I recently purchased a red '93 R1 with 35k original miles. I have been taking care of the general maintenance/reliability mods on the car to start with a fresh slate. I have so far installed a new fuel filter (What a pain in the a$$, but made a big difference, eliminated light throttle hesitation and lack of power up top), AST removal mod, Bonez downpipe w/ header wrap (not to hard of an install, just time consuming due to fitment, and refitment issues, but again a nice performance boost with an additional +1psi), Changed Tranny fluid to Neo HD synthetic (really smoothed out notchy shifting), Oil change and filter, air filter, and installed a boost and A/F gauge in the TriPower dash pod. The car runs much smoother and has quite a bit more power since the addition of these parts. I still have a new set of NGK plugwires and plugs to install. I have a feeling that the fuel filter, air filter, plugs and wires were the originals so they were due for a change.
Anyhow, I want to check with everyone here since I haven't gotten a Mazda maintenance manual yet. Here are my results from the boost gauge. I get -18 in/hg on cold idle, -18 to -17 in/hg on warm idle, boost pattern is 11-9-11 due to downpipe. I get -22 to -24 in/hg at cruise with 0 throttle dependent on which gear Im in. I haven't had a chance to do a compression test yet but are these numbers a solid baseline for a strong engine and vacuum system? The car idles smoothly and accelerates without hesitation. Do these numbers sound right?
A side note, the fuel filter definately made the biggest improvement in drivability. I had some serious hesitation on initial throttle and letting off throttle. Made the car jerk a bit. Replaced the fuel filter and now is super smooth. I decided to check the filter and blew air through the outlet side of the filter and a brown almost coffee w/ creamer colored fuel came out the other side. This thing was seriously blocked up.
Sorry for rambling but Im just excited at the improvments from just this simple general maintenance.

 

Your vacuum levels at idle and cruise look very healthy. I'd be a bit concerned about your boost pattern at WOT. You're getting to close to the "pop goes the 13B-REW engine" song.

Do you have a mid pipe? if so, consider installing a hi-flow cat converter on the MP, or....a boost controller to help control excessive boost issues.

 

11 psi isn't bad at all, for adding just a downpipe.

Just keep an eye on the boost gauge that it doesn't spike or creep up on you and you'll be perfectly fine.

 

No, the only exhaust mod or performance mod for that matter, is the downpipe. What is so extreme about 11-9-11. The bone stock setting is 10-8-10. Not saying that one psi isnt dangerous but from everything I have seen, you should gain .5 to 1 psi with a downpipe, and just a downpipe is not going to throw the tuning of the stock ECU off that much that is will blow the motor. From everything I have read, just a downpipe is a safe and beneficial mod not only for the power gains but for the decrease of underhood temps due to the retention of heat by the stock precat.

 

Nothing to be scared about at all. 1 psi isn't much of a difference. Some people just worry more than others.

 

What he said^. But one psi will creep faster that the reaction time you'll have when the Eyes tell the Brain to send a message to get your Foot off the accelerator. The winter air in PA will play another important roll in boost issues as well.

 

Sounds like you got a very healthy car! Good luck!