2.4 Liter racing engine

[neilca]

I am using what I have learned on this forum. My new engine is coming together. Here is a picture of the long block



The engine is a 70.4mm X 86mm, 12.3:1 compression, DC70 cams, twin plug, Polaris 46mm throttle bodies, cross drilled crank with grooved bearings, 993 oil pump, and stock rods with ARP bolts. I plan on using a Megasquirt 3 as the ECU.






Here is a shot down the intake. I did some porting too.

[silverc4s]

Looks really nice. You have some good innovations there. What is the cam driven distributor doing? You said twin plug right?and I thought I saw a position sensor on the front of the crank.
Keep us up to date. Thanks,

[neilca]

I am running two distributors, one off the cam the other in the normal spot. The crank trigger will go to the computer and the computer will tell the coils when to fire. The distributors will only be used to distribute the fire. The cam distributor will go to the lower plugs. BTW that is a 009 distributor from a VW. I cut a groove in the back of the cam to drive it. The 6 cylinder caps fits and the rotors are the same.

[lupin..the..3rd]

Originally Posted by neilca

I am running two distributors, one off the cam the other in the normal spot. The crank trigger will go to the computer and the computer will tell the coils when to fire. The distributors will only be used to distribute the fire. The cam distributor will go to the lower plugs. BTW that is a 009 distributor from a VW. I cut a groove in the back of the cam to drive it. The 6 cylinder caps fits and the rotors are the same.

How will this work? The advance curves are different between an 009 and the Porsche distributor. The sparks will arrive at different times. Unless you've modified them both to disable the mechanical advance?

Also, the 009 is known to be pretty sloppy, lots of timing scatter at high rpms. I've seen 3 or 4 degrees of scatter at just 4500 rpm on several different 009's I've tested.

[neilca]

I have welded up both distributors so they have no advance. The computer will provide all the timing inputs needed.

The distributors need only be indexed to the correct plug. Moving them will not change the timing since the triggering will be done by the crank sensor telling the computer when to fire. A normal distributor does two jobs. First it triggers the firing via points or some other pickup. Second it distributes the fire to the plugs. I have split these two tasks.

[Henry Schmidt]

Originally Posted by neilca

I have welded up both distributors so they have no advance. The computer will provide all the timing inputs needed.

The distributors need only be indexed to the correct plug. Moving them will not change the timing since the triggering will be done by the crank sensor telling the computer when to fire. A normal distributor does two jobs. First it triggers the firing via points or some other pickup. Second it distributes the fire to the plugs. I have split these two tasks.

Generally a distributor has an advance mechanism to keep the rotor in proximity to the cap contact to the wire, close as the timing changes.
Evidenced in Carrera and Carrera II distributors.
Here is another way to run a cam driven distributor.
This one was used on a version of the 962.

[neilca]

I was debating what heat range plug I should run in this engine. Using the Bosch numbers, I am thinking about WR5DC or WR4DC. What does the forum think?

[Walt Fricke]

I'd start cold and go hotter until I didn't like what the plug looked like. I use NGKs, so the Bosch system doesn't mean as much to me any more.

[Raceboy]

NGK 7's are good starting point and I also prefer NGK's over Bosch.

[neilca]

I just ordered some BPR8ES NGK's last night. I believe these are colder than the 7 so I should be good. Is that correct?

[Raceboy]

Yes, 8's are colder when it comes to NGK's. With too cold plugs there is a risc of fouling them on a cold startup but 8's aren't that cold yet.

Just for the information, I wouldn't run as hot plug as it is possible (or even on the edge), I prefer the one that gives clean side electrode until maximum of 2/3 of the lenth. I would leave some safety regarding the plug so it doesn't cause pre-ignition and/or detonation.