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Tuning with jets, Power valves and an O2 guage

That seems to make sense to me: tighter lash = valves open sooner = lower cylinder pressure. Like a "bigger" cam with more duration will give you lower cranking pressure with the same static compression ratio & a smaller cam. Wider lash = valves stay closed longer = higher cylinder pressure?

I'm surprised the pressure change a small amount of lash change made, though.
 
Running a looser lash makes the lobes open later and close sooner.
Apparantly IQ52 thinks I'm on the road to ruin. I respect him and appreciate his concern so I'll call Lunati directly tomorrow. I haven't started the engine yet to see how it runs. My goals were to improve the lower rpm performance. I also intended to advance the cam from its 106 installed centerline. If the tech guys at Lunati don't approve of the wider lash setting, I'll move forward with advancing the cam after returning the lash to the "correct" spec. I have a mile of piston to valve clearance so no foreseeable problems there.
 
Wider lash will also kill overlap and the opposite will be true with tighter lash. By increasing the lash .004" on I and E on a .528" MoPar cam I was able to make my 68 RR pass smog in the 80's.
 
On the advice of IQ52, I did call the Lunati Tech line today. The man said that they do NOT suggest to run the lash more than .004 beyond the published .020 & .022 spec. He didn't elaborate on why, maybe because I called nearing the end of their business day.
Thats enough for me. I may return the lash to the listed spec and then advance the cam. If the advance helps, I'll leave it as is.
 
I'm not all that great in cam lobe theory but here goes. There is an opening ramp on the cam that gently closes the lash as the lifter approaches the cam flank. This opening ramp prevents a shock that would be transmitted to the valve train through the lifter, pushrod, rocker and valve when the lifter hits the acceleration portion of the lobe. The greater lash the more the lifter skips the opening ramp (or clearance ramp) and slams into the acceleration portion of the lobe. Sorta like trying to open a door by pushing on it or hitting it with a hammer. There is a closing ramp that gently sets the valve against the seat in the head rather than slamming it shut also. Too much lash and the lifter just skips the closing ramp and drops on the base circle, the valve whacks the seat and bounces back up.

Boing......
Boing....
Boing..

Pretty wierd horsepower graph on the dyno.
 
I decided to see what effect I'd have by advancing the cam 4 degrees. From my understanding, this is supposed to shift the power band lower in the rpm scale.
I finished up today. The timing was reset to account for the 4 degree cam advance. It fired up quickly and once it was warmed up, it seemed to idle smoother. I did go back and relash the LH bank to the spec on the cam card. I figure it makes more sense to do one change at a time so I'll know exactly what effect each change has. It was raining this afternoon so I have yet to road test it.
I didn't put a vacuum guage on it. I just didn't think of it until I started writing this just now. The idle speed went up about 100 rpms.
Along with trying to make the car more civilized, I'm still working on the Air/Fuel ratio tuning. Now that I have the MP Chrome ECU back in I'll probably go back to using vacuum advance. I'm sure that will improve the burn cycle at idle and cruise speeds
 
This car runs friggin strong.
The cam advance really helped make the car feel more responsive in the midrange. Tooling around in the 2500-3500 range the car feels much more snappy than before. I am to the point where I might be content leaving the engine as is for now. I only advanced the cam as a means to see if it might help. I didn't expect much from such a simple change. I was prepared to swap in another cam!
I haven't resumed the tuning though. I ordered a 3" X pipe kit with mandrel bent pipes. I also bought a pair of Dynomax welded Ultra Flo mufflers. I figure that the changes will increase exhaust flow and that may require richer jetting. The guage still reads in the high 13s at cruise currently. Who knows.... maybe after installing the 3" stuff the jetting might be spot-on.
 
I installed the X pipe and 3" pipes and while power did improve, the guage still showed me to be running rich.
I just drove the car on a 950 mile round trip from Nor Cal to LA for their Spring Fling. The car consistently read 11.9 to 13.0 at level ground 65-70 mph cruise.
back at home I went from #83 primary jets to #81s. The A/F did lean out a bit to the 12.5 to 13.8 range but power dropped off too. I also had detonation during one hard WOT run. I swapped the #83 jets back in and readjusted the idle mixture screws. The power came back and the A/F numbers were a bit leaner than they were before with the #83s. This engine likes a richer mixture than I thought. It almost makes me want to try bigger jets!
I think I'm going to leave it as is for now.
 
