Miata Mailing List: November 1997, Message #49
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From: 	Tony Cooper <tonyc07@ibm.net>

Subject: Re: MCA Mag Dyno Database

Date: 	Sat, 1 Nov 1997 13:04:23 +0000



Allan (BBB) wrote:

> 

> M'lord, ladies and gentlemen .On 31 Oct 97 at 22:41, Tony Cooper was

> known to say

> 

> > My Sebring w/ AVC mod is producing 7.5-8 PSI  @ WOT in 5th (around

> > 80mph) I do have an MSD unit and I have no pinging at all.

> >

> > Hope I'm not destroying / damaging something and not knowing it! (I

> > don't think so...)

> >

> 

> Tony,

> 

> Just a quick question, I'm installing my Sebring next week with an

> MSD unit and the AVC mod.Here in Begium we have the same two sorts of

> fuel you guys have + a third with even higher octane (89,92 and 93).

> Most ralley car drivers and performance car drivers use the (more

> expensive) 93. How high did you set your timing to get the 8psi ?

> I'll start off at 10 and hope to go to 14 (after a test).



I get about 7.75 PSI (boost gauge needle much closer to 8 PSI than 7)

under WOT in 5th gear @ 80MPH. I have set timing as high as 16 and never

had pinging. I have it set at 12 right now as it seems to give me the

smoothest power curve from idle to 7K RPMs. At 16 the car felt anemic at

lower RPMs and had a sudden "major" jolt of torque starting at about 4K

RPM. The car wasn't a drivable or enjoyable at 16 so I backed it down to

12.



Has anyone thought about adjusting the vacuum cutoff mechanism in the

bypass system of the supercharger? Lowering the vacuum required to

activate should see an increase in boost under most conditions. I

suspect boost is being lost under WOT when the vacuum begins to drop. I

see highest boost when the car is climbing a hill in WOT (engine under

load, vacuum highest).  Is this a sound 

assumption?



I don't even know if the mechanism is adjustable - have not had the time

to look yet. I am sure fuel mileage would be adversely affected.



Tony