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Old 26-08-2011, 01:34 PM   #1
Fosgate
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BP NA with Turbo

Hello,

Just wondering if anyone converted their BP NA to turbo and how its going?
I guess I'm more interested in the NA high compression pistons then BP NA engine is whole.

Im planning to build a BPT with high compression NA pistons so need to know how would the engine coupe with NA compression of 9:1 compared to Turbo compression of 8.2:1.

Thanks

Edit: sorry I didn't notice there was another specific section for Forced Induction discussion.

Last edited by Fosgate; 26-08-2011 at 02:31 PM.
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Old 26-08-2011, 03:38 PM   #2
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it'll cope fine. there are BP engine out there that came from factory with 9.5:1 pistons. i wouldn't be running a gtx/r ecu if using 9.1:1 pistons, (which i assume are aftermarket?)

if you run low boost to prevent detination, i doubt you'll kill them. will spool up alot quicker also, but will reduce peak rpm kW.

the 2 main inturnal differences in the 2 engines is the exhaust cam and pistons.
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Old 26-08-2011, 03:53 PM   #3
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Yeah Im quite familiar with both engine and have rebuilt couple of them. Its going to be a full BPT engine running all the BPT management (BP26) but will have BP NA pistons with 9.0:1 compression ratio.
The reason I want to do this is because the engine will be running 4 speed auto BG Astina box that have longer ratios... so high compression will compensate for that.
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Old 26-08-2011, 04:16 PM   #4
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will need to advance the timing alot to allow for 9.0:1. and run very low boost to prevent detination and cracking the brittle pistons. without the use of a knock sensor, the only fail safe will be your ears. dunno if you wanna make it that hard on yourslef. already running the bg sohc parrallel with the gtx ecu if gonna be a pain in the butt as it is.

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Old 26-08-2011, 05:48 PM   #5
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Don't think it would be so problematic.. essentially it would be a BPT engine with full BPT management so knock sensor and everything would be there. And advancing the timing not sure how that is going to help with higher compressor setup when BPT management will be used.
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Old 26-08-2011, 06:05 PM   #6
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Quote:
Originally Posted by Fosgate View Post
Don't think it would be so problematic.. essentially it would be a BPT engine with full BPT management so knock sensor and everything would be there. And advancing the timing not sure how that is going to help with higher compressor setup when BPT management will be used.
but the auto box need the auto ecu to control it doesnt it???
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Old 26-08-2011, 06:11 PM   #7
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Quote:
Originally Posted by Fosgate View Post
Don't think it would be so problematic.. essentially it would be a BPT engine with full BPT management so knock sensor and everything would be there. And advancing the timing not sure how that is going to help with higher compressor setup when BPT management will be used.
you drilling a hole in the block for the knock sensor then?

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but the auto box need the auto ecu to control it doesnt it???
correct.
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Old 26-08-2011, 06:20 PM   #8
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I thought Auto box had a separate ECU ... I guess I need to go back to the schematics to check this out.

Project.r.racing. Im not using BP NA... The engine is a genuine BPT (I have 3 of them here in the garage) and I just want to use High compression NA pistons in them so it will have all the holes for knock sensor, oil and water lines for the turbo....
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Old 26-08-2011, 06:28 PM   #9
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Plenty of Mx-5s use turbo kits on stock engines. If I had my choice though i would use high comp turbo pistons over NA pistons.
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Old 26-08-2011, 06:47 PM   #10
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argh makes more sense now.

but as above, if you are gonna open up a bpt and put in higher comp pistons, then you might as well send $500 on forged 9.1:1 pistons. massive strength difference.

not too sure why you'd wanna do it though. just using a regular bpt and running 5psi and a very small ID intake piping + IC should result in faster spool and alot less gearbox breaking torque. should still net 25-30kW extra over a stock bp. and 50-55Nm or torque.
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Old 26-08-2011, 07:21 PM   #11
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Just spoke to Brad (BPT_TX3) he has done this same thing (minus high comp pistons) on one of his cars 6 months ago. So the engine ECU does not control the Auto tranny. The tranny has its own computer which shares some of the signal with the ECU so I can easily replace the SOHC ecu with BPT one after modifying the engine loom ... which shouldn't too hard.
He also reconed stock BPT with low compression pistons had no problems with lag even on longer ratio auto gears but I still wonder how more responsive would be high compression pistons be in such a setup.
Do you know where can I get those forgies for $500? I was thinking ebay Hypertech ones for $100 something....
I generally run low (read stock) boost of 7-8psi on my setups so I wouldn't need to increase the boost with high comp pistons to get that extra 15-20kw
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Old 27-08-2011, 07:34 AM   #12
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ebay is where they are at. just search "miata piston" including international sales. USA has heaps of cheap forged pistons, and the AUD vs USD = more money in your pocket.

forgot the BGs had a seperate controller for the auto. probably the last car in the world ever manufactured that had one. lol
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