So I blew my engine over the weekend

[Rotarydave]

Originally Posted by Jeff20B

I have a 5" SC that has a -7 pulley and it has always sucked; takes forever to get into boost, will only boost under high load conditions like going up a steep hill etc.

you will def like the -10 better than the -7, with a -7 you were pulling maybe 5lbs of boost total they use that setup on a 22R toyota engine that can't handle alot of boost.

It came like this from Atkins during the days when they were recommending 7" SCs for everything......probably an honest mistake on their part .... We also recieved the wrong length belt for the 5", sure enough. It is the correct belt for a 7" SC with a -7 pulley, but was way too long for a 5", even with a -7 pulley. I had to get a shorter gatorback, which stretched a little and caused the alt to need to be lifted to its maximum on the bracket, and it would still slip sometimes.

I experimented with several different belt lengths including a little adj on the braket to get some more adj, my question would be which alt are you using these were more designed to go with the 84 and up style than the older bigger ones, Roaching belts was and is not uncommon for me, as long as I treat it good I have no problems I also started using a belt dressing for a little more grab, if I roach it I have to tighten the belt again as i just streched the hell out of it, the other thing is make sure you have the belt wrapped the right way, i had it wrong once, the system worked but i could not get enough tension, then found my problem went oh crap used the right belt and was ok.... You have to really reef on this sucker that belt is so tight for my application I can play a tune on it.

My friend has a 7" SC in his REPU with a -8 pulley and it seems to have problems such as belt slipping even thought it's tight as heck, even while still in vacuum before it transitions from vacuum to boost; sounds like marbles rattling around in a coffee can

DETONATION ALERT...... DETONATION ALERT, HE NEEDS TO ADJUST HIS TIMING AND MAKE SURE HIS MIXTURE IS RICH ENOUGH OR HE WILL POP THE ENGINE, THAT IS THE MARBLES SOUND. I am willing to bet that it does not make that sound if he is easy on it like about 1/2 throttle.... it also sounds to me that he is really hammering it that is more than anything what causes the belts to do that, not really shavings but is dust

look familiar? (this is the 7inch look at all the belt dust )

He also has a 5" SC with a -10 pulley in a rotary converted 510. He doesn't like how quickly the boost kicks in and would like to try a -8. I'm not going to argue with that because it means I'll be able to get his -10 pulley and a good used belt.

Now that sounds like the 5" that I am used to they spool fast, i am willing to bet that he has something like 4.11 rear gears and a close ratio tranny as well the reason, the engine spools so fast you almost can't shift fast enough and it doesn't get the benefit of all that power, that was what worked on the Rx4 with the low rear gear.

[PercentSevenC]

Dave, what was your exhaust setup like? Primary lengths, collected diameter, silencers, etc.?

I learned a new car smell yesterday: toasted clutch. Not surprising, given how worn it was before it went in the car, but I'll need to deal with that before doing much else.

[Rotarydave]

Originally i had a RB 1st Gen type Header on there with a single large presilencer running to a RB muffler, but that is all 2in stuff. I felt I was getting to much restriction, therefore I switched to a road race header that I had, had a 2:1 fabbed up with a 2.5in join then used a RB 2nd Gen type presilencer and custom built the exhaust back to a racing application muffler. I can't say as I noticed a difference but we were changing a whole bunch of stuff at one time. Yes toasted clutch is a smell I was familiar with as well, if you are going to play with it at the strip don't think that RBs street and strip clutch will hold up cause it won't you'll burn it down just as fast, I ran a Center Force DF disk and PP for awhile it did ok but I was still not happy and just jumped straight to a puck clutch which typically overpowers the rear wheels, I did have one prick of a cop pull me over for peeling out I got out of it by asking him if he could take off from a stop in my car without doing it, and he couldn't...

Hope this helps

[PercentSevenC]

Similar to the setup I was planning. Modified RB header, collect to 2.5" somewhere within the recommended 22-25" range if I can, an RB universal presilencer, and out through a Borla ProXS.

An old RB S/S clutch disc was what I was using. I liked how easy it was to live with. I'm still mulling over my options, but I think I'll just replace it with another one for the time being, maybe combined with a heavier pressure plate. I'm not planning on doing a lot of drag racing with it; just some occasional autocross and back road thrashing. Once I upgrade to a TII tranny and 240mm clutch components, I'll consider something beefier.

[Rotarydave]

If you can find a CF DF disk and plate I was really happy with that for street use it was pretty easy on the take off and then clamped harder the more I spun it so it worked well just not for the strip.

[Jeff20B]

Dave, I have a used 215mm CF DF disc and p-plate that look to be in decent shape, plus an old style RB light steel flywheel that lacks the clearancing for 225mm pressure plates, so it can only be used with 215mm plates even though the friction surface extends out to 225mm. I also have a new 225mm RB SS p-plate, HD disc and light steel flywheel that has these 225mm clearances. Lastly I have a CF 215mm p-plate by itself, a stock 215mm clutch disc and an aluminum flywheel (again lacks clearances but the steel friction surface extends out to 225mm and I got away with a 225mm disc and a 215mm pressure plate - it had a funny 5mm lip of disc on the outer edge hehe - didn't cause any problems).

