Re: "Maybe a new thread for cold side"

A lot of good questions about BOVs or By-pass valves. Proper technique says that you "Y" the flow on a Waste-gate and Turbocharger so that when the Waste-gate opens the flow is split and the Turbo sees a "partial flow" and the waste-gate passes whatever is necessary to maintain a given boost pressure.

When you put a BOVs or By-pass valve on the outside of a "curve", whatever volume is in the tube or flange going to the BOVs or By-pass valve fills with air and because that volume is now "FULL" the air travels on to the Throttle Body/Bonnet like the BOVs or By-pass valve was not even there. There will be no turbulence because the cavity will be full. If you put the BOVs or By-pass valve at 90 degrees to the pipe you could have a pressure drop but very little actual mass flow change because the air is "blasting past the side street" and can't turn fast enough to go that way. If it does go that way it will be at a smaller flow rate than if the path were the "Y" mentioned earlier in the Turbo/waste-gate example. Sometimes you need to dump a bunch of air quickly or you throw the belt off the blower.

As far as the By-pass before the inter-cooler, think about it this way: I have high pressure in the system. It goes from the boosting device thru the inter-cooler and on to the throttle body or carb. Now if you put the BOV or by-pass valve after the boosting device and before the inter-cooler the system is say at 20 psi and you slam the throttle shut. The Bov/By-pass opens keeping the Turbo/ compressor out of surge BUT the Inter-cooler sees the high pressure spike EVERY TIME this spike happens. This is why you fatigue the sides of an inter-cooler and have a "panel blow-out" occasionally. You blame it on the Welder's crappy weld but the issue was really the metal fatigued from the high pressure spikes over time. Inter-coolers are expensive . Why subject the Inter-cooler to the stress when putting the BOVs or By-pass valve in the right spot can eliminate the potential issue in the first place?

Turbochargers and other boosting devices can see some surge at given mass flow and still not have mechanical issues. You are trying to remove enough of a pressure spike to not hurt parts/ throw belts from the massive speed/load change of the boosting device that occurred in the spike.

Tom Vaught

 

Re: "Maybe a new thread for cold side"

Thanks for the info Tom .

 

Re: "Maybe a new thread for cold side"

I probably dont belong in this section posting but i had a comment on bov/bpv.
I would think it should be placed on the outside of a bend as specified but to go deeper should the inlet into the bov be facing downstream?
My thought is first, when operating in closed position, less air would be trying to enter it and not try to lift it open (ram air effect). Second, when the throttle is closed the high pressure wave would be entering it as a ram air effect and allow the bov to release more mass air.

Another thought was placement. As 10sec said, if it is mounted close to the throttle i don't think the bov would mechanically react quick enough to release all pressure. I also understand the need to protect other expensive pieces in the system so maybe it should be placed at the outlet of the last part you wish to protect?

I know every system is different and this is theory. Trying to understand things on a higher scale.

 

Re: "Maybe a new thread for cold side"

Typically the Boost System side of the air path goes to the inlet side of the By-pass /BOV valve.
This does add some force against the valve (trying to push it open) But also speeds up the reaction time when vacuum is also applied to the diaphragm/spool valve from the other side vs spring pressure keeping it closed. Getting rid of the surge spike is a combination of initial reaction time and flow capacity to remove the majority of the surge event. Some valves "start later" (slow reaction times) but still win the race at the end (with better flow capacity) vs a smaller valve.

Racers found out over the years that the typical Bosch "street" plastic valve was not going to cut it in a race application, (especially on the belt driven boosting devices). So then you had one big "Mondo" BOV, then two "Mondo" BOVs, then bigger single BOVs, etc.

The comment about getting away from the 'Dump" style BOV and going to the BY-Pass style unit where you recirculate mass flow "to keep the system charged up" when the throttle reopens has a lot of merit.

Tom Vaught

 

Re: "Maybe a new thread for cold side"

In a scenario that benefits from keeping the system "charged up", it would seem pre IC BOV would also be of benefit because of discharging hot air, not Post IC, wasting cooled air.

 

Re: "Maybe a new thread for cold side"

I'm not sure it would be wasting cool air, the PR of the compressor is going to be much lower when the bov/bpv is open, not much heating will take place.

Another thought about putting the valve closer to the throttle, the entire column of air in the pipes will maintain velocity when the valve vents. If the valve is right near the compressor, the air in the piping between the bov and the throttle will stop, and consequently need to be accelerated back up to speed when you get back on the throttle.

 

Re: "Maybe a new thread for cold side"

if you are doing a BPV, then you would definitely not want to mount the valve before the intercooler and recirculate hot air to the compressor inlet.

