|
|
Thread: 20b into an repu
[' This thread is 2 pages long: (1)
2 '] |
Jeff20B
Moderator
Posts: 661
|
posted November 11, 2001 02:56 PM |
 Edited By: Jeff20B on 11 Nov 2001 23:29 |
20B into an REPU
I've recently been racking my brain about 20B stuff, you know, learning all that I possibly can about them, in order to install one in one of my vehicles (listed in my sig). Go ahead and scroll down to look. Here they are on my web page. http://www.geocities.com/cd23c/cars.html#mg I'll wait... Ok. The MG can barely hold a 13B and the baja has cracked metal here and there from a VW 1600! Well, as you can see, the two most likely candidates are my truck and Cosmo. They are both heavy by Mazda's rotary standards (the Cosmo is heaviest, with the REPU about a hundred pounds less, give or take what ever is in the bed). Both of these came stock with the old school 4 port 13Bs. I've felt the accleration of a street ported 13B with an RB Holley 550 in an REPU, and I might get a ride in Dave Atkin's supercharged Cosmo some day. It does 18 in the quarter mile so its not all that quick, but wins because it is very reliable and consistant. http://www.atkinsrotary.com
For a while now, I've figured that my Cosmo would be the best car to put a 20B into because it has the largest rotary engine bay I've ever seen. The 13B is dwarfed in there. It could fairly easily hold a 20B I think. It also has an automatic which would eliminate the need to move a stick shift rearward, and there is no slave cylinder to have to make room for on the firewall. Ah yes, only minor problems were coming up, which I kept on solving pretty easily, untill it dawned on me that the Cosmo has a unibody. There is no way that it can handle tons of power without tons of mods. Otherwise, the frame would get tweaked. I hadn't planned on 500HP or even 400. I wanted a very basic torque improvement over stock, not to mention the wonderful 20B exhaust note singing in the background. But the stock auto tranny wouldn't like all that extra torque, and I wasn't about to cut up my tranny hump to fit a powerglide or whatever in there.
I know of a Chevy Vega that got a tweaked frame from a 350 V8 that a guy installed in it. You know, the chevy Monza was supposed to get a rotary engine. The Vega is the same platform, as well as the Pontiac Astre (Astra), Sunbird, and the buick skylark. Well no wonder it is so easy to fit a V8 in those cars! Just make sure you upgrade lots of other stuff to handle the torque!
So what do I do? Install a gutless 20B? All that extra weight without much more than stock power? I could get as much torque from a supercharged 13B, and save weight! I wanted to continue using an automatic because this is supposed to be Mazda's Thunderbird/Impala/Cadilac. A stickshift is cool, but this car is staying an automatic... for now. I didn't want to spend over $10k with most of it going to frame mods either. I also wanted to keep the stock diff because its already geared pretty high (3.636). The pros: The diff gearing is great, and the engine bay is large enough. The cons: no limited slip, the automatic tranny can't handle mamoth amounts fo torque, the unibody can't either. So I had a dilema on my hands.
My friend would like to put a 20B in his REPU and I figured it would be better for me to put one in my REPU rather than my Cosmo because the REPU has a ladder frame. Bingo! The ladder frame is plenty strong enough for 200+ HP, and the rear axle is bulletproof (though geared hidiously low at 4.60). I'm thinking with a few mods to the engine bay, tranny shifter location, possibly driveshaft and rearend, that this might actually work!
I've already taken lots of measurements of my Cosmo for a 20B, but not too many of my truck. What do you guys think?
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
repuguru
Redlining
Posts: 319
|
|
posted November 11, 2001 08:23 PM |
|
Big Power
You know I don't think I'd stop with the motor. Get some fender flares and make it a dually. You need to figure some way of putting that kind of power on the ground.
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted November 11, 2001 11:19 PM |
|
I might start with an NA carb setup because I won't have enough money for any kind of turbo or supercharger at first. This should keep the power low enough for stock parts, for now. I want to upgrade in stages. I might get a supercharger for my 13B first just to get used to the extra power. I've thought about tubbing the rear and getting super wide tires, but I suppose duallies would be cheaper (and more truck-like).
