L-72 tune up

[JimM]

I like to work backwards, start the tune for good idle, tip in response, and midrange, then recurve the mechanical advance for the correct total timing.

Most of the cars I've tuned like a LOT of initial, assuming you're not ping limited due to too much compression. My car runs GREAT with 18 degrees initial and another 18 from vacaum on full manifold. That's right, idling with 36 degrees in it!

As long as it will crank hot, and not ping at part throttle with the vac advance unhooked, you don't have too much initial. If it pings at part throttle with vac advance, get an adjustable canister and tune it out.

Continually work the idle speed, idle mixture, and then power valve / primary metering rods as you do this.

Jim

[Chevy454]

Post the cam card...being it's not the GM cam, and that it looks fairly larger than the original 143, it may just be the cam is weak down low because of the cam timing/duration and what not...

[HS PROFESSOR]

albert.....all that work on a real car and you put in a solid roller???? its all about the combination. factory intake?? factory holley?? points distributor?? exhaust manifolds?? it may be a small roller, but its never gonna work well with all the factory L-72 stuff.you need a good curve in the dist.as much initial as possible,with total being at least 36-38 degrees.stick a MSD distributor in it and paint it black.nobody will ever notice,and forget the vacuum advance,not needed.are you running a correct holley?? if so put it on the shelf,and throw on a regular 4779 750 dp.drill the rear throttle blades and it should idle at 800 rpm's no problem.is the car an auto ?? stock converter??that could be a problem. post some more info on the combo.between craig and i we should have enough parts laying around to try. car looks great by the way!!!

Bob Gonier

[Alss]

Rob, .575 intake .597 exhaust..110 lobe center....358, 364 @.050 duration.

Bob..come on..its a stocker!! factory intake, points, carb etc..got to make it work!. The key is I dont have alot of time playing with it yet..hopefully this week will generate some rainey dasy so I can play with it. I was also using a POS timing lite for the initial fire up and that will be changing as well. Just want to have some idea of where to look and what to play with. Lots of great ideas ..thanks to everyone who replied.

ALbert

[Chevy454]

Al, what is the LSA (lobe seperation angle) on the cam? Also, recheck the duration, and if the card lists both, post both the advertised and @ .050" or .010" or whatever numbers. That roller has a lot more duration than the factory 143...I'm gonna guess it has a tight LSA, which is gonna hurt anything down around where you're wanting to put the idle...

And a word of advice, don't go swapping carbs/distributor just yet...I've heard *rumors* of folks getting those factory parts to work "ok"...

[Alss]

[ QUOTE ]
Al, what is the LSA (lobe seperation angle) on the cam? Also, recheck the duration, and if the card lists both, post both the advertised and @ .050" or .010" or whatever numbers. That roller has a lot more duration than the factory 143...I'm gonna guess it has a tight LSA, which is gonna hurt anything down around where you're wanting to put the idle...

And a word of advice, don't go swapping carbs/distributor just yet...I've heard *rumors* of folks getting those factory parts to work "ok"...

[/ QUOTE ]

OK Rob, I have the cam card in front of me here are teh specs:

Lift at valve .575 intake .597 exhaust
lash .024 intake .026 exhaust
duration at .050 256 intake 264 exhaust
advertised duration 296 intake 300 exhaust
exhaust closes 18 Deg ATDC
exhaust opens 66 Deg BBDC
intake opens 18 Deg BTDC
intake closes 58 Deg ABDC
Lobe separation 112
Center line of 110 Deg will make the cam 2 Deg advanced

And no worries about the "stock" parts leaving anytime soon..I WILL make them work. I can build the car just have not alot of experience with tuning them..a new learning curve for me. Thanks for the help.

Albert

[YENKO DEUCE REGISTRY]

I have to agree with Rob on the LSA thing - I too tried a 'better' cam when I built my engine, and kept all else stock. I could not get that thing to idle at less than 1300+/- RPM because of the tight cam.

I then took it out, put in the stock cam that I bought from my local dealership, and was able to get the engine tuned through conventional means - with the help of others

Now, it's a solid 14.2 @ 99MPH runner, looking to get another tenth out of it at SCR9

[Mr70]

With that ET,what RPM does it idle at now Marlin?

[Alss]

Cam was selected as it was suppoed to be close to the stock L-72 cam but be a roller..machinist is very knowledgable and has done alot of motors for me. Going to try the dialback method when I get some time to play. I have had bigger cams work with stock components..this one will just require some time..and I'm learning as I go Thaks for all your inputs

ALbert

[Alss]

OK, had some time to play with the motor a bit..here are the results..set timing by ear and test drove..ran good but.....timing mark(flash) is at 12 o'clock instead of on the tabat 2 o'clock!!!!, almost 50 degress out of place!!..any ideas of what I have skrewed up!! Runs great otherwise..HELP!!!!!!

ALbert