Dc20 cam timing

[sp_cs]

Have dropped John Dougherty an email re the dc20 cams on my 3.4 - they've been verified at the upper overlap mark of 2.4mm (specified range is 2.2-2.4mm).

My 3.4 is built with 98mm Mahle, dc20 cams, 10.45:1, single plug (99ron fuel) and with a standard 3.2 exhaust it's dyno'd at 270bhp/240 lbft - after a second rebuild to investigate a suspected valve train noise, it's now delivering 240bhp/230 lbft on the same dyno.

Could cam timing have such an affect on output? I don't know anything about cam timing, and do not know what it was set to during the first rebuild, but wondering if cam timing was set at a lower overlap, what difference this would make to delivery?

It doesn't feel like it lost 30 odd bhp, but this is what the dyno is suggesting (same one it hit it's higher figures on)

Aside from fitting 1 5/8" headers which improved the top end and an early dansk 2in 1out, it's the same spec/build as before.

I've now fitted ssi which appears to have improved the bottom-midrange somewhat at the slight expense of topend which is fine for my driving. Not been dyno'd since.

Im planning on getting a leakdown undertaken to see what that shows.

Thoughts would be appreciated

SP

[safe]

SSI will definitely strangle your engine.

[sp_cs]

Agreed to an extent - ssi design suggests you're correct how there are a number of 3.4s I googled achieving 270bhp/240 with ssi's here in Europe so I don't believe they're as limiting as made out. Depends where you want the power delivery i guess.

In my case the lower figures were recorded with headers fitted so I don't believe now I fitted ssi that the exhaust is the issue as it doesn't feel that much different

[sp_cs]

In the absence of a reply from John, would appreciate thoughts on expected changes to power delivery if overlap was reduced to 2.2mm (currently 2.4mm)

TIA

[YTNUKLR]

Won't be much difference.

I recommend degreeing them if possible.

Get a degree wheel (generic cheap is fine). Obtain a true TDC indicator. Stomski Racing makes a good one.

Rotate the engine to BDC, install the TDC indicator (and the degree wheel--doesnt matter its orientation).

Now, the TDC indicator should interfere with the piston so CAREFULLY rotate the engine until you feel the piston lock against the TDC indicator. Mark the number of degrees.

Reverse the rotation carefully until the piston locks onto the TDC indicator again. Mark the number of degrees again.

The measurement will give you TDC--it's split exactly between your two measurements.

Now (VERY IMPORTANT) with the dial indicator mounted, adjust the valve clearance so clearance=0.

Next, rotate the cam to begin lifting the intake valve 0.050".

The DC20 cam is supposed to lift the valve 0.050" when the engine is 8deg BTDC on Cyl#1.

Remember where you marked TDC? Go clockwise 8deg with the crank, holding the cam in position.

Then, holding everything steady, snug down the bolt!

This is a more accurate method than the lift way(2.2-2.4mm) because it takes out of the equation the valve clearance. Also the degree wheel is MUCH more fine grained than the crank pulley.

Shirish, you need some 993 heat exchangers on that motor

*****************

This is the general formula for determining at what degree setting you should set cams:
This is for a 0.050" lift setting. (Per cam mfg specs.)

Deg BTDC=((Intake Duration measured at 0.050")/2)-(LobeCenterAngle)

In this case, (242/2)-113=8

[sp_cs]

Thanks Scott, but I only understood the first line

If cam timing won't make much difference, I've another problem which has caused the power loss.

Will get the leak down done

Don't tempt me with the 993 h/ex's !