OBX intake manifold

[Locke]

Largely, the volume of the plenum should be matched to the air consumption of the motor, and the design of the runners. If your motor begins consuming a lot of air, the plenum will begin to choke the cylinders farthest from the TB, and the distribution of available air will become uneven between the cylinders..

 

[Slippi84]

Larger, shorter runners, with a high volume plenum, will yield gains in the upper RPM area. (such as with the OBX and Venom IM's)

I know what they're SUPOSED to do but the key is will they actually do it. When the Venom gets here I'll take picture to compare the twi units then its show time.

 

[bullettdsm]

Largely, the volume of the plenum should be matched to the air consumption of the motor, and the design of the runners. If your motor begins consuming a lot of air, the plenum will begin to choke the cylinders farthest from the TB, and the distribution of available air will become uneven between the cylinders..

Yeah, I'm OK with that. I'm looking at the OBX plenum (disregarding the runner size and length and alignment) as being too big and and thus actually causing a drop in velocity and even possibly generating interference with flow (and remember that I'm pulling the air in, not forcing it in). That's where I'm getting a little lost...........

MB

 

[Locke]

Yeah, I'm OK with that. I'm looking at the OBX plenum (disregarding the runner size and length and alignment) as being too big and and thus actually causing a drop in velocity and even possibly generating interference with flow (and remember that I'm pulling the air in, not forcing it in). That's where I'm getting a little lost...........

MB

Thats true, you can go too large.

IMO, with the larger-than-stock OBX plenum, you would want the air flowing into the plenum to be at a lower velocity in an NA application, so that it would more readily flow into runner #4. (angular momentum) That is a sharp turn in the OBX manifold from the TB to the first runner. Paul could chime in with his thoughts on this?

Usually, an increase in plenum volume also means raising the plenum's ceiling, which lengthens the path to the major point of reflection.

I wouldn't know if the plenum on the OBX is of suitable volume and design for it's purpose. I'm no scientist.

 

[all_motor_mike]

Oh man of great knowledge, can you please explain your reasoning . You guys know way more about the intricacies of air dynamics than I do.

'Appreciate,

MB

there are alot of thoughts on plenum size............ im more concerned with plenum shape rather than size. i do indeed make my turbo manifold plenums bigger than my NA plenums though.


mike

 

[Slippi84]

its all about velocity

Well not all about velocity as drastically less air at a higher velocity then a lower velocity but much more volume will still be more beneficial depending on the setup.

 

[VelocitàPaola]

Well not all about velocity as drastically less air at a higher velocity then a lower velocity but much more volume will still be more beneficial depending on the setup.

Ok... maybe "it's all about velocity" is an oversimplification of the matter.

It's all really about volume; but volume is determined by velocity and port/valve size. It's certainly a trade off: big ports can help facilitate large volumes, but without the proper velocity, that air isn't going anywhere at low RPMs. Smaller ports might help increase velocity, but they become restrictions at high RPMs.

As for the plenum, I've heard many theories regarding their shape and size. Based on everything I know, it seems that the plenum size should be at least half the size of the displacement of the engine, if not the same size, or twice the size. Large plena are great for high horsepower (boosted) applications, when rapid throttle movements might starve the engine if there isn't enough air in reserve. Smaller plena work well for N/A applications where too large of a plenum might cause an unresponsive throttle and poor intake velocity.

If I were to design an intake manifold for an N/A car (not saying that I'm not already...), I'd make an 1.0L plenum with a progressively tapered body and flat floor. The runners would have a rectangular cross section, with a 2% taper, and they'd be as straight as possible without sacrificing plenum placement in relation to the head.

Another idea would be something like this...

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I just bought a 8th generation Corolla (98-02) for a family member, and the intake manifold is similar to that, only with no plenum. I thought it was a little over-engineered at first, but I must say, it gives the small 1.8L engine some pep.

 

[Locke]

Another idea would be something like this...

Thats lunacy! All I see is craziness, without the third dimension to help my mind picture it. Oh yeah, real subtle watermark you got there, Paul.

 

[Shadow98]

I think I see what Paul has posted up, but I don't understand it completely.

 

[Slippi84]

Ok... maybe "it's all about velocity" is an oversimplification of the matter.

It's all really about volume; but volume is determined by velocity and port/valve size. It's certainly a trade off: big ports can help facilitate large volumes, but without the proper velocity, that air isn't going anywhere at low RPMs. Smaller ports might help increase velocity, but they become restrictions at high RPMs.

As for the plenum, I've heard many theories regarding their shape and size. Based on everything I know, it seems that the plenum size should be at least half the size of the displacement of the engine, if not the same size, or twice the size. Large plena are great for high horsepower (boosted) applications, when rapid throttle movements might starve the engine if there isn't enough air in reserve. Smaller plena work well for N/A applications where too large of a plenum might cause an unresponsive throttle and poor intake velocity.

If I were to design an intake manifold for an N/A car (not saying that I'm not already...), I'd make an 1.0L plenum with a progressively tapered body and flat floor. The runners would have a rectangular cross section, with a 2% taper, and they'd be as straight as possible without sacrificing plenum placement in relation to the head.