You should go back to the 81's or even 80's but open the PVCR a tad to get your power circuit a little richer. For a street car you want the cruise to be lean and crisp, but when you roll the throttle on hard it should richen up immediately. Power valve selection based on vacuum rating will help time the power circuit. Just curious, how much fuel to make the trip (as in MPG) if you have that data.
 
Meep-Meep said:
You should go back to the 81's or even 80's but open the PVCR a tad to get your power circuit a little richer. For a street car you want the cruise to be lean and crisp, but when you roll the throttle on hard it should richen up immediately. Power valve selection based on vacuum rating will help time the power circuit. Just curious, how much fuel to make the trip (as in MPG) if you have that data.
Click to expand...

I averaged 10.5 mpg with the 3.91 gear and the .78 Gear vendors overdrive. The OD made the final drive 3.05.

Please elaborate on the PVCR mods. Am I to understand that this is a way to have part throttle economy with additional fuel delivery ONLY on demand? Is it fair to say that the power with these mods would equal what I have now while giving better part throttle economy?
 
I did buy and install a "Quick Fuel" metering block with replaceable PVCR jets. I've yet to try tuning with it.
 
Yes, opening up the PVCR and keeping the smaller jets will tend to give more fuel on demand, which is what you want. Power valve selection should be critical too as that's the switch from cruise mode to full power. Get the cruise as lean as you can and use the ported vacuum advance port. As you roll in and vacuum drops the PV will open for more fuel and the vac advance will go away essentially defaulting the timing back to the mech curve at that RPM. Your mech curve should be 38 deg all in by 2500 or so. Unless you have a more radical cam then you'll want to take some out of the distributor and put it towards the initial. I was just working on my big cammed hemi and it seems to like most of the timing at initial - currently at 32 deg.
 
Wondering what cam you have? Sounds like a solid Flat tappet? I'm curious about your setup/reliability because it seems you put a lot of street miles on. Asking because I'm unexperienced in this area and have considered solid flat tappet but It would be daily driven 6 month a year.

Another option for guys having detonation issues is water injection. Works Awesome. I have only used it with boost but it can be used on an NA setup as well. I am thinking of putting together a high compression 440, A CR of 11.5 or so and running a street cam with little valve overlap for fuel efficiency. My dynamic compresion will be really high but water injection should sort it out when I'm on the gas or going up a hill. My thinking is I should get some good low-mid end power and improved fuel economy. It would be a daily driver setup.

This is where I got the components from, looks like their pumps have changed since I got my last one a few years ago, though there are other manufactures.

http://www.snowperformance.net/

This would help out guys having detonation problems going up hills ect.

http://www.snowperformance.net/ProductDetails.asp?ProductCode=220

Don't intend to threadjack, just thought I would put this out there. Good thread.
 
I ran hydraulic cams for years. I went to adjustable roller rocker arms with a 1.6 ratio a couple of years ago when I still had the MP 292/509 cam. I figured that since I already had an adjustable valvetrain, I'd try a mechanical flat tappet cam. These oil-through EDM solid lifters really help these flat tappet cams live. They shoot a stream of oil directly to the cam lobes along with the traditional oiling method all cams get. (Oil thrown off of the crank)
The Lunati solid I had made great mid range to top end power. It is actually a great drag race, WOT cam making more power than I had with any other cam I've tried. The problem is though than I need power off idle and in the 2500-3500 range. The 727 trans needs an engine with a wider power band than a 6 or 8 speed transmission would need. I want to run autocross and road courses with the car and the MP 528 has been well documented to be a really good street cam. The 1.6 ratio rockers take it up a notch. A friend with a similar build recorded Dyno numbers of 530 HP and 603 ft/lbs or torque at flywheel.
 
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