12A vs 13B weight

Rogue_Wulff · 07-20-2009, 11:20 AM

Is there any real difference between an 83-85 12A and 84/85 6P 13B, when it comes to weight? Near as I can figure, they should be within 10-15 LBS of each other, with the 13B having slightly more metal.
I've got an '83 GS with a 12A/5 spd, and the engine is having oil consumption/smoking issues, but runs fine otherwise. The car is in rather nice shape, aside from the smokey exhaust. The 12A has been rebuilt at some point, and still makes good compression, but it had the beehive oil heater on it (now has FMOC).
I also have an '84 GSL-SE that has a good engine, converted to carb with the RB intake and edelbrock 600. But, the interior is in bad need of attention, as well as the paint and windshield. Likely needs suspension work too.
I'm thinking about swapping the SE engine/trans into the GS, so I can continue to drive it, until I can freshen up the 12A. Although, I could build a 1/2 BP or full BP 12A, and use the SE chassis as a track car. Or, swap in a TII engine/trans.......
Near as I figure, the SE engine/trans would be a bolt-in swap, aside from the engine mount bar. Both cars have RB headers, so even that would be a simple swap. If I really wanted to get fancy, I guess I could swap the front crossmembers, eliminating the mount bar mods required to install the non-stock engine.
I'm figuring the extra HP/TQ of the 13B would be way more than enough to offset the minor increase in weight, especially since the swap would actually be legal in CSP, where I've run the GS for several years, and it has most of the suspension mods needed to be competitive in the class.

Jeff20B · 07-20-2009, 11:57 AM

Yes, do it! You have my full support. Swapping the crossmembers, so no front bar mods needed, is a good idea. The RB headers are indeed swappable. Daily drive the nice one with the bigger engine (it will reward you with more torque and stuff and you'll quickly fall in love with it) and race the ugly one with the built 12A. The extra weight of the 13B is a non-issue. The reduced weight of the 12A, for the race car, is also a non-issue, but I'm sure both make you feel a little better inside.

Rogue_Wulff · 07-20-2009, 12:13 PM

LOL, I figured I could count on Jeff's full support.
I already sourced a TII throttle cable for the 13B/edelbrock combo, and it should be quite easy to hook up the cruise and an A/C throttle kicker on the GS. It has both, and they both function, therefore they will remain.
Heck, the SE doesn't even have a heater right now, much less A/C. I was pretty much planning to use the SE as a track car, since it's in overall poor condition, but does have the bigger brakes (much needed for a track car).

Am I right about the weight difference being in the 10-15LBS range? If so, it's totally a non-factor. I'm just curious if I'll have to make a minor adjustment on the GC coilovers under the front of the GS......

Jeff20B · 07-20-2009, 01:10 PM

Yeah, 10 to 15 pounds. The 13B rotors are 11.5 compared to 9.5ish for the '83-'85 12A rotors. The 13B rotor housings are about 1 pound more each, and the shaft is only slightly longer so not much weight gained there. The tension bolts by the same amount, but there are 17 or 18 of them so it adds up to a small amount. The rest is in the water pumps (same weights if both are cast iron) and the flywheels. 26 pounds stock for "31" (late 12A) and "304" (GSL-SE) style. You can drop the 13B weight below a 12A just in the flywheel if you go aftermarket. Maybe do an FC aluminum waterpump too.

15-16 pounds for full cast iron. An aftermarket GMB aluminum housing with the stamped steel impeller drops the weight a bit. The other option is an FC waterpump which is about 6 pounds if I remember correctly.

One option which you might consider but shouldn't do unless you're running an electric fan is an FC housing and a GMB 1st gen impeller. Ultra light weight but not very strong so you shouldn't use a stock clutch fan with it. I did this for my rotary baja project. I added a stud to the alt bracket hole on the GMB and filled the hole in the FC housing with sealant. The engine plates are 1st gen Y castings so no provision for the FC alt braket bolt. If you already have an idea as to what I'm talking about, you should be able to replicate this setup for the lightest waterpump just short of the no longer available racing aluminum waterpump from the '80s. Otherwise don't do this because I haven't run it long enough to know how the parts hold up over time.

