OK, this thing is not a dog by any means, but I think there is substantially more power to be had. Here are the things I am thinking.

With the engine running good and warmed up, I have had to reduce my total timing to 32-34 degrees to prevent detonation. Anything over that and I get a mid-range ping. Not good.

I have noticed in my test runs that I am getting a labored exhaust note, hard to describe, but I am positive that the engine needs more advance. I think I am losing power out the exhaust. When I took the wife for a ride yesterday, I rolled into the throttle in third gear from about 3000 RPM. She said it took her breath away, but I expected it to break the tires loose when it hit the power band, and it didn't.

Back to detonation. I am forming a theory that even though dynamic compression is figured off of the advertised duration of a cam, that the .050 duration and ramp angle have a part to play. Even though my new cam actually has a larger adv duration than the old one by 1 degree, it has 8 degrees less at .050. It seems to be more prone to detonation than the old one.

To test my theory, I am going to fill her up with 110 octane race gas tomorrow and reset my timing curve to something like 28/40 and see what it does. I'll bet it makes a HUGE difference. If so, I have too much compression for this cam. Bad thing. Fortunately, these are domed pistons, so I could take them out and have the tops milled slightly to remove a point of compression and it should fix it. I don't really want to do that though.

I'll post again tomorrow with results.

-Scouder

 

You should try to mix a little race fuel with 92 pump stuff. Also you may want to try a cold set of plugs for it as well. I run Iron heads on my 428 with 11to1's with a small Solid Roller cam. I did a compretion test on it after it was warmed up and I had 220psi. I do run a cold set of plugs in it and that helps out a lot. "JMO"

Wes Adams

 

Are you still running on the stock NP435?

Is this transfer case full-time 4wd?

A couple of basics I purged from my brain at some point :-)

 

GTEX, If you mean me, You bet I am. I'm running a stock NP435 with a NP 205 case. No its not a full time 4wd.

Wes Adams

 

And if you mean me, 435, part time. But I really have my eye on a Richmond 5.

-Scouder

 

If it does turn out to be a compression issue, I'll start experimenting with mixtures to see what it takes to solve the problem. I'll test at full race, then 50/50, then lower.

I also started thinking that it could be fuel related. I have a pretty severe hesitation when I punch it, and this could be a starvation issue creating a lean condition and starting the ping.

Oh the fun of hot rodding.

-Scouder

 

Yeah Scoot even with the Mild mannered D2TE all Iron build..at 10 to 1 with Iron Heads and the XE Comp Cam.. I still think I'll have to add some Spirits to the 93 octane..according to the sim..It seems to be border line..and stops the midrange detonation with 94 octane??

Just what I have came accross??

Keep us posted...

Russ

 

Im thinking you have to just drop the cash, put some street tires on and take her over to the dyno. In the long run it will be the cheeper route, and a faster one too. What do your plugs look like?

 

Scouder,

The Intake closing point on the cam timing is what plays a role in the compression of the engine.

A early closing intake will add compression.

What is your closing point now as compared to the prior cam you had in there?

Tmod

 

OK, just got back from some test runs. The engine likes about 40 total, and it makes a BIG difference. Now I have a foundation to tune on.

It still doesn't quite break the tires loose at the top of third gear, but she's close. I think with my bigger cam it would have done it. This new cam has a little broader power, but I gave up a little on top.

My plugs aren't tan, more of a dark brown, so I'm guessing 1 jet size reduction should bring it in pretty well. And to answer Tmod's question, yes, with my cam advanced to 102.5 I lost 3 degrees of intake closing point.

One thing I just discovered you DO NOT do is downshift from a lazy 4th gear to a powerband 3rd gear while in a long sweeping corner and nail the throttle. Unless you want to see what the back of your truck looks like, cuz it'll be right outside the drivers window if you do. Gotta love them Detroit lockers.

On a good note, no pun intended, the truck sounds GREAT. I had my cousing get in and take it for a few little rides in the pasture behind his house and I loved it. I even had him tag it a couple of times, and it has a very mellow exhaust note now that the timing is right. I was worried because it is SO loud in the cab. I guess once I get a back window, insulation and carpet it will get better.

Also, it looks like my oil leak is the base of the dipstick. I'm going to have to put my pan evac system back on. Too much pressure in the crankcase.

-Scouder

 

Well Brian, Sounds like ya got her dailed in...Cool.. Also sounds like ya dont have to run her on the pipe now...and that should be good for street driving... I just hope I get the same responce out of my Victor,cam and gears, with the auto and stall...

Were still looking forward to that BIG Smokey!!! LOL..

Russ, and happy Pappy's Day!!

 

Very good! Did you do anything with the distributor advance curve? That's how I cured the ping in my 390.

 

Not to answer for Brian,...but I'm quite sure he did. He was making his own custom bushings for the MSD to get it in the sweet spot. I know he wanted a lof initial, but then had to keep it under control at full advance.

I'm guessing he's around 26/40 ???

Man, I got to get to wrenching.....I think me an Kurt should be contenders for the National rally burnout contest. I need to find me some old soft rubber.

 

Greg is right. I have been manipulating the curve ALOT over the past weeks. I'm not done, but at least I'm in the ballpark. I am thinking now that I might go back to straight Premium fuel and experiment with my upper end timing set right where it is, and play with the initial and heavier springs. My ping is mid range, so it might be that with my high initial it doesn't want any more advance until the rpms come up. Heavier springs would hold it off until higher up, where it might take it better.

I have also decided that the next time I tear this thing apart I am going to thread the dipstick hole and fabricate a leak-proof dipstick. Maybe something where the tube threads into the block, and the stick threads into the tube. Hmmmmm.

It's quite fun trying to tune these high-strung engines. A little here, a little there, and before you know it you are sneaking up on a well balanced tune-up.

-Scouder

 

Oh, I forgot. Greg, you are almost dead on. I think right now it's around 28/40. Good guess.

-Scouder