facel6

The engine of my 58 is equipped with a crank with casting number 3815822.
Is this the correct number ?

It also has a camshaft with mechanical instead of hydraulic lifters, which obviously is not correct for a 245HP 4 carb. engine

Is the camshaft on my car corresponding to the SP. cam of a 270HP ?
If yes, i guess i have to tune-up the engine in the same way of a 270HP (7° BTDC instead of 4, R.P.M idle speed 800 instead of 475, ...)

MelWff

Unless you measure actual lift and duration and compare it to a known cam there is no way of knowing what cam is in the car.

Frankie the Fink

If its running strong then I wouldn't worry too much about the cam...not sure if that GM number is for the Duntov 097 cam, which is what a 270hp car should have.

I do have a 270 car with the Duntov cam and dual quads and I run the timing at about 14*. Stock specs for timing on these cars is conservative. You will be leaving HP on the table if you go with that - besides your engine appears modified. Point begin you may have to play with things to get optimal bang out of it...

facel6

currently, i have set the idle at about 800 - 850 rpm
the timing advance is about 20° at idle, maybe a little bit to high ...

MelWff

is that 20 with or without the distributor vacuum line connected?

Frankie the Fink

20* is high if that is the initial with the vac advance (if you have one) plugged...you'll want to get that idle down as low as you can so the centrifugal weights aren't kicking in while you are trying to set initial timing. I'd start around 12* and (vac advance still plugged) you would like the centrifugal to be 'all on' at 2500-2900 RPM with 36* total timing. Then you can crank your idle back up to a nice steady speed.

THEN you can plug the vac advance in and see where things fall. Best to take a test drive and make sure you don't have any trailer-hitching at cruise...that means you have too much advance with everything connected. You can't really measure what the vac advance adds because it is load driven...so you have to go by how the car feels and the configuration of the can (e.g. what number is on it).

Lots of good papers on here about setting timing if you search...

facel6

OK Frankie

will make some tries tomorrow. It's late here in France and i would not wake up the whole neighborhood

My car has it's stock distributor (GM 1110891) which has no vacuum

just for information, what's the idle speed you have on your 270 ?
Also around 800 rpm ?

facel6

According to the previous owner that had the engine rebuild,
it's a Duntov cam that's in the car (same as on a 57 270 hp)
Hope this is not a problem with the 245 hp carburetors

Frankie the Fink

No. The cam will do fine with the 245hp carbs....I ran them for a while before finding the 270hp carbs. Dual quad cars with that cam will not have a stable idle below about 750RPM....I run my car between 825 and 850 RPM....

facel6

OK

Once again, thanks a lot Frankie
I think i'm on the good way :-)

Last question (for today): What's the advantage of changing the carburetors ? A pair of 270 carburetors will at least cost about 4'000 $ or more

Frankie the Fink

270 hp carbs ?

Well they'll make you poorer -- you might get a little bit of a performance boost but I don't think it would justify the expense....you can get your 245hp carbs set up to perform just like the 270s. The 270s have different counterweights and arms to activate the flappers for the rear barrels and different springs/metering etc. to accommodate the lower vacuum of cars running the Duntov cam..

MikeM

If your camshaft IS the 097 cam that belongs in the 270 hp engine you're in good shape.

Should idle fine at 750 rpm.

If you do nothing to your present 245 carbs to match the cam, you may lose a little something in performance. Maybe not. There was a reason the carbs were different for the solid lifter cam but I doubt making the change would make more than an insignificant difference.

facel6

Are the 097 camshaft and the carburetors the only difference between a 245 and a 270 hp ?

MikeM

Intake and exhaust valves are different as are the piston rings and crankshaft rod/main bearings. There be other unique parts, I don't remember. Been too long ago.

facel6

with my current settings, i could measure 14° advance at 620 RPM and about 40° at 3'000 RPM

Are these values correct or do i have a little bit too much advance ?

MelWff

unless you have really high octane gas, the total should be no more than 36

facel6

In France, the lowest octane gas you can find is 95. It's what i put in my car

JohnZ

The French pump octane number is based on a completely different system than it is in the U.S. - the U.S. system uses research octane plus motor octane divided by two. The French system uses just one number (don't know which one, but the result is WAY different).

facel6

Yes John, you're right.

In France, we only consider the RON (research octane)
In the states, (RON+MON)/2


In France, we have 2 quality of gas:
with RON 95 (MON = 85) => equivalent US = 90
with RON 98 (MON = 88) => equivalent US = 93

Now the next question: what kind of gas do you usually use for your 283 engines ?

JohnZ

In most places in the U.S., we have three grades of fuel - "Regular" (87 PON), "Mid-Grade" (89 PON), and "Premium" 93 PON (except California, where "Premium" is 91 PON).

Except for solid-lifter fuelies, most 283's had compression ratios between 9.5:1 and 10:1, and should run fine on Mid-Grade (89 PON); some will run OK on Regular.