I have reviewed most of the vacuum at idle threads and have not found an answer concerning my new engine. I have an IRP built stage 3 large street port engine that was built back in late 2020 and sat in a crate in my heated garage until 3 months ago. Here are the specs from IRP:

13B REW IR Performance Stage 3 Race build

• New Mazda 13B REW crate motor
• Extensive intake porting of primary and secondary side housing intakes
• Extensive rotor housing exhaust porting
• Rotor lightening
• Rotor side clearancing
• Rotor balancing
• Mazda Performance Racing rotor bearings
• Race balancing of rotating assembly
• 2mm Rx Parts apex seals with anti-friction coating
• Turblown Engineering engine studs
• Solid engine dowels with oil pass-through channels
• Mazda OEM RX8 Viton oil control rings
• Oil passage flow mods
• Coolant passage flow mods
• IR Performance oil pan brace

I installed the engine myself and I was very particular in mounting all the swapped accessories, with the engine on an engine stand, and used either very good condition used gaskets or new gaskets, where needed. Since installation, the vacuum at idle with around 950-975 rpm has been around 8-8.5 inHG. I get a very nice steady idle except for some surging and hunting when coming off throttle, which I believe may simply be related to needing some throttle body adjustments. I have the ISC still and cleaned it well and it passes ohm testing. I first thought I had a significant vacuum leak but have done extensive smoke testing, which showed no leak except for a minor leak along the throttle body accelerator butterfly rod gasket area. I did find a few small boost leaks, which I fixed, which would not account for the vacuum leak. I still pulled the UIM and did find a small split in a vacuum hose, which I fixed. The vacuum tank holds vacuum now. I even checked the primary and secondary injectors, which all have brand new grommets/O-rings, with no detectable leaks or fuel leaks. I smell no fuel at all under the hood even after driving a while. I checked the lower LIM gasket (metal 3-layer) from what I can see, passed smoke testing even with the UIM off, and again looks fine from the top (hard to see since I am still twin turbo). I plugged the line going to the oil filler neck, no change. I checked my boost gauge reading compared to my Power FC readout compared to a digital manometer and they all matched pretty well. I did compression testing with the Rotary Compression Tester and both rotors were around 115-118 on all faces except for one face on the rear varying between 105-112.

Is this normal for an IRP stage 3 large street port engine? Does anyone have a similar engine? What is your typical vacuum at idle if you have this engine?

Thanks
Mike

 

I would expect a large street port to have a lower vacuum than stock port for sure. Also it's really hard to say until the engine is more broken in, that should increase vacuum some as time goes along.

That'a going to always be the downside of a more aggressive port - lower idle vacuum and a rougher idle.

Dale

 

Mike, we have identical setups minus the race bearings. Mine are just factory clearance. My target idle rpm is 980 ish and it holds 12-13” mercury. How much smoke is coming out of the throttle body shaft?



~ GW

 

The smoke machine puts out 1 psi and the amount of smoke is quite small and doesn't leak until most of the system is completely filled with smoke. It is more small whiffs rather than any steady stream. I would doubt that would account for that low of vacuum, wouldn't you agree?
Mike

 

I wouldn’t necessarily agree, nor would I necessarily disagree. I’ve seen stuff not leak under pressure, but leak under vacuum and vice versa That’s why when I do AC systems, I put both pressure and vacuum on them. I believe Howard Coleman had something similar happen recently to his. I don’t remember what the difference before and after was exactly when he replaced the quad rings. Perhaps he could chime in and speak to that. I will say that your reading is about two psi roughly different than mine. Here is a write up I did some years back if you decide to replace that quad ring. https://www.rx7club.com/3rd-generati...rbish-1144243/



~ GW

 

Unless you are having to run very retarded ignition timing the leaks can't be that large, else the engine would run at a higher speed with conventional AFRs and timing, energy in=parasitic loads. Just like you can't increase wastegate flow "to reduce backpressure" without dropping boost. Energy has to balance.

If it's got solid overlap and late close it won't make a lot of vacuum by its nature. You draw more exhaust cycle losing pressure drop at the start of the intake and blow some charge back out if the chamber with late close at the end.

If it's running well I wouldn't be concerned. If you want to see more run it at 12.7:1 or a touch leaner and feel in timing and less bypass air to balance it out, but it will be more temperamental and gives you less flexibility to shape the ignition curve to assist the idle control to catch loads and deal with different ambient conditions.