 

Re: "Maybe a new thread for cold side"

Something else to be said about this, we had a discussion about bypass valve response time- Isn't it true that closer to the turbo will increase the response time of the BOV? Plumbing and intercoolers all function as delays in venting the surge.

With that said I find my self having to put a BOV after the intercooler on a twin system due the the other side having a merge and need 2 bovs pre-intercooler. Yes I have shelves of bovs but there is something to be said about simplicity....

I think with the wide available BOV assortment available today its more/less packaging that dictates placement more than anything.

 

Re: "Maybe a new thread for cold side"

In the case of the BOV's I've played with, they snap open quickly when the throttle is dropped, no need for boost pressure to open them.

There is also the option of plumbing them as a 'fast acting valve', like some factory BPV's and this greddy I have sitting here. The top of the diaphragm(the side with the compression spring) is plumbed to the intake manifold, the bottom(opposing the spring) is plumbed to somewhere in the IC pipe or compressor housing.

During WOT there is a relatively low pressure difference across the diaphragm. When the throttle is released the difference in pressure across the diaphragm will be boost pressure+10 or so psi(assuming you get 20ish inhg vacuum on throttle drop) also the boost pressure against the face of the valve will act to open it.

The downside is that the spring force must be greater than the boost pressure*valve area to keep the valve closed during WOT, but this can be worked around.

 

Re: "Maybe a new thread for cold side"

Back to #7. I never understood the carb hat, except from a packaging standpoint. Wouldn't a plenum style hat solve the distribution and turbulence variances? The typical FI system uses a relatively large plenum for the runners to draw from, and I would think a carb or carb style tb would benefit by drawing from a plenum. Even the typical FI system might benefit from a pre-throttle plenum. :hmm:
What do you guy's think?

 

Re: "Maybe a new thread for cold side"

Sluggo the 90* elbow carb hats that most guys run are crap from my dyno findings. On my friends 417 cu in mopar it had an EGT variance of 280* per cylinder with the "good" hat everyone runs and was near melt down.

We then switched to my hat which is more like a tank with a stack in it and the EGT's varied no more than 80* per cylinder which allowed us to run more boost or timing. You cannot tell people this as they don't want to hear it so i ususlly don't bother but thought the guys in here might like to know.

This engine made 1237hp and 996 ft lbs with 18psi non intercooled with my carb hat, my meth kit and my blow through carb.

 

Re: "Maybe a new thread for cold side"

Some of us are open. I don't give a shit who it is, if you have to data to back claims, let em whine.

 

Re: "Maybe a new thread for cold side"

I forgot to add that we were able to pull massive amounts of fuel out with my hat also, i think it was like 8-12 jet sizes, i would have to find the dyno papers but i'm pretty sure that it was. It made the same power with that much less fuel which was really amazing to see.


I also did some track testing with both hats but on my mild turbo 2.3 blow through carb setup. It went 1-1.5 tenths quicker with the same jetting when i switched to my hat which isn't much but on a 12 second car with only a 2.3 it helped some. I didn't measure EGT's on it so i only have the track data on that setup.

 

Re: "Maybe a new thread for cold side"

I can pull all 8 of my plugs and you can not tell a difference in fuel .

I run my carb pretty much square . 68/70 jetting , 1:1 linkage , .080 pvcrs .

EV hat with 3" of spacing .

Just went 147mph in a 4450lb pick up truck at 21psi with a fuel curve that will make an EFI jealous .

 

Re: "Maybe a new thread for cold side"

Mind telling why you have 3" of spacing?

 

Re: "Maybe a new thread for cold side"

Because it fits .

 

Re: "Maybe a new thread for cold side"

Just dumb luck with no thought, because it fit?
Nice!

 

Re: "Maybe a new thread for cold side"

Nothing Dave does is dumb or just luck. Its 3 inches because 5 wouldnt fit.

Straighter you make the air before it hits the top of the venturis the better and more even it eill be.


If your hat was that much better than an EV it sounds like someone needed to install some vent tube extensions. An inhierent problem when the hat is short. Thats the same amount of jet i normally pull after installing extensions and figuring out how big to make the bellmouth on said extensions. Amazing what an extra .125 in diameter does to a fuel curve.

 

Re: "Maybe a new thread for cold side"

Why would we install band aid vent tube extensions on the crappy hat when the EGT's still varied by a mile and would have hurt the engine. We put the better hat on and fixed the problem, it was a very simple fix.

 

Re: "Maybe a new thread for cold side"