mk1-forum.net

Hi all

i like to have you advice on the dyno result of my engine, the power curve go flat from 6750 to 8000 rpm and i am thinking about the point going bouncing,

my engine specification is

gt block bored out to 1293
forged omega 5.8cc pistons
36/31 race head
1.5 forged rocker
12/1 cr
sw23 cam
twin h4 with bg needle and blue spring
stg 3 race maniflow lcb with race reverse cone system
full straight cut box
ultralight fly
wedged crank
aldon red distributor with point timed at 28° full advance

would fitting of electronic module in the distributor change someting or this is a normal curve for these profil of cam, have asked swiftune but no reply at the moment

here the dyno graph, make 109 hp and 122nm, AFR is good from 5000 to 8000 at 12.5

thank for you advice

Looking at the plot for a sw23 on Swiftunes website, it shows the power curve relatively flat after about 6900 through to 8000, so your motor appears to be similar. Obviously difficult to do a direct comparison unless the engine is to the same spec and on the same dyno!
http://www.swiftune.com/Product/625/swi ... shaft.aspx

Would have though that power would drop a lot more if you get points bounce, I don't think going electronic will make a massive difference.

You mention 28 degrees advance - is that the total maximum advance you are using? Sounds a bit on the low side unless you are limited by low octane fuel.

Yes total d'avance, Will try With a couple of dégrée more béfore changing to electronique

Fuel is 98 octane here, but can add octane booster

i would measure inlet manifold pressure on full rpm . it should be close to 14.7 psi , but if its dropping a bit i would try bigger carbs .and a well ported inlet. i feel a pair of H4's are a bit small .


robert.

Power going flat like this or going down with increasing rpm happens in every motor. I have not seen a good explanation why. I think one of the causes is the spark degradation. As the rpm increases the dwell time decreases. Shorter dwell time means lower and lower current in the primary windings of the coil hence less secondary voltage to fire the spark plugs.

What's wrong with that curve? Looks great if you ask me...