pistons for PSI

351C_TurboCoupe · 04-13-2001, 11:28 PM

I think I'm going into uncharted territory with my 351C turbo project.

Here's my dilemma.
I want some low end power, and I don't want to advance my timing too far just to get quick turbo response. I can live with some turbo lag. I'm thinking of using a static compression of at least 9.5:1 and running lower boost (like 8-11 PSI).

I know alot of you guys with blowers go with deep dish pistons to get that static compression down to 8.5:1 So, are you guys getting better times with:

A) higher static compression with lower boost (psi)

or

B) lower static compression with high boost?

Thanks for your input,
corey

NO SLO PK · 04-14-2001, 12:04 AM

Hey Corey, in my experience you'll make more power with higher boost/lower compression. You lose 4 percent power for every 1 point drop in compression. You more than make that up by running higher boost.

Honestly, I wouldn't go any higher than 9:1 if you want to run forced induction with unleaded premium.

By the way my engine has 10.5:1 with a 9psi blower. It's a really bad combination because of constant problems with detonation. I'm swapping to aluminum heads with bigger chambers asap. I'll be able to run more boost, more timing, and a leaner A/F ratio. Should be sweet.

Good Luck!

------------------
Russ L
'91 LX
Procharger, 3 row intercooler, extrude honed Cobra intake, Mac full Length Headers, 30# inj., 73mm C&L, 75mm tb, E303 cam, 289 rods, ported E7 heads, MSD, T-Rex w/255 lph Walbro, 5 lug conversion, Cobra R wheels, 3.27 gears and Moser Axles.

[This message has been edited by NO SLO PK (edited 04-14-2001).]

351C_TurboCoupe · 04-14-2001, 12:14 AM

Quote:

Originally posted by NO SLO PK:
It's a really bad combination because of constant problems with detonation.

Can't detonation be controlled by retarding the timing as the boost level goes up?

I thought MSD made a ignition control box that worked off boost? Er, maybe it was another manufacturer.

Thanks for the reply,
Corey

NO SLO PK · 04-14-2001, 12:23 PM

Well retarding the timing reduces power, and noticeably. At some point, you're better off reducing boost instead or decreasing compression.

A lot of blower guys will set initial timing at 14 degrees, but use the MSD6BTM to back off timing under boost. This gives the best of both worlds...crisp response at low rpm and detonation control under boost.

If you have an intercooler/aftercooler, you typically won't need timing retard.

Hope this helps.

------------------
Russ L
'91 LX
Procharger, 3 row intercooler, extrude honed Cobra intake, Mac full Length Headers, 30# inj., 73mm C&L, 75mm tb, E303 cam, 289 rods, ported E7 heads, MSD, T-Rex w/255 lph Walbro, 5 lug conversion, Cobra R wheels, 3.27 gears and Moser Axles.

04-13-2001, 11:28 PM	#1
351C_TurboCoupe Registered Member Join Date: Apr 2001 Location: Rapid City SD Posts: 5	pistons for PSI I think I'm going into uncharted territory with my 351C turbo project. Here's my dilemma. I want some low end power, and I don't want to advance my timing too far just to get quick turbo response. I can live with some turbo lag. I'm thinking of using a static compression of at least 9.5:1 and running lower boost (like 8-11 PSI). I know alot of you guys with blowers go with deep dish pistons to get that static compression down to 8.5:1 So, are you guys getting better times with: A) higher static compression with lower boost (psi) or B) lower static compression with high boost? Thanks for your input, corey

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04-14-2001, 12:04 AM	#2
NO SLO PK Registered Member Join Date: Mar 1999 Location: Arcadia, CA, USA Posts: 731	Hey Corey, in my experience you'll make more power with higher boost/lower compression. You lose 4 percent power for every 1 point drop in compression. You more than make that up by running higher boost. Honestly, I wouldn't go any higher than 9:1 if you want to run forced induction with unleaded premium. By the way my engine has 10.5:1 with a 9psi blower. It's a really bad combination because of constant problems with detonation. I'm swapping to aluminum heads with bigger chambers asap. I'll be able to run more boost, more timing, and a leaner A/F ratio. Should be sweet. Good Luck! ------------------ Russ L '91 LX Procharger, 3 row intercooler, extrude honed Cobra intake, Mac full Length Headers, 30# inj., 73mm C&L, 75mm tb, E303 cam, 289 rods, ported E7 heads, MSD, T-Rex w/255 lph Walbro, 5 lug conversion, Cobra R wheels, 3.27 gears and Moser Axles. [This message has been edited by NO SLO PK (edited 04-14-2001).]

04-14-2001, 12:23 PM	#4
NO SLO PK Registered Member Join Date: Mar 1999 Location: Arcadia, CA, USA Posts: 731	Well retarding the timing reduces power, and noticeably. At some point, you're better off reducing boost instead or decreasing compression. A lot of blower guys will set initial timing at 14 degrees, but use the MSD6BTM to back off timing under boost. This gives the best of both worlds...crisp response at low rpm and detonation control under boost. If you have an intercooler/aftercooler, you typically won't need timing retard. Hope this helps. ------------------ Russ L '91 LX Procharger, 3 row intercooler, extrude honed Cobra intake, Mac full Length Headers, 30# inj., 73mm C&L, 75mm tb, E303 cam, 289 rods, ported E7 heads, MSD, T-Rex w/255 lph Walbro, 5 lug conversion, Cobra R wheels, 3.27 gears and Moser Axles.