Manifold design: Does boost mean you can get lazy? - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > General Technical Discussions > Engines & Drivetrain > Manifold design: Does boost mean you can get lazy?

Spartan Locker Promo Running now @ ROCKRIDGE 4WD plus FREEG2 Disc Brake Conversion Kit for Jeep Wrangler YJ TJ LJ ChTJ Wrangler 4" Rough Country Suspension Lift Kits in

Reply
Unread 07-18-2011, 01:45 PM   #1
child9
Registered User
1996 XJ Cherokee 
 
Join Date: Nov 2010
Location: Austin, Texas
Posts: 157
Manifold design: Does boost mean you can get lazy?

So I've heard a lot of people say in various communities that when you turbo a vehicle and are building the manifold for it, things like the collector smoothness and runner lengths don't matter as much as they do for an NA vehicle.

This contradicts what I believe, but I was curious if anyone on here strongly agrees with that and why.

I think that runner length, smoothness of merges and collectors, and other factors all mean much much more when you start adding boost. For example, friction and drag caused by wind resistance increases as velocity squared. I think this also applies to the gasses in the manifold. If you are doubling the amount of air molecules being pushed through the engine by running 1 bar of boost, any disturbances in the flow of these gasses through the manifold will be exponentially increased...I suspect as velocity squared also. The density of the fluid has been doubled and I believe the relationship there to be exponential, not linear.

Does anyone know any different? Thoughts?

__________________
"We exist to do great things." -CT Kassem
. '96 Jeep Cherokee XJ "R2" .
. Bring on the apocalypse .
child9 is offline   Reply With Quote Quick reply to this message
Unread 07-18-2011, 03:14 PM   #2
cruiser54
Web Wheeler
 
cruiser54's Avatar
1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 10,323
You're in Texas. Contact Corky Bell at Bell Engineering. He knows his stuff.
cruiser54 is offline   Reply With Quote Quick reply to this message
Unread 07-18-2011, 03:25 PM   #3
MONSooNmonkey
Registered User
1998 XJ Cherokee 
 
Join Date: Jan 2011
Location: boggerville, pennsylvania
Posts: 1,293
Quote:
Originally Posted by child9 View Post
So I've heard a lot of people say in various communities that when you turbo a vehicle and are building the manifold for it, things like the collector smoothness and runner lengths don't matter as much as they do for an NA vehicle.

This contradicts what I believe, but I was curious if anyone on here strongly agrees with that and why.

I think that runner length, smoothness of merges and collectors, and other factors all mean much much more when you start adding boost. For example, friction and drag caused by wind resistance increases as velocity squared. I think this also applies to the gasses in the manifold. If you are doubling the amount of air molecules being pushed through the engine by running 1 bar of boost, any disturbances in the flow of these gasses through the manifold will be exponentially increased...I suspect as velocity squared also. The density of the fluid has been doubled and I believe the relationship there to be exponential, not linear.

Does anyone know any different? Thoughts?
Pressure is pressure, the roughness makes turbulance that helps mix the air\fuel, which is why they went from making the smoothest intake possible to 'roughing' up the surface of the intake slightly.

Just like the surface of shark skin is rough and makes it possible to sharks move quickly.
__________________
Sadface :(
MONSooNmonkey is offline   Reply With Quote Quick reply to this message
Unread 07-18-2011, 03:40 PM   #4
Boodyrider
Registered User
1997 TJ Wrangler 
 
Join Date: Feb 2008
Location: Maryland
Posts: 2,526
Actual experience with a modified Dodge Daytona at 26 psi boost on pump gas:

Manifold design on the intake side can be lazy, because boost trumps trying to pull air into the motor with vac. However... remember you're not always in boost with a turbo. Good design still matters for efficiency and VE during all those times you are cruising without being in boost.

Good design on the turbo and exhaust side though... that's critical. A rough rule of thumb was you'd see about 3 times as much backpressure on the upstream side of the turbo at a given boost pressure... meaning that the more you can do to get air past the turbo and out the exhaust, the better, since that backpressure in the cylinder is part of what causes excess EGTS, and means boosted vehicles hate cam overlap....