I have to ask myself how much chassis stuff I want to spend money on. My friend's Rotoscoot (REPU) is the product of $15,000 and unknown amounts of man hours. It handles better than most cars. I'd like to at least come close to it in handling, but again, how much should I spend? Mods for more power in a straight line can detract from cornering ability. I want a good balance of both (is it possible?).
The 20B has 9.0:1 compression rotors stock. The REPU has 9.2 rotors, while the GSL-SE has 9.4. Our engines seem ok with 9.2 compression. My point is the 20B, with its 9.0 compression, should still be rather powerfull in NA form. I'll just need to find some sort of carb that will work. I'll also need to either build an intake manifold, or have somebody build one for me.
All I want is the awesome 20B sound and more torque than stock. You can only achieve one of those with a supercharged 13B.
It will add more weight to the front end, but REPUs are back heavy already, so I'm curious to see how low it drops the front end. How much more can a 20B weigh than an old style 13B with its cast iron water pump and 30-40 pound flywheel? The weight of one extra rotor, one rotor housing, one 20B-only side housing that holds the extra stationary gear, and a piece of eccentric shaft. Hmm... A hundred pounds? Well, I weigh more than that, and when I step on my front bumper, it lowers the truck only a tiny bit. This is at the far edge of the front end so the lever effect is much greater than it would be if the weight was further rearward, like centered over the wheels for instance. The 20B will have a light steel flywheel and aluminum waterpump. That'll shave a few pounds. I'm no longer worried about needing a heavy flywheel... not with an extra rotor spinnin' in there.
Any thoughts?
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted November 19, 2001 03:28 AM |
|
I've seen a Ford Courier with a V8 in it. The guy had to put his battery in his bed (right above where our batteries are located hehe). The stock diff handled the torque just fine. It was a Mustang 289 I believe (it was a light weight V8, heh, right... light V8). It also had an auto tranny and the rad was mounted right against the grill to clear the water pump. He also had to cut some of the sheet metal up there to clear the top of the rad and cap (I don't think it rubbed the hood). The ugliest part was how he ran the header pipes through the firewall. Uhg! Pipes were going every which way like spaghetti! It reminded me of some sort of a Fiat or something (joke!).
Ahem. I can see putting a powerful boinger into a Courier, but I don't really like the thought of putting one into an REPU. Just my personal preference I suppose. (I'd like to see a rotary in everything! cars, boats, planes, bikes, gocarts, lawnmowers, sewing machines, oops). So for me, putting a boinger in a rotary vehicle is a giant leap backwards.
I've been gathering info on my swap, from what kind of tranny to use, to the ignition system, to where to get the 20B. I think I've answered all 3 pretty well. If only I could get them all for xmas!
So for starters, I'll look into a TII engine and tranny to see if I like the extra power. Well, maybe I'll just put an SC on my current engine and see how long it takes to break my poor tired old SA tranny. Ah, decisions decisions decisions.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted February 06, 2002 05:28 PM |
Edited By: Jeff20B on 23 Jun 2002 01:13
|
Uncle-Jim, I read on the Leaking Windshield thread that you would love to put a 20B together. Same here! I've thought long and hard about the pros and cons of doing a 20B in either my Cosmo or truck. Still nothing concrete as of yet, but I would love to post here any answers you may have questions for about installing a 20B into your Cosmos
I sent an email to Cal at http://www.geocities.com/mazdarx5/ asking how much HP our Cosmos' unibody could handle and he said he would only worry if putting one of those engines into an R100. The Cosmo can handle heaps and his ran fine with 450+HP from a large turbo on a 13B and the stock tranny (it has a modified valve body and a shift kit, that's it). This is very promising!
I would have continued with all of the measurements but I needed to shift my attention to some computers around here that were acting up. I also got some cool hardware for mine for xmas so I spent some time setting everything up. Only since the beginning of this week have I had any time to work on cars again. I had some trouble with my Cosmo's carb on my truck's engine (way too lean) while my truck's carb is on my Cosmo in order to get it running. More about this in another thread, but it is currently what I've been working on.
So, what sort of stuff were you going to do with your Cosmo?
