91 hc question about engine mods

[chevyboy6902]

I was told by a mechanic friend of mine that i can put bigger injectors in my 929 and all i will have to do is tweak the ecu to get them to work. this along wit cold air intake and bigger exhaust will raise my horsepower. how difficult is it to do on the 929. I have done this before on chevys and some hondas but this is the first time i have done anything with the 3.0 mazda engine. any help would be great. and it is the dohc.

[JAY-929]

I'm looking into modding the SOHC 3 litre myself. The first things I'm going to do is bolt on the DOHC head

Modding these kinds of motors WILL cost you a few dollars. They weren't intentionally built to be a powerhouse, so it will mean some cash to make it go harder.

Having said all this, it can still be done, no doubt Cold air intake is easy and as far as I know, I could only obtain a custom made 2.25" exhaust (I wouln't go any bigger unless you're going forced induction) for my 929. If I'm spending money on a custom made exhaust... spend that little more and get a mandrel bent exhaust... not press bent. ECU is a mechanics job (or an auto electrician.. unless you can do it yourself) and bigger injectors... I'm not sure about that one. I'll look into it myself. I wouldn't look at increasing the fuel intake though UNLESS there was a dramatic intake of air coupled with it (eg: turbocharger or supercharger).

All, I'm looking at doing is to obtain the DOHC head and modify it (port and polish it), mild cams (to the point where you don't need to change valve springs and whatever), CAI, exhaust and reprogram the ECU to make the car run on a higher octane fuel (like 98 octane over here). THAT would see some mega improvement.

Hope this gives you more insight.

[2jz929]

Chevyboy - Bigger injectors will give you zero horsepower gain, dont bother. A retune on the ecu, on the other hand, will give you noticeable gains when mixed with a suitable exhaust and cold air intake, would be well worth it.

Jay929 - For the DOHC swap, you will need to swap the whole motor, you cant just swap the heads. Swapping the whole motor will be easier anyway, because then you dont have to keep the loom for the lower half of the motor, and splice in the new one for the top half. The pistons in the SOHC have three valve cut out, whereas the pistons in the DOHC have four. Ported head and cams would be very nice. The factory head has roller rockers, and you should be able to go fairly large on the cam.

[JAY-929]

That just made a WHOLE lotta sense! Thanks for that, 2je!

[Matsuda9]

with SOHC you have an option of getting the JF-T hardware (but in US the fitting it is a nightmare (due to steering column), SOHC heads are relatively good, they are tall and have close to 45 degree valve facing.

with DOHCs you have a few options... the HC, HD, HE.... they are all a little different, also there was the J5 which was 2.5, probably one to avoid.

if you are adventurous there is always KIA enterprise motor, the 3.6 J6D...... trying to find it that what is adventurous

the J family motors are strong, the internals are not so, i have seen totally water logged JE once pulled all it had is bent rod on the 2nd cylinder an that is (block would need clean up)

to do anything to these motors you looking at custom or matching something from some other cars (although with 4 Cyl you have much more after-market support thanks to 626/mx6/probe)

if you looking to try and build a power house out of J motor, be prepared, no one really done anything and you will be the first so it will cost and probably will cost again once it breaks.

however, you do have other options.

1. F family motors: F2 2.2l (from B/E2200, 626/mx6/probe), turbo would be the option to go for (very torque motor). or import FE-DOHC from japan (some europe) with a turbo VERY good motor

2. Rotors. well not much needed to be said about this

or go further like 2jz929 did and dump a toyota motor


here some FE DOHC goodness:

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in FWD form (11.66 = 401WHP @ Front wheels)
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in RWD form (8.92 @ 147 mph)
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[chevyboy6902]

Thankyou for the steer in the right direction. my my ex boss owns own dealership and was at one time really into mazdas so he has a few leftover 929 bits in storage that he gave to me, gotta love free brand new spare parts. pulled the car out of the garage today put in fresh gas and new fluids and fired right up, this car has not ran in 3 years. these cars my be expensive to fix and hard to upgrade but i love this car even more.

[JAY-929]

:O Free parts!! Can NOT complain about that! What an awesome ex-boss!

And yes, the Mazda is definitely an "exclusive" vehicle to deal with!