SPEC Clutch: Proper Selection

Installs & Reviews Dave Pankew Photos By: www.specclutch.com

When it comes to making some horsepower, we shouldn’t have to tell you your stock clutch will not cut it. But there are literally hundreds of different clutches to choose from that are manufactured all over the world. We wanted to round up some different clutch designs and materials to explain the differences, in order to eliminate the possibly of linking up the wrong clutch for your application.

One of the most important things to remember when clutch shopping is to be realistic. Although we’d like 1000whp, we don’t need to buy a low-priced clutch that will hold that because it is simply too aggressive for what we’re driving. According to the experts at SPEC clutch , they say that the mistakes tuners make most often today is buying a clutch that is not enough for their future power plans or buying a clutch that does not match their driving preferences. SPEC offers many options that allow for good drivability AND high torque capacities.

The proper criteria by which to rate a clutch is lb-ft torque, not horsepower! Considering the level of your modification and, even better, with the help of some dyno runs you should be able to get a realistic torque number. Ideally, you want to choose a clutch with a capacity 10-15% beyond your car’s torque output, so you don’t have to worry about future mods or a surprisingly positive dyno number. If your car is NA now and you plan on adding a turbo, sorry, but the same clutch isn’t going to be applicable with almost double the factory output of your car! At that point, it’s time to consider a new clutch.

The next consideration is drivability. How do you want the clutch to feel at engagement? How much pressure does the clutch pedal require? Having driven everything up to a triple plate clutch, we can assure you there are some clutches that are not acceptable for street use. The feel at engagement is important since most tuners drive their car on the street and that includes traffic. The choices for a street use are geared towards the sprung hub (dampened) disc and a material configuration because it has some forgiveness in the neutral area and does not have an ON/OFF switch engagement. However, in the case of a multidisc unit, the extra surface area can provide a progressive engagement, even with 2 rigid hub discs, that mirrors a dampened single disc.

Another consideration is life expectancy and warranty. Most aftermarket clutches have limited warranties against defects in workmanship and materials, but because performance clutches are used and abused, they wear faster. Some SPEC Clutch products will last much longer if the instructions are followed to the letter and the break-in period is observed. A break-in period is normal driving with no launching or burnouts for a period of up to 500miles. Doing this prevents any hotspots from forming on the clutch surfaces. Hotspots will hinder clutch to surface contact glaze over and can cause a brand new clutch to start slipping. As hard as it is, when you have a new clutch and some punk is revving on you, just let it go. Replacing a clutch is not cheap in terms of parts and labor.

After a clutch is selected, we highly recommend addressing your flywheel. Your factory flywheel is big, heavy and prone to cracking. The face of the flywheel is almost always littered with hot spots as well which do not engage as well with the clutch, especially your new one. There is always the option of machining your flywheel face to form a new bond with your fresh clutch, but we recommend a lightweight billet aluminum or steel flywheel. A lot of late model flywheels are of dual mass or modular design. These flywheels are not serviceable and should be discarded at the first clutch change. Attempts to service these units can result in pitting, uneven surfaces, imbalance and worst case flywheel body cracking, compromising structural integrity.

SPEC CLUTCH STAGES:

Stage One

Kevlar/metal woven organic with a steel backing/sprung hub
Types of driving: street, drag, drift, road race, rally, autocross.

For bolt on naturally aspirated and mildly modified forced induction engines. Stock-like daily drivability and very good wear characteristics.

Stage Two

Segmented Kevlar/sprung hub
Types of driving: street, drag, road race, rally, autocross.

For all mild to moderately modified naturally aspirated and power adder engines. Also good for stock power levels and spirited driving when good daily drivability and extremely long life are the goal. Stock-like daily drivability and excellent wear characteristics.

Stage Two+

Carbon graphite/kevlar multi-friction/sprung hub
Types of driving: street, drag, road race, rally, autocross.

For all modified engines with more torque than the Stage 2 can support. Maintains Stage 2 feel for good daily drivability and offers very good wear characteristics, but with a higher torque capacity.

Stage Three

Carbon graphite puck/sprung hub
Types of driving: street, drag, drift, road race, rally, autocross.

For heavily modified street and race engines. Offers sufficient daily drivability with a comfortable pedal feel and quick engagement. Offers good wear characteristics under low and high stress usage. 4 or 6 puck carbon semi-metallic friction with high torque sprung hub and disc assembly.

Stage Three+

Carbon graphite semi-metallic full faced/sprung hub
Types of driving: street, drag, drift, road race.

For heavily modified street and race engines generating more torque than the Stage 3 can support. Offers good daily drivability and better manageability than the Stage 3 with even better wear characteristics.

Stage Four

Carbon graphite puck/rigid hub
Types of driving: drag, drift, road race, rally.

For heavily modified engines or engines of any modification level used in the above driving environments where instantaneous engagement and light weight are beneficial. Not street-friendly due to harsh engagement. Offered with 3, 4, or 6 puck carbon semi-metallic friction with high torque rigid hub and carrier assembly.

Stage Five

Full metallic/rigid hub
Types of driving: drag.

For extremely modified drag race cars that call for a “slipper” clutch/progressive torque-induced engagement. These clutches are best ordered as custom configured and should be ordered after providing specific information about the car and its purpose. Not street-friendly due to harsh engagement.

Mini Twin/Triple

Carbon graphite Semi-metallic or full carbon/carbon/rigid hub
Types of driving: street, limited street, drag, drift, rallye.

All billet low inertia multidisc that can be configured for different loads, disc configurations and types of driving

Super Twin

All staged materials or carbon on carbon/rigid or sprung hub
Types of driving: street, road race, rallye, autocross,drag, drift.

All billet larger diameter twin disc that can be configured for all types of driving. Designed to provide near stock drivability and torque capacity levels up to 1400 ft lbs.

Source:
SPEC Clutch
Clutches & Flywheels
www.specclutch.com

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