Ok I've been trying to get an answer on LT1_TECH but noone answers the question, after 1 week of TTT's it got deleted!!! This pisses me off, so I descided to ask some of you guys on here, please don't move this to LT1_TECH I'll get no answers there.


My question, I just got a Mcleod Stree Twin for my LT1 & among other things I weighed the thing & it weighs TWICE more then the stock clutch??? I don't know about everyone else but wouldn't that 30LB's really hard to spin? Now I'm wondering how much HP I'll acctually loose with this thing. Did anyone dyno before & after the Mcleod street twin install?

This is the steel version, also, I'm well aware of weight helping drivability & track times, but I"m worried about DYNO numbers, thanx guys.

 

Coupla hp at most. Don't sweat it.

Rich Krause

 

I'd guess more than "a couple HP" if it really weighs twice as much. Kieth at WS6 got "a couple HP" when he substituted an aluminum DS for the stock steel, and that's only a few pounds lighter, with a very small radius to the center of mass. Adding 30# with a much larger diameter is probably going to absorb a little more HP when you do a dyno pull, and it has to be accelerated with the rest of the drive train. Maybe somebody has time to do the calculation.....

 

Fred: I am not talking calculations but what I have seen on a Dynojet. Maybe his weights are wrong? I never weighed them.

Rich Krause

 

I was going to point out my setup only had 12.8% drivetrain loss with the Street Twin, and then it dawned on me that at least some part of that weight was already on the engine when it was on the engine dyno... at least the flywheel. The part I'm not sure about was whether the complete clutch was installed, or whether they used something that was part of their engine dyno setup... it was all hidden in the engine dyno bellhousing and I don't know what it was.

Even on the dyno, the HP absorbed/"lost" would depend on the rpm/sec rate, and how well that approximated the actual track performance.

As far as actual track performance, it would almost be a "wash".... if you were doing 6K clutch dumps, you would have all that stored energy in the flywheel/pressure plate mass, and, depending on how much the engine rpm dropped when the clutch hooked, you would recover some of it.

In any case, it isn't a huge number. I think the "coastdown" HP on Keith's tests was only like 16-18HP for the entire drivetrain, and that seems similar to the "fixed" portion of my drivetrain loss (inertia) if I solve for for fixed and variable components using simultaneous equations.

Bunker... how accurate are your weights... I thought my coimplete Street Twin shipping wieght was around 60-65#, but my memory could be way off.

 

I think that's about right - the flywheel is around 40# by itself.

As far as HP "losses" go when on the dyno, it really depends on how fast the motor gains revs, and the total effect is going to differ depending on how heavy the rest of the drivetrain is. The real-world results will also be impacted by the weight of the vehicle. This is not a simple question to answer. Why don't you do a before-and-after test with your vehicle on the dyno and tell us the results?

 

before & after test? my tranny is already out & my stock clutch is toast. When I weighed my stock flywheel it was 30 pounds & the mcleod was a bit over 60!!!! now I"m acctually thinking this mcleod idea is stupid to be honest, I don't care about track times, I street race a lot & if I loose HP I'm gonna be mad.

But seriously, adding 30+ pounds seems like a lot.

 

I don't know about power losses with a street twin but I do have results from going from a 6 spd with a street twin to a th400 with a tight nitrous converter. With my 6 spd and street twin I ran an 11.88@116mph with a 1.65 60ft. With a th400 I ran the times in the sig with a best mph of 119mph on another 11.4 pass. The street twin is a really heavy clutch and I thought the same thing as you as far as horsepower losses and I do think it could have an effect on 1/4 mile times. I picked up 4 tenths in the 1/4 from a 6 speed street twin setup o a th400 setup though.
Later
Matt

 

I tuned one 96 vette - solid roller 396 - it made 472rwhp with a stock vette clutch / dual mass flywheel (which is heavier than the f-body), 4.10 (or whatever the dana ratio came to), and 17x11 GM GS wheels. With nothing but a swap to the steel mcleod twin disk it dynoed 461 rwhp (both at 6500) on the same dyno ( 2 days later).

The twin disk is still the way to go I would submit - 11 hp at the 450+ rwhp level on the street is pretty immaterial - traction, driving, etc. are all going to have effects that are magnitudes greater - and you have the advantage of not having to worry about clutch slip, etc - with near stock drivability (my experience with the steel mcleod).


Chris

 

While it may only lose 10-15hp on an engine dyno, or 4th gear on a dynojet, it's greatest loss will come at the track in the lower gears when inertial loss is greatest.

That being said, I wouldn't use any other clutch

 

Just curious... are these steel flywheel Street Twins being discussed, or aluminum flywheel Street Twins?

It's been a long time since I've seen mine, but I could probably dig up the shipping receipt for sending it down to Mark if I had to. I'm fairly sure that the aluminum flywheel version is in the 35-36 lb. range though.

Considering that there's an extra clutch plate and a floater (not to mention the floater stands), it's not surprising that the steel version weighs more than stock. It grips a lot more than stock too... which would you rather have?

 

Man thats like a 2% loss, thats quite a bit if you asked me if you get 390RWHP instead of 400 I would get pissed off, maybe I should save up for the Alluminum one, mine is used who wants it for $650 ?

Ps. the steel was discussed here.

 

I think you are worried over nothing. I went from stock clutch to a steel street twin and my MPH stayed the same in the 1/4. Of course I lost my ability to be able to hook on drag radials because the ST shocks the tires so badly, but I recovered that with ET Streets (and another 3 tenths on top of that). Who cares about dyno numbers when all that matters is how the car performs?

 

I almost have to agree with Rich. This board in general (not this section) has become so dependant on dyno numbers for reasons that have escaped me.Dyno numbers dont win races,and are more or less "bragging rights",as Dyno's are very useful in tuning.
2% loss can occur with weather,and as some have stated,there isnt a better clutch out there for you 6 speed guys.

 

If dyno numbers are what you want from your car, then yes, the steel McLeod is not the best choice - a stock setup with a lightweight Al flywheel would be better.

Now if dyno numbers are not your only metric, but you include other things like longevity, drivability, track, etc. it is all going to depend on how you weight each one of those factors.

Of course if you make a decision there to get rid of the McLeod steel twin disk that brings up other questions - things like gears? Sure, 3.73's/4.10's are nice, but if you throw in some 2.45's you can probably dyno much better - is another 10rwhp worth it for you?

etc...

The correct choice is going to depend on what your goals are for your car and what makes you happy. In my estimation the twin disk is the way to go though.


Chris