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Detuing boost for EFi conversion

Hey fellas, i've bought an SDS EFI kit from another local Pelican. I'll be doing the conversion over the winter. I just want to start preparing for the conversion.

I hear EFI unlocks a bunch of power, and with my 915 its days are numbered as is with my current 355 RWHP. With my engine set up in my signature below, do you have any idea of the Rear Wheel Horse Power jump, could it be 50 or 75?

I'd like to lower my boost to maintain a similar power as what I have, maybe a little more power would be nice. So with my 8.5:1 CR & .9 bar of boost, i'm wondering what the power drop is roughly with each point of bar I drop. Should I drop .1 or .2 points?

I'm doing the EFI swap to have better running characteristics than CIS. I dont want to crank up the boost til I have a better tranny swapped maybe in a couple years.
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Cheers, Chris
1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 07-05-2018, 11:23 AM
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I work on 15Hp per 0.1bar.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 07-05-2018, 12:02 PM
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OK, so maybe I should start looking for a .6 or .7 spring?
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Cheers, Chris
1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 07-06-2018, 02:39 AM
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I have a .5 bar spring. I won't need it once I install my new clutch.
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Old 07-06-2018, 08:12 AM
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Thanks Quattro, I'll keep that in mind.

Are all springs created equal? I have a Tial wastegate as opposed to stock.
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1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 07-07-2018, 03:30 AM
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Quote:
Originally Posted by puddy View Post
Thanks Quattro, I'll keep that in mind.

Are all springs created equal? I have a Tial wastegate as opposed to stock.
I'm told you don't want a spring too light as it may fail to do the job, but 0.5 bar shouldn't be an issue. With EFI, just dial up wastegate control after the fact to get your target boost.

Biggest issue is probably header design around the wastegate, bad ones can cause overshoot - if not, should be all good...
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'77 S with '78 930 power and a few other things.
Old 07-09-2018, 09:41 AM
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OK thanks Spuggy. I was hoping to get a rough power estimate from someone so I could hunt for the right sized spring in advance. But perhaps i'm asking alot?

I don't know if its realistic that EFI could increase my power upto 450 RWHP. If it does and I subtract 15 hp per point of BAR, then at .5 BAR i should be at 390 RWHP. If power only goes upto say 415 RWHP, and I do the same math i'm down to 355 RWHP which I have now.
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Cheers, Chris
1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 07-09-2018, 12:12 PM
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You should talk to Chris at turbokraft.
After speaking with him it helped me realize my setup was around what you describe. At .5 bar I feel like I'm getting 350+ and is making more at .5 than the 930/51 with sc cams and cis was at .9bar. My other engine only spun the clutch at a slip from standing start but now it spins at full throttle at anything over .7bar.
At 1.1 bar 450whp is realistic with carrera intake and large intercooling.
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Last edited by quattrorunner; 07-09-2018 at 12:44 PM..
Old 07-09-2018, 12:39 PM
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Great thanks for the info Quattro!

Spuggy - how do you control the wastegate with EFI, do I have to get a electronic wastegate? Can I keep my .9 bar spring and dial the boost down somehow with EFI controls?
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1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 07-10-2018, 02:46 AM
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You can't run less boost than your spring.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 07-10-2018, 11:49 AM
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Best bet is a low boost spring and control the rest by your efi or an aftermarket ebc or regular boost control system.
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Old 07-10-2018, 12:05 PM
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I run a 0.7 spring, and do the rest with EBC -2 boost settings, 0.8 and 1.0.
You either have a spring fixed at what you want, or run a lower default boost spring and select the rest via EBC.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 07-10-2018, 12:20 PM
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Great thanks for the info Quattro!

Spuggy - how do you control the wastegate with EFI, do I have to get a electronic wastegate?
Add a solenoid (electric valve) on the wastegate control/signal line; keep it closed until you hit the boost you want.

