Interesting SDS EFI results, Stock 1.8 vs. a 2.0 with a Scat C-25 cam Options

[Mark Henry]

I sold the 2.0 junkyard dog (a 2.0 I made from scrap parts) it was stock except for the C-25 Scat cam and installed my bone stock 1.8
Here’s what’s happening.

I haven’t even adjusted my values and I still have an OK reading on my narrow-band (Haltec AF 30) meter. I have a wide-band on the way from SDS, so I’ll have a direct comparison in about 1-1/2 weeks.

My duty cycles are down about 10% across the board, I get no more than 40% (WOT) duty cycle. At highway speed I’m no more than 20% DC. I’m still using the 2.0 injectors…I think I’ll swap them out for 1.7’s and see what happens.

The main interesting point is the 2.0 always lurched a bit at 1500 to 2500rpm, it was a bit of a PITA in stop and go traffic, never at normal rpms. My manifold pressure was always all over the place. I have since installed this engine in a bug with 44mm Webers and an A-1 header and it now has none of the lurching.

The stock 1.8 has no lurching at all and the manifold pressure is now rock solid! Power is down from the 2.0, but that was expected. It is just as smooth as the old L-jet except for start up, as I have no cold enrichment.

Cam choice is very important!

When I get the 2.6 done (looks like late summer now) it will have a special MassIVe cam so we’ll see how it compares in the drivability department.

Jake and I will be comparing notes to figure out the best combo’s for his and my customers.

[DNHunt]

I'm intriqued by the muffler in the vacuum line. My MAP signal flucuates most the nearer I get to atmospheric pressure (WOT). I suppose this shouldn't be that much of a surprise. This also where pulsewidths are the largest.

MS and I suspect other speed density EFI's use an equation to figure pulse width that is the product a constant (injector flow rate, engine size) X a value from a lookup table (MAP vs RPM) X MAP + any enrichments. It is the second use of MAP in the equation that is the reason I'm hung up on getting a stable MAP signal. It is the only variable that is used twice.

At some point I'll have to compromise.

Dave