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Comment
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John Harris
Registered User
Posts: 147
(6/13/01 9:02:46 pm)
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BOV
"but would work fine as a "pressure to" throttle setup."
Well why don't you go ahead and build this? I couldn't think of anyone whose money I'd rather waste.
John
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John Harris
Registered User
Posts: 148
(6/13/01 9:12:25 pm)
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BOV
Mr Jspec,
No, a BOV won't do anything in the setup you described except make a rice sound. The whole idea of a BOV is to prevent compressor deacceleration on throttle close. Obviously not relevant on a displacement pump like a roots blower. And in my opinion wouldn't work on this magical "pressure to" system either.
John
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aw101x
Registered User
Posts: 50
(6/13/01 10:55:30 pm)
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Re: supercharger
i have to disagree.
assume you are drag racing.
you are shifting at or very near redline very quickly.
superchargers are dependent upon engine rpm.assuming the throttle is directly after the s/c.
everytime you take your foot off the gas to shift (assuming you are) the throttle closes, pressure between the throttle and the head disappears. you complete your shift and step on the gas again. the throttle opens but even though you are at 6500 rpm say, the s/c has to pressurize the entire length of the intake track between the throttle and the intake valves. this takes time and since you are only at 500-1000 rpm away you have very limited time to reach full boost again. having the throttle before the s/c would also mean pressurizing the entire intake track.
blow off valves are boost dependant, but factory wise, air piling up against the throttle is sometimes circulated back around by a bypass gate. a blow off valve would work just fine though.
something should be in place, you don't want the rotors beating the air any more than you have to, especially if it is not moving, it makes the air very hot. on top of presssurizing it. whichever system is more efficient i have no idea. this would also allow some load to be taken off the engine. whether it is a huge benefit in this situation i do not know.
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MechaMegloManiac
Registered User
Posts: 1616
(6/13/01 11:33:34 pm)
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Re: supercharger
101.thats my point exactly,allowing the trapped air to escape is going to take the heat with it,we breath to cool ourselves down after running,air we breath out,takes heat from our bodies with it,pretty simple for some to grasp I geuss,Harris you goon,in case you havent caught on,I'm presently busy building a blacktop,after that,I'll be building a turbo 20V,then maybe,I might build a twin charger for the hell of it,see,I'm torquing,while your talking...see the difference?? I geuss you cant.
Smuggla.
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John Harris
Registered User
Posts: 149
(6/14/01 2:47:14 am)
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Re: supercharger
101, a supercharger running at some drive factor about 6500rpm will take milliseconds to fill the manifold up again, all the time while you're waiting for the BOV to open, bleed off all this nice compressed air that has just cost your motor power to make, then close again (within 1-2psi of design pressure).I know which setup I'd have. And what about when you're just cruising around? It would be venting the whole time. The solution Shano2 was going to use was complicated and involved the need for programmable outputs on aftermarket ECU's, turning the charger on and off dependent on MAP and Throttle position.
Smuggla, if this BOV you're talking about vents hot air, why don't you get one installed in your head? You'd walk around with a constant hissing noise. I'll add this theory of yours to the already quite large archive we have here at Club4ag on "smuggisms."
John
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aw101x
Registered User
Posts: 51
(6/14/01 5:01:32 am)
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Re: supercharger
about the s/c, john harris, i still must disagree. and remember i am theorizing here, i don't know this to be fact, but what you are saying still doesn't make sense to me.....
in a hydrolic system i would agree, that pressure is instantanious, but with compressed air i still don't see it. the setup he was mentioning involved a front mount intercooler. lot's of track correct? even if the s/c was capable of producing max boost pressure in milliseconds, it is still limited by the intake air supply. that is a huge volume of air to move in that short of time. not only that but the engine using much of the air already as the throttle has opened, but the s/c still must pressurize the air to max pressure. assuming we are at high rpm still.
i realize that this isn't extremely important in the grand scheme of things, but 10ths of a second wins races.
