How much HP is lost with the Mcleod Street Twin???

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.....

Originally posted by Injuneer
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.

Originally posted by Injuneer
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

I guess so thanx guys.

I see that you just sold your Street Twin on the classified section of this board. What are you going to replace it with? BTW, in case you hadn't noticed, this same topic has been under discussion on the Forced Induction part of the forum:

http://web.camaross.com/forums/showthread.php?s=&threadid=127086

This guy starting this thread probably would have been happy to buy just your steel flywheel if you are only changing to aluminum.

I was just going to point him at that thread…

For all the “I don’t know, I haven’t weighed one” responses here I’ll reprint part of what I wrote there:

Some weights for you guys:
Stock (well worn) LT1 assembly that I just ran across in my basement:
Everything + hardware: 41lb 11oz
Flywheel: 20lb 5oz
Clutch disk: 4lb 5oz
Pressure plate: 14lb 7oz

Weighed on a different scale (but accurate as far as I remember):
Street twin, aluminum: 38.5lb
Street twin, steel 51lb

bunker, your measurements are WAY off on the weight of the ST.

shipping weight of the steel ST is 63lbs and that includes the master cylinder.

Thanx guys, I'm just gonna buy a new alluminum version instead of putting things together, the alluminum version disks look a bit different, so I'd rather not put things together :) as far as measurements, you're probalby right, my scale is weird, but hmm.. so the alluminum version ST full assembly weighs less then the stock steel full assembly? wow.

You realize that now you are giving up the inertia stored in that heavy steel flywheel at launch?

Somehow, I think you are totally over reacting to what is not a lot of HP on a dyno, and probably closer to "0" on the street.

Originally posted by Injuneer
You realize that now you are giving up the inertia stored in that heavy steel flywheel at launch?

Somehow, I think you are totally over reacting to what is not a lot of HP on a dyno, and probably closer to "0" on the street.

Yep, there's a reason cars have flywheels. If I were buying another ST, I'd save the $200 and get the steel flywheel. Better for drag racing and street driving. Road racing would be different.

Rich Krause

Dyno numbers are very important to me, I'd rather not sacrifice, I mean I'd rather not go through all the trouble but something inside tells me to do it, the thing will be heavy enough to move I'm sure, even though like you guys said the extra weight is needed for a clutch with not dampened disks, but I hope it'll be drivable enough, I mean look at my setup, I think its very drivable :)

Originally posted by rskrause
Yep, there's a reason cars have flywheels. If I were buying another ST, I'd save the $200 and get the steel flywheel. Better for drag racing and street driving. Road racing would be different.

Rich Krause
Why for road racing???

I have an Al flywheel with a Cengerforce DF... Needless to say it holds up my 600rwhp car... I am not fond of the dragstrip as I say its worth crap to me... When you race on the street you need all the power you can have over 120mph.

Hehe I'm not fond of the drag strip either, aparently people say you don't loose any power on the street, what they mean is what you loose you gain from inertia, but whatever.

Originally posted by The Highlander
Why for road racing???




I think the common thought with that is that in a road race situation and other higher rpm racing where you are never at a stop, you can benefit more from the higher hp of the lighter flywheel . The revs are usually always up quite a bit so "stored energy" is not as much of a concern(except for in corners).

Although it would seem that a heavier one would help comming out of corners though , on some road courses. And some would argue that a drag car could just use a light flywheel, and leave at any rpm they want (High Rpm). Although there still probably would not be as much "stored energy".

Anyways, I'm not sure which is best, because of course it depends on the combination, but I think the interatia/ "stored energy" for street /drag - vs- . the higher hp from less weight in road racing or circle track, is what some argue regarding heavy and light flywheels.

In a drag racing , or street situation, the intertia / "stored energy" I think is the benefit. A harder launch off the line at the strip , and less chance of bogging when leaving the from a dead stop on the street. ( Although in cars with more tourque , i think this is less of/ or not a problem when leaving a light or stop sign.)


It seems like a lot of people DON'T recomend light flywheels for street cars, unless they have good TQ, but like them for racing where there is no stopping, and the engine is at higher rpm for longer periods or time (like circle track) so as to benefit from the higher hp.

i have seen alot of posts refering the ST as an on or off clutch. now on or of meansto me that it is going to desrtoy my STOCK rear:(. now i do plan on going to the track a few times a year and having some fun on the highway once and a while but i dont beat my car everyday. so my questions is will the ST kill my rear and other parts with jsut DD????:confused:

oo and Al or steel for me??? sugestions?? :cool:

A light flywheel is of great benefit in road racing because you're downshifting in addition to upshifting. Not many folks rev-match when dragracing, so the time that it'd take for the revs to drop with a heavy flywheel isn't important. When in the twisties, though, you need to be able to drop or gain revs as quickly as possible when shifting, as harsh shifts and heavy cornering don't go well together.

camaroz28_97, I wouldn't say that a ST is a switch - it's just a bit touchy. What will kill your rear end is the fact that it's a solid-hub design, with no springs to damp the forces generated when the clutch engages. This "minor" detail went unnoticed by me until I killed my trans doing clutch drops at the strip.

[QUOTE]Originally posted by Eric Bryant
[B]A light flywheel is of great benefit in road racing because you're downshifting in addition to upshifting.


how much of a defference are we talking here?? is it really enough to spend the extra cash??? i dont street race that much.

Originally posted by camaroz28_97
how much of a defference are we talking here?? is it really enough to spend the extra cash???


Not enough for me to spend the extra money, and my Impala's primary purpose is attacking twisties.


i dont street race that much.

Road racing is not the same as street racing :) We're talking about running a car around a closed road course.

Originally posted by Eric Bryant

A light flywheel is of great benefit in road racing because you're downshifting in addition to upshifting. Not many folks rev-match when dragracing, so the time that it'd take for the revs to drop with a heavy flywheel isn't important.


The lighter flywheel/clutch assemblies are desireable when you want the 'noload' RPM's to come up quickly and for the engine to drop RPM's quickly especially when decellerating. Both conditions you see when running the 'twisties'.

Conversely, when drag racing you want to hold the RPM's not only on initial lauch, but at each shift point. The heavier flywheel/clutch combos assist in that effort by, as several folks have pointed out, storing energy that can cushion the RPM drop both the at the initial launch and again at each shift point.

One of the quickest ways to drop ET's in an otherwise stock vehicle is adding in a heavier flywheel/clutch combo. It used to be a tech inspection point in the stock classes in NHRA but it's been awhile since I've raced so I don't know if it still is.

Bill