Rogue_Wulff · 07-20-2009, 01:26 PM

I'd like to go with a light steel flywheel, but it's not in the budget right now.

I'm about 90-95% certain I'll be doing this soon. I could always just drop the 12A into the SE chassis "as-is" and let my 17 year old son have it, or use the carb and starter on the GSL I have stored away. I think it would bother me less if he were to crash the SE than it would the GSL. Besides, if he got ahold of the GSL, he'd prolly try swiping the new Konig's when I wasn't looking........ He really likes those wheels, especially after seeing pics of OOT's car with them on it. The GSL is white, and the Graphite Rewinds look amazing on a white car.

Rogue_Wulff · 07-21-2009, 01:29 PM

My son is also wanting me to do this. He wants the SE, but knows there's no way I'll let him loose on the street with that monster 13B. It's just a bit too much for an inexperienced driver. He also knows the 12A isn't exactly a slouch, and is very capable of getting 20+ MPG, seeing as I have done so for more than 4.5 years.
I still have the old ST springs that came under the GS, and a set of 15s to fit the SE bolt pattern, so he could easily pursue his desire to run autocross with that car. The stock 14s have nearly new tires (under 500 miles) in spite of being 3-4 years old.
I'll prolly take the DLIDFIS off, and convert back to stock ignition on the SE. I just don't trust those GM HEI's enough for a daily driver. Even with the new mounting plate and best thermal goo, they run extremely hot.
I guess this swap is almost ready to take place. Kinda wish I had the funds to freshen up both engines during the swap, but that can be done a little later down the road.

My 12A header/presilencer uses 12mm studs. Does the SE header/presilencer use 10mm or 12mm? I've never got around to installing the presilencer on the 12A car, but the SE has the full street RB system, with an aftermarket muffler. I can always hook the 12A header to the SE presilencer even if it uses the 10mm studs. I could also use a different type presilencer under the other car, if the 13B header is only designed for 10mm studs, or just enlarge the holes in the flange......
I'll likely insist he change the rear muffler on the SE chassis. Being a bit older (and presumably wiser), I can get away with a bit louder exhaust than a teenager. Particularly when the SE looks rather shabby, due to being 1/2 covered with rattle can primer (previous owners doing). Cops love to pick on younger guys with shabby looking, loud cars, while ignoring older guys with better looking cars, even if it makes a lot more noise.

Rotary Inspired · 07-21-2009, 01:40 PM

That car had rattle can primer when marc got it. too funny. Good luck with the work.

Rogue_Wulff · 07-21-2009, 02:59 PM

Quote:

Originally Posted by Rotary Inspired

That car had rattle can primer when marc got it. too funny. Good luck with the work.

Yeah, I hoped he would finish doing the job, but he never did. He just applied more in the same basic areas. At least he took the time to prevent the primer from covering the side markers, unlike the guy ahead of him.
BTW Brad, the 13B will likely be coming your way in the near (ish) future. I've got an idea I wanna try with it......

Rotary Inspired · 07-21-2009, 08:05 PM

Sounds good let me know.

Jeff20B · 07-22-2009, 10:21 AM

I'd personally drill the flange holes a little larger for 12mm studs if necessary. I can't recall what GSL-SE presilencers used.

Rogue_Wulff · 07-22-2009, 10:29 PM

That's pretty much my plan, if it is even needed. I'll have to redo the pipe to fit a presilencer, which is why I haven't yet installed the dern thing.
I'm thinking an increase from 2" to 2.25" or 2.5" might be a good idea for the 13B, particularly after I freshen it up, and do the porting I want to do. Every little bit will help.....

