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Hi since this topic is about turbos and superchargers I would just like to ask a few questions about blow of valves. What are the advantages and disadvantages of an atmospheric BOV compared to a plumb-back BOV? My friend said that atmospheric BOV's can confuse sensitive Air/Fuel metres because of the sudden decrease in air, is that true? Also on some cars instead of the conventional WHOOSH or PSSSH it emitts a whistling sound, is that just a different kind of BOV? Thanks in advance for any info.

Ya it can- the afm will have said t the ecu "theres this much air", Ecu goes "ok!" then the bov opens, and that amount of air is now much less, causing a pretty rich mixture to run through the engine (resulting in a back fire sometimes). And as for the sound- ya just different bovs. A lot of different factors can cause a different sound- The type of bov, the amount of boost, the shape of the piping on the vehicle, what engine, the way in which the throttle was released- etc.

Ah yep thanks for the info, I got another question regarding vtec turbos. Is it really that difficult to turbo a vtec engine? I heard that what you have to do is tune your vtec so it kicks in just as the turbo hits the peak so you can stay on the power. I thought that doing that will increase the wear on the turbo because say if the turbo maxes out at 6000rpms, but your engine revs to 8400rpms. It's going to be spinning at the same rate at 8400rpms and 6000pms since the turbo has maxes out. However since the engine revs are higher shouldn't that mean more exhaust gases are "trying" to flow through the turbo? If the turbo only lets 6000rpms "worth" of exhaust gases through and you try putting 8400rpms "worth" of gases through wouldn't there be a build up of pressure in the exhaust manifold/turbine section of the turbo? Sorry if that's completely wrong, if it is feel free to correct as I'm here to learn as well

No, the revolutions-per-minute of the turbo compressor doesn't correlate like that to the rpm of the engine.

The main problem with boosting a Vtec engine is that Vtec ups the compression ratio of the engine when it's activated (I think), so with turbocharging you're adding even more pressure, making the engine much more fragile. Then again, when I visited the Clubrsx forums a few weeks ago, boosting the RSX-S seemed to be quite a popular mod.

Vtak just changes the charecteristics of the cam shaft. Duration, timing, lift. Its very possible to turbo a vtec engine with great results- they however do use high compression pistons (doesnt change, not to my knowledge.. thatd be one hell of a feat), but you can boost it too high without going to lower-compression pistons.

Yeah, you're right. I wasn't thinking correctly, woops. Not the first time I've misunderstood Vtec, either, heh... Do you know why Vtec engines use high compression pistons, though?

Yea thats another thing since Vtec engines usually have compression ratios of 10:1 or above, while turbo engines have lower compression ratios. How would you determine what the best compression ratio would be on a vtec turbo?

yea I was gonna say v-Tak (Takumi) doesnt change the compression ratio otherwise it would of been alot bigger and more popular. Variable compression ratios would be sweet if it were possible with what we know today.

It's not Vtec itself that ups the compression of the engine. The Vtec engines we usually think about (B18C's, B16A's, K's, F20/F22) are engines that Honda tried to get as much power out of, without boost. So they'll use a higher compression to get the power, because they have no plans to ever see these engines boosted. The relationship between Vtec and high-compression may have a high correlation, but it isn't cause-and-effect.

If you're looking to boost a Vtec engine I'd look at those crappy D-series engines from the EX Civics, or a LS Vtec creation. And if you really want to break axles, a B20 with a B16 head, then boosted would be pretty nuts.

I see this has gone a bit off topic...

a crude explanation of vtec:

at low rpm, a certain set of timings and allow for more power.

at high rpm, a different set of timings and etc allow for more power.


VTEC is a solution for an engine to have the advantages of both.

e.g. if a viper, in theory, were to be able to rev to 9000 rpm, its torque would seriously drop off, because the engine is designed for lower RPM use.

on the other hand, if a s2000 were permanently stuck in vtec (which is actually done, although its not 'stuck' in race cars), it would have even LESS power in the low end than a civic dx.


vtec basically allows for a change in the rpm range which allows you to have the best of both worlds, at the cost of engine complexity and some weight.



on the other hand, im surprised the different types of superchargers havnt come up...

roots, twin screw, centrifugal, axial flow...

since i drive a s2000, i'd prefer the latter two, since they have a gas mileage impact similar to having your a/c on as long as you dont drive TOO spirited...

Basically, VTEC makes it so the valves open for a longer time at certain higher RPMs so enough air can flow in, no?

But nobody was asking how VTEC works.

meh.

as for the turbo vs suprcharger,

if the car is originally NA, well.... you got a lot of work to do if you turbo it... I'd budget at least 10k to get it done properly. If you dont, you'll end up regretting it.

If the car is already turbo from the factory, then basic work is a lot easier.


As for supercharging, well, it really depends on what youre after.

no more talk of vtec .

a budget of at least 10k? Make sure youre applying astro-glide as you bend over or that shit will hurt.

My roommate is working on a "junkyard turbo-kit" with a budget of about $600. He already has most of the stuff he needs. We pulled a turbo from some SAAB, but it's the KKK26(iirc) which is the same used on a Porsche 944. He puts together his own fuel management systems (Megasquirt), already welded-up a manifold, very few things he's had to buy new (eg. FMIC). We should know how bad it fails within the next couple of months... Hopefully he'll have a fast car for at least a week... we'll get videos of the inevitable thrown rod(s)

I'd feel guilty about taking this thread off-topic, but the topic's kinda lame after the initial "what's the difference between the two" discussion.

if you want to run high boost on a high compression motor you WILL need to run water methonal injection under boost to prevent predet. also you should upgrade the head gasket and the head bolts.

high boost and high compression generally dont mix...

even the best build high compression motors were not originally designed for the additional stresses of having boost.

in addition to what he said, LOWER COMPRESSION PISTONS! =\

When it comes to turbos, i trust starion like no other, his skill behind the wheel can be scary at times But his skills with mechanics are like no other (still wonder whos working for who, when it comes to u and kdm starion ). methonal/alcohol injection to my knowledge is like running race fuel- you could def have some boost on a moderate compression engine without much worry.

meh.

If for some reason I actually DID run high boost, I'd still like to keep it streetable/travelable...

I dont always have the ability to change maps when I find myself with lower-than-91 octane gas available...

or in the case of high boost, whatever octane fuel you're running.

thats the wonders of running water methonal injection. you can buy the alcohol at any homedeopt or lowes and it allows you to run high boost on pump gas. my friend is running 30psi on a bone stock starion motor. he is using the water meth injection to fight knock it also help clean the cylenders and cool the charge. its like running rcae gas but its actually 91 pump gas.

Not only that the stuff is dirt cheap, top it off each time you fill up your tank, no big deal. And if for some reason you cant, thats the nice thing about turbo- you can turn down the boost.

it all depends on what the original NA engine is. If it has a low compression a greddy turbo kit wil be fine for the job. Its all about the stock compression and internals when you turbo a NA car.

Yup.

Now someone was talking about high RPMS and superchargers not being a normal thing...

And I have an article hear on a salt flat setup Mk2 MR2 with a 4AGE 20V supercharged at 45 PSI and destroked to 1.5L for class, and then running 9.1 compression for 600 plus HP. Spinning up to 11k RPM

Of course, it broke something that day

http://www.bobnorwood.com/The%20Fastest%20...20in%20Utah.htm

That is a pretty interesting article. Good read on the MR2

Turbo so you get the awesome blow off sound.

Superchargers have blow off/bypass valves to.