam, etc.....

Fordstrokers built 427w on the engine stand, soon to be in the car !!!!
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post #2 of 7 Old 07-23-2016, 11:21 AM
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I would go with whatever Jack tells you; that being said, I would take a look at MM's dampner FAQ sheet and find the max spring rate recommended and use that. For instance, Koni yellows have a max rate of 375# coil overs. Then you pick the rear rates to match based on suspension setup.

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post #3 of 7 Old 07-23-2016, 11:10 PM
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I think this is the FAQ that aurdraco is referring to - Matching spring rates with dampers. As you can see, 325# is as high as they recommend for Illuminas. I ran 300# coilovers years ago, they were OK but a bit soft. I don't know if you're budgeting for new struts to go along with the rest of the MM front end stuff, but it would probably be worthwhile. I'd probably be looking for 350 or 375# springs up front due to the added weight.

'89 GT convertible, N/A 357W, MM front susp w/425# coil-overs and Koni D/As, MM TA/PB rear setup (Koni Yellows, 390-430# springs), Stoptech 332mm / 12" Baers, MM 6 point rollbar, Maier 1.5" flared fenders & quarters, 18x9.5" front/18x10.5" rear Enkei RPF-1s (street), 18x10" CCW C-10s (track), etc...
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post #4 of 7 Old 07-29-2016, 02:37 PM Thread Starter
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Heard back from Jack and got everything ordered..... Should be here next week.

Thanks for the help guys!

1993 Cobra #235. Stage 2+ TFS TW heads from TEA, Stage 1 TFS cam, etc.....

Fordstrokers built 427w on the engine stand, soon to be in the car !!!!
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post #5 of 7 Old 07-30-2016, 01:56 AM
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So what did you end up ordering?
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post #6 of 7 Old 08-03-2016, 02:32 PM Thread Starter
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Right now because so much stuff is in flux he had me order 175# springs so they will essentially remain the same as I currently experience with my current setup.

Then once I switch over to IRS in the rear, I will then switch that to coil over, and then order new Koni struts for up front to match the rear coil overs, and then I will also buy new springs for the front that will match.

The biggest thing is just getting it all setup for me, then once I get the parts to match correctly he will get me into a final set of springs that are better suited to my needs.

1993 Cobra #235. Stage 2+ TFS TW heads from TEA, Stage 1 TFS cam, etc.....

Fordstrokers built 427w on the engine stand, soon to be in the car !!!!
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post #7 of 7 Old 08-10-2016, 12:10 PM
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I have a notch with the MM Koni coil overs all around and the IRS in the rear. I love it but went heavier on the spring rates and having the IRS in the rear did influence Jack's thoughts on spring rate somewhat for the front but in your case just order the right springs later like he suggested. The biggest problem with the IRS is the wheel choices are very limited given you need no more than a 9" wide wheel and 275 tire to tuck in the wheel well but you'll want a 6.75" BS on that 9" wide wheel.

All that said I still don't regret going IRS on my car at all, but I would say you should replace all the control arm bushings on it with AT LEAST poly bushings before you install it.

1992 5.0 5sp coupe, ported GT-40 intake, TFS 170 heads, Scorpion 1.72 RR, TFS1 Cam, BBK longtubes, BBK H-pipe, MSPNP2 ECU, Full Koni MM coilovers, SVE S1 seats, Moda R6 Wheels, full Cobra Brakes, 2004 Cobra IRS, MM SFC's,
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