Budget 12A SP build

NoDOHC · 12-21-2010, 12:01 AM

Those pictures reminded me, you have to keep the rotors separate on a 12A (they are different). I had forgotten that.

Let me put the porting to you this way, you can always take more out later. You can't easily add it back. Small porting is your friend.

Intake port cross section should not exceed cross section of intake runner feeding it.

Later close is only better if it greatly improves flow, don't dig a corner upwards just to match the majority of porting templates on the market today. I prefer the port to follow the shape of the rotor (quicker close = optimum dynamic charging, maximum port area without expense of compression displacement).

Exhaust port should increase in cross-sectional area.

t_g_farrell · 12-21-2010, 08:02 AM

Excellent advice on the porting. I'll definitely keep it in mind when planning the
ports. Since I'm using the later 12a irons I do get a little larger intake runner
size.

I still have to decide which housings to use. First I have to get everything
all cleaned up and measured to see what parts are even good

t_g_farrell · 01-03-2011, 08:51 PM

Not much new to report yet. I've been cleaning rotors, housings and irons.
I think I can reuse the dented rotor. It seems fine other than the dent near
the combustion indent. I was able to get all the side seals out of it and the
rest of the rotor appears fine.

I think most of the A engine can be reused except for the rear iron. I think
the rear iron from the B engine is actually in better shape. There is some
mild stepping at the spark plug side but I'm thinking it will be in spec. I have
yet to get some feeler guages for thousandths of an inch. The A engine irons
are all Ys whereas the B engine irons are Rs. Is it ok to use the R iron with
the other Y irons? Now that I cleaned em up I don't see huge differences
between them.

The stationary bearings don't look new like the rotor bearings. Some copper
showing on the lower part of the bearing and at the seams. They don't look
that much different from the ones in the B engine, which had a lot of hard
miles on it. Thinking I may need to change those out.

I pulled the e-shaft oil jets and they had disintegrated o-rings in them. I
think I can safely say those were never replaced.

I'm thinking about doing the oil pressure mod to the regulator where you
mash down the tip to get it to about 90 psi and shim the front one. This
will be a SP with spirited driving and some track days. Is it worth it? I don't
think I need to do anything with the e-shaft jets other than new o-rings.
I can't see having extra pressure being a problem as long as my lines and
cooler can handle it.

12-21-2010, 12:01 AM	#1
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin Posts: 855 Rep Power: 17	Those pictures reminded me, you have to keep the rotors separate on a 12A (they are different). I had forgotten that. Let me put the porting to you this way, you can always take more out later. You can't easily add it back. Small porting is your friend. Intake port cross section should not exceed cross section of intake runner feeding it. Later close is only better if it greatly improves flow, don't dig a corner upwards just to match the majority of porting templates on the market today. I prefer the port to follow the shape of the rotor (quicker close = optimum dynamic charging, maximum port area without expense of compression displacement). Exhaust port should increase in cross-sectional area. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

12-21-2010, 08:02 AM	#2
t_g_farrell Waffles - hmmm good Join Date: Aug 2008 Location: Huntersville, NC Posts: 757 Rep Power: 0	Excellent advice on the porting. I'll definitely keep it in mind when planning the ports. Since I'm using the later 12a irons I do get a little larger intake runner size. I still have to decide which housings to use. First I have to get everything all cleaned up and measured to see what parts are even good __________________ 1980 GS stockport, Fat Nikki, RB Dual Facetfuel pumps, Holley regulator, RB Street port exhaust, 2GDFIS, MR2 MK I electric fans, 2G strut bar, relayed fans, lights and fuel pump, LEDs Project Fat Nikki Budget 12A rebuild Video setup < $30.00

01-03-2011, 08:51 PM	#3
t_g_farrell Waffles - hmmm good Join Date: Aug 2008 Location: Huntersville, NC Posts: 757 Rep Power: 0	Not much new to report yet. I've been cleaning rotors, housings and irons. I think I can reuse the dented rotor. It seems fine other than the dent near the combustion indent. I was able to get all the side seals out of it and the rest of the rotor appears fine. I think most of the A engine can be reused except for the rear iron. I think the rear iron from the B engine is actually in better shape. There is some mild stepping at the spark plug side but I'm thinking it will be in spec. I have yet to get some feeler guages for thousandths of an inch. The A engine irons are all Ys whereas the B engine irons are Rs. Is it ok to use the R iron with the other Y irons? Now that I cleaned em up I don't see huge differences between them. The stationary bearings don't look new like the rotor bearings. Some copper showing on the lower part of the bearing and at the seams. They don't look that much different from the ones in the B engine, which had a lot of hard miles on it. Thinking I may need to change those out. I pulled the e-shaft oil jets and they had disintegrated o-rings in them. I think I can safely say those were never replaced. I'm thinking about doing the oil pressure mod to the regulator where you mash down the tip to get it to about 90 psi and shim the front one. This will be a SP with spirited driving and some track days. Is it worth it? I don't think I need to do anything with the e-shaft jets other than new o-rings. I can't see having extra pressure being a problem as long as my lines and cooler can handle it. __________________ 1980 GS stockport, Fat Nikki, RB Dual Facetfuel pumps, Holley regulator, RB Street port exhaust, 2GDFIS, MR2 MK I electric fans, 2G strut bar, relayed fans, lights and fuel pump, LEDs Project Fat Nikki Budget 12A rebuild Video setup < $30.00