Hello all

I need your help!

its a 455 olds, edlebrook heads, 030 over, lunati 60803 cam

cam specs
Advertised Duration (Int/Exh): 268/276
Duration @ .050 (Int/Exh): 227/233
Gross Valve Lift (Int/Exh): .510/.522
LSA/ICL: 110/106
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1600-5800

I sent my Distributor (HEI) out with cam card to be rebuilt and recurve. its back and it has a tag on it with the following

curve starts @ 1,100 rpm
20 deg @ 2,600
8 vac
set timing 12 to 14 a idle

my question is what do i set total timing at ? is it 34 at 2600 rpm, Im confused,,,dose this sound right for this cam

Thanks Kevin

 

As much as you can get away with!
The VA is pretty short at 8 degrees.
Try for 36 total with VA disco'd and engine at 3000 RPM. [your specs do not indicate engine RPM or dist'r RPM]

Then connect your vacuum canister to the MANIFOLD vacuum and set the idle down to suit.

This way, it will not have the hesitation or backpedaling upon start, will idle nicely, not overheat, and generally be very well behaved.

Or, so was my experience with a similar cam and an HEI from Lord knows what.

 

What gears are you running? Automatic... what stall speed?

 

Im runing 2500 stall....and 308 for now

 

I'm running 2500 stall....and 308

 

I'd be curious how that setup runs.

 

32-36* total with the vacuum advance disconnected. This is the ballpark you will need to test to see where it likes it the best. I personally would try 36* with premium fuel to start.

 

I agree, 34-36 total with the vac line disconnected. That would put you at 14-16 initial, respectively.

 

I think that's too aggressive of a curve, too quick. That cam will retain cyl pressure down low, 3000rpm would be better.

 

Cutflassefi...u think the curve is to quick? In other words change the spings to stiffer?

 

Yes I do. 2600 rpm is awfully early unless your have a very loose converter and/or high numerical gear.


Jmo.

 

Hello all update

my tag did not come yet cant drive

but i did set the total at 34! 36 seem to ping under a power brake simulation ..... Man the front of the car wants to leave the ground and lots of rubber lol lol

dose this mean 34 is it or should i try something else?

 

i have another Question.

when setting total timing do i raise RPM till i see no more advance on balancer or just till 3000 rpm?

the reason I'm asking is at 3000 rpm it seems that it will take more rpm before it stop advancing??? wondering if that's why it wont take 36 total

thanks All

 

KDW, nice car, looks just like my SX. My timing is set @36, But i have an ignition cut off to get it started when hot and it will ping very heavily when hot and/or low octane rating. But i do not know what my cam numbers are.

 

Yes raise your RPM and see where it stop advancing. From your distributor guy said it should have stopped advancing at 2600.

 

lol its advancing pass 2600 more than 3000 more like 3200 or 3300

 

You want to set it so that the total is at the rpm it stops advancing with the vac canister disconnected, then connect the canister and see what your total is with vacuum. You really don't want it to exceed 50.

 

One thing to watch out for is that distributor RPM is half of crank RPM. Sometimes distributor specs are stated in distributor RPM, not crank RPM.

 

Brian

So if distributor RPM is half of crank RPM.....what are you setting RPM too, to get total 36 total???

 

I'm not quite sure what you're asking. If some one told me that they had recurved their distributor so that the advance was "all in" by 2600 RPM, I would assume they were talking about crank RPM. But if I purchased a distributor stand-alone and it had documentation saying the advance was all-in by 2600 RPM, I would be uncertain and suspect they're talking about distributor RPM. A phone call would be in order.


For what it's worth, I agree with what others have said: with your converter and gears and weight, I'd suggest the advance be all-in near 3000 RPM (crank), not 2600.

 

We may be muddying the water here. RPM is almost always Crank RPM. Never heard anyone ask me what my dizzy RPM was...........

 

Hello all update

I wont reinvent the wheel...lol

I went with This! I raised RPM till I did not see anymore advancing and set it at 36! i dont hear any pinging with stepping on brake and gas ( in driveway) it seem really strong. i will take it this weekend will keep you updated.....

