Hi AZ.
I've been waiting to upgrade my clutch trying to make sure I get the right combination for my street-ability and torque holding needs. I live in a very hilly area and my drive to work likewise has multiple stoplight/intense hill situations that need to be managed in rush hour traffic, yet need to hold the designed power of my build to avoid needing to upgrade the clutch system again. My targeted HP/TQ range is 440-550, although working with custom rods and pistons I may want something able to go a bit higher if I can push these heads, as long as I can get street-ability out of the system where I'm not stalling or having to give the next car 3s lead off a light to avoid jumping into their bumper trying to feather and modulate on a hill. Durability of the system is also a concern, as higher power can burn through clutches quickly sometimes a bit of overkill is a good thing for longevity as long as it doesnt impact street-ability too much. This build is meant to be done with a LWFW so for all possible builds assume that unless otherwise specified a sprung clutch will be used with the corresponding manufacturers LWFW.
So far the options within the single disc option are ClutchMasters FX350, which gives "110% holding capacity over stock"(525ft/lb?) using segmented kevlar and "New Formula Button" Discs that appear to be 8 puck discs that would allow plenty of street-ability, but the barely more than double holding capacity concerns me for the longevity of this clutch as my build will be near it's holding capacity and could cause high wear. For slightly more holding capacity at 170% over stock (687 ft/lb?) the FX400 uses ceramic 6 puck 4 wing "Ceramic Button" discs, however the listing for this item warns of high chatter and quick engagement due to the ceramic. This makes me concerned for the featherability of the system without jumping the car drastically with higher hp.
Some members I know on this board have the Spec Stage 3+ system installed currently and are loving the 679ft/lb holding capacity of the plate without having to go to a puck design. However I have read a ton on quality control issues and general quality issues with this system and would like to avoid it unless absolutely necessary. This disc does feature carbon semi-metallic full faced material which could provide great surface area for durability, given a high build quality. The appearance of the plate leads me to believe they are a ceramic metallic mix, and could still be jumpy discs. Given that these are the popular single disc options and the latter ones that should hold my target hp well are not the most durable or street-able options, I looked into twin discs.
ClutchMasters FX 400 with "Ceramic Button" 4-wing 6 puck design
ClutchMasters FX 350 with "New Formula Button" Disc
Spec Mini Twin R-Spec Weight Reduced LWFW System
The conversation switches to single disc vs. twin disc at this point, Spec has both a single and twin disc option, although their highest rated street system is rated at 679 ft/lb vs 800 on the twin disc. Their stage 5 710 ft/lb holding clutch is terrible for modulation as it's a full race build, would a twin disc allow for reasonable street-ability at a high holding tq.? The flywheel for the Spec twin disc appears to have weight reduction holes cut from it, which both makes me concerned for it's durability and too light a flywheel.
My top pick for this clutch system was originally the 725 Clutchmasters kit, which features 2x 7.25" clutch discs for surface area but low rotating mass for better response (similar to Spec's "Ralley" classification vs their "Drag" twin). I'm thinking CM did the original tooling for a twin on this vehicle, and Spec got ahold of some tooling and made a similar one. CM claims "The cover assembly is machined from billet aluminum with 25% more tensile strength than the competitions cast unit." and Spec loudly states on its Stage 1-5 clutches that they've redesigned the pressure plate with a billet pressure plate, on it's twin listing no such literature is found. This makes me suspect Spec is using cast covers to allow their own tooling, which would explain their 3 puck option in the absence of CM having a 3 disc unit. The unit states in it's description that the CM twins "... are designed to hold high hp/tq while retaining a very smooth operation" leading me to believe the 725 genuinely will be a smooth engage with two smaller clutches and a minor increase in clamping force, where the 850 would be the model oriented for track/drag/intense usage.
Typically twin discs are on/off switches, at least that's the impression i've been lead to believe, however CM offers what they call a "Race/Street TD7S" twin disc kit which HeelToe calls "Street" which through research on their BMW Twin FX725 system I found has one "fiber tuff" rigid disc, and one ceramic rigid disc in the "Race/Street TD7S" system and two ceramic discs in the "Race TD7R" package which HeelToe calls "Street/Race". This rewording by a company that's been around the model for a while makes me believe CM genuinely did get the FX725 system streetable if HeelToe has rewritten the classes of those clutches one step down each.
ClutchMasters FX725 7.25" Twin Disc System
Stumbled across a custom AASCO/Tilton listing on heeltoe that i've got to assume is something they must have set up independently, as even on the site it allows input for "Power Holding Needs" and "Engine/Trans Application" and a "completely custom billet flywheel"(like AASCO or otherwise per application? Unknown). The twin system uses 4 puck cerametallic discs, and later in the listing mentions "Suitable for most racing application where limited clutch slippage/modulation is desired" leading me to believe this would be worse street-ability wise in comparison with the CM systems either 725 or 850. If anyone has further information on this combination, I know Tilton makes great clutches and has for a long time, would love to know if there are more modulatable options for the discs and if the weight of the flywheel can be custom or what that aspect of the listing meant.
AASCO/Tilton Twin 4 Puck "CeraMetallic" System
The choice between Spec's twin disc and ClutchMasters's seems easy where the CM even claims by description to have higher build quality and part strength. Hard to do that in 2019 and be wrong, worth the extra $300 for durability and a description that claims smooth driving. Unless i'm missing something about the intricacies of twin discs, a 4 puck with ceramic in the mix is going to cause a jumpy response with the Tilton option. That same trait may be great for a true rally/drift car that could use the quick engagement and wants fast response on the pedal with high TQ requirements, but here I need the slippiest twin setup possible to retain streetability. CM's twin kits do not have sprung clutches, so any driveline harshness will be felt in full, which makes me wary of the modulatability of these twins but would that also not make it easier to feather with improved feel on what's going on at the discs?
I've put this up as an open discussion for the viability of each of these high power holding designs, and to open a discussion on the benefits and drawbacks of each system. If anyone has a twin disc system or has had one on their AZ car, please give us your input from experience as nothing beats pedal feel for knowing how well a clutch works for a car in a certain situation. Price point of the system is not to be a discussion point, as this is meant to be an even comparison of features of each system unmotivated by finance. Likewise I would like to hear thoughts from those of you with experience with these systems for my application, I can feel the end of this clutch coming up and I would like to get this next system decided on soon and value y'all's input.