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
repuguru
Redlining
Posts: 319
|
|
posted February 06, 2002 05:34 PM |
|
|
Hey Jeff have you seen the thread over on the RX7Club forun talking about the custom cranks to make a 20b out of 13b parts? Some guy in NZ is turning down billet 3 rotor cranks. They're saying they are shorter motors than the actual 20b. But with all the power of course. The crank it self is like 2 or 3 thousand.
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted February 06, 2002 08:20 PM |
Edited By: Jeff20B on 6 Feb 2002 20:46
|
Bruce builds them. The NOT20B yellow RX-7 had one of those as well. From memory, it used Cosmo engine parts and a Supra tranny gearbox with a ribcase bellhousing and some sort of adaptor inbetween and a really cool hydrolic throwout bearing/clutch slave cylinder pusher thing. It allowed the HITman to mount his tranny really far back without the need to modify his firewall to fit a standard Mazda style slave cylinder. I even downloaded the MPEGs that used to be linked to his site. This was a couple years ago, but I guess it left a big impression on me.
Bruce made a 4 rotor shaft a bit more recently, but I'm not sure of any NOT26Bs running around at the moment.
I'll go look for that thread...
Edit: just saw the thread. Looks like same old-same old to me. Were you interested in anything in particular? Maybe I could add two cents...
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
Klaus43
Rotorhead
Posts: 1259
|
posted February 07, 2002 09:44 AM |
|
3 rotors, 4 rotors, duallies; rotaries in everything...!
Ah yes!...The speeddream continues! I've heard many stories... but seen few results that fit my pocketbook.
Personally, I'd do whatever it takes to avoid tubbing or dually-ing a REPU, to keep it more original and versatile, unless I was building an all-out dragtruck or "mini bigrig". I think you're right about needing to find a way to put the power to the ground, tho--and REPU's aren't heavy in the front, but they sure are light in the back without a load! I'd want to lower, maybe mess w./ the spring rates, and do all the susp. mods possible to increase "handling" (traction bars?)--but what we really need then is a limited-slip differential...
All the info I've heard says there's room in a REPU for 3 or even 4 rotors, done correctly and carefully. Of course, your choice of trannies will affect this... Two to three grand for a custom e-shaft? Nice idea, but not cost-effective in my reality, unless I win the lottery... Alternative: a complete nose-chop off a 20B car, like Atkins has advertised for ~$6,000 seems the most cost-effective, tho not brand-new way to get there.
Don't stop dreaming! --K.
|
|
repuguru
Redlining
Posts: 319
|
|
posted February 07, 2002 11:00 AM |
|
I hear all the horror stories of the time and money these guys are paying to shoehorn a 20b in their 3rd gen cars and wonder to myself this? How much would a 4 rotor engine cost to construct? How do you set up an ignition for one? If this guy has parts to create you own monster motors from 13b parts then I can run high comp rotors. No Turbo.
Heck I bet two big double pumpers would look cool as hell feeding the thing. If a ported NA 13b is capable of 200hp, surely you gain something when you have two working as one.
I'd ditch the Mazda line of tranny selection and adapt a Turbo400 or something with an overdrive out of a full size car.
Of course all this is pending my Powerball ticket hitting this weekend. If not I'll be heading back to the Turbo 13b drawing board.
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted February 07, 2002 12:52 PM |
|
Well I hope your ticket comes through for you!
One thing about the ignition and rotor phasing, I'm with peejay in that I'd go for 90º of offset between the two sets of rotors as well. The reason why is because it will probably make the exhaust note sound like a real 26B. However the ignition will be a bit more complicated though. The reason why granny's suggests having the engines at 0º or 180º offset is because you can get away with a single dizzy wired to two sets of ignitors. Or maybe I'm wrong about that. But it'd still be easier to accomplish than running 90º because there is no provision inside a 1st gen dizzy to easily trigger all the pickups you'd need. But then ofcourse some sort of ignition computer could take care of it.