Another idea would be something like this...

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I just bought a 8th generation Corolla (98-02) for a family member, and the intake manifold is similar to that, only with no plenum. I thought it was a little over-engineered at first, but I must say, it gives the small 1.8L engine some pep.

That looks like you literally brain farted onto a post I won't even begin to pretend I understand that picture or some of the stuff your talking about but I get the general idea and besides I'm more of a does it work or doesn't we'll worry about why later .

 

[InfiniteGSX]

Watching too much "Matrix" I think Paul!

 

[bullettdsm]

Stop stealing my idea's Paul! I understand exactly what is going on there. I have a design that is pretty close to the same thing (mine is center mounted throttle body). But the intention of that set-up (as far as I can see) is for rally/autocross type racing where you would benefit from quick response and a little longer/higher torque range but don't have the need for a high top end.

MB

Oh yeah, like Locke says, quite the subtle watermark

 

[Blitzeclips]

That really is nicely designed Paul. Although I'd vouch to say you'd want to flip the inlet from the left to the right. Unless you want to set-up your intake on the opposite side: like 4g63s.

 

[all_motor_mike]

If I were to design an intake manifold for an N/A car (not saying that I'm not already...), I'd make an 1.0L plenum with a progressively tapered body and flat floor. The runners would have a rectangular cross section, with a 2% taper, and they'd be as straight as possible without sacrificing plenum placement in relation to the head.

very similar to my short runner intake sir except my plenum is a little bigger.......

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[VelocitàPaola]

very similar to my short runner intake sir except my plenum is a little bigger.......

http://www.hostdub.com/albums/mike/IM000611.sized.jpg

Yep, that'd be exactly what I'd do... only I'd put the intake manifold on the intake side of the head, not the exhaust. You Neon guys are crazy...

 

[4UH8ERS]

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BETTER VIEW

 

[InfiniteGSX]

very similar to my short runner intake sir except my plenum is a little bigger.......

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Thats what I want right there! I was thinking about making one but afraid of screwing the flow up.

 

[all_motor_mike]

Yep, that'd be exactly what I'd do... only I'd put the intake manifold on the intake side of the head, not the exhaust. You Neon guys are crazy...

yeah i dont know if u guys know who steve lockett is but on his black SFWD car........... that intake (w/ the mustang 65mm t-body) made 71 whp over the stock intake manifold and stock 52mm t-body and moved his power band up 1000 rpms all at the same boost levels.


heres a ported runner from that manifold...........

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[Shadow98]

Looks pretty nice and sounds like it performs rather well.

 

[all_motor_mike]

yeah......... we'll find out how my long runner ("N/A") intake does against another "box" manifold, a ported stocker, an indy and an extrude honed stocker also in about a week and a half here.

 

[Shadow98]

Then you'll have to make one that fits our cars and compare it to Paul's... I'll buy the winner (IM that is, ).

 

[Slippi84]

Well my test might not to be 100% usefull now I just ordered a q45 tb to go with the venom manifold . I think the venom will get here first so I might still test it without the q45 but if they're like 2 days a part in arrival I'm not gonna install the intake manifold twice. Overkill? Def but I think it will be a bad ass setup. While I'm N/A I will have a 3" intake that goes right into pretty much a 3" tb and into the big plenum. When I go turbo it may get tricky cause I'm still gonna want the same 3" upic piping to utilize that big tb but pressurizing a pipe that big without a big turbo might prove to be sluggish. We'll just have to wait and see.

 

[Blitzeclips]

Slippi, I don't know if 3" is a good idea. It's way too big if you ask me. 2" should do it fine, and decrease turbo lag, but 3" seems unecessary. Of anything, 3" would be most benficial before the intercooler. Once the charge passes the I/C the air becomes more dense. So technically, you would want any larger charge pipes clamped before the I/C.

But hey, if you have a 2" AND 3" pipe laying around: why the hell not? Let us know!

 

[Slippi84]

Slippi, I don't know if 3" is a good idea. It's way too big if you ask me. 2" should do it fine, and decrease turbo lag, but 3" seems unecessary. Of anything, 3" would be most benficial before the intercooler. Once the charge passes the I/C the air becomes more dense. So technically, you would want any larger charge pipes clamped before the I/C.

But hey, if you have a 2" AND 3" pipe laying around: why the hell not? Let us know!

Yeah that's what I thought to but I mean from talking to everyone who had input on the subject no one could seem to come up with any neggative side affects to a BIG tb just a twitchy throttle which I can live with. The q45 is probbaly the most cost efective and reliable tb you can put on a dsm. The acufabs break shafts the modern performace is 200+ shipping and it's only 60mm not much upgrade from stock. Like I said before too the dyno test will be while NA to be more beneficial to more people then later I'll do a boosted test when I go that route.

 

[all_motor_mike]

Then you'll have to make one that fits our cars and compare it to Paul's... I'll buy the winner (IM that is, ).

im already making a short runner for marks car.