It all depends on engine speed, porting, and engine health (good compression).

I would say anything above 17 inches of mercury (In HG) is good for you at this time. MSPs don't have overlap so it should be relatively high. You would be doing it more to just track the change. Someone may know better.

When I was REW street-ported I would get 15-17 at 900-1000 idle, which isn't great. When I chipped an apex seal, my car idled at like 10 in HG (lost compression in 2 chambers on the front rotor).

When I fired up my bridgeport I originally had 10-12 in HG at 1,500 idle speed, now its 13-14 in HG at 1,500 idle speed. So over the past thousand or so miles the motor makes better vacuum, which should relate primarily to compression numbers since my porting/engine speed hasn't changed.

I always keep an eye on vacuum, it'll be the first thing that drops if you hurt the motor.

Growling a bit before this mornings run... :cool:

Stroker, Good info. Just checked... she idles at ~14-15 inHG @ ~925 rpm. I'll periodically keep an eye & track. Thanks.

Break-in process update:

Investigated break-in processes and discovered they were … all over the map regarding philosophy, rpm restrictions, & increment ranges, and overall break-in miles. All that aside from any good qualitative discussion I could find re: the break-in process of a rebuild w/ used components. :confused: So, I adopted what I considered to be a moderate process having tried to understand the underlying thinking of the varying processes.

My process:
- < 100 mi, < 4500rpm (oil & filter changed)
- <160 mi, <5000 rpm
- < 220 mi, <5500 rpm
- <280 mi, <6000 rpm *current mileage
- < 340 mi, <6500 rpm
- <400 mi, <7000 rpm
- < 460 mi, <7000 rpm
- <520 mi, <7200rpm
- < 580 mi, <7200rpm (oil & filter changed)
*Note: Revised upper mile rpm restrictions…just because. So, still no WOT, no redline.

After initial starting, and temp issues discussed in earlier posts…as expected I observed …especially early on, but throughout… steady moderate improvement in idle, smoothness, and response under increasingly firm accelerations. I’m seeing reasonably good idle now (hard to compare b/c I expect it w/b “different” d/t porting), and ~ 280 mi mark she began reliably starting cold. :) Other vitals are as listed in the above post.

Upon completing my defined break-in period where I’d been on a 1.5# WG spring w/ EBC off, I installed a 6# spring in my WG. It became obvious pretty quickly that wasn’t a good idea :nono:: rougher running, shifted to a deeper “labored” note, unresponsive acceleration, etc. It appeared too heavy a load …especially w/ my turbo spooling earlier. More on that. :) So, back to the house reduced to 4.5# spring w/ EBC off and she’s happy. Engine “note” is normalized, moderate accelerations are responsive. She’s starting cold & hot now. Having experienced this…plan now is to keep this configuration for an extended period, e.g. up to ~2,500 miles.

As mentioned...definitely seeing improved turbo response, haven't quantified it via M/E logs as yet…, but likely at the cost of some fuel economy. More to come on quantifying both of those.

Rougher running is more likely to be running rich than anything else.

Understood, and agreed. I've been working out a suitable configuration to move forward, and having horrible weather...hard rain everyday, etc. Hoping to get better weather and opportunity to grab some moderate acceleration logs. Hopefully, it is running rich... so it c/b leaned out a bit and recover some fuel economy. :lol:

What kind of plugs are you running in that motor? After I completed my first build about 5 years I put brand new $40 NGK plugs in the motor for the break in. They weren't that cold either (9 trailing and 7 leading). After a few hundred miles my car would break up pretty bad if I boosted over 5 psi. After checking everything twice, I decided the plugs were the only thing that were left. Turns out the brand new plugs were fouled, which is very common during the break-in process. The theory is lower compression, lower combustion pressure, and less heat, which tends to never get the plug hot enough to burn off the deposits. I put some $2.99 Autolites in there and the car woke up. Moral of the story, check yo plugs....

I also had spark plug issues when I initially upped by boost pressure from 6psi to 9psi after installing my EBC. Felt like the car would stumble/misfire at certain RPMs with a full load on. Went through a lot of analysis always leading to a dead end until I swapped to these plugs on Brett's recommendation. One log/tune later Brett had me running right as rain. Beware they are pricey though.

Spark Plug - Racing for NGK R6725-10.5 - Racing Beat

I've NGK R6725 10.5 plugs installed w/ an extra washer at the trailing positions. Regardless, point taken. :icon_tup: Will do. Thx.