I need to get my REPU running soon and a new engine will be built for use with the 5" SC and -10 pulley. It will be expected to tow a load no heavier than a GSL-SE complete car on a trailer or a VW baja with one of those front beam tow hitch things. My friend tows stuff like this all the time with his '77 REPU and the 7" SC as described above. His clutch setup consists of a 225mm SS p-plate, 225mm HD disc (it shudders a lot, I'm sorry to say, but grips just fine) and a light steel flywheel. The tranny is a '76 5 speed and the rear end gearing has got to be the tall '77 3.9 set because it just seems to be geared a might bit taller than what I would consider to be ideal.

My REPU is a '74 but apparently has the same rear gear ratios as his '77 because when we drive the same speed in the same gear, our RPM sounds the same. I too have a '76 5 speed (it has the far spread between 2nd and 3rd and 5th is short). It drives a lot like his '77 due to the rear end. A high idle makes it hard to creep along in parking lots because it feels like you're in 2nd gear sometimes.

I'm asking for opinions on which clutch/disc/flywheel combo I should use. The engine and intake are already known. The tranny and rear gear ratios are already know. The exhaust is just an RB collected header for REPU (they don't make them anymore) into a single 2" system routed through two RE glasspacks. This keeps velocity high for good low RPM performance. I assume the -10 pulley will kick in soon and then run out of breath right around when the exhaust becomes a bottleneck. The engine ports will be small stock '76 Cosmo size for maximum low end. R5 side plates. Stock exhaust port timing (they close early compared to GSL-SE for less overlap and less wasted boost out through the exhaust system).

I thought about using the CF DF and the old style light steel flywheel in the REPU because I want relatively easy pedal effort, due to the REPU's shorter pedal travel, but my friend's REPU has decent effort like how mine did with a dead stock REPU clutch setup (the disc was worn down to less than 7mm and was stiffer and more grabby than it should have been). I hated the stock 30 pound flywheel with a passion. If I were staying NA, I'd have gone with a GSL-SE flywheel, but I feel the SC will add a bit of rotational mass+drag so it will make the light steel feel heavier. My bro's RX-4 had a GSL-SE flywheel with the SC and it felt just as heavy as it did with the stock 30 pound flywheel, but while NA felt lighter and matched the tall '78 3.636 rear gears quite nicely. If we would have known this about the SC during the planning stage we would have gone with a light steel. It worked out for the best though because the SC came off the RX-4, but I don't want a repeat in the REPU since I plan to keep the SC in it. So light steel all the way.

Do you think a CF DF would stand up to years of REPU usage? Or would I be better off with the SS p-plate? I don't think the HD disc would be ideal since my friend's shudders so much. I have a good used stock 225mm disc ready to get. Does the CF DF disc shudder like an HD disc? I heard the dual friction discs don't last long. Any input you can add is greatly appreciated.

Last but not least, I have a 1st gen that needs a clutch setup as well. It's getting a 13B while I gather funds to build an NA 20B. No plans to upgrade the tranny or rearend. I'd rather have the tires slip than break drivetrain components all the time. So 225mm is the maximum size I can go until I'm forced to upgrade to T2 components. I wish I knew more about the holding capabilities of RB vs CF, you know? All I have to go on is what others have said about them.

Do you think a CF DF could hold between 250 and 300HP behind an NA 20B? Or should I plunk the CF DF into the REPU? I sort of wanted to max out the clutch setup for the 20B, including the 225mm HD disc, since shuddering wouldn't be an issue in a 1st gen, and it is kind of a spicy meat ball, you know? but would entertain the CF DF since the car is lightweight and it's getting a 13B first anyway. The truck needs a good relible clutch setup that will last for years, and so far, despite the shuddering, the RB setup has worn well in my friend's REPU. I figure I can cure the shuddering with a stock disc. Well, I've rambled long enough. Thanks for any input.

[Rotarydave]

I don't think that you will be happy with the CF setup in that configuration, as for why the stock REPU setup preformed well in the application you had, the stock setup has more buffer built into the disk and more clamping force on the pp this was based on it being a 3/4ton truck not a sport coupe. You need to check your gears if you can I would recommend going to a high ratio rear esp if you plan on doing the towing, not the 4.44 or 4.60 (don't have notes with me) from the 74 auto but you def don't want the 77 gear either a nice compromise would help, for your application I would def go with a steel flywheel prefer the 225 one I would recommend a stock one because the rotational mass you need is on the output side to keep the driveshaft spinning. The s/s plus HD disk is going to shudder a little bit but you will destroy a DF disk with the starts. The reason it worked for me is my problem came at higher RPM when the PP didn't have the increase in clamping force that the DF setup did.

