12R Performance

[old_school_jap1]

12r's have a ghey setup in that part of the bellhousing is actually a cast part of the block, so if you're looking at going to an 18r you'll have to change the gearbox. there is a problem with mounts, but i have solved it. there are about 6 different types of engine brackets for 18r's because they were in so many different cars. the engine brackets (that being the part between the engine rubber mounts and the block) you need to put the 18r on a 12r crossmember can be found in a rt72 corona mark II, good luck finding one though

[thdevilshands]

Thanks for the info guys

What has to be done to keep the colum shift when converting to a W5# box?

I really like the old school style of this thing so if I have to change the gear shift to floor mount then I'll just keep the 12R and go a mild cam, 36/36 DCD weber and good extractors, as I said the diff is so tall it gets sideways real easy, power to weight won't be a problem ; ) Just parts. Might have to make a custom twin weber manifold up and play around with the head a bit to see where we can get.

As an A series Datsun fan I know all about the rarity of certain heads and engine bits, try finding a genuine 1200GX head that someone is willing to part with, not a snowballs chance really.

Brett, I was sort of assuming that using the 12R bottom end and 4R head would increase compression? or is the bottom the same bore w diff crank, rods etc?

SBFoot - Those cam specs look good, I'm gonna have a chat with my head porting guru and see what he thinks can be done with the 12R head and how crazy you could go ; )

Does anyone have a pic of a 12R head, or, even better a cross section pic showing port sizes and wall thicknesses?

Thanks for all the advice, an 18R/RG swap would be great, just as long as I can keep the cars current flavour,

Keep it all coming

Cheers, Jon

[thdevilshands]

Maybe given enough info these guys could make a new 4R or 9R head, given they can do new cylinder heads for 12R (or at least claim they can),

http://www.made-in-china.com/china-p...d-SN4108-.html

anyone able to provide specs / pics of 4R and 9R heads?

[crowncustom]

12R and 4R bottom ends are identical except the high comp pistons.
12R and 18R block mounts are totally different.The 12R runs cast steel mounts right at the front of the block where 18Rs are almost centre to the block.But going from 12R to 18R is easy as.
I will have a talk to a mate of mine who still has his old race 12R in a RT 80 Rona which runs twin 2T downdraught carbs with home made mani,cam,extractors,modified 18R oil pump and a few more mods I cant think of off the top of my head.
Cheers Brett.

[o_man_ra23]

Have a look in the RN4x and later 2WD Hilux range (must be RNxx) for something with column shift. The gearbox from that will be what you want (if there is such an animal) to change to 18R.

[Dazza]

Look for an early Hiace gearbox to bolt up to an 18R with column shift. They are only 4 speed but were the same housing as used in RN46 Hilux 4X4 but with different selector housing that just bolts onto the side of the gearbox. The ratio's were different between the 2WD box and 4X4 box. The 4X4 box had a more even spresd of ratio's where as the 2WD box had a lower 1st 2nd and 3rd and a big jump up to 4th.
The Hiace box you need would be out of an early 80s model. I did have one once but i gave it away when i sold my old Hilux.

[thdevilshands]

Thanks Brett, I'm not real up to spec on my toyota engines,

so stock 4r pistons in 12r block would be a good mod for increased compression, very good

I'd be really keen to hear any extra info on your mates engine, and some pics if possible would be really great!!!!

Dazza and o man Ra23 thanks heaps for the g/box info, looks like its 80's hiace/rnXX hilux hunting I will go.

Cheers guys, Jon

[Dazza]

I forgot to mention that the output shaft on the 2WD gearbox is longer than the 4X4 version so if you use the 4X4 box for the closer ratio's then you will need to swap the output shaft to a longer one. The only other difference internally between the two box's is the different number of teeth on the input shaft and the front gear of the layshaft, which is what changes the ratio's.
The 4X4 has 17 teeth on the input shaft and the 2WD has 16 teeth.
The 4X4 has 32 teeth on the front of the layshaft and the 2WD has 33 teeth.

[thdevilshands]

Ha just worked out what all this rep business is about so +REP 4 everyone.

I think, given the minimal cc advantage to be gained from an 18R swap and having to find a new g/box etc I will keep the 12R and set about some modifications untill I can build up a nice 12A or 13B rotor to go in there. mmmmmm buzzzzzzzzzzzzzzzy

Brett, I'd really like to see this homemade twin d/draft carby setup, and get some specs on the cam and what bits can be pillaged from the 18R (like the oil pump), gotta love the ol pushrod engines...

Cant wait to get my Twin 45mm sidedraft webers, extractors, head work, cam, zorst on this beast, will be heaps of fun!!!!

Cheers, Jon

[dsh04]

I think I will eventually go a 4agte in mine as it looks like it should fit, for now I will just do extractors/exhaust and a decent carby plus electronic ignition and electric radiator fan.
Are extractors for the 12r available off the shelf?
cheers

[crowncustom]

Extractors are no longer available but a good competent exhaust shop should be able to whip a set up at a cost.I will try and get a pic of the twin carb manifold.
Cheers Brett.

[thdevilshands]

thanks brett, twin d/drafts is quite unusual, why that choice over s/draft for a race car? seen a couple of Datsun Z cars w em but not a lot else... that could be related to where I'm lookin tho...

[crowncustom]

Toyota did this on the 2T-B,3K-B and M-D.Mazda also did this on the late 60's early 70's 1500 SS and 1800 SS.Ford also did it in the 80's with the Laser and Meteor.Holden also did this with the HR X 2 Premier.
Just a matter of choice.
But I will try and get those pics and more info on the said engine.
Cheers Brett.

[o_man_ra23]

Ford also did it in the 80's with the Laser and Meteor.

Ford never made a Laser or Meteor. They were Mazda 323s with a defect badge.

On the note that devilshands made about the minimal cc difference going from a 12R to 18R, if you were to utilise the 18R-C I would agree with you. But the 18R-G put out 146Hp in factory guise (early models with 88210 and 88230 heads, 9.7:1 compression), which is a very far cry from anything you will get from a 12R. And then the 18R-G can be worked a lot further. If you are going to put a rotor into a ute, say goodbye to towing or carrying a load, they just lack torque and should be reserved for use in sporty type cars, plus the fitment would be a nightmare compared to dropping an RG in. Just a thought...

[thdevilshands]

I agree with you o man ra23,

I have an 18R From a '74 Corona sitting there so thats why I didn't really consider the 18R-G route, just use whats available,

for a more serious build tho I'd like to go rotor and stretch my mechanical abilities a bit. It wont be towing anything or carrying loads I have other cars for that ; )