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The VIPER Garage  |  How To Instructions  |  How-to section  |  Modify or replace Intake Manifold reasons.
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Author Topic: Modify or replace Intake Manifold reasons.  (Read 747 times)
RTTTTed
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Viper Nation - ezine
« on: December 04, 2015, 08:07:07 PM »

I have researched all aspects of performance engineering ever since I first received my Driver's License back n the seventies.  I hung around Speed shops, drag strips and every automotive expert I could find.  I asked them questions like a little kid.  The more I learned and researched with my own cars as well as friend and customer cars the more questions I asked.  The more you learn, the more you see the knowledge that you DON'T have.   On the fastest cars there are NO stock intake manifolds.  Owning a 1500whp TT GTS I knew that just smoothing the internal passages flowing media through it only allows a small percentage improvement and the Intake is the closest piece of my engine to stock.  It needs to go!  I did contemplate welding plates between the intake runners, cutting the sides out of the runner to shorten the runner length and increase the plenum area.  I contemplated buying a Gen 3 Intake, cutting the tops off the manifold and welding the middle bottom, welding a spacer to raise the roof and/or weld a box underneath the manifold to increase plenum area.  I even bought a Gen 3 and will probably chop it up and weld together a Twin Screw top plate during my future plans to mount a Kennie Bell watercooled MegaBlower on my other Viper.

Couple ways to modify and improve  hp by upgrading any intake manifold for better performance is to shorten the runners and increase the plenum Volume of the intake.   This is not something to do to a stock engine, but once the engine had a power adder (Forced Induction), cam, exhaust, bigger Tbs altered timing, or ported heads the intake should also be upgraded.  Stock is designed mostly for emissions and after that changes are made to improve mileage (smaller runners and less plenum volume).  Once the engine has been modified to upgrade the hp an upgraded intake manifold is not always affordable or available.  Stock manifolds can be modified to realize big horsepower increases.  Stock manifolds become the biggest restriction once the heads are ported or a larger camshaft is installed with headers and exhaust.  Obviously the manifold is what needs to be upgraded next.  The Intake is the distribution center for the air and fuel into the various cylinders of the engine.

When there are no after market intakes available sheet metal tunnel rams realize the largest hp gains.  Stock Intakes can be ported, smoothed internally and match ported for small gains of increased flows, but larger, tapered, shorter ports are needed for big hp gains.  A stock engine, like the 8L V10 Viper engine accepts Forced Induction well, but Forced Induction rule of thumb is that Plenum Volume needs to be double the engine volume.  That would require 16L of volume.  Near as I can figure (manifold is not even or smooth) the volume of my Gen 2 intake's plenum is about 154 cubic inches feeding my 520 cubic inch Forced Induction engine!  The modified stock Intake runners of my Gen 2 intake seem to measure about 12" long!   With only 15% of optimal plenum capacity and triple the length of recommended runner length it is easy to see that any modifications to the intake would have big gains.  Add that the Bellmouth runner opening gains significant flow into the port and helps equalize port distribution as do tapered runners ...


I did that on my Stealth TT manifold by cutting the bottom out of the plenum side of the manifold , cutting the dividing walls of the intake runners back about 5" and then bellmouthing the available port openings.  After I did all the grinding inside the manifold I merely welded a plate where I'd cut the manifold open.  I'd tripled the plenum volume and shortened the runners to half length.  Although I was supposed to lose torque all I noticed was that my power was increased from 2200rpm and up.  The little 3L engine performed the same under 2200rpm as it did before I chopped the manifold, but it had noticeably more power above that.

Chrysler invented the tunnel ram for racing in the early 60s with the Staged Max Wedge engines.  The manifold runners were so long that the carbs mounted beside the engine.  The first manifold design maxed torque around 3500rpm and wanting a higher power curve the Chrysler engineers cut the dividing wall between the paired intake runners from the bottom for about 6" and then welded the tube solid with the port dividing wall removed.  This effectively shortened the individual runners and raised the power curve to 4500rpm. 

A Forced Induction engine needs an intake with Double the volume of the engine size ...  N/A works best with an equal sized plenum compared to the engine size.  IE: normally aspirated hp works best with 4 - 6" manifold runners and am 8L engine would be best if the plenum was 8L.  Forced Induction would be best with 16L of volume and 4 to 6" length runners.

I made an offer on a Billet Viper Intake, but the cost was prohibitive at $4000.  A Mitech sheet metal Intake was offered by Paolo as a reasonable cost and I decided to purchase that instead.  I am expecting to need to run the car to figure out the port flows and balancing before tuning my TT Viper which will allow the a/f of each cylinder to be perfected.

« Last Edit: December 04, 2015, 11:52:19 PM by RTTTTed » Logged
1999 1200rwhp TT GTS - ART, 2001 Roe sc GTS- (4 sale), 440 Duster restomod (sold), 3x Stealth TTs, 92 Daytona IROC with T3, 580whp/1080wtq Cummins pickup.
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Viper Nation - ezine
« Reply #1 on: February 05, 2017, 07:48:51 PM »

I built a flowbench (as advised by the experts) for my Mitech intake and the flows were Terrible.  5cfm through front ports while back 4 ports were as high as 28cfm.  I'll be raising the plenum volume to 940cubic inches and reshaping the front Throttle Body plate to point to the roof of the manifold and life the TB opening to 3" higher so that it blows past the front ports instead the TB having the flow pointing past the front ports which are blocking the velocity and creating turbulence in front of the intake ports mis-directling the airflow. 

I tested a stock Ben 3 intake and because of it's having a solid wall directly behind the TBs that intake has bad flows off the sides of their plenum bouncing the airflows past the front ports. 

Normally aspirated suck the air into the ports and when they all suck equal they all flow equal.  Forced Induction is different as the high velocity airflows are high speed and double to quadruple the amount of air flowing through the intake manifold. 
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1999 1200rwhp TT GTS - ART, 2001 Roe sc GTS- (4 sale), 440 Duster restomod (sold), 3x Stealth TTs, 92 Daytona IROC with T3, 580whp/1080wtq Cummins pickup.
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