AS for the 20b I would ask Mazdatrix for their opinion.

if you need to ask a little bit more pointed questions call me Sunday

210-391-6871

[Jeff20B]

From memory, the REPU rear gear list is:

74 manual 4.625
74 auto 4.3
75 manual 4.3
75 auto 4.11
76 manual 4.11
76 auto 3.9
77 auto and manual 3.9

I don't know what year or gear ratio my truck has, but it is a later '74 model, so could actually have a '75 rear gear ratio, or could have started life as an auto truck. Is there anything in the VIN that would say?

I have towed with the truck before, but the engine was never all that powerful. It has always been a gutless wonder, with power robbers ranging from a crappy restrictive exhaust to a crappy engine that Ken Durkee built using an NO intermediate plate (small ports) and lots of missing chrome in the rotor housings. Those issues have been solved and now I'm just wondering about the clutch setup.

I really did appreciate the stock REPU setup for its smoothness and strength. I just didn't like the heavy flywheel under normal driving conditions, and my disc was worn to less than 7mm uncompressed. My old white REPU that percent now has, has a much less worn stock setup, and it drives wonderfully (although still on the heavy side if you've just driven something light).

For the new engine, I was going to use the 225mm SS pressure plate for its similar gripping force and a light steel flywheel and the added weight of the SC would probably add up to nearly the weight of a GSL-SE flywheel (or at least that is kinda how it felt in the blue RX-7). I was fighting with myself over whether or not to use an HD disc or a stock disc. Then along came the CF DF setup.

Hey, if you say the CF DF setup won't last long in the REPU like getting things rolling from a stop, where my friend's setup has the most trouble, I'm all for changing my plans.

How long do you think a stock 225mm disc will live in an REPU? Or am I better off with an HD disc and live with the shuddering? It's very awesome to have you input on this since you've driven a CF DF before.

[Rotarydave]

Jeff call me

[Jeff20B]

I've given it some thought and I think I'll go with the Racing Beat SS 225mm pressure plate because, as you said, it's a 3/4 ton truck and needs a stronger pressure plate than say a small coupe; also it needs good grip at a low RPM so centerforce is out. The RB SS pressure plate will mimic the decent grip of a stock REPU pressure plate. Pedal effort is also acceptable to me. It feels fine in my friend's REPU with the same pressure plate.

The flywheel is going to be a Racing Beat light steel. I'd have gone with a GSL-SE flywheel if NA, but since I'm going with a 5" SC, I feel the reduced weight of the flywheel will be made up for with the extra rotational weight and drag of the SC. Besides my friend's REPU does well enough with the same flywheel.

The one and only question I have for you is about the clutch disc itself. My two choices are an HD 225mm and a stock 225mm. You said something about using an HD disc and to put up with the shuddering. It shudders because it has no springy marcels between friction surfaces. However it is plenty strong enough to handle towing and other heavy duty use in an REPU. My only gripe, I guess, is that it might shudder from time to time.

Now we take a look at a stock disc. It's one of those common '83-'92 Daikin discs with the rubber spings (sprung center) and springy marcels. This disc has a lot of buffer. I put one in my '76 Cosmo with a GSL-SE flywheel and the silly disc seems to take forever to grab. It's not an issue of grip, because it has plenty to spin the rear tires, but what I'm taking about is how long the "buffer zone" is while you're letting the clutch pedal out. If I had the engine or tranny out right now I'd have swapped in an HD disc because I'm really not very happy with the long friction point of this type of disc after having driven HD discs for any length of time. It's smooth as silk though, which I must admit does suit the character of the Cosmo. I could get used to it.

So what's the question then? Well, we know the pedal travel of an REPU is shorter than a Cosmo or 1st gen, and we know a stock REPU disc does have marcels between disc friction surfaces. I was merely wondering whether a stock Daikin disc, with its wide friction point would suit the REPU better than an HD disc. I'm starting to think no it wouldn't. The way I see it, the Daikin disc is lightest duty or stock duty (I've seen the aftermath of one used really harshly in some guy's FC; the rubber spring things popped out of the center lol), the REPU stock disc is probably closer to heavy duty like the HD, but with marcels helping to add buffer. Then finally the HD is, I guess should be considered extreme duty as far as 225mm organic friction type discs go. To get anything stronger or more reliable you'd need a solid center, and there goes the rest of your buffer. I don't know of any discs like that and I certainly won't use a puck disc in the truck.

Wow, just having a chance to type it all out has helped a lot. I now know that I'll be best off using the HD disc in the REPU. If it shudders a little on take off, who cares? I'll be employing two competition motor mounts to help steady the engine if and when it shudders, to help minimize the effects.

All three clutch components are either brand new, hardly used (less than 5 miles) or in the case of the flywheel, less than 200 miles. I'll scuff it up just to be sure the disc breaks in on a roughened surface. This should help prevent the conditions which produce shuddering from even begining.

Thanks Dave.

[Rotarydave]

you can also use a solid tranny mount and a tranny torque brace like the ones RB has it will help.

I think you will be happy with the HD disk it may still shudder a little you just have to remember your friction points and the rate of release that works best.