Probably the easiest 4 rotor engine would be two 13Bs bolted together. Then phasing and ignition wouldn't be a problem, but length would be. I doubt two 13Bs would fit in an REPU engine bay.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
Draggin_2600i
Redlining
Posts: 235
|
|
posted July 31, 2002 10:41 AM |
|
I have a few questions about 20B's. The new sequential twin turbo 20B seems to kick ass. even though I have read it has just a bit more horses than a 13-REW, it has a hell of alot of torque and a higher potential.
This would be a cool engine but, what a bout when it is time to maintain it or do a rebuild? Are parts for this engine readily availiable in the States? or are parts from other rotaries compatible incase things need to be replaced?
oh well just doin' research for my Dreams.........
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted June 07, 2003 10:37 AM |
|
I'm getting a 20B on Monday. It'll probably need a rebuild as the importer said it had low compression. I've already had an offer on it to double my money spent on the purchase of this engine. I still haven't decided which vehicle to install it in. Just yesterday I was thinking I'd like to install it in my REPU. Then I read this thread and am now leaning more towards my Cosmo.
When the engine gets here, I'll take off the turbos and inspect the apex seals. If they feel good, I'll do an MMO treatment. If the springs have gone flat, I'll need to rebuild it.
I basically want to leave the outside of the vehicle as stock-looking as possible. No duallies or racing stripes or anything like that.
The funny thing about my Cosmo is it's been sitting since late last summer. I pushed it out of the garage and cranked the key. It fired up within the first second of cranking. Holy crap! How can this be? All I did was change the fuel pump and run fresh gas into the carb. Not even a modern fuel injected car fires that quickly. Is my Cosmo trying to tell me something? Its engine was slated to go into my rotary GLC project to get it going, and then it was going into my REPU because I've got a bridgey in the works for the GLC. The REPU's engine was going into my MG Midget rotary project. I was going to play musical engines, but only this time, there wouldn't be one left-over seat, or engine. Even my old RX-2 12A is going into a street bug. But why would the Cosmo fire up so fast and easily? I even grabbed my can of starting fluid just in case. My facial expression was simply shock.
So what should I do? What is my Cosmo trying to tell me? Is it wanting my to leave the 13B in it because it ran perfectly? Or is it showing me that its excellent running engine would be perfect for my REPU eventually (after the GLC)?
Don't get me wrong, I'm extremely happy it ran as well as it did. I know an REPU would be really fun with mountains of torque. The Cosmo is more of a luxury cruiser type car. There's also no gaurantees of the drivability of an NA 20B with a holley on it. Drivability is "A" #1 at the top of my list with the Cosmo. However, the REPU has some fudge-facter, what with a stick shift and all. So why not install an S5 T2 5 speed from an FC into the Cosmo? Yeah, some day. Also, it's possible the extra torque, even at idle, would allow enough fudge-factor to use a Holley on a 20B in the Cosmo? MAybe I'm just affraid to ruin a (currently) good (running) thing?
I've just got to weigh the costs of doing each vehicle and sell my baja to try to help offset them. In the Cosmo, I won't need a flywheel. In the REPU, I'll need which ever flywheel will fit which ever tranny I'll use. Either 225 (stock) or 240mm (T2) from Racing Beat most likely.
If I put the 20B in my REPU, it would have to be taken offline for a few months during the conversion. The REPU's old 13B would work well in the GLC to get it running. The bridgey will also get built during that time. All the while the Cosmo should run ok as-is, I'm hoping.
You know what? One of the main things keeping me from doing a 20B in my REPU is the diff gearing of 4.6. Lots of FC 20B guys say 1st gear becomes useless. Heh, what about a diff geared much lower like our '74 trucks? Well, I guess I could search out a '77 with its 3.90, or whatever. Or a simple Ford 9" with posi or whatever.
Man, it's Saturday and I've got till Monday to think about it. After that, it's 20B time!
Thoughts?
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted June 07, 2003 12:07 PM |
|
I think I'll just use my REPU as a test-bed for the NA 20B swap. Then, when all the drivability issues are solved, I'll then be able to install another 20B in the Cosmo and not ruin the car in the process.
Ok, this is for all you 20-wanna-Bs. My setup will consist of these parts.
Modified FB dizzy with three pickups mounted 120º apart. Running Leading ignition only with 0º and 180º sparks (to take care of the Trailing squish effect).
