Tuesday, November 25, 2014

Silent Running... or Am I Going to Damage The Engine?

By now, everyone knows that the Tomei Powered EXPREME titanium exhaust which I fitted to my car (after having served as the jig during the design of the EXPREME exhaust) is loud. In fact, for use in Japan, the exhaust is labelled as for off-road use only.  Clearly it does not have the JASMA sticker which would indicate it passes certain criteria to be considered "street legal."

In any case, the loudness does me no favors - if I want to leave my house early, or come home late, it wakes up the neighbors.  Of course I use the Tomei supplied bung, but it still doesn't really quiet it to the level of a regular road car.  And of course, the bung defeats the purpose of a race exhaust, as it means I run around with a half blocked exhaust.

Of course I'd run the car without the bung, and the response is noticeably improved.  It makes the connection between right foot and engine, extremely direct.

So basically, I got tired of the compromise known as the "exhaust bung"

This lead me to some research. I quickly learned that A'PEXi had produced a manual, wire operated "Exhaust Control Valve":

However, not only is there no cool factor, but the prospect of having to drill a hole somewhere, plus the need to always think about whether the valve was fully open or closed, was too much for me. I needed something automatic.

And then I saw an article in GT-R magazine for a product that appeared to be designed for the R35 - the Blitz E-ESC.

Basically, this is a fully programmable, motorized exhaust valve - it combines a motorized version of the A'PEXi valve:
From: http://www.blitz.co.jp/products/exsystem/eesc/e_esc.html
 With a computer brain and a controller:

Normally I might do the install myself, but I figured the scraped knuckles, and time away from family was not worth it.

So off to Be Ambitious, where Ninomiya-san did his usual great job.  I also consulted him for some other work, which will likely end up done and thus posted to this blog.
The view tonight as I picked up the car

There was also something else very weird he was working on....
Ninomiya-san, however, warned me that he thought that this device had the potential to damage the engine, due to back pressure caused by the valve in its closed position.  Further he explained, basically there was no difference in exhaust sound, from about 20% to 100%.  Which meant that any value to this device, would be from 0% to 15%.

However, at 0% the valve is closed, and the only avenue for the exhaust to escape is a small hole:

He felt that running around with the valve in this position, would cause premature wear on the engine, with the increased back pressure. There would be no advance warning either.

So he set up the device so that it would fully open at 1200 rpm. Granted, my idle is about 900-1000 rpm, so this device is closed at 0% only when I am idling, at a stop light. As soon as I step on the gas, the valve opens up to 100%.

I don't have a sound clip yet, but from driving the car home tonight, yes the car is ridiculously quiet at red lights. In fact so quiet if I didn't hear the engine noise I would wonder if the car was on.  I played with the unit a bit, and while 0% is extremely quiet, at 15%, even 20%, the car is quieter than before with the bung inserted. So if 0% puts a stress on the engine, maybe 15-20% is the way to go?

The irony, of course, is that in parking the car, I have to step on the accelerator to get the car to back into my garage.  This raises the RPMs to above 1200, which results in the full roar of the exhaust.  My wife confirmed that, from inside the house, she did not notice any difference as compared to before.

In any case - my plan for the moment is to set the device to open fully at 1200 RPMs (or should it be a higher number?), but also to set the minimum value at 15% or 20%.  What do you guys think - will this result in premature wear to my engine?  Or is this relatively harmless? Maybe there is a way I can program it so it only goes to 10% or less when I need it to....

Let me know your thoughts, please!


マット said...

That small hole does make it a bit worrisome. HKS makes a programmable valve actuated exhaust for the BNR34. Let's hope the model gets extended to the rest of the GT-R range.

Aki said...

Hi マット、

Yeah that is a great solution, except I would want it in titanium... in any case, I will likely keep it mostly open, and use "silent mode" only when I have to...

Stj88 said...

I used to have a apexi one on my straight pipe GTST and when closed it did wonders, i installed it to pass a inspection that i had to go to because my car was found too loud by a police officer that hated imports.

When i imported my current 660HP R33 GTR i had one fitted to pass the first inspection... and it hardly did anything to quit my car down. Had to add a DB killer to the mix to pass the inspection.

I guess the Tomei outlett + Trust downpipe + Trust decat + Tomei expreme is just too loud to quit down by only using the valve. Its crazy loud but i drive it that way, neighbors got used to it!

My only tip for you if you really want a loud straight pipe that can be quit and safe when needed is to get a Australian Varex exhaust. Its like the new designs for the R35 from Top Secret and other brands. It closes the valve and recirculates the gasses through a silencer. But normally operates like a true straight pipe.

Aussie R33 GTR said...

Hey Aki, your mechanic is spot on with potential engine damage with that valve when driving. Personally I wouldn't take the risk. The issues would occur when the engine is under load more than just revving a bit higher than 1200 rpm. So you you could set it higher so it stays closed for the neighbours and city low speed traffic when it must be quiet, but I wouldn't be using it at all when driving normally as all it would take is one on boost event and back pressure and heat could lead to detonation and premature wear. Another idea would to drill a bigger hole just to be sure but I still wouldn't drive your car with it closed. Cheers.

Aussie R33 GTR said...

And to add I have an apexi active tailpipe silencer on mine and it does make a huge difference on drone when cruising and takes the edge off the note when idling. Keeps the law and neighbours happy but not me. Nothing sounds better than a loud RB26 ha ha

Aki said...

LOL Stj88 - I'm too lazy and poor at the moment to invest in another exhaust, but that is one interesting suggestion. Although it appears at minimum I would have to buy at least the muffler portion (no GTR fitment?). But then I'd lose the titanium awesomeness. Your car sounds (from the description) awesome, BTW!

Aussie - I agree, RBs properly tuned sound great when not muffled. I guess, so long as I am not on boost (and I won't be as boost begins to come on about 2000rpm) the valve won't be as bad as it could be... although I DO like your idea of drilling the hole out more. This weekend I'll see if I can set it so the default is NOT "0" but instead "15" in which case there will be that much less pressure on the engine.

Stj88 said...

Thanks Aki my car does sound very good, took me more than a year and half to find a BCNR33 that fitted my criteria!

And about the Varex they do sell a R33 specific catback, but i do get you i wouldn't either want to part with my Tomei expreme TI (Oke i would if someone would swap me a Amuse R1 Titan for free LOL).

Tadahisa Boskovic said...

Hey aki. I wanted to know, how is the tomei exhaust in cabin droan and 5th gear 100kph long distance cruising?

Aki said...


Well let's just say that wind noise is not a problem at 100kph, as the exhaust is still loud. It depends of course on what gear you are in, as well as how much sound deadening you have on your car.

IF you crank up the stereo though you won't be able to hear it I think...

flovv said...

Hi Aki,
Very interesting that you mounted a exhaust bung as I'm in the process of doing just the same on my bcnr33! In my case I want to use it when I'm driving longer distances, for less noise in the cabin. I will though get a cheaper bung than you, yours seems to be great, but a little pricey for me unfortunately (mine is 1/5 of the blitz, though not programmable).
My plan is to drill quite a some holes, or a few larger ones (not to large though).
Do you think this will help the problem with back pressure?

flovv said...

This is the one btw:
It seems to have quite some space for the exhaust on the sides already, maybe don't need that many holes. What do you think?