 

Be careful with the vacuum advance, again you don't want more than 50 degrees total with vacuum under light cruise. What was the final Rpm you set the distributor for your 36 degrees?

 

How did this turnout KDW?

 

Hello, sorry for the delay....! The car ran great at 34, 36 seem to ping; I had to go back and re tune crab! I had to richen up the idle circuit seem to pop a little at idle it’s gone know. Going to check jets next to see where I at, I think its 74 primaries and 78 secondary’s (does this sound rich) I think it wants more. I have a 750 Quick Fuel on it....I’m think of bolting my 750 speed demon and see what happens. I hear there more aggressive.

 

KDW, curious what engine temp are running? Timing can sometimes really effect engine temp. My 455 has the e-brock heads, Torker intake with an Aluminum later model Suburban radiator ( its a direct bolt in on a 67 Cutlass-442). Lots of aluminum to dissipate heat. Motor runs this time of year in Texas 160 degress, middle of 105 degree heat 170-180. I can can get away with 20 degrees initial and 36 degrees at throttle no pings at all on 93 octane, M21 4-speed, 355 rear.

 

I think you're making this more complicated then it is. Your distributor guy told you he put 20 degrees of mechanical advance in the distributor. He no doubt used a distributor machine for this so if he said it was all in by 2600 then it's accurate assuming his machine is accurate. He suggested you use 12-14 initial timing as read at idle off the balancer. Initial + mechanical = total. You put 14 + the 20 built into the distributor which gave you 34 total degrees. You said it ran great at 34 but pinged at 36. Leave it at 34 and call it good.
The vacuum advance is adding 8 more degrees so you have 42 degrees while cruising. I think that's a little low but that's not a big deal atm. Don't get hung up about the vacuum advance. Just remember it's initial + mechanical = total. 14 + 20 = 34 in your case.
Your carbs jetting does sound a little rich to me. The fact that you even brought that up kinda confirms that. My old 455 build used a 780 Holley with 72 jets in the primary side. The secondary used a metering plate which should have been equivalent to a 76 jet. Your spark plugs should give you a good indication of where you are on the rich/lean scale.
I'm not saying yours are wrong because every car might be different but you did bring up the rich question which leads me to believe you're already thinking about it and there's probably a reason why?

 

therobski, my car runs 180 all day...I live in SoCal so my local station only has 91 OC!

 

What TripDueces said. Initial + mechanical = Total

What a car can tolerate for advance total and rate (curve) depends on a number of factors, you can't pick it entirely on engine/cam, and stall. Gears for one play a factor, as does vehicle weight. Outside temps, altitude, driving style, carb tuning, and a number of other factors play a part too. So you have to only use the original config as a base, and adjust from there once it's in the car and you're driving it.

Starting at 1100 rpm sound a little aggressive for 308 gears to me, but if there's no indication of detonation then I would assume it's ok. I generally shoot for starting at 1600, but there's a number of factors there as mentioned. A symptom of the advance starting too low is the idle RPM has a delay returning to it's 'low' setting.

As for vacuum, I've found that Olds' doesn't particularly care for too much vacuum advance when setup in a 'performance' static compression ratio. OE engines with low SCR, like in the < 9:1 range can use 'typical' vacuum advance numbers. This in general relates to iron head apps, I don't have experience with aluminum heads on Olds (yet). Under 12 is what I've been finding, or you get light throttle ping, again, with iron heads and higher SCRs.

I believe the Quick Fuel carbs, even the vacuum models, have secondary metering plates that have removable jets. Anyway, with today's fuels, and HEIs, it's a little more difficult to read plugs, and usually I lean more towards using the tail pipes as an indication of rich/lean conditions, and the butt-o-meter.

More gear likes more advance and richer carb settings, less gear the opposite. Higher stall can mask settings that are less than optimum.

Trial and error are the only way to get the final optimum tune.

.

 

KDW, just ruling engine temp out, good discussion on this thread especially when I get the 64 F-85 pro-touring car running I will most likely lean on some of this info.