if the throttle was right before the head, with max pressure held before it by bov or bypass or whatever, when the throttle opens there is a much smaller demand easier for the s/c to regain max pressure in the system.
if i am wrong about this, that is fine, i am not trying to argue. just presenting my view.
bov's. old conventional spring type i would also agree that they are not as acurate as one would like.
electronically controlled solonoid operated bov's are much more accurate, and can be controlled very easily.
also, john, just cruising around causing the bov to continuously vent? that would depend on what pressure you set it at. if you were to set it just above max boost pressure, then only when you shift it would vent, as when you shift the throttle closes, and the s/c is still trying to push in air, and the air that is there is expanding due to heat. so if it is vented then all is well, it maintains instead of beating the air. vortech has recently released a supercharger system for the honda civic's that uses a blow off valve. it only purges when shifting.
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Gino
Registered User
Posts: 59
(6/14/01 10:59:13 am)
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Re: supercharger
Aren't the SC12 AND 14 clutch controlled blowers? If so I don't see the need for a BOV if you're still utilising stock factory ECU . Now, with a VORTECH blower you will have to use a BOV.
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MechaMegloManiac
Registered User
Posts: 1622
(6/14/01 5:37:49 pm)
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Re: supercharger
Harris,you just proved how little you understand,you think light throttle would cause a BOV to open constantly...your
funny,very ignorant,a little daft,but very funny,I find you amusing,I'm actually larfing at you now see...I'm larfing,your making a fool of yourself,theres more than just me who see things my way...pretty simple really,see how good this forum is here now,more people with more opinions,and there posting them now,not having to fear the dreaded Sherwood speels,can you not see us simply chatting over machines...no 1 is getting upset,theres no abuse,well..apart from your ignorant arse,your just a gunna man...your "gunna"
set the world on fire you no nuthin gunna you
Smuggla.
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AE86 Sprinter
Registered User
Posts: 17
(6/14/01 7:19:52 pm)
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bov's
i have been watching this thread for a while but I decided not to post until now.
ok, lets say we are talking about a normal spring/trigger line(the tube from the intake manifold) operated BOV. electronic solenoid BOVS are different.
on a turbo car with a "pressure into throttle" as smuggs put it when you are flat to the floor, the turbo is boosting say 14psi, you also have 14psi in the intake manifold where the trigger line takes its pressure reading from.
so the BOV sees 14psi underneath it and 14psi on top of it from the trigger line so combined with the spring force the BOV stays shut. 14spi on top cancels the 14psi beneath + spring force to close it.
Now, you lift off the throttle, there is now negative pressure after the throttle where the trigger line takes it's pressure from. this then places a vacuum on top of the BOV.
so the BOV now has 14psi or more underneath it because the turbo is still trying to push the air into the engine ( for a tiny amount of time) and because of the shut throttle there is vacuum above it, hence there is a large difference in pressure across the BOV piston and this pressure difference overcomes the spring force and the BOV opens, venting out and making the big wanky PPPTTTTTSSSCHHHHHHH! noise we are all familia with.
so do we all agree with this rough description of how the BOV works???
well if we replace the turbo with a supercharger, there will be boost before the throttle even if u are at idle because it is a positive displacement air pump. it does not require high engine air flow to produce boost.
so if u are cruising down the highway, 3000rpm, the sc12 will make about 5psi from experience at these revs, so there will be a constant 5psi underneath the BOV. because you are at a tiny throttle opening there will be a vacuum in the intake after the throttle so the trigger line will cause a vacuum to be present above the BOV so it will open, hence venting all the time under no or partial throttle. under high or full throttle there will be boost in the intake manifold and there will be minimal pressure difference across the BOV so the spring force will keep it closed and it will not open.
of couse the amount of spring pressure can be varied and if u tighten it up enough to stop venting at partial throttle, the amount of venting at a full thotlle lift off will be neglible.
on the different matter of the intake plumbing taking time to pressurise, i agree with dennis on this matter.
i have performed two AE86 + gze conversions, mine and a mates.
