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Cutting the Edge

 

Before/After

  Start of Machining  

Machining

 

Cosworthvega.com

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Installation Instructions

An EXCHANGE/PURCHASE program for modifying your cam sprockets to increase performance and enjoyment of your Twin Cam Cosworth Vega.

 

A Service of

Mark Rock
Roy Linenberger

   

Improve the Driveability
of your Cosworth. 

Lower idle
Smoother idle

 
Higher vacuum

   

Better throttle response

   

Better low-end performance (torque)

No loss of HP
 or high-end performance
Lower EGT
 (means lower under hood temps)

   

Retain Stock Settings

Exchange Program for Quick Turnaround

   

Details?

 

Specifications

Download the printer friendly order instructions

Justifications

 
What About Dyno Tests?  
What about emissions levels?  
 

Payment and shipping information

   

 

 

Payment and Shipping Information

Payment:

Please send a cashier's/bank check, or a money order (you can easily get a money order at any Post Office) for $160 ($150 machining fee and a $10 shipping and handling fee) to:

Mark A. Rock
25480 Nichols Road
Columbia Station, OH 44028-9525

Please include your telephone number and e-mail address with your payment. Alternatively you may use PayPal. Send your $160 (www.paypal.com)payment to the markarock@gmail.com account.

Shipping of Your Sprockets:

Send your thoroughly cleaned sprockets to:

Roy Linenberger
3434 S Paw Paw Rd.
Paw Paw, IL 61353-9526 

Enclose a note with your sprockets indicating to Roy whether you want to receive your own sprockets back, or if you will accept a set from our inventory. Be sure to include in your note your ship-to address! NOTE: Your reindexed sprockets will not be shipped unless and until we receive your cores. As an alternative, you can use our "core" program.

Acceptable Payment Forms:

Cashier's Check
Money Order
PayPal to markarock@gmail.com

Acceptable Cores

Rust free
Pit free
Grease free
Otherwise undamaged

A $35 cleaning fee will be added if your cores are not clean and rust free

Purchase Using Core Charge:

Sprockets can be shipped from inventory and you can return your cores later. A $200 core charge is required, in addition to the $150 machining fee and the $10 shipping/handling fee

Core Charge Refund

All but $10 of your core charge will be refunded upon receipt of acceptable cores. With this option you can remove and install sprockets in one garage/driveway session.

 

 

 

Have your own sprockets machined and returned

 

If you want your own sprockets back, we can accommodate you. 

Your sprockets will be marked for identification and kept until the next batch of sprockets is machined. WARNING: It could be up to six (6) months before your own sprockets are machined--demand for these sprockets has tapered off to only a few orders per year.

 The time frame for machining your sprockets will thus vary: the completion date will depend upon how quickly additional orders come in.  Machining is done in batches to minimize the impact of set-up time. 

 There is no additional charge to have your own sprockets machined and returned. Do it while your Cosworth is hibernating for the winter and avoid down time. 

Purchase a spare set of machined sprockets.

For those concerned about "originality" and want to retain their own sprockets, unmodified, a purchase option is available. Supplies are very limited, and neither price nor availability can be guaranteed. The current price for an outright purchase of a set of reindexed sprockets is $325 due to the rarity of cores.  

A set of reindexed sprockets may thus be purchased outright for $325 plus $10 shipping and handling (price subject to change without notice--check before sending in your money). 

Reasonable Price 

            Only $150 per machined pair, plus $10.00 shipping and handling. 

 

Specifications:


The Intake cam is retarded 8 crank (4 cam) degrees.
The Exhaust cam is advanced 8 crank (4 cam) degrees.
This is accomplished in the following manner:
A new alignment/index/rollpin hole is drilled 116 or 124 degrees away from its current location, depending upon the sprocket.
In addition, the three boltholes are slotted a tad (4.5 degrees) to insure that the bolts will engage the threads in the cam.
Finally, new perimeter timing marks are added: two dots and a wider dash-to insure proper orientation during installation.

 

Justifications:



Duke Williams made "hundreds" of runs on Desktop Dyno and Engine Analyzer computer simulation programs in an effort to determine the optimum camshaft timing specifications for essentially stock Cosworth Vegas.

According to Duke, the seat-to-seat duration of the Cosworth camshafts is 268 degrees.  Further, with the production indexing, the timing points are 32-56/64-24, with an intake centerline of 102 degrees ATC and a lobe center angle of 106 degrees.  According to Duke, these are "rather weird numbers" and indicate an awful lot of overlap relative to duration.  By retarding the inlet cam 8 crank (4 cam) degrees and advancing the exhaust cam an equal amount, the new timing numbers become 24-72/64-16 with an IC of 110 and LCA of 114.  This cam phasing eliminates much of the overlap that is there with the OEM phasing to provide EGR for NOx control.  The result is vastly improved idle quality at a more normal idle speed and greater low-end torque due to reduced overlap.  Top end power is also improved because of the later closing inlet valve.  The point that the inlet valve closes has the greatest influence on top end power of any of the four valve events.  The later it closes the more top end power an engine will make, but it also hurts low-end torque.  The tradeoff between the inlet valve closing point and overlap results in net better low-end torque with the new lobe phasing.

