Help tuning mystery motor?

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Thanatos340

Thanatos340

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I bought a 71 Duster a while back that spent most of its life as a Bracket car.
What I do know about it is:
440, 906 heads, Single Plane Strip Dominator, Large tube Fender well headers, 4" exhaust, 3:91 Suegrip, Subframe connectors, 727 with Reverse Pattern Manual VB. Running on 295/60 R15 drag radials.

The guy I bought it from had bought it from one of his employees. He did not know much about the motor other than it had a wiped lobe on the cam when he got it so he installed a new 509 Lift Cam and put it up for sale. He did not have a spec sheet for the cam.

After I Bought it, I put in an MSD Billet Distributor, 6AL-2, Rewired It as it has the typical Race car wiring, Added a new Proform 850 DP carb and took it to the track.

Initially it had 78/80 jets and 6.5 power valve.
Best Vacuum I could get was 8 inches so Dropped to 4.5 PV. Plugs read lean so I went to 80/82 jets. Timing was set at 17 initial and 36 all in at 2800.

Very disappointing. Best of 8.63 @ 80 MPH in the 8th mile.
This was on 110 Octane race gas. I ran out of that after a few passes and had to switch to 93 octane Pump gas. It slowed to 8.83 and was pinging and knocking so Took it home.

Now I am trying to Tune a Motor that I don't really know what I have internally. I suspect I have a higher compression motor as that would explain the knocking and pinging when I switched Fuel and not really sure what cam it has.

I am hoping to not have to pull the motor and tear it down to get a rough idea of what's inside. My plan is to pop the valve covers and try to use a dial indicator to see if I can figure out lift and duration of the cam in it and then pull the Plugs and run a compression check to get a rough idea of compression.

Would love to hear from others that know more than I on how they would approach this? Any and all suggestions welcome.
 
Run a compression test. See what kind of cylinder pressure you are dealing with first and then we can better advise a tune.
 
shift points? stall on the converter? Are you getting full throttle?
 
Start with the carb and timing make sure that carb is opening all the way. Then check the timing. Then check cylinder pressure.
Do you know if the cam the previous owner installed was degreed? Or did he just throw it together to get it sold?
 
Also, what kind of plugs? Be sure you're running copper core instead of the fancy iridium platinum unobtanium ping-a-ling wonders. If it's a 509 Mopar cam, it's a single pattern cam with either 112 or 108 degree LSA with 292 degrees of duration. Only a degree wheel or a cam card would tell the tale.
 
jaws said:
shift points? stall on the converter? Are you getting full throttle?
Click to expand...

Yes on the full throttle. I have check and verified that several times.
As to Stall, That is another unknown but it is definitely looser than stock but I am not sure .

I have been leaving at about 2,500 rpms and have a digital shift Light tach. Set at 6000. The second to third shift light comes on right as cross the finish line so never getting to High gear.
 
dartfreak75 said:
Start with the carb and timing make sure that carb is opening all the way. Then check the timing. Then check cylinder pressure.
Do you know if the cam the previous owner installed was degreed? Or did he just throw it together to get it sold?
Click to expand...

I know that it was NOT degreed in. I asked the seller about it when I bought the car and he said No, He did not have a degree wheel and just lined up the dots.
 
Garrett Ellison said:
Also, what kind of plugs? Be sure you're running copper core instead of the fancy iridium platinum unobtanium ping-a-ling wonders. If it's a 509 Mopar cam, it's a single pattern cam with either 112 or 108 degree LSA with 292 degrees of duration. Only a degree wheel or a cam card would tell the tale.
Click to expand...

Yep. I am running MSD Iridium Plugs. will be ordering a set of NGK`s tonight.
 
Let us know the cranking psi. If it’s under 200, I’d run it again on 100 octane race fuel after changing the plugs and see what it does. I bet you were lightly pinging on the 110 octane. 906 heads will usually take about 38 degrees of total advance.
 
First off, don't set power valve opening off idle vacuum. That lie seems like it will never die.

Second, you need to stop and degree the cam. There is no reason not to. You'll need to know which cam it is, but if it's on a 108 it needs to go in at 106 at the latest and probably 104 would be better.

You need to get to at least 38 total. If you can't, there are other issues like the plug is too hot or something.

Just a whole lot of mixed up stuff that needs to be sorted out before doing anything else. Finding out what cam you have and degreeing it is step one.
 
At 80 MPH in the 1/8th mile, its making dismal power. For sure a full check of the basics is in order as previously mentioned.
 
BTW, can you post a picture of the plugs? Get up as close as you can to the porcelain and the ground strap. My bet is what you think is lean is really pig rich.
 
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