Diffrent aproach to RB24

[Mr_Efficiency]

I'm looking at putting an RB series engine into my Z31 and to save you from a long story just say I have a RB20 and RB25 sitting in my garage. I could just swap in the RB25 and be done with it.

But I have heard of a RB24 using the RB25 block and head with the RB20 crank and rods. This combo would retain the 25 bore but shorten the stroke making the RB25 more rev happy which would be nice for keeping the turbo spooled and I dont think torque would fall off much if at all given the displacment dosent fall of much.

My question tho is, is all that work worth it for just shortening the stroke? I'd only be changing the stroke from 71.7 to 69.7, that seems like such a minimal diffrence to me. But I'm not an expert on engine geometry so I'm looking for opinions.

Also a bonus for this frankenstien is that its something diffrent. I'm not sure what would be done about pistons tho but 86mm is a popular size in GM land and comes in several diffrent cc's and pin heights, also several forgred versions are available as well.

 

More than likely I'll just end up throwing the RB25 in, but just for the sake of curiosity lets say I want to try this 2.4 thing.

 

Edit, I've searched on this for a while now and everything I find is people using the RB20 block for some reason. I figure the hole purpose of the 24 would be to make the 25 more rev happy.

[amorfin]

The reason for the RB24 is to get more displacement out of the RB20. If those people had an RB25, they would just throw that in there. And that's what I would do too. Don't get yourself into more trouble than you need to. The RB25 might be enough "rev happy" stock.

[Cal Poly Zmanaustin]

Don't get yourself into more trouble than you need to. The RB25 might be enough "rev happy" stock.

 

Agreed RB25. These motors love to rev already. If you really want it to be more rev happy start looking at 272 cams, valve springs, ATI Damper, N1 oil & water pumps,free flowing exhaust, ect. Better use of your money IMHO.

[Careless]

Hey, where in Ontario are you?

 

The RB25 is a better choice here... The RB24 would probably be done to get some extra displacement out of the 2.0, which is a tad smaller and would probably pass inspection in some countries where the engines must remain the same size as they were before upgrades and whatnot. or in race classes... and that means you'd be cheating!

 

The RB25's rev a lot more than the VG30ET's do, but they pull in the top-end. The VG30's have some great low-end grunt for a 6 cylinder turbo motor.

 

Racinjitter went from a VG to a 25 in his Z31, and now he's going RB30... But he can spill the beans on why he's doing that. I do remember him telling me that the VG30 had more torque down-low though.

 

But you're looking to rev high, and the RB25 makes more power up there than the VG, so you might as well just drop the stock RB25 in there and do some valvetrain mods, which can be done with the engine in the car, as the cams are loaded from the top of the head, and not the front! (bonus!!!!)

[Mr_Efficiency]

I'm in Peterborough, about 2 hours from Toronto.

 

Reason for asking was I came acrossed a RB20 for cheap and was thinking if anything off it would be worth while but i guess not. Are the tranny's the same for the RB20 and 25?

 

Right now I'm just collecting parts and once I have just about everything I'll bring it all into my garage and start assembly (just wraping up another project in the next week or so first), for now the car is stored at a friends. I'm not looking for anything crazy power wise right out of the box, I'm planning on building the car for time attack and autocross, maybe the odd drift day.

And of course to beat my friends Honda's at the strip, lol One has a Del sol with a B16 and the other has an older accord with an H22 swap. The RB25 already has more power than them both bone stock. An all out motor build is in the dream plans for another year tho, first I just want an RB powered Z to play around with, power will come later.

[jerryb]

Just go with the RB25, it will have more than enough power and revs to put a smile on your face...right out of the box! If there were a lot of benefits to doing this swap Im sure it would be a hot topic here and the Skyline forums.....but its not.

 

I run a RB20 in my S30 because ultimate power wasnt that important, if it is to you then the RB25 is a better platform to start with. And dont forget, your Z31 is a fair bit heavier than my S30 so go with the setup that offers more torque!

 

The RB25 tranny is better, stronger and typicaly worth a lot more! Overall there isnt much that you would want to keep off the RB20 and use in place of RB25 parts.....nothing. There may be a few spares, ignitor...coil packs..... Injectors are not compatible.

 

And on a selfish note, ....I may be interested in a spare RB20! Cambridge isnt that far and I need more clutter in my garage! Just pm if you interested.

[Careless]

lol. nice. another z31 owner in Ontario with honda buddies! I didn't think this day would come!

 

RB20 = FS5W71C Trans, similar to L28, KA24, CA18, SR20 trans.

RB25 = FS5R30A Trans, a lot more stout.

[Mr_Efficiency]

Cool to see some more Ontario guys around here.

 

jerryb, Thanks for the info, and the motor I was looking at is just a deal on a importer site. An RB25 with tranny harnesss etc is 1900 and a RB20 with the same parts is only 900, but a RB25 (engine only) is 900.

So I was thinking if i could buy the RB20 with harness and trans and the RB25 motor I would have spent the same as I would for the RB25 swap but I'd have a extra RB20 laying around. But since the tranny and now that i have been looking around the harnees is probly diffrent as well, so that idea is out the window. Was worth a shot.

 

You also have some honda buddies Careless?, how bad does the Z31 dominate them, haha My friend with the H22 accord weighs about the same as the Z31, its a tank, has power everything. He has done a little bit to it, just cams, a flywheel and an lsd so far. Who knows what he will have next summer when i get this thing together.

 

Also I keep hearing a lot about how much these cars weigh, anyone really tried any serious weight reduction. I had a good look at the car lastnight but I havent tore into it or anything yet. I plan to put it on quite a diet and having the interior consist of nothing more than a cage, 2 buckets, a shifter, some pedals and a steering wheel.... actually the rules say i have to keep the dash to, but everything behind it will be gone. Car will see a lot more track than street use, would still like to keep it semi streetable tho for days i feel like testing it out or just driving it.

[Careless]

Well to be honest, most of my friends have never been exposed to really really fast cars. I do have car buddies that are really good friends that have fast cars, like 400ci camaros and bla bla bla.

 

But the Z31 has some good kick in the balls torque for an 80's car. Even when they aren't fast, they feel really fast compared to any honda.

 

Honda's start to grow wings in 3rd gear, so up until that point, you could probably take your buddy. By that time the car's got enough rolling momentum to propel it to higher speeds quite quick.

 

I only drove my car for 10 days before a whole lot of stuff needed to be looked after. It should be ready as soon as I get the T3 turbo back. But I will say that most of my friends who had a ride or two in the car said "holy ♥♥♥♥, you sure this is an 87, man"

 

They are friends that never really felt a torquey motor WITH boost on top of that. I've always known the VG's had torque, there was a 95 pathfinder we had that was pretty ballzy, but the turbo is just so much quicker to respond.

 

I'd say for an 80's car, looking at the prices you can get one for... if you're willing to take care of the common problems and freshen up the engine some or replace with a RB25 or VG33 or so, I'd say they are quite the car for the price. And did It has every option that a lot of cars today don't come with standard if you get the GLL model.