Control Overboosting with BOV??
 

OK, so i have become bored as I wait for the final bits and peices of my Turbo swap to arrive and in the meantime have continued to order additional parts.. This is getting stupid.

I am very concerned about my setup because everything I am reading says that I have a pretty good setup to blow up my engine... I have an S5 T2 engine with a 3" straight through Corksport N1 Style exhaust, I have a larger diameter charge pipe, aftermarket BOV, Manual boost controller, Blitz Intake and short ram 3" intake tubing.

I have not added any fuel yet, but want to get the engine running reliably before I go modifying any further.

My question is: How controllable is the boost using the BOV? Can I just set the BOV and Boost controller to dump pressure and keep the turbo at 8psi or so?

Thanks for the insight between my modifications (720 secondaries and Rtek in my future..)

https://www.rx7club.com/attachment.p...1&d=1327979827

Boost controllers can never lower boost pressure or control boost spikes, the strength of the WG spring will determine minimum boost. BOVs are not used to limit boost pressure(except in newer electronic versions) A pop-off valve could be used...but it's only a last resort/bandaid.

Boost creep will be the biggest contributor to popping the motor with your setup. You need to port the wastegate as much as possible, and possibly either restrict the intake or exhaust(or both) to keep it stabilized at a safe level.

OK, I just bought a reducer for the muffler. Perhaps that will help on the exhaust side.. I was aware that a boost controller is more to set the boost higher, but Can't wrap my head around why a BOV wouldnt dump at a determined pressure enough to keep things safe..

because thats not what they are designed for? they are there to vent boost pressure so when the throttle is closed it doesn't return through the turbo. mmm surge. they dont open at a predetermined boost pressure thats the job of a wastegate.

The adjustment on a BOV is for how responsive it is to opening. It won't open unless it sees a pressure differential on its diaphragm(the reference port). Some of the poorly designed valves begin to leak at higher boost levels, but that won't stop boost creep. The old greddy type-s may have had a provision for being used as a pop-off valve.

its not bad to have a pop off valve but it is just a bandaid fix as K-tune said.

If you want to know how it feels like when the pop off valve vents the boost, if you've ever had a intercooler pipe pop off during boost.....yea, same feeling lol

it is nice to have it for that just incase moment it does boost creep, or your wastegate feels like it doesnt want to work anymore....

So you want to control boost by causing a controllable leak? Good way to kill a turbo by over spooling it.

Better a turbo than an engine.

I guess until I upgrade fuel I will keep my foot out of it. Thanks for clearing up my lack of understanding.

So if one was to install a Walbro 255 and hot wire it would that be good to keep the engine from blowing up?

I don't think so, I have that installed, but the injectors can only push as much flow as they are rated for.

Ok so pretty much you need bigger injectors,fuel pump, and a tuner like a SAFC2/Neo?

My only mods are pretty much a FCD,Intake,Downpipe,3inch exhaust, BOV? can I still blow my engine>?

Technically no, because you haven't gotten rid of the main cat. Freeing up the exhaust flow is the main reason for over boosting. In my personal opinion, you should not have an FCD on this set-up. Fuel cut is there to in a way protect your engine, by cutting fuel to the rear rotor. Some people say that fuel-cut can cause an engine to blow as well though so if you're constantly hitting fuel cut this all needs to be addressed. Regardless, I believe you should remove the FCD until your adding more fuel to the set-up and have a way to monitor it. Also, take your stock turbo out and port out that waste-gate to control boost pressures.

Once again my opinion: Remove FCD immediately, Upon removing the main cat, remove the turbo and port the waste gate to control boost pressure. Re-install Turbo and install cat deletion pipe. Also as an extra safety precaution, it would be a good idea to runner a larger fuel pump because this is by far the weakest link in the fuel system. FD fuel pumps go for around 50$ on here, drop right in, and do the job nicely.

No engine blow! :)

I did that accidentally. The blitz bov would open way early and the turbo would spin like crazy. Didnt figure out the problem until was too late.

Good info there thank you! I'm going to be running a downpipe from RX7store there is no cat I got this car with no engine,I'm installing a JDM replacement thats why I needed to know, do you have a link to the --HOW TO-- on porting the waste gate? I'm not running a boost controller I plan on leaving it up to the turbo.. so I will have the basic mods like I listed then adding some porting to the waste gate and a Walbro 255 hot wired. Sound good? also will have a nice boost gauge and Wideband

I wouldn't trust a Jspec with any sort of mods done to it. That's almost begging for frustration and problems.

True, but then there is the chance of compressor blade shrapnel heading into the engine to have a playdate with the housings. Since you have some downtime before the finishing touches arrive, get that wastegate ported. Besides, what's the point of putting all that work into that beautiful engine bay and not using it! :bigthumb: Nice work BTW!

the only way to run your setup with any safety margin is to port the wastegate as large as you can get it.

your aim is to keep the boost level under the factory boost cut level at 7.5psi and remove any FCD you may have installed.

Off topic, sorry.
How about posting some pics of that SP20 you've got there? I've been rocking my Protege5 for over 10 years and love it. :icon_tup: Check my cardomain page in my sig for pix of mine.

On topic: IMO the best way to control boost creep is to put some kind of restriction in the exhaust. I use a Bonez cat and have no issues with an intake, DP, cat back, Pettit turbos, and an SMIC.

I can't give you any advice on the JDM engine, but there's a nice little walkthrough on porting the wastegate: http://www.aaroncake.net/rx-7/s4wastegate.htm I don't know what your planning to do with your car later on, but an FD fuel pump would be cheaper I think and it wouldn't over run the stock FPR like the Walbro would. also have you looked into the Corksport dp? Nice quality there.

I'm on Mazdas247.com also what about a High flow cat? will that work? is that what the Bonze cat is?


Thank you! I really just want to have basic bolt ons with stock boost I have had fast cars in the past and all's what I really want now is a RX7 with BPUs and whatever I need to keep it from blowing up at stock boost lmao

Yes, Bonez is a brand of high-flow catalytic converter.
Mazda24/7 is a tiny bit evil, imo. Antoine is a cool guy, but some of the mods there are power hungry to say the least. I also got ripped off more than once in the FS section there.
Anyway, nice P5.

Thanks and yeah I can agree with you there about Mazdas247 lol
anyways if I had a High flow cat with the turbo's actuator ported I should be good? right

You're going to pay out the nose for a bonez cat. If you have any skills in welding, or know a guy who can weld, then buying a magnaflow cat (with an air pipe if needed) will save you some cash. I run one on my setup and experience little to no back pressure issues. (I also ran 3" piping though).