07-20-2009, 11:20 AM	#1
Rogue_Wulff Non Member Join Date: Jun 2008 iTrader: (0) Posts: 310 Rep Power: 17	12A vs 13B weight Is there any real difference between an 83-85 12A and 84/85 6P 13B, when it comes to weight? Near as I can figure, they should be within 10-15 LBS of each other, with the 13B having slightly more metal. I've got an '83 GS with a 12A/5 spd, and the engine is having oil consumption/smoking issues, but runs fine otherwise. The car is in rather nice shape, aside from the smokey exhaust. The 12A has been rebuilt at some point, and still makes good compression, but it had the beehive oil heater on it (now has FMOC). I also have an '84 GSL-SE that has a good engine, converted to carb with the RB intake and edelbrock 600. But, the interior is in bad need of attention, as well as the paint and windshield. Likely needs suspension work too. I'm thinking about swapping the SE engine/trans into the GS, so I can continue to drive it, until I can freshen up the 12A. Although, I could build a 1/2 BP or full BP 12A, and use the SE chassis as a track car. Or, swap in a TII engine/trans....... Near as I figure, the SE engine/trans would be a bolt-in swap, aside from the engine mount bar. Both cars have RB headers, so even that would be a simple swap. If I really wanted to get fancy, I guess I could swap the front crossmembers, eliminating the mount bar mods required to install the non-stock engine. I'm figuring the extra HP/TQ of the 13B would be way more than enough to offset the minor increase in weight, especially since the swap would actually be legal in CSP, where I've run the GS for several years, and it has most of the suspension mods needed to be competitive in the class.

07-20-2009, 01:10 PM	#4
Jeff20B Rotary Fanatic Join Date: Mar 2008 iTrader: (1) Posts: 215 Rep Power: 17	Yeah, 10 to 15 pounds. The 13B rotors are 11.5 compared to 9.5ish for the '83-'85 12A rotors. The 13B rotor housings are about 1 pound more each, and the shaft is only slightly longer so not much weight gained there. The tension bolts by the same amount, but there are 17 or 18 of them so it adds up to a small amount. The rest is in the water pumps (same weights if both are cast iron) and the flywheels. 26 pounds stock for "31" (late 12A) and "304" (GSL-SE) style. You can drop the 13B weight below a 12A just in the flywheel if you go aftermarket. Maybe do an FC aluminum waterpump too. 15-16 pounds for full cast iron. An aftermarket GMB aluminum housing with the stamped steel impeller drops the weight a bit. The other option is an FC waterpump which is about 6 pounds if I remember correctly. One option which you might consider but shouldn't do unless you're running an electric fan is an FC housing and a GMB 1st gen impeller. Ultra light weight but not very strong so you shouldn't use a stock clutch fan with it. I did this for my rotary baja project. I added a stud to the alt bracket hole on the GMB and filled the hole in the FC housing with sealant. The engine plates are 1st gen Y castings so no provision for the FC alt braket bolt. If you already have an idea as to what I'm talking about, you should be able to replicate this setup for the lightest waterpump just short of the no longer available racing aluminum waterpump from the '80s. Otherwise don't do this because I haven't run it long enough to know how the parts hold up over time. Last edited by Jeff20B; 07-20-2009 at 01:26 PM..

07-21-2009, 01:40 PM	#7
Rotary Inspired Rotary Fan in Training Join Date: Feb 2008 Location: SW OKC iTrader: (0) Posts: 75 Rep Power: 17	That car had rattle can primer when marc got it. too funny. Good luck with the work. __________________ If you wanna become ASE certified buy the RX7.

07-21-2009, 08:05 PM	#9
Rotary Inspired Rotary Fan in Training Join Date: Feb 2008 Location: SW OKC iTrader: (0) Posts: 75 Rep Power: 17	Sounds good let me know. __________________ If you wanna become ASE certified buy the RX7.

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07-20-2009, 11:57 AM	#2
Jeff20B Rotary Fanatic Join Date: Mar 2008 iTrader: (1) Posts: 215 Rep Power: 17	Yes, do it! You have my full support. Swapping the crossmembers, so no front bar mods needed, is a good idea. The RB headers are indeed swappable. Daily drive the nice one with the bigger engine (it will reward you with more torque and stuff and you'll quickly fall in love with it) and race the ugly one with the built 12A. The extra weight of the 13B is a non-issue. The reduced weight of the 12A, for the race car, is also a non-issue, but I'm sure both make you feel a little better inside.

