B6t Engine Build

[99EJ6T]

back when i was deep into toyotas, they spoke of 8.7/8:1 being the most ideal cr for a street car. however, most other companies i have seen doing boosted engines factory were in the 7.x:1 area for compression.

personally, i would rather have 9:1 with good internals. during previous turbo engine builds (honda, mostly), i have found this number to be the best for a street car application (300-ish whp). for those with higher goals, but small pockets, lower cr would be better due to the margin of error with the lower cr.

just remember, it takes more "psi", from the same set-up (turbo, etc), for a lower cr (7:1) engine to make the same power as one with higher (9:1) cr. there is a limit to the application of that comment though, but thats a different conversation.

[therieldeal]

the GTR motor runs an 8.2:1 compression. for the most part i'm happy with it, i'd probably go 8.5:1 if i were to rebuild it.

[Scott@USRT]

It largely boils down to engine management. Back in the day when the B6T was hot stuff the factory engineers went with a 7.x:1 CR because it was safe. If they had modern control tech options they'd surely have gone with something much higher.

Consider that while the air/fuel control is done well with a reasonable EFI system the ignition is ridiculously obsolete -especially for a boosted engine. If matched to a proper management system, that silly low CR is a great match for a huge turbo. However, the power that such a turbo would support is simply too much for the glass transmission to hold.

Thus, when I rebuilt my B6T I elected to go in the opposite direction with a 9.5:1 CR via forged Wiseco pistons. No, I'll never be able to run a big air blower, but that's just not practical anyway. Instead, I upgraded to the classic VJ-14/11 combination which is plenty good for 225bhp and a wide and safe torque band. The raised compression spools the larger unit just about as fast as the low CR spun up the stock VJ-14. Off boost response is a night/day in difference and cruise fuel efficiency picked up by several miles per gallon. Of course, mid-range and top end power is serious. MegaSquirt runs the show and water/alcohol injection keeps things very happy -even when I "over" boost in 3rd through 5th gears.

This combination is perfect for carving up back roads. There's always enough torque to control chassis balance while cornering and enough "go" to accelerate down the straights. Again, the management is the key. Don't try a 9.5:1 with the original ECU and ignition.

[99EJ6T]

Thus, when I rebuilt my B6T I elected to go in the opposite direction with a 9.5:1 CR via forged Wiseco pistons. No, I'll never be able to run a big air blower, but that's just not practical anyway. Instead, I upgraded to the classic VJ-14/11 combination which is plenty good for 225bhp and a wide and safe torque band. The raised compression spools the larger unit just about as fast as the low CR spun up the stock VJ-14. Off boost response is a night/day in difference and cruise fuel efficiency picked up by several miles per gallon. Of course, mid-range and top end power is serious. MegaSquirt runs the show and water/alcohol injection keeps things very happy -even when I "over" boost in 3rd through 5th gears.

awesome, might just have to "steal" your plans, so to speak. sounds like just my type of build.

[leary393]

Thanks Guys for all the valueable info. Engine is on the stand and comming apart today. After the last posts I'm thinking of 8.5.1 comp as a happy medium. will tackle turbo sizing, ECU, manifold and gearbox once motor is back together

[808]

Let us know how it goes.. I'll be watching.

[psiturbo]

Don't try a 9.5:1 with the original ECU and ignition.

With minor tweaking it can be done with the original ECU and ignition, trust me it can be done and run very well.

[Scott@USRT]

With minor tweaking it can be done with the original ECU and ignition, trust me it can be done and run very well.

I meant with stock ECU programming + bigger turbo. You might find that acceptable but I sure don't.

[leary393]

Have just Hit the first hurdle. All was goin well until I removed Crank and was ready to remove oil squirters. Then I noticed, Holy hell the block has let go beteen the water jacket and the sump on cyl No 4. Looks like I'll be using my other block. I decided to use this motor because it was standard bore and had no scratches or marks in the bore, I don't know the history of the motor



Uploaded with ImageShack.us



Uploaded with ImageShack.us

Looks like a rebore for my motor with scratched bores

[leary393]

Need Help with ordering parts. Finding it hard to get the info I need when talking to the people I'm trying to order parts through. Because its not listed under the B6T, I'm buying miata stuff and I'm being told that I can't buy a kit with a high volume oil pump because mine is turbo so it will take a different pump. Here's a link to the kit I'm trying to buy. http://www.importperformanceparts.net/ If you click HPengine kits and then Mazda. go through the list and it says kit number 7 is for miata mx3's and 323's.
When you scroll down it lists 5 different kits. I'm being told to order th EKMA95MPX. But I would think the EKMA14MPXG would be better because it comes with a high volume oil pump. Am I right or wrong here. Appreciate all feedback.

[therieldeal]

i think that hole is supposed to be there.

[psiturbo]

Its hard to see, I got a block tore open right now and will take a look and maybe snap a few to see if it looks like what your talkin about.

[leary393]

Ok my mistake. now that i've had a closer look it is the oil return to the sump. at first glance it looked like a piece of the block has blown out, as it has rough edges like its broken away. Must be just rough casting. When I looked through it i could see day light, Stuck my finger over the hole on the bottom and it felt like i was covering a water jacket hole, assumed it was into the water jacket. After now turning the block over. It has an oil return down the outside of the water jacket. Learning as I go with this one.

[leary393]

Ok guys Still can't get this rebuild kit sorted. If anyone has had any previous experience. Should I go for the kit with the high volume oil pump or the one with out. The guy at Import perfornce parts recomends I go for the kit without the oil pump. If I havn't herd any other suggestions By monday I will order the kit without the oil pump and then try source one from somewhere else.
Just wanna get this thing moving

[maz323gtx]

Are you still chipping Mazda GTX ECUs?