Timing and Dieseling Issue

[Collin]

A12 yeah I had a 65 block originally that we traded the shop for a 69 HP block so you are correct, we just gave him all the internals how we wanted it built.

Engine shop would have preferred dome pistons and had a difficult time with the compression. They milled the heads and sunk the valves, they also CC'd the heads to get 10.1:1 compression

 

[69hemibeep]

Hmmm. Play with the timing but you may need better fuel or a fat head gasket might be enough.

 

[Ranger]

Are you guys saying that .1 compression (10.1:1 vs 10.0:1) is enough to cause compression ignition?
assuming that is the case, what would timing have to do with it when the ignition is turned off?

 

[69hemibeep]

Are you guys saying that .1 compression (10.1:1 vs 10.0:1) is enough to cause compression ignition?
assuming that is the case, what would timing have to do with it when the ignition is turned off?

If your using the advertised compression ratio as 10.0:1 that would be in a perfect world but they were usually lower. Retarded ignition timing can cause this because when the initial is retarded you must open the throttle more to maintain a certain idle sped. Opening the throttle blades can cause run on. Advancing your inital will allow you to close the throttle more at idle and reduce the chances of run on. Also, a cam being advanced can cause extremely high cylinder pressures because the intake valves will close sooner. High cylinder pressures can also cause run on. With high pressure and hot iron heads it will ignite the fuel just like a diesel

 

[69hemibeep]

.040 head gasket probably get you down around 9.6 or so. Do you know if the cam was installed strait up or did they degree some advance into it. Lots of performance cams have advance ground into them strait up, your cam card will show it. Aluminum heads will cure it :jester:

 

[IQ52]

This whole combination is right on the edge. Timing and fuel mixture changes may help, less or more spark advance, richer fuel mixture. Even a colder spark plug might help. Retarding the cam could, but if you don't know where the cam is timed now you'd have to check first. Anywhere around 10:1 compression and the poor combustion chamber shape of 906 heads with that cam is going to be dicey. Its probably best to go to a FelPro 8519PT1 .039 head gasket and get the compression down to 9.5:1. If you are making 400 HP with 10:1 and you reduce the compression to 9.5 you will lose about 8 HP.......big deal. You don't need any more compression to make safe horsepower with today's crappy gas. I've made 690 HP with our ported 906 heads and 9.7:1 compression in a 451 stroker on 91 octane.

 

[Collin]

Thank you everyone for your input I'm working to try to solve this issue. The car is finally done after 7 years of restorations and I just need this motor to work so I can actually drive it!!

 

[Roadcuda]

Thank you everyone for your input I'm working to try to solve this issue. The car is finally done after 7 years of restorations and I just need this motor to work so I can actually drive it!!

That's great. If you get it figured out our first Mopars in Motion show is at Papa's CDJ on May 22nd. It would be a great place for it's first show!! If you want more details just shoot me a pm.

 

[Collin]

Cam is comp cam XR280HR-10 with ICL ( Intake center line ) of 106. Installed at 0.

If we run an octane higher than 93 should this solve our problems?

 

[69hemibeep]

Blend some race fuel into it

 

[Collin]

Set the timing to 20 initial all in at total of 34. Set the idle 50 rpms lower. Runs pretty good . No dieseling .

 

[Collin]

Never mind still diesels..... The hotter the motor is the worse it diesels

 

[bigmanjbmopar]

Did you try the tune steps in the mopar article? http://www.mopar1.us/engine2.html

 

[Ranger]

Is total timing set with or without vacuum advance connected?

 

[Collin]

Without

 

[Collin]

Going to try the race fuel in it tomorrow see if that helps.... In other news I finally took the car out on its maiden voyage. Went to get vin verification so I can get my plates and front end alignment tomorrow

 

[Ranger]

Is total timing set with or without vacuum advance connected?

Without

That's what I thought. Thanks for the confirmation.

 

[Collin]

Added 5 gallons 107 octane race fuel and no diesel, drove it around town for about 30 min got up to 185 degrees.... Blended in another 5 gallons of 93 octane and once shut off hot at 183 degrees temp it did not diesel

 

[Roadcuda]

Going to try the race fuel in it tomorrow see if that helps.... In other news I finally took the car out on its maiden voyage. Went to get vin verification so I can get my plates and front end alignment tomorrow

What DMV branch did you go to Collin. Did you bring your camping gear?!?! (inside joke)

 

[Collin]

Hamden on Wedneday for 4 hours and Old Saybrook today for 4 hours