Atkins 20B supercharger manifold without the SC on it.
Some sort of Holley carb with enough CFM to feed a 20B in NA form. The common way to measure it is to take the displacement of a rotary and multiply by 2. 1962CC x 2 = 3924CC or 4.0 liters. I think a 390CFM carb will work (it's what Atkins uses on their SC kits). If not, a regualr Edlebrock 600 or Holley 600 or 700 will work on an open plenum manifold.
My truck's exhaust needs to be redone since the header is 20 years old and has been patched a couple times where it cracked. It'll get three pipes and Rotary Engineering glasspacks (they're out of bussiness). The three pipes will Y together and then into 3 inch pipe through three of glasspacks. Three for three, hehe.
I'll probably install an original Cosmo/RX-4/REPU ribcase 5 speed because the 20B is NA. It might have around 250HP and 200lbsft of torque. Or maybe a T2? But the rest of the 240mm hardware to go along with it, would cost more. I currently have two spare 215mm discs and pressure plates. A little smallish, but if something's gonna slip, I'd rather have it be a clutch. SPRT came up with that one. My truck needs a tranny very soon anyway. I'll think about it.
Weighing only 75-100 more LBS than a 13B shortblock, I've got a few ways to bring the actual installed weight of the 20B down a little. The stock 33LBS REPU flywheel is getting replaced with a light steel from RB. Even the starter will be out of an '86 FC NA 6 port car. They're small and light. I've got an electric fan to use. The 20B's waterpump is aluminum but shaped oddly. I do however have a spare FC aluminum waterpump with fan. The extra length may not allow me to use the fan though. I'd need to move the rad up against the grill like the V8 Courier guys did. A little metal cutting was required though. Youch!
You know, the stock twin turbos could probably be used in an REPU because there is no idler arm in the way, like there is in a Cosmo. Well, it's still an option for the future.
Tell you what. I'll go ahead with the NA 20B with Holley and 20B dizzy first. Then I'll upgrade the power capability when the truck's power handling capacity is uh capable. Yeah, that will do... for now.
Now I'm off to go pull some engines out of a couple of FBs. :)
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
Klaus43
Rotorhead
Posts: 1259
|
posted June 07, 2003 01:34 PM |
|
You may want to check out
the Predator carb. ...capable of all the flow you could want, and, much like our engines, 'so simple it works'...uses standard holley, etc. style bolt pattern... My guess, you'll be wishing for a limited slip soon. Then again, there's the question of the clutch... I recall hearing of a dual-stock spring homemade setup...? Glasspacks? That last? I'd believe that when I see it... must be a reason that Co. went under... Before cutting frontend metal, how about a custom fit radiator with electronic fan(s)? Just my $0.02... :)
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted June 07, 2003 11:52 PM |
|
All valid points. Thanks for your input.
Predator, huh? Isn't that like a 700CFM carb? Is it highly adjustable? I'll consult with Atkins before I purchase a carb.
LSD is good to have. :)
I need another tranny anyway, so I figured I'd just go with a good old ribcase for now. That means I'm limited to a 225mm disc. It'll probably be ok with around 225HP. I'll upgrade in stages, so it's no sweat. Or maybe if I can find a T2 for a reasonable price?
Currently, my REPU's got six glasspacks. It's never gotten any louder since I installed the system back in '97. It came out of a different truck and was built in '91. My MG Midget also has a single glasspack and it's still good. They're the only rotary-worthy glasspacks ever made, to the best of my knowledge. They don't seem to wear out. Maybe that's why the company is no longer with us? Their product was too good? I wish they were still in business.
I've got several ideas for a radiator. I'll look into it more thoroughly soon. I have an electric fan to use. If I could run a clutch fan, I would. With as much HP as I plan to run, it shouldn't make much of a difference. The HITman runs a stock fan too. He says, what's 5HP going to the fan when you've got hundreds to spare? Hehe.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted June 08, 2003 09:45 AM |
|
According to j9fd3s, a GSL-SE tranny can handle around 220-250RWHP, but it also depends on the way you drive. I know the ribcase trannies are stronger. Heh, maybe I'm just trying to avoid the whole T2 setup because of all the extra stuff I'd need.
Well, now that I've had a chance to sleep on it, and I know of a good used Cosmo 5 speed that I could get for $200, I think I'll go ahead and get it. I know better deals are out there, but I think I get a 90 day no-workey policy with the trans, or something like that. Yeah, for simplicity's sake, I'm better off going with a regular old ribcase for now. I won't need a T2 driveshaft, or slave cylinder, or starter, or clutch and PP.
I've gotten good at keeping my SA trans alive. I think a ribcase will live for a while.
It'll be here tomorrow. C'mon guys. Any other thoughts? Am I the first to attempt a 20B in an REPU? I know Rob Golden of Pineapple Racing was thinking about doing one, and even had a custom license plate for it, but he decided to go with a P-port 13B instead.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
Klaus43
Rotorhead
Posts: 1259
|
|
posted June 08, 2003 02:23 PM |
|
Trannies/Predator
Perhaps the GSL-SE 5speed will indeed handle the HP no problem, but what comes to mind is that trans. propensity for input-shaft bearing failure... As far as the old ribcase, the synchro's going out seems to be the main issue...other than the increasing rarity of internals... not that power handling should be an issue as long as everything works... I don't have any personal experience with any newer versions... What I would do, though, is drain and refill either with AmSoil gear lube, consider replacing input and output seals while at it, and proceed to run it. That AmSoil is darn near a miracle in terms of function actually improving over time!
Predator carburetor: (732)367-8487 ...also on the 'net...
Zero personal experience, but it always struck me as the ideal rotary performance carb, as it can flow like crazy, and is motorcycle-carb simple in design. You might also want to follow up on ebay item #2406832689...this closed out item was a predator set-up rotary...
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted June 08, 2003 09:19 PM |
|
Thanks for the link. I've seen a predator carb on eBay before, but didn't remember it until I saw it again. Those square butterflies and everything else sure looks... different. I wonder how the drivability is on one of those.
Yeah, I'm not too worried about the power handling capacity of a ribcase tranny. But I am worried about the synchros. I'll give the Amsoil a try.
I measured some stuff under the hood today and figured 80mm forward and 80mm back ought to do it. I'll need two 12 inch electric fans or maybe one 10 on the front and one 14 or 16 on the rear, mounted so it's sucking through the oil cooler as well as the rad. Low speed towing is an important part of this project, so lots of airflow is needed. Too bad the engine bay is too short for a clutch fan. Anyway, 80/80 will allow the stock rad to stay where it is.
The ribcase tranny has a better location to mount the slave cylinder than the SA does. Also, the top nut on the engine lifting hook bolt will be under the spotwelded lip, but it'll have enough clearance behind it for add-uh-quit access. Infact, after doing an engine install in an automatic '84 FB, my top nut will be a piece of cake.
There's just one weird thing about the 20B. It's got an extra upper bolt hole that may interfere with the slave cylinder. As far as I know, only the JC Cosmo's automatic tranny has this upper hole. Some people out there have gotten away with only 3 to 5 bolts on their 20B projects instead of all 6. The long starter bolt will not hook to the engine either because the 20B has a different kind of starter.
I'm thinking about going with a '74-'85 front cover so I can have front motor mounts. But there may not be enough room. I'll just have to see what it would take to fabricate side mounts. There are motormount pads on the main crossmember for mounting a boinger in our trucks. Maybe I could use them?
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
brad
Rotorhead
Posts: 1672
|
|
posted June 09, 2003 01:15 PM |
|
quote:
You know what? One of the main things keeping me from doing a 20B in my REPU is the diff gearing of 4.6. Lots of FC 20B guys say 1st gear becomes useless. Heh, what about a diff geared much lower like our '74 trucks? Well, I guess I could search out a '77 with its 3.90, or whatever. Or a simple Ford 9" with posi or whatever.
Thoughts?
Don't sweat it jeff. Keep the REPU diff. Enjoy the short gearing. Spins up motor faster in every gear, 4.65 will really help in gears 3-5. I got 4.444 gears, 626 RWD tranny and 21" tall slicks on my racecar and I do zip thru 1st gear quickly, but it's no big deal. I wouldn't say 1st gear is useless, it is used to get into 2nd gear!