mine has a rs turbo water to air intercoler mounted inside the engine bay so the intake tract is very short, almost as short as the stock one. the lag after a shift or when planting the right foot is neglible..i cannot notice any lag at all above 2500rpm..it just aint there..
my mate decided to install a large mitsubishi VR4 intercooler down in front of the radiator so the intake tract is very long..too long in fact. when driving this car around there is a noticable lag when cruising around..not too bad but it is noticable. if u are at 2500rpm and floor it in 4th gear, it boosts up to about 5psi..if u lift off and pop the clutch in the revs shoot up to about 5000rpm from the compressed air that is stored in the intake tract( and no my foot is OFF the throttle when i pop the clutch).
BUT..when you are thrashing the tits off it and shifting at 7500rpm, there is no lag either because the engine spinning at 7500rpm uses the air in the intake track so damn fast it there is no surge after a shift. the same with flooring it after a shift, the blower supplys so much air at those revs that it pressurises the intake without any percivable lag. so for roud town drivability there is slight problem, but for outright speed, there is no difference at all.
this last section is not theory ...it is ACTAULL DRIVING.i have actually driven these two setups so i am not guessing this and guessing that.
cheers
mike
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aw101x
Registered User
Posts: 52
(6/14/01 11:01:29 pm)
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Re: bov's
mike, that is good. hope you weren't taking offence to my guess', as i have not been so fortunate, but to learn, one must discuss. i just had the rpm area for lag backwards yes?
also, @#%$, hang on i must do some re-reading...
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aw101x
Registered User
Posts: 53
(6/14/01 11:06:39 pm)
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Re: bov's
but, why is there vaccuum after the throttle plate?
also - i thought that the real old blow off valves simply used a spring calibrated to x psi - when that psi was reached then it would push the spring up and vent until the pressure had dropped low enough to allow the spring to seat again.
just questions...
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MechaMegloManiac
Registered User
Posts: 1623
(6/14/01 11:10:09 pm)
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Re: bov's
101,theres vacuum after the throttle plate because of the cylindersdrawing air,all TCBOV's are spring controlled,only wastegates are controlled electronically.
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aw101x
Registered User
Posts: 55
(6/14/01 11:17:48 pm)
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Re: bov's
o.k. i just thought that the positive pressure would remain so (or almost the same anywayz) right to the head.
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AE86 Sprinter
Registered User
Posts: 18
(6/14/01 11:29:35 pm)
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bits and pieces
101, i take no offense to you asking questions and taking a guess at things. that is what these forums are for, to learn stuff
the reason i posted all this stuff up was the fact that every1 is fighting with each other, saying this, saying that but no actual data or first hand experience had been posted. you can argue against peoples words but facts are facts.
i know dennis has a gze AE86 and i know that smuggs has a 20v in a ae92(?).
smuggs, do you have a gze powered car? or have you driven one? if you have, then it is all good, if not i say it is a bit hard to get into a great big brawl if u do not have first hand experience with the topic of discussion. you can put your point forwards and bounce ideas as 101 has, but to outright call someone an idiot when they have a great deal of experience in that area is a little rough.
i admit i Sweet F all about the 20v rolla's ( well a little bit) and hence i do not go near a 20v dispute.
i dunno if that is going to sound right but what the hell, i'm late so i gotta run
cheers
mike
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MechaMegloManiac
Registered User
Posts: 1625
(6/15/01 12:23:43 am)
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Re: bits and pieces
I dont have to drive something to understand it's modus operande,I've never called any1 stupid,though I cop it a lot,
Boost is boost,BOV's are BOV's,if some1 has built what we are speaking of,and can clarify that a BOV will not operate,which it will..in the instance I have given,then I'll listen,BTW,who is Dennis? if you mean Harris,then,sorry,I dont care what his credentials are,I've seen nothing to impress me,no pics...no vids,nothing,just a lot of talk.I may talk a little,but,I torque a lot,thats what counts,as for 101,he has good understanding,
but,that post of yours(AE86 sprinter) actually made no sense to me,what was it you were actually trying to say?? can you clarify?
Smuggla.
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