bottom end

[windy1]

thanks a bunch festyboy. you and christ are right on. some of the best advice,ive gotten to date

[FB71]

Arty, I think you mean the GTA?

That had the BJ engine; a B6 block with B1 crank and rods and DOHC head. Made 98HP at 7k.

[htchbck]

^^ yep... wasn't GTU a first gen RX7 trim?

[blkfordsedan]

Isn't the 1.6 sohc essentially a b3 bored over? So any over bore in between
would yield results in between those two, barring the many improvements
that should be made in such a project.

Yes, but waaaay over bored. Like 71mm vs. 78mm. Also larger valves, ports, chambers and shorter rods. Same stroke, but rod journals are different as well. So +1.00mm is only adding like ~40cc displacement.

I thought the B1 had a smaller (68mm) bore than the B3 with the B5 stroke (78.4mm), and the BJ had a shorter (67.5mm) stroke. I could be wrong.

[sketchman]

.....So +1.00mm is only adding like ~40cc displacement.

It's also adding just over 20% more area to the piston to push down on. Don't know if it'd be a measurable difference, though.

[FB71]

Yes, but waaaay over bored. Like 71mm vs. 78mm. Also larger valves, ports, chambers and shorter rods. Same stroke, but rod journals are different as well. So +1.00mm is only adding like ~40cc displacement.

I thought the B1 had a smaller (68mm) bore than the B3 with the B5 stroke (78.4mm), and the BJ had a shorter (67.5mm) stroke. I could be wrong.

hmmm... my info said 71mm bore and around 68mm stroke for the B1. But, I've been wrong before!

[FB71]

looks like you may be right! I need to go back and do more homework!

[windy1]

engine is presently in shop. doing the tests u,mentioned. otherwise it runs fine.i do own tuning. no reason to replace it,other than i like fresh engines. and enjoy blu printing them,to my specs. but,festy is not a car to be changed so easily. [like people] it manages itself. when i refresh engine,ill concentrate on up grading efficiency,not performance. thanks to all u,festy guys.

[FestYboy]

Arty, I think you mean the GTA?

That had the BJ engine; a B6 block with B1 crank and rods and DOHC head. Made 98HP at 7k.

you're correct, the GTA is what i'm refering to. but i still mean use the B3 block (71mm bore) and B5 (78.4mm stroke)... it'll be slightly larger than a B1 but i doubt you can get your hands on a BJ crank anymore... and use a BJ head (which according to Wiki is ment for a 78mm bore, and therefore a B6D head as well. given that info, i wonder if a B6-ME head would be more suitable).

[BigElCat]

I'm still thinking a fresh carby B3 long block, with the cam advanced about 4 degrees would be sweet. Fast and fuel thrifty.

Advancing the cam timing lowers the power band. Off idle to 5000rpm, pulling hard. Never rev above 5K.

[Christ]

I'm still thinking a fresh carby B3 long block, with the cam advanced about 4 degrees would be sweet. Fast and fuel thrifty.

Advancing the cam timing lowers the power band. Off idle to 5000rpm, pulling hard. Never rev above 5K.

I don't anyway. You'd need an adjustable cam gear to get 4* tho, right? I don't remember what each tooth represents.

[BigElCat]

Christ, I've been meaning to count the teeth. 360 divided by number of teeth will give degree per tooth. One tooth would maybe be 6 degrees.

4 degrees isn't carved in stone. It's what distinguishes the Metro Xfi from a non-Xfi 3 banger. My Xfi 1.0L three banger pulls strong and smooth. I bet the B3 would respond to cam advance really well.

I may have to look into fabbing an adjustable cam gear, or adapting one from a Suzuki.

I'll be coming back to this idea.

I'll go count the teeth right now.

[FestYboy]

it's 8* per tooth (rounded off, actual measurement is 7.8 or something)

and you can use miata adjustable gears for all B series engines.

[Christ]

So a crank tooth is 16* (basically), right?

There's a way to get adjustability without cam gears, but most ppl don't like to do it.... add a second tensioner and use it to take up half tooth belt slack. You put it on the opposite side of the first one. Adjustables are easier, but I've seen ppl do it that way too.

[FestYboy]

that would be the math!!