____________
-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge
|
|
Jeff20B
Moderator
Posts: 661
|
|
posted June 10, 2003 10:21 AM |
|
Thanks for the post, Brad. Now that I'm leaning towards installing it in the REPU nearly 100%, I'm thinking the same way. I'll still be able to go the same speed in any gear; it'll just accelerate faster, and tow stuff better. I'll tell you my 2nd gear in the SA tranny totally sucks for towing a GLC (missing an engine so it's lighter than stock) up a hill near my house. 1st gear was ok, but 2nd bogged terribly. I couldn't help but think a torqueyer engine would have been less emberrasing. But then again, the gear ratios in the SA tranny are different than a ribcase. Basically, the SA trans is a close ratio 5 speed meant for a sports car. The ribcase has 1st and 2nd closer together, but 3rd is really far and 4th is still 1.0 like all Mazda's manuals. My REPU, with its gutless engine, would have done ok up that hill if it would have had a ribcase in it. But for daily driving, the SA trans is great. Hmm... maybe I could keep the SA trans until it actually looses a gear. I don't shift fast and rarely burn out, so maybe it'll last a while longer. It'll save me like $200 as well. Sorry for the long paragraph by the way. The GLC has a ribcase 5 speed in it. No, I must control myself hehe. I just need to keep the cost of the conversion low. Both trannies are similar in shape. Only the slave cylinder is in a different spot. D'oh, I need to use a ribcase afterall. An SA trans would cause the slave to be under the tranny tunnel, while a ribcase would remain accessible.
Man, what was I thinking? Oh right, it's too early to think. The 20B showed up yesterday around 11:50AM and I worked on it untill 11:50PM or thereabouts. I'm tired, heh.
Spinning the engine by hand, the compression is low. But after we finally got the turbos off (very time consuming), I could feel that the apex seals are carboned up a bit. Only rotor #2 (middle) had conistantly ok sounding pfffts out the Leading plug holes. It was the only rotor with apex seals that could be pushed in a little. The other six apex seals didn't want to move.
The only bad thing that happened was we snapped two exhaust studs. The first snapped with no effort, and you could tell that particular gasket was leaking as well. The other came loose but then the nut encountered some bad threads or something and the stud snapped. Two other studs came completely out fo the engine and were tight coming out. The other two studs are still in the engine, but one has damaged threads near the end. The other is rusty. I've never seen a rusty exhaust stud before. I think Mazda used non stainless steel on the 20B for some reason. I've got a few rotor housings laying around with studs that I could extract. They're the regular stainless kind. I think the nuts Mazda used are stainless steel, but they have a crimped section at the end, like nylon locking nuts. I think this crimped section is the cause of all the problems we had.
It's not unheard of to break studs on a 20B, appearantly. Rob's 4 door HB Cosmo snapped one or more durring some spirited driving (he kept the stock twins and just wired the flapper door thing open). "now" on the RX-7 club forum took a 20B apart and in the pic, at least one stud is missing or broken in an upper hole. I guess I'll need to drill them out and use an easy-out or something.
I didn't really want to do that much work to this engine. I just wanted to do an MMO treatment, swap manifolds, and throw it (carefully) into my truck. Or should I tear it down and port it? I'm not sure exactly how many miles are on this engine, but there's a good way to check certain things to get a basic idea.
One easy way to tell if an engine will develope a dowel pin leak from high mileage, is to remove the oil filter pedistal and check the condition of the O rings. If they're hard and stuck to the cast iron, it needs a rebuild. If they're still soft, partially round, and not stuck, the engine could go on for another couple thousand or so. Maybe I'll check the 20B's O rings since I have a few that came out of a low mileage engine. Also, my Comso's O rings were as described above (in resuable condition) when I had to put the filter in a vice and wrench on the pedistal because a previous mechanic didn't use any oil on the gasket. It was totally dry!
Today I get to remove the intake manifolding and the rat's nest. Fun fun FUN!
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
|
|
| All times are PST (US)
[' This thread is 2 pages long: (1)
2 '] |
|
|
|