HTH
__________________
97 TJ Sport - 4.0/HP D30 w ARB/8.8 w LS/4.88s; 35s and flat fenders on 2.5 lift

84 CJ7; frame off restoration in progress.

The technical advice you get from me here is worth exactly what you paid me for it. Warranty issues will be reimbursed at double what you paid me for the advice.
Boodyrider is offline   Reply With Quote Quick reply to this message
Unread 07-18-2011, 08:41 PM   #5
child9
Registered User
1996 XJ Cherokee 
 
Join Date: Nov 2010
Location: Austin, Texas
Posts: 157
Yeah, I probably should have specified that I was actually referring to the exhaust side of things.

Speaking of the intake side, fuel injectors are usually pretty close to the intake valve openings, so I can't imagine that turbulence is helping much with breaking up the liquid molecules at that point. Doubly so for a direct-injection vehicle. It does seem like it could help matters somewhat in a TBI setup though, since the air/fuel mixture actually travels through the intake in that case (get a "Tornado", LOFL). I bet it may be difficult for the intake manifold to be limiting the overall flow through the entire system BEFORE the exhaust system would, given back pressure at the turbine, mufflers, cats and all that.

If you are trying to eek every last horse out of a specialized setup, at some point would it be safe to say that characteristics that are conducive to velocity and smooth, laminar flow will outweigh any benefits that a rough wall may give to the a/f mixture? I mean, at it's lowest common denominator, the power an IC engine can produce is based on how much air it can pump through it. Meh, maybe I just answered my own question.
__________________
"We exist to do great things." -CT Kassem
. '96 Jeep Cherokee XJ "R2" .
. Bring on the apocalypse .
child9 is offline   Reply With Quote Quick reply to this message
Unread 07-18-2011, 08:55 PM   #6
flatlander757
Registered User
2003 TJ Wrangler 
 
Join Date: Nov 2006
Location: Dayton, Ohio
Posts: 5,417
Quote:
Originally Posted by Boodyrider View Post
Actual experience with a modified Dodge Daytona at 26 psi boost on pump gas:

Manifold design on the intake side can be lazy, because boost trumps trying to pull air into the motor with vac. However... remember you're not always in boost with a turbo. Good design still matters for efficiency and VE during all those times you are cruising without being in boost.

Good design on the turbo and exhaust side though... that's critical. A rough rule of thumb was you'd see about 3 times as much backpressure on the upstream side of the turbo at a given boost pressure... meaning that the more you can do to get air past the turbo and out the exhaust, the better, since that backpressure in the cylinder is part of what causes excess EGTS, and means boosted vehicles hate cam overlap....

HTH
Ha! You were into the Turbo Dodges too I see!

I was going to mention those... they're the most horribly designed motors for boost, the solution that most have is to just throw more at it and deal with a head gasket popping every so often... it takes all of 40 min to replace

OP: Check out www.thedodgegarage.com and look at the Reliant, the Caravan(yes turbo Caravan), and the Daytona in particular... that is some old school turbo car building and stuff like aftermarket intake manifolds simply don't exist or didn't exist at the time... and the stock ones are pretty bad.... yet with the right turbo and some slicks they can put a FWD car in the 10s...




Also, click on "turbo database" on the left, then click on "intake manifolds" and stuff... that is the exact info you're after there... restrictive intake manifolds and how to modify them and then compensate with boost.
__________________
SOLDThe lumbering steel-laden pig - 2003 TJ - 40" LTBs - D60/D70HD - 5.86s - Detroit lockers - 110" wheelbase
Build thread here.

Quote:
Originally Posted by 2006 Sport
Being able to make vroom vroom noises in Tonys Jeep was the highlight of my life.
Currently Jeepless.
flatlander757 is offline   Reply With Quote Quick reply to this message
Reply

Tags
boost , manifold , turbo

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.


Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.