b20 into GSR

I have a B17 in my GSR right now, and am looking for more power. After reading up on the GREAT ls/vtec threads here at G2IC, I’ve learned alot about motors and how they get faster and where at on the powerband, but now I have some questions. Before I ask though, please don’t give me the classic “keep the b17, its rare!” stuff. At least not yet :wink: And yes, I’ve looked through 9 pages of a search on b20s.

Okay: Will my b17 y1 transmission hook right up to the b20? What about the intake manifold and throttle body? Keep in mind that the b17 head or anything vtec is staying off the b20, I just want to use some of the stuff for it. Will a Comptech ITR header fit directly on the b20? And will the b20 drop right into the DB2, or will I need custom mounts?

Also, how will my high end be? I’m really worried about how I’d do vs. the b17 on the highway. Would my high acceleration increase or decrase? :think:

For the record, I plan on boosting the b20 eventually. Crower cams will most likely go in as well.

your transmission will bolt up fine and the motor mounts are the same. as for the IM and TB i don’t think so, not totally sure, but i believe the non-vtec heads have a different bolt pattern or port size, like i said, i’m not sure though. as for the header it should work fine(not 100% sure).

i don’t have any personal experience with b20’s but i’ve heard they have great low-midrange power with a lack of any top end. you might wanna ask(possibly email) some of the members on here with that swap.


If you want to have the most reliable B20 and are willing to put the effort into it, DE-stroke the B20 by using the B17a crank in the bottom end of the B20 with the VTEC head up top. DE-Stroking it gets rid of that nasty rod/stroke ratio that the B20 has. By changing the r/s ratio you can rev higher, more reliably. Yes, you lose .2L by de-stroking your B20, but you will make up for that loss in displacement by being able to rev higher.

I personally think that if I was to build a B20, I would take this route. You have more displacement (read: more torque) than your B17, and if I’m correct (please tell me if I’m wrong) more displacement than B18s too. But revving an extra 1000 rpms will make up for the loss in displacement & you won’t have to worry about the bottom end coming apart due to revving higher than stock.

The downside to this swap: The b17 crank is almost impossible to find & expensive too. But since you already have the much-in-demand crank in your current engine, that should not be a problem. I also think that the main-bearing journals on the B20 are smaller than those found on B16 & B17 engines, so that means that you would have to get the main journals reduced to the B20 size.

Keep looking for more information & options on B20 swaps. Don’t just listen to one person/shop on what is “best”. The choices are endless & everbody will have a different opinion on what is the best. I would rather lose a little bit of torque & displacement all the while, not have to worry about a thrown rod, or any other catostropic bottom end failure.

But I STRESS - the more you dig into your options, the happier you will be once you have done the swap. Hope that helps!