07-20-2009, 12:13 PM	#3
Rogue_Wulff Non Member Join Date: Jun 2008 iTrader: (0) Posts: 310 Rep Power: 17	LOL, I figured I could count on Jeff's full support. I already sourced a TII throttle cable for the 13B/edelbrock combo, and it should be quite easy to hook up the cruise and an A/C throttle kicker on the GS. It has both, and they both function, therefore they will remain. Heck, the SE doesn't even have a heater right now, much less A/C. I was pretty much planning to use the SE as a track car, since it's in overall poor condition, but does have the bigger brakes (much needed for a track car). Am I right about the weight difference being in the 10-15LBS range? If so, it's totally a non-factor. I'm just curious if I'll have to make a minor adjustment on the GC coilovers under the front of the GS......

07-20-2009, 01:26 PM	#5
Rogue_Wulff Non Member Join Date: Jun 2008 iTrader: (0) Posts: 310 Rep Power: 17	I'd like to go with a light steel flywheel, but it's not in the budget right now. I'm about 90-95% certain I'll be doing this soon. I could always just drop the 12A into the SE chassis "as-is" and let my 17 year old son have it, or use the carb and starter on the GSL I have stored away. I think it would bother me less if he were to crash the SE than it would the GSL. Besides, if he got ahold of the GSL, he'd prolly try swiping the new Konig's when I wasn't looking........ He really likes those wheels, especially after seeing pics of OOT's car with them on it. The GSL is white, and the Graphite Rewinds look amazing on a white car.

07-21-2009, 01:29 PM	#6
Rogue_Wulff Non Member Join Date: Jun 2008 iTrader: (0) Posts: 310 Rep Power: 17	My son is also wanting me to do this. He wants the SE, but knows there's no way I'll let him loose on the street with that monster 13B. It's just a bit too much for an inexperienced driver. He also knows the 12A isn't exactly a slouch, and is very capable of getting 20+ MPG, seeing as I have done so for more than 4.5 years. I still have the old ST springs that came under the GS, and a set of 15s to fit the SE bolt pattern, so he could easily pursue his desire to run autocross with that car. The stock 14s have nearly new tires (under 500 miles) in spite of being 3-4 years old. I'll prolly take the DLIDFIS off, and convert back to stock ignition on the SE. I just don't trust those GM HEI's enough for a daily driver. Even with the new mounting plate and best thermal goo, they run extremely hot. I guess this swap is almost ready to take place. Kinda wish I had the funds to freshen up both engines during the swap, but that can be done a little later down the road. My 12A header/presilencer uses 12mm studs. Does the SE header/presilencer use 10mm or 12mm? I've never got around to installing the presilencer on the 12A car, but the SE has the full street RB system, with an aftermarket muffler. I can always hook the 12A header to the SE presilencer even if it uses the 10mm studs. I could also use a different type presilencer under the other car, if the 13B header is only designed for 10mm studs, or just enlarge the holes in the flange...... I'll likely insist he change the rear muffler on the SE chassis. Being a bit older (and presumably wiser), I can get away with a bit louder exhaust than a teenager. Particularly when the SE looks rather shabby, due to being 1/2 covered with rattle can primer (previous owners doing). Cops love to pick on younger guys with shabby looking, loud cars, while ignoring older guys with better looking cars, even if it makes a lot more noise.

07-22-2009, 10:21 AM	#10
Jeff20B Rotary Fanatic Join Date: Mar 2008 iTrader: (1) Posts: 215 Rep Power: 17	I'd personally drill the flange holes a little larger for 12mm studs if necessary. I can't recall what GSL-SE presilencers used.

07-22-2009, 10:29 PM	#11
Rogue_Wulff Non Member Join Date: Jun 2008 iTrader: (0) Posts: 310 Rep Power: 17	That's pretty much my plan, if it is even needed. I'll have to redo the pipe to fit a presilencer, which is why I haven't yet installed the dern thing. I'm thinking an increase from 2" to 2.25" or 2.5" might be a good idea for the 13B, particularly after I freshen it up, and do the porting I want to do. Every little bit will help.....