Haha, I guess my comment is moot. If the spark plugs look fine when you check them my guess would be running too rich with the extra load on your current tune.

I wouldn't run 10.5s in leading ... 9s ideally ...possibly 10s max.

I was able to run 9s (leading/trailing) up to about 20 psi started getting knock, moved to 10's (leading/trailing) above 20 psi and knock went away.

I just started running 11s in the trailing position because the plug was light tan color and maybe a tad too hot. Probably would have not been an issue to stay with the 10s in the trailing position, but since my plugs are $2.99 each its good insurance. I change plugs like every 30-90 days so its not a big deal.

So I agree with Brett, 10.5 leading is very cold to be running in the leading position at very conservative driving conditions. Its just begging to foul. I bet you could go with 9s and stay with 9s even with a decent amount of boost. They would probably outlast those 10.5s by a factor of 10 or more.

Quick feedback:
I'd been experiencing some repeatable engine "stumbling / hesitation" only in the rpm range consistent w/ the onset of boost since my rebuild. I was unsure of it's root cause, e.g. rebuild components, assembly, normal break-in, etc. Determined that if not resolved during the break-in (which is what I expected) I'd trouble shoot & resolve it. I never considered the plugs (R6725 105s) b/c they're the same as I ran prior to the re-build. However, after swapping plugs, 4x R6725 105s for 4x BUR9EQs, during today's drive under similar driving circumstances and style; I experienced no stumbling / hesitation at any point. Smooth as butter again. :)

I think I may h/b on the ragged heat range edge before my rebuild, but not experiencing any issues. But m/h sufficiently increased flow d/t the exhaust porting and finally sealing my ex-mani.; that I was experiencing the fouling / spark blow-out issue now . :dunno:

I'll continue to monitor as I increase rpm and load thru break-in.

Those spark plugs look nasty for only 1000 miles. I have had issues with plugs that look half that bad.

Glad you got it all sorted out.

I had this exact same issue after installing my EBC and upping my boost; except I was the opposite (stumbled/hesitated on the BU9's but the R6725's resolved the issue). Was happening just as the turbo was reaching full spool (peak engine load) and only when the EBC was on. Would get a half second of stumble/hesitation then it would pull strong all the way to redline. Found that it was not related to RPM but rather to peak load.

When I take my car out of winter storage I'm going to pull the plugs to examine and maybe try the BU9EQ's (much less costly plug). My theory is that because I am pushing 9psi on the stock GReddy I am essentially pushing it to it's max meaning charge air is hotter and the cooler plugs help to counter this.

The next logical step for me is to try and get some analytical data on whether the car performs better with more boost and cooler plugs or slightly less boost and hotter plugs.

hmm...I wonder how the balance of our set-ups m/h contributed, e.g. turbine / compressor size, manifold design, piping dia., IC, etc. all which would impact flow & heat. :dunno: Hurts my brain to consider. :yelrotflm

Perhaps some of the SMEs will chime in...

Well, ...during my drive last night... i experienced significant rough running & stumbling. Grabbed the below screenshot of CEL codes. Did the brake stomp reset this morning followed by a short drive, but still not right.

P2070 is d/t a failing SSV valve bump switch (but SSV is working), but the P0335, P0172, & P2097 are new.... Will do some t-shooting today... beginning w/ inspecting the Eccentric shaft sensor, connector and wiring.

https://cimg2.ibsrv.net/gimg/www.rx8...4967cb5b66.png

Walked thru the DTC P0335 t-shooting process. My e-shaft pos. sensor is / was clean and registers 1080 ohms resistance. No opens or shorts to ground or power found on A or B sensor terminals, PCM connector wires and pins look fine. :icon_tup:

Reassembled everything and whala... the worst kind of fix IMO - having no idea what resolved it; but the CEL is gone and she's purring like a cat. I'll take it... :rolleyes:, but don't trust it. :suspect:

Just returned from ~ 40 mi drive. Idle & smoothness are fine and the CEL has not returned. :fingersx: On w/ it...

edit: the P0335 DTC for reference: http://www.rx8ownersclub.co.uk/faq/m...200300W05.html

Ahh, the intermittent electrical gremlin. Those are always so much fun to track down.

It seems to me that these cars offer up phantom faults on a regular basis . I often have to just shake my head and put this kind of fault behind me ...never having found the problem (if there even was one).

i blame lucas.

beers :beer: