MR2 GEN IV BOV Issues

Hi Guys

I own a Gen IV MR2 by my understanding the Gen III and up dont use an airflow sensor but somethin different, correct me if im wrong but installing a blow off valve on a car that has an air flow sensor causes it to richen up momentarilly and other side effects would it be different if I drop a BOV on my GEN IV? ive always wanted a blow off valve on the car but always hesitated since ive read of certain side effects on GEN 1&2 cars.

Im looking the the HKS SSBOV coz i love the sound it makes,i know that there are no performance gain by puting on a BOV but i wouldnt put one on if its going to make the car run rough or loose performance, any help would be greatly appreicated.

[c.stratton04]

BOV do decrease performance a little and gas milage, but its not going to be very noticeable. In my opinion, having a BOV is worth the small performance lose. You will run rich whenever you shit due to the air that has already been measured not being burned.

[drazhartd]

Aftermarket BOVs I believe cause the same problem for every car, right? Shooting unmetered air out into the atmosphere...

but for a lot of people, the cool sound outweighs the consequences.

[HondaChili]

BOV's generally have the same sideeffects but diff cars have it worse. my friend bought the same BOV as mine but he had a 240 sx and the car just wont run right, even with reallocations.

[KiwiMR2]

I have a Type III 3sgte....have been running an HRF-L bov for around 2 years, NO issue's what so ever!! No NOTICABLE performance gains OR drops. I ran one on my Type II for around 2 years and the new owner has been for the 2 since then, again no problems and the Type II is over 200,000 km's on stock everything.

Being a Type III without the AFM means it is even safer to do so. Get one and enjoy

Cheers
KiwiMR2

[JekylandHyde]

Originally Posted by c.stratton04

You will run rich whenever you shit due to the air that has already been measured not being burned.

... but I believe he is stating that he does not have the AFM due to the generation of his engine.

snk33y, if you do not have the AFM, and you go with the HKS unit, you should be fine. You are only losing the by-pass feature which adds a bit of responsitivity and slightly better gas mileage. I wouls trongly urge avoiding the aftermarket valves that have a spring design (Almost all of them except the HKS).

Another option you have, is you can also vent your BPV to atmoshpere.
Just make sure to put a FILTER on it since it will allow air into your system. Look at the engine bay photos on my site to see what I mean.
Doing it this way you get all of the benefits of the OEM valve and the "noise".

[sn34k]

As i understand it "to atmosphear" bov are fine on speed density engines. All MKII mr2s are problem of re speed density, thunning rich is when the air is already meterd then releaced, on a speed density system the air is never actualy measured the PCM uses an algorythem along with the map sensor to figure out how much air it thinks is there. Because of this it is still going to go a little rich but nothing that is even a big enough deal to worry about, One of my friends dyno'd his turbo'd civic before and after we installd a greddy Type S BOV. installd while on the dyno, no change in temp, NO HP DIFF. his A/F didn't change at all from before. The problem comes if you have a MAF sensor. anyone who has ever seen a 3rd gen DSM or a WRX with a BOV can tell easy, when you shift you will actualy see a dark cloud from the exhaust. And it WILL noticably bog down.

Anyone who is still worried i found a BOV that is adjustable from 10-100% of how much is vented, at 50/50 you wouln't lose anything and would still get the fun noise. I don't remember who makes it off the top of my head but if any1 is intrested i could look it up.

[KiwiMR2]

Originally Posted by sn34k

Anyone who is still worried i found a BOV that is adjustable from 10-100% of how much is vented, at 50/50 you wouln't lose anything and would still get the fun noise. I don't remember who makes it off the top of my head but if any1 is intrested i could look it up.

GFB...Go Fast Bit's

Cheers
KiwiMR2

[JekylandHyde]

No BOV's would make a HP difference on a dyno ... the BOV is closed when you are dynoing.

The issue with the MR2 is not just the AFM, it is also the nice little by-pass feature of the OEM valve which greatly increases fuel economy. No other valve has this feature.

If the MR2 is running a speed density set up, the OEM valve can safely be vented to atmosphere for the "noise", BUT you must put a filter on the end of it sicne it allows air back into the system during by-pass. See my Web site for a photo of my engine bay with the K&N filter on the oem valve.

[KiwiMR2]

Originally Posted by JekylandHyde

the OEM vavel can ssafely be vented to atmosphere

AFAIT On Gen II & Gen I engines the air passes through the AFM before getting to the turbo, so if you vent some of it back to atmo then it's already been metered, and, since there is now less air than the ECU thinks there is, it runs rich. Any BOV vented to atmo will do this. Where the stock BOV differs from aftermarket is that it also functions as a bypass valve, bypassing the turbo off boost, if the stock BOV is vented the incoming air that flows (when it's functioning as a bypass valve) is not metered and the engine will run lean. However, as this is only off boost, and reduces as the manifold pressure increases (AFAIK it will not IMO be sufficient to melt pistons)

It runs rough because there is only a limited range of AFR's where combustion is possible, go too lean and no combustion event takes place (same if you go too rich). When it doesn't ignite because it's too lean you don't have a high cylinder temp problem, but you can cause backfires and damage to the cat as the unburnt mixture accumulates in the exhaust, when there is sufficient fuel it is ignited by the residual heat in the exhaust system. Simple answer is don't vent the Stock BOV, if you want the pssst noise by and aftermarket one.

Cheers
KiwiMR2

[JekylandHyde]

Kiwi, you eliminated the key first part of my post:
"If the MR2 is running a speed density set up"
Gen Is and Gen IIs can be converted form the AFM to speed density in a variety of ways. Mine is.

My system IS speed density now and I AM safely venting to atmosphere. As for the by-pass feature, that is why I said you need a filter on it.

If you go with aftermarket BOVs, you lose the by-pass feature and will most likely lose the performance of the OEM valves air design.

The only way to get the "best performing" valve andthe "cool noise" is to convert the car to speed density adn throw a filter on the OEM valve like I did.

[sn34k]

ok, this has gotten a little over my head but for anyone who is intrested here is that adjustable BOV. i'ts made for a WRX but it's supost to work with any intercooler, so with an adapter plate or a little welding it should be no big deal.

http://boostkits.com/worx_tuning_dual_stage_bov.html

[TRD2000]

By Bypass Are We Talking About The "plumb Back" Line From The Bov To The Intake?

It Is Possible To Get Aftermarket Bov's With This Setup, Try Gfb Or Turbosmart, Also You Can Get A Hybrid Unit Which Under Normal Driving Plumbs Back And When Driven Hard Will Exit To Atmosphere... With A Woosh Sound. So It'll Be All Normal, Normally.

[JekylandHyde]

TRD2000, the pipe you are referring to is used two ways:
*recirculation -The air that is "blown off" and is recirculated back into the system. This is key for the AFM since it has measured that air and it needs to be accoutned for int he engine some where

*by-pass - during most non-boosted times, the OEM BPV is open to let air by-pass the turbo and go to the engine. THAT is the by-pass feature. This increases fuel mileage and responsitivity since the engine does not have to "suck" air over the turbo. It makes life easier ont he system. No aftermarket valve offers this feature.

Basically put, that pipe allows air to flow in BOTH directions at different times.

[TRD2000]

ahhh that makes sense.... and it goes a long way to explain the funny doonk noises mine seems to be making during transition to boost (when i previously thought the bov to be completely dormant)