New Engine Low Vac?
05-18-2005, 05:37 AM
#14
Senior Member
Join Date: Jul 2002
Posts: 2,315
vacuum is directly related to altitude and barometric pressure. think about it, if the air is thinner the maximum amount of possible vacuum the engine could make is lower....if your reading is stable and your car runs fine i wouldn't worry about it.
05-18-2005, 05:50 AM
#15
Senior Member
Thread Starter
Join Date: Feb 2003
Posts: 241
ErnieT sorry didn't want to reitterated the thing again i was jsut trying to answer the post above it asked by TampaFD.. Just for piece of mind i'm got a compressor tester and going to check it out (granted it is sort of inaccurate but piece of mind is always nice)
05-18-2005, 05:56 AM
#16
Senior Member
Thread Starter
Join Date: Feb 2003
Posts: 241
the main reason why i posted it is because i've heard many ppl getting higher vac levels etc and i'm trying to make sure this motor is good. Living in hawaii shipping is a real pain in the butt and i want to reduce the amoutn of hassles involved. thank you for all the helpful comments much appericiated
05-18-2005, 09:09 AM
#18
Senior Member
Join Date: Dec 2003
Location: Mid-West
Posts: 791
FWIW,
I don't remember the exact numbers, but a friend rebuilt his engine according to clearance specs for the side seals in the Rotary Aviation video. His vac was lower than what he expected with the fresh engine as well. He recently mentioned that when he was getting a tune he spoke with Steve Kan about it, who recommended much tighter clearances than the video, for that very reason. Still, I don't think that it was considered a big deal. In any event IIRC, that car still dynoed at about 360 RWHP with basic bolt-ons.
I don't remember the exact numbers, but a friend rebuilt his engine according to clearance specs for the side seals in the Rotary Aviation video. His vac was lower than what he expected with the fresh engine as well. He recently mentioned that when he was getting a tune he spoke with Steve Kan about it, who recommended much tighter clearances than the video, for that very reason. Still, I don't think that it was considered a big deal. In any event IIRC, that car still dynoed at about 360 RWHP with basic bolt-ons.
05-18-2005, 10:28 AM
#19
Junior Member
Join Date: Sep 2004
Location: Pensacola, FL
Posts: 6
The problem is no air pump - if you're running the stock ECU, you'll lose a few inches of vacuum with no air pump, have a rough idle, and have bad on/off throttle transition. IMHO you shouldn't be ditching the air pump with the stock ECU - not only will the car not run so hot, but with no cats you're getting into the danger zone with the stock ECU.
Dale
Dale
08-18-2005, 03:04 PM
#20
Member
Join Date: Dec 2004
Posts: 49
[quote name='ErnieT' date='May 17 2005, 11:22 PM']15inches is fine. If you want to be really sure, go to Sears, buy a compression tester, take out the shrader valve, and as one person cranks the engine you look at the gauge. You should have 3 consecutive hits at around 90/90/90. Anything below 70 isn't really good.
[/quote]
I get 3 hits in the mid 90s. The vacuum on my all stock Rx7 is 16.75 to 17. Skip at KDRotary says that my vacuum is on the low side. My Rx7 doesn't recover back to idle very quick. Here is the e-mail exchange between us:
"Sure sounds like a lazy idle air control valve! If the codition of the engine is getting week the vacumn is low the valve will be slow in reacting! Hope this helps...Skip"
.........................................
"Well at the normal idle with the engine warmed up the vacuum floats between 16.75 and 17. I'll look into the idle air control valve.
Thanks for you help,
Keith"
.........................................
"Yeah that's on the low side"...Skip
In addition, regarding compression, the Mazda manual says that "compression pressure" should be 100 psi "minimum".
So with all of these numbers floating around from different posts I'd have to say that my Mazda engine is getting weak with my posted numbers. But it's very unclear from the manual and from these posts what good is for vacuum and compression. Guess I'll just look for burning oil.
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[/quote]
I get 3 hits in the mid 90s. The vacuum on my all stock Rx7 is 16.75 to 17. Skip at KDRotary says that my vacuum is on the low side. My Rx7 doesn't recover back to idle very quick. Here is the e-mail exchange between us:
"Sure sounds like a lazy idle air control valve! If the codition of the engine is getting week the vacumn is low the valve will be slow in reacting! Hope this helps...Skip"
.........................................
"Well at the normal idle with the engine warmed up the vacuum floats between 16.75 and 17. I'll look into the idle air control valve.
Thanks for you help,
Keith"
.........................................
"Yeah that's on the low side"...Skip
In addition, regarding compression, the Mazda manual says that "compression pressure" should be 100 psi "minimum".
So with all of these numbers floating around from different posts I'd have to say that my Mazda engine is getting weak with my posted numbers. But it's very unclear from the manual and from these posts what good is for vacuum and compression. Guess I'll just look for burning oil.