Utilizing adjustable sprockets set to the dyno program recommended parameters on his #2110, Duke reported the following:

 With the inlet cam retarded eight [crank] degrees and the exhaust advanced the same, I now have the idle set at 950, and it pulls 18.5" Hg of manifold vacuum.  I could idle it lower, but I think I'm just about out of throttle body adjustment.  I can keep adding electrical load until I run out of alternator capacity (voltmeter at 12.5), and it [the idle] drops to 775/16", but is still very stable - guess I won't be installing an underdrive alternator pulley! 

 To test low speed tractability I lugged up a hill at 1500 in fifth - no problem.  I don't plan to drive the car that way.  It was just a test.  I can also drag the brake at idle in first gear down to 200 RPM (yes, Duke affirms it is not a typo--an incredible 200 RPM!), and it just keeps chugging along, like a good little diesel should! He says, "Just find a slight upgrade, put it in first gear and let off the throttle. My tach was actually reading zero, but I know from my calibration that it reads 200 revs low in the idle range, so I figure it was chugging along at 200 revs. I have not been able to duplicate this in a modern EFI car! Apparently the digital logic gets confused and they start bucking or stall. The CV's analog system just keeps working."   Duke also says that, "It's tough to feel the increase in low-end torque because the engine revs up so fast, but the torque curve is better across the range." 

 The power doesn't seem to have rolled off even at 7000 RPM despite the fact that I am still losing about 40 HP at that speed with the OEM exhaust.  BTW, I had my tach calibrated to be dead on at high revs, so when my tach says 7000, the engine is really turning 7000.  Most CV tachs read 200-400 revs high in the upper range.  Imagine revving to nearly 7500 indicated on your tach, and the engine is still pulling strong! 

 After extensive idling the header pipes at the flanges measure 500 F with an IR gun.  The engine runs so cool that you barely know it's running.  No doubt the freshly rebuilt OEM radiator helps. 

 Also, the idle is very smooth - smoother than my six-cylinder Mercedes, in fact.  No more engine shaking and jumping around.  It just purrs like a kitten.  Duke

 So far all my expectations from the simulation work have come true.  When I first fired the engine up it ran real snotty, and I had to turn the MAP sensor adjustment 1/2 turn CCW (rich) to smooth it out.  Subsequent testing and tuning now have the MAP a quarter turn CCW, and the idle pot is two notches from full rich.  Because of the increased idle/part throttle manifold vacuum, the EFI is injecting less fuel, thus the lean condition with the OEM settings, but there is enough adjustment in the EFI to tune it out.  Throttle response is much improved as evidenced by cleaner rev pickup in response to throttle blips for double-clutch downshifts.  Cold fast idle starts out at about 1600 at 65 F ambient.  Once it comes off the cold idle the speed drops to about 800, then creeps back to the 950 hot setting when it's fully warmed up.  Duke

 The fatter torque curve from off idle to redline, and butter smooth 900 RPM idle, makes the car a lot more enjoyable to drive.

 At idle the engine barely makes enough heat to crack open the thermostat.  It's much nicer to drive in warm weather, especially in low-speed traffic situations. 

 It will pull smoothly from 1500 in fifth.  The combination of the smooth 900 RPM idle, decent low end torque, and strong pull to 7000, makes it unlike any CV engine I've ever experienced.  I can put it in first gear and drag the brake until the engine comes down to 200 RPM, and it just keeps putting along.  Amazing!  Duke

 The re-phased OEM cams provide very good idle quality with better low and mid range torque, and top end power of anywhere between 130 and 210 HP (flywheel) at a peaking speed of somewhere between 6000 and 7500 depending on CR, head work, fan configuration, and the exhaust system, with the latter having the single biggest influence on the engine's top end power potential.

 

 

What about dyno tests?

 Duke eschews dyno tests for evaluating the impact of 8 crank degree cam sprocket re-indexing.  "Dyno data and computer dyno simulations only yield the WOT torque and power curves.  Part throttle driveability, flexibility, throttle response, and idle quality can't be tested on the dyno or on the computer.  That's where the development engineer's SOTP comes in." 

 

We agree.

 

Nevertheless, computer dyno simulation runs reveal that nothing is "lost" with these changes, and indeed small but significant gains can be expected both in torque and HP.

 

 

What about emissions levels?

 According to Duke:  "The reduced overlap will likely increase NOx emissions, and I will find out how much when I go in for my biennial emission test early next year (2003).  The car currently is only 20 percent of the limit, but I don't have a good feel for how much the new cam timing will increase NOx, so I'll just have to wait and see.  I don't expect to see much if any change in HC and CO, and I am so low on those relative to standard, I'm not worried even if they increase tenfold, which they probably won't.  The OEM bead bed converters are very inefficient from a flow standpoint.  Dave McClellan says in his new book that they increased backpressure on the Corvette by over half an atmosphere.  If you want to run a converter, the Walker/NAPA bolt in replacement (Walker # 15510) is the way to go because it is a monolithic design and is also a three-way (will reduce NOx) instead of a two-way (oxidizing only, as are our originals)."

 In any event, as the sprockets retain their original roll pin locator hole, they can always be reinstalled in their stock position in the unlikely event of a problematic increase in emissions levels.