Honda D15B6

[civic lover]

I was wonder if anyone out there has some MPG numbers for the swap I am about to do. I want to swap a D15B6 head on my D15b2 and put the HF tranny in but keep the DPFI for now. Does anyone have this setup.

[FritzR]

I have that setup in my CRX HF. I have the MPFI though. I don't know how it would work with the DPFI, but my guess is that it would not work worth a damn, when cold, because you would still be using the DX ECU. It would probably work OK in closed loop. I get about 55 MPG at 60 MPH and 44 around town but I have to work at it to get that. I think in a civic it would be about 40 town 50 highway but that would be MPFI.

I know from reading here you don't want to put the HF tranny with the stock D15B2. It is just too luggy.

[GasSavers_bobski]

I think this is going to be a try it and find out situation. The HF head and cam are built to maximize low end torque, so that should go well with the HF transmission. But then, who knows what the DX fuel and ignition timing maps are like compared to the HF maps. The engine displacements are the same, so the open loop A/F ratio should be about right, but timing could be kinda messy. Also, there's the issue of port matching on the head - the DX intake and exhaust manifold ports are significantly larger than the HF's, so there will be a harsh step in the air flow going into and coming out of the engine.

[civic lover]

Originally Posted by FritzR

I know from reading here you don't want to put the HF tranny with the stock D15B2. It is just too luggy.

Yeah I actually already tried that about a year ago. It had no power to pull it self and I lost MPG. I think I will just have to try the setup and see what it does. I have the mpfi intake and the wiring(kinda messy) But I can't have my car down for too long of time. SO I will do the mpfi swap later.

[StorminMatt]

Originally Posted by civic lover

Yeah I actually already tried that about a year ago. It had no power to pull it self and I lost MPG. I think I will just have to try the setup and see what it does. I have the mpfi intake and the wiring(kinda messy) But I can't have my car down for too long of time. SO I will do the mpfi swap later.

SO I'm not the only one here who has had bad luck with slapping an HF transmission on a DX motor. Mine also lost a TON of power. And as for MPG, I have not measured it. But I can tell you that it was not helpful, even coming from an SI transmission.

As for the MPFI swap, it is actually easier than you might think. The wiring changes are not too bad. And because this is a route that ALOT of people have taken, it's pretty well established. There is no reason why the MPFI conversion should take more than a day. And if you think it will take you longer than this to change the engine harness itself I would recommend going to a pick-and-pull type of junkyard and getting a harness to modify so that you can still drive you car while you are doing so. But do this BEFORE swapping the head, as one of the WORST things about the job is scraping the gasket from the head/intake manifold. This is a job that you DON'T want to do more than you have to.

[Brian D.]

Isn't that the setup that Ben (aka- SVO Boy) from Dartmouth have on his CRX? I believe he had a '90 CRX DX (with the DPFI and 16 valve head). He swapped in an HF transmission...but I'm not actually sure if he kept the 16 valve head or not. Interesting, though...how it would work out to have DPFI on the HF's 8-valve head.

[StorminMatt]

Originally Posted by Brian D.

Interesting, though...how it would work out to have DPFI on the HF's 8-valve head.

It couldn't possibly work out too well, given the disparity when it comes to port/runner size AND the fact that the fuel maps are going to be off.

[crzyflyboy]

Just wondering if you were able to get the HF head and tranny to work on the DX block?