Official 2012 whatever thread

[DuRWooD]

Rod ratio importance is debatable. Really depends on the engine. My thoughts are, a high rod ratio decreases piston speed. No one is revving the BP high enough to worry about out running the flame front, however there are other benefits to this. We all know the BP's head doesnt flow the greatest. As RPMs, and thus piston speed increases, air velocity increases; a weak point for the BP head. Slowing piston speed should really help in the respect. On the negative side, there's a proportional increase in TDC dwell time, which may cause issues, I don't know.

[Boosted Escort]

I have a built short block waiting to go in. how safe would it be to spin a stock na head to 7500rpm? I want to run around 30lbs on a hy35. I would love to have oversized valves but I don't trust any of the shops around here to do the work properly.

[DuRWooD]

I don't think a stock head would flow well enough to see much of a difference between 25 and 30 lbs. Might want an IAT probe and take it up slow on the dyno. From everything I've seen that'll be right around the limit. No personal experience though.

[atomicEGT]

bunch of ****ing nerd **** up in here.

stock head is fine at 7500, OP gears aren't.

[KAinjection]

An engine with a better rod ratio (FE3, 2.0/2.3MZR) has less side loading and less friction then one with a lower ratio (BP, 2.5 MZR)

Yes the BP can rev fine to 8K but there is more stress on the bottem end then a FE3 at 8K for example. There is more potential for more power/less fuel consumption with the better ratio. Mazda tried to address this with its new 2.5 MZR by putting a coating on the piston sleeve/liner to reduce friction since it has a worse rod ratio then a BP does. Goodwin racing has a Miata with a World Challenge built 2.5 that revs safely to the 7800 RPM rev limit and makes 270WHP, so the bad rod ratio can be revved if the bottom end can handle it.

There is always a trade off though, lower piston speed does not breathe as well at lower RPM as higher piston speed on the same size port.

My personal theory is this:
high rod ratio=slower piston speed=head with smaller ports (MZR 2.0)
low rod ratio=faster piston speed=head with large ports (MZR 2.5)

Again its only my theory and have no way to prove it at this point.


Bottom line is this though, the BP is fine for the job intended (turbo power), and it can make N/A power but its not ideal and is more work. The bottom end is strong enough to take it.

Rod ratios:
BP-1.54
FE3-1.74
MZR 2.0-1.86
MZR 2.3-1.64
MZR 2.3 DISI-1.60
MZR 2.5-1.51

[Racerboy]

stock head is fine at 7500, OP gears aren't.

Yeah, I forgot about the oil pump gears. Those are the only things I am worried about when running my engine at 8000 rpm. I wish billet gears were in my budget. Although, that gives me an idea.... Maybe I can make a set myself at school on the cnc machine.

[atomicEGT]

you're not making enough power for it to be an issue.

[Oz-28Gs]

Shiet I got a 94 mazda protege with 205k and she still running fresh :D

Sent from my SPH-M820-BST using Tapatalk 2

[atomicEGT]

u go girl

[Turpro]

So tell me, what could I get for a escort 1.9motor, 5spd trans and all harnesses?

Because I find 5spd wagons all over for good prices but it would be converted to either an auto bp or auto kl so I would have to convert all those harnesses and **** anyways.

[atomicEGT]

$20?

Also, look for a 93, apparently swapped cars have airbag issues.

[Turpro]

Even on feoa?

[KAinjection]

You will have better luck selling it on feoa but everyone will want it for nothing, but I did manage to sell all the parts needed for a auto-5spd coversion locally for about $140. It took a while to sell though. I am sure you could get about $200-300 for a running engine, especially since they have the valve seat issue and people are always looking for one.

Since my engine swap my airbag light flashes, but i have never bothered to find out why. One of these days i will get to it though.

[atomicEGT]

it's gotta be something in the 1.9 harness that isn't present in the BP harness, MazdaNoob mentioned it being related to a VSS and something else in the auto harness.

[KAinjection]

Just checked the wiring manual. Apparently the GT never came with airbags?

The schematic says "1.9L only" but it appears the only thing that would be missing to make it work is an airbag fuse located in the engine compartment fuse box that I know for sure the GT fuse box does not have.

It supplies the R/W wire going to the airbag module with 12v constant. I will check it out tomorrow if I get time.