Front suspension - does everyone need SAI mod and a bumpsteer kit? - FFCars.com : Factory Five Racing Discussion Forum
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Old 02-28-2007, 07:31 PM   #1 (permalink)
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I've got an mk1 and a flaming river manaul rack.

I ordered the high ackerman, solid offset bushings from Breeze and I will be relocating the rack to behind the ears.

My question is does everyone need the SAI mod and bumpsteer kit or how do I determine if I do?

I haven't finished building my car, but my dad's Cobra is downright scary on the hwy and I want to avoid that. His is twitchy and just goes wherever it wants in the lanes. I honestly don't like taking it above 60mph.

I'd like to be able to do high speeds without any concerns, so what do I need?

Also, can I run them on 95GT brakes and 16x8's?

Lastly, best price I've seen is $300 for the SAI mod and $150 for the bumpsteer kit, anyone know of better prices?

Thanks guys!
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Old 02-28-2007, 07:53 PM   #2 (permalink)
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I am building my car for extreme speeds and have the same concernes. Building for stability is very different than an autocross set-up. I am using Levey's front end kit which is an entirely different approach than the ackerman mod and SIA mod. His kit eliminates bump steer, raises the roll center, and runs 0 ackerman. The entire kit is designed to slow down the handling and make the car easier to handle on the edge. I suggest you call Gordon Levey.
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Old 02-28-2007, 08:50 PM   #3 (permalink)
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Hey guys, what is a SAI Mod


Thanks
Tony [img]graemlins/silver.gif[/img]
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Old 02-28-2007, 09:00 PM   #4 (permalink)
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I must have missed class that day too. I have built 3 and do not know.
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Old 02-28-2007, 09:08 PM   #5 (permalink)
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Called and spoke with Gordon, good guy and helped explain a few things to me. I'd like to find some actual pictures of his setup to get a better idea. I'm not too keen on lengthing my steering shaft myself though.

Guys do a search for SAI mod, but whitby sells the kit...http://www.whitbymotorsports.com/UIn...ventoryid=1604

Hope that helps.

And thanks Mike, I'll give you a call here in a short while.
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Old 02-28-2007, 09:08 PM   #6 (permalink)
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BAM,
reset the toe on your dad's car and see if that helps. A hair of toe OUT will make a world of difference.
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Old 02-28-2007, 09:37 PM   #7 (permalink)
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SAI is steering axis of inclanation (also known as the kingpin angle). Stock FFRs have a very high (abnormally high) kingpin angle to keep the UCA ball joint out of the wheel to allow the use of period-correct 15" wheels. The SAI mod moves the UCA mounting points at both ends outward. While they were at it, the designers also lowered the front roll center to better match the IRS rear and reduced the anti-dive to allow better brake modulation with strong springs. Aparently it improves caster trail, reduces jacking, and reduces the twitchiness around center of the steering. While it was designed for autocross, it has aparently improved street manners as well.

It is designed to be used with high Ackermann (as on the Mk III or older cars with an Ackermann mod) and is not a complete solution (some kind of bump steer solution is needed).

Gordon's kit uses zero (or slight negative Ackermann) to tame the steering, allows for an adjustable roll center, and virtually eliminates bump steer by putting the tie rods in the same plane as the LCAs. It is designed for track and street but not autocross.

If you don't think you will ever do autocross, Gordon's kit is probably the most direct route to get a car that is stable at speed. Whether 16" wheels will work with the SAI mod will depend on offset. Several of the autocross guys run 15" or 16" wheels for their rain tires, which tend to be narrower.

Scrub and steering effort was not really a consideration in the SAI mod since all serious autocrossers use power steering. Whereas with Gordon's kit, steering effort for a manual rack is greatly improved. Much of this comes from the fact that will less agressive turn-in (from the zero Ackermann) you can run much less caster.

These are two different aproaches, both "work", but they are not compatible with one another. Both are less twitchy than the stock FFR. One is designed for low-speed maneuverability and the other for high speed stability. One works better with power steering and the other works better with manual steering.

Mike

PS. One can reduce bumpsteer by changing how the tie rods mount on the spindle arm, but the only way to eliminate it is to make the tie rods track in harmony with the suspension. There are two ways to do that. 1. put the tie rods in the same plane as either the UCAs or LCAs or 2. increase the rack length so that the tie rods have the same effective length as the control arms. Gordon's kit does the former, some others have started experimening with the latter.

[ February 28, 2007, 09:32 PM: Message edited by: Michael Stora ]
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Old 02-28-2007, 10:11 PM   #8 (permalink)
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Well put Mike
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Old 02-28-2007, 11:13 PM   #9 (permalink)
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Quote:
These are two different aproaches, both "work", but they are not compatible with one another. [/QB]
I was discussing this with Gordon a while back and he told me that he thought the SAI mod and his bumpsteer solution would compliment each other. Maybe he'll chime in here.
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Old 03-01-2007, 02:33 AM   #10 (permalink)
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Quote:
Originally posted by John Card:
</font><blockquote>quote:</font><hr />These are two different aproaches, both "work", but they are not compatible with one another.
I was discussing this with Gordon a while back and he told me that he thought the SAI mod and his bumpsteer solution would compliment each other. Maybe he'll chime in here. [/QB]</font>[/QUOTE]I was refering more to the high Ackermann setup that the SAI mod was developed for. That would be in interesting combination.

Mike
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Old 03-01-2007, 04:00 AM   #11 (permalink)
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i dont believe the SAI mod is related to the ackermann mod.

the stock SAI is really, really high, and although justifiable in the stock design, just isnt a design thats associated with a high performance car.

ive driven a levy 5 link/bump steer modded car and it was very nicely set up, however it still exhibited odd characteristics in medium sharp corners- the feedback was weird and that might be because the caster trail is messed up- dont know for sure but it felt like that. might have been something else with that car, but i am very happy with the production SAI adapter parts ive been using this season.
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Old 03-01-2007, 09:44 AM   #12 (permalink)
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My car exceeded my expectations with regard
to handling.. I have the solid offset bushings
an have not installed the bump steer kit yet.
The rack is in the normal location.
Actually it feels so good I may not install the
bump steer kit... I don't do any racing, but
it is not twitchy up to 90..
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Old 03-03-2007, 05:55 AM   #13 (permalink)
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Quote:
Originally posted by Dan B:
My car exceeded my expectations with regard
to handling.. I have the solid offset bushings
an have not installed the bump steer kit yet.
The rack is in the normal location.
Actually it feels so good I may not install the
bump steer kit... I don't do any racing, but
it is not twitchy up to 90..
Good news, do you have fox spindles or SN95? Also, do you remember your alignment settings? Do you have a power or manual rack and do you know the ratio? Just trying to find a few things out and see if I might have the same luck on my build.

Thanks
Matt
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Old 03-03-2007, 11:42 AM   #14 (permalink)
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At speeds over 100 mph you also need to worrt about aero problems and front end lift.

Charlie
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