 

I am running it leaner around 13.2:1 and have the *** screw only around 1/4 turn out. Secondary butterfly's are adjusted sealed and primary butterfly is minimally open. Timing is set by the ECU using the IAC system. I am again having trouble with hunting and surging when coming off revs and/or boost. This may be due to these factors, as you pointed out. What recommendations to fix the hunting/surging?
Mike

 

Give it more air with the screw and retard timing a bit on the higher rpm and pressure side of target idle. Maybe add a few degrees to the rpm points below target speed.

Anything with a significant port will generally want to pigroot a bit on a partial throttle at low rpm however.

 

Are you still using the extruded honed manifolds and a power fc?


~ GW

 

I have the EXACT same issue. Ultimately I've just lived with it, because the car runs like a stuck pig, but it has always been in the back of my mind that something was wrong. Then after Howards "I smoke" thread, I've really been trying to dig into this issue.
My setup is an IRP medium SP (stage 2) and IRP single turbo setup. Best vacuum I can get at idle is ~ -8.3. My *** screw is roughly 1 full turn out (I have not dared to touch any of the other TB screws). ECU is controlling the IAC. My timing at idle is 15deg (if I run any more retarded timing, the idle gets even more erratic because if the jump up to cruise timing is too big, so 15 is my compromise), and I allow the ECU to compensate timing +/- 2.5deg to help stabilize idle). Once the hunting stops and I get to a good idle, I also cannot get the car to idle less than 1000 RPM, even though my idle control is set to try and idle the car at 900 RPM. I think I can get closer with a half turn or so of the *** screw, but I think mine is already turned in quite a bit more than normal. I'll also note that once my idle has calmed, the ECU is sending full duty cycle to the IAC (closing it completely) just to get the idle that I have. [I have also bench tested the IAC, and even swapped out for another just for good measure...no change]

My research leads me to believe I have a vacuum leak somewhere post TB (or the TB itself). From Dale's idle control thread, a higher idle would indicate this is the case. I have tried spraying starting fluid all around the LIM/UIM to try and see if it will effect idle, and I have not seen any indications of a leak (spraying does not change idle at all). My next step was going to be taking the elbow off, and spraying directly into the face of the TB and see if that is my issue. If I can't find the culprit this way, I'll have to try and do a makeshift smoke machine.

Though, reading through this thread, I had not considered the injector O rings as the leak, so I am going to try and spray some starting fluid around the injectors to see if that may be my issue (though, I've never smelt fuel around there). I'd also like to try and borrow a known good TB off of one of the local FD guys to test my theory.

 

Yes to both. Extrude honed UIM/LIM and a RC ported throttle body on the secondaries butterfly's only. Primary butterfly is stock.
Mike

 

Another thing to look at is if you retain the stock PCV valve in a pre 1995 model. My PCV valve was bad, stuck mostly wide open with associated slight vacuum and greater boost leak. In another thread, I have changed my oil catch can setup and PCV valve, with the multiple stage fully adjustable W/E Wagner PCV valve for more ideal cleansing of the crankcase.
Mike

 

What ECU are you using?

I started messing around with my ISC control using my idle settings and F/C settings on the PowerFC. I found any old thread from Arghx (Raymond), where he was looking into the function of the ISC/IAC control. At the time, he had a large street port. In the Power FC, he would set his target idle for no load higher than his desired rpm (even higher than E/L or A/C), which would fool the PowerFc trying to maintain idle, into adding more timing and relying less on the IAC to compensate air for coming back to idle from higher rpm's. I added 1 turn to my *** (now 1 1/2 turns) and set my no load idle to 1000 from 950.I set my no load F/C to 1320, which now allowed the IAC to be more in the 50% duty cycle area target. The key to his idea is to make the IAC operate in more of the mid point range, so it can truly compensate air for idle, and use the added timing more to help control idle. This made an improvement on my hunting/surging and my actual no load idle went down to 890 from 960 instead of up (weird). Lead timing went from 4-5 to 10-11 and trailing went from around -10 to around -4, when coming into idle. I had to quit for the evening and will try to raise the no load idle setting even more tomorrow and see if the hunting/surging disappears. Here is the old thread:
Power FC Any way to Log Idle Speed Control Duty Cycle with Datalogit? - RX7Club.com - Mazda RX7 Forum

Mike

 

Mike,

Take a log of the car running at idle warmed up to at least 80c for a few minutes and post the log files here. Make sure advanced and aux a/d are checked in the monitor window. Try to get it with no load ( cooling fans off / eld off ) and do not touch the throttle.