An EBC (electronic boost controller) can do this for ya (or even a manual dial'of'death) on a CIS car, with EFI, you just set target boost rate in the ECU and let it manage the the solenoid, opening it (so the wastegate spring takes over) once the MAP "sees" target boost.

Quote:
Can I keep my .9 bar spring and dial the boost down somehow with EFI controls?
Like Alan/quattro say, can't run less boost than the spring..

I almost let my Tial come with (their) stock fitment, a 6 PSI spring - which would probably have been fine, unlikely to be too light - but said "why would I ever want that little boost?" and fitted a 0.8 bar one instead...
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Old 07-10-2018, 12:38 PM
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I don't know if its realistic that EFI could increase my power upto 450 RWHP. If it does and I subtract 15 hp per point of BAR, then at .5 BAR i should be at 390 RWHP. If power only goes upto say 415 RWHP, and I do the same math i'm down to 355 RWHP which I have now.

as a point of reference I make 460 RWHP at 0.9bar. The choice of turbo, intercooler and related plumbing makes big differences.
Have fun with the conversion,
Dave
Old 07-11-2018, 03:55 AM
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Quote:
Originally Posted by spuggy View Post
Add a solenoid (electric valve) on the wastegate control/signal line; keep it closed until you hit the boost you want.

An EBC (electronic boost controller) can do this for ya (or even a manual dial'of'death) on a CIS car, with EFI, you just set target boost rate in the ECU and let it manage the the solenoid, opening it (so the wastegate spring takes over) once the MAP "sees" target boost.



Like Alan/quattro say, can't run less boost than the spring..

I almost let my Tial come with (their) stock fitment, a 6 PSI spring - which would probably have been fine, unlikely to be too light - but said "why would I ever want that little boost?" and fitted a 0.8 bar one instead...
One reason for that low a boost would be a "valet mode" where the EBC is open and essentially prevents the valet from joyriding with any level of boost. A few of the hobbiest ECU's support a switch selectable tune.
Old 07-11-2018, 07:05 AM
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Thanks for the info fellas, So it souldnt like I may as well keep my .9 bar spring, and i'll do some searching and see if the SDS EFI kit i bought will control an electronic boost controller.
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1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 07-11-2018, 08:11 AM
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if .9 bar is safe for you're tranny then ok. If you need less boost then no you'll need a lighter spring.
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Old 07-11-2018, 08:13 AM
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OK maybe I misunderstood the above, I thought I can electronically limit my boost. That the .9 spring would be the upper limit, but I can tune the EBC down to .5 or .6 BAR. No my tranny wont handle the extra EFI power at .9 bar, but if my EBC is turned down it should be ok, i hope!
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1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 07-11-2018, 08:20 AM
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If your spring is a light one, like .5 or .6 then that's the starting point. The ebc will "allow" more boost than that not less.
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Old 07-11-2018, 08:27 AM
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I was hoping to get a rough power estimate from someone so I could hunt for the right sized spring in advance. But perhaps i'm asking alot?
My SWAG is that you'll get around 40-50HP gain, for ~400 RWHP after EFI, everything else staying the same, just from better fuel atomisation/control. You already have ignition control, so probably no gains there.

Think you'd need to upgrade intake/turbo to realize more gains than that (which you can then trivially tune for once you're on EFI, of course)

Maybe run a weak spring - like 5-6 PSI (.3, .4 bar) - and either link boost control to RPM (supposedly torque down low that really hurts the 915) or adjust overall boost to your comfort level.

If the 915 you're running isn't built (gone through/good condition, billet cover, LSD and WEVO bearing retainer), should maybe buy a spare. You already know what the long-term fixes are...

I treated my 915 really considerately, and still worried about it. Rolling on the throttle and granny-shifting got kinda old. And despite that, it still ate 4 teeth off my (admittedly old) 2nd gearset one day with no warning.

Good luck!
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'77 S with '78 930 power and a few other things.
Old 07-11-2018, 09:00 AM
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