~ GW

 

I do have a log from yesterday, but it is from Xavier's FC-Connect (FC Tweak). His logs don't have all the advanced options and Aux a/d options. In particular, it doesn't have the "?" in aux, which is the duty of the IAC. I do still have the Datalogit in the chain of the PC Connect DL Box and could likely still hook up my laptop to it to run the Datalogit logs. I will try to see if I can get it to work. For this log I'm including, I did a PowerFC reset prior to logging to reset the idle learning and look at the end of the log, since I adjusted the *** at 1 1/2 turn the last time I revved the engine to see how much it would hunt/surge at this *** setting. The hunting/surging was much less on this log than on prior tests and was better after increasing the ***. Also, I was much leaner on this test from start to finish due to the added air on the *** through the test (my fuel was set to an *** of 1/4 to 1/2 turn from prior tests) and the added timing (from the raised no load idle setting forcing the ISC to raise timing), which could not be compensated for. Because of this, I will add fuel before I try again.
Mike

 

It really depends on the definition of 'large' street port and more specifically overlap - generally by moving the exhaust closing upwards in their case as most street ports don't tend to open crazily to the right on the port. Really big ones I've rigged for E production setups are in the 10", sometimes 11". I see other 'big' street ports pulling 15" - not what I'd consider 'big'.

 

I am not sure how big my "port" is that IRP does on its Stage 3. I have messaged Ihor from IRP and he has not responded to my inquiry. Does any out there know how "ported" this Stage 3 IRP engine is? If the overlap is significant, that would most likely account for my low vacuum and I would not chase a contributing cause such as a vacuum leak or internal engine problem.
Mike

 

Mike,
The log from the XB will record everything. It can be viewed in the log viewer or the old method with fc edit / charts as long as the file size isn't over capacity. Isc duty is labeled " Advanced ???(2)". It appears you have that confused with the other thats "???". I can see your isc duty just fine. You can remove the old datalogit box, its no longer needed. If you did the relearn on the pfc, the log file wont be of any help since it will be varying isc duty and timing to reach its target. Just to confirm you reset the powerfc and let it run for ten minutes no load, ten with load, and ten with ac. Now run another log with it like suggested in post 14, since the relearn is complete. The power fc gets a little grumpy the further away from stock you get. When you send me your log file, send me the dat file also. I just want to take a peek at the whole picture of what you're working with.

I do have pictures of what a IRP stage three port looks like. Its not overly huge, just healthy.

Also, which map sensor are you using?


~ GW

 

GW,
Thanks. I didn't realize I can view the whole log through the XB. I kept the datalogit for now since I have two thermocouples hooked up to it, I have used in the past, a EGT sensor and an AIT pre intercooler. I won't need the Datalogit once I get Xavier's new device and hook these up to it.
I did do about 8-10 minutes no load and about 5-10 load due to coolant fans coming on. Only about 2-3 minutes with A/C on (my A/C is a little low freon, so it cycles the compressor likely related to the pressure switch). The log was 20 minutes long.

If the overlap and ports are not that big, why the low vacuum? Again, compression was fine except slightly low on one face of one rotor. No other vacuum leak I can find as I mentioned earlier. Maybe it just needs to break in. I only have about 200-250 miles on the engine and I am waiting on a few parts from Japan to fix a turbo problem before I put it through the paces.

I am using the Apexi 3 bar. I even correlated it with a digital manometer. It's a good match.

It wouldn't let me attach the dat file. Not an acceptable format.

Mike

 

Mike, will shoot you a PM on the dat file.

It very well may just need some bed in time. But we seem to have near identical setups and I pull over - 2 psi more than you. I found the thread that Howard stated he lost from around -15 to -13 from a leaking throttle body quad ring. It’s worth a read. https://www.rx7club.com/3rd-generati...smoke-1167168/

~ GW

 

I just finished a second smoke test on the car. It is almost certainly the throttlebody. It was more obvious the second time since I fixed all the other leaks.
The more obvious video was too long to post. It leaks one of the main shafts up front and even leaks more on the opposite side TPS seal.
Mike

 

We offer TB rebuilds if interested - more info here: https://jp3motorsports.com/products/...dy-restoration