Zündzeitpunkt Chevy SB

[CarstenKujanek]

Wo finde ich Infos über die Einstellung vom Zündzetpunkt /WERTE im Leerlauf und ausgeregelt) für einen 350er Corvette Motor ,BJ ca. 71 oder 72 , hohe Verdichtung , mit HEI Verteiler ? Müsste nach meinen Recherchen der 340/350 PS Motor sein mit Camelhump Köpfen ( Gussnummer Köpfe) , Blocknummer ist nicht lesbar nur engine suffix , die ist VK , aber da finde ich nichts zu ! In meinen Rep Anleitungen finde ich nichts über den Motor :-(
Danke , Carsten

[LUV Truck]

Hello Carsten,

Are you trying to get the stock timing settings? Is the car an automatic? Probably around 4 BTDC degrees in drive at around 800 rpm or so with the vacuum hose unhooked and plugged. I don't think your engine combination is original so you can't really cross reference. Camel hump heads I think were until 68 and had no accessory holes. Where the 71/72 motor has accessory holes in the head. If you are looking for the best perfomance just keep advancing the timing a degree or so at a time until you start loosing mph at the track. BTW. try to use ported and manifold vaccum with the vacuum advance. My 70 pickup likes ported vacuum the best since manifold vacuum advances the timing too much for starting but it does keep the plugs cleaner and allows you to close the throttle blades more on the carb.

Cheers,

[CarstenKujanek]

It is automatic . Engine seems to have a different cam and has 1.52 to 1 roller rocker arms , accel hei ignition with msd module , weiand 360° intake and 750cfm Holley , vacuum secondary. I use the vacuum at the carb not from the manifold. It is now set at 6 degrees at 1000 , lower rpm is difficult , when you put in D , it goes down to much... I use 100 octane fuel , because with that it runs much better. I ask because of the timing , because i don not want to kill the engine with a wrong set timing on full throttle ;-)

[LUV Truck]

Carsten,
Holley 4150 style carbs usually have two vacuum ports at the front. One is usually on the metering block behind the front bowl and that is 'ported' vacuum, and the other is on the front of the baseplate under the bowl which is 'manifold' vacuum. The manifold vacuum will advance your timing with vacuum advance even though your carb's throttle blades are in the 'idle' position because it is pulling vacuum from under the baseplate. The ported vacuum will only apply vacuum to the distributor advance can when you open the throttle blades since it is pulling vacuum from above the baseplate.

Try both ports. Both will pull vaccum when you are cruising and should pull the vacuum to 50 some odd degrees when cruising in high gear on the highway. Is it 6 degrees at 1000 in gear or in park with the vacuum line to the distributor unhooked and the vacuum port plugged? What is your timing at 3000 rpm with the car in park and the vacuum line to the distributor unhooked and plugged? You want to check your timing without the vacuum canister hooked up.

Cheers,

[CarstenKujanek]

I used the ported vacuum , the manifold vacuum of the carb is connected to the transmission.
I will check out tomorrow and hope to find the "stripe" to put on front pulley , with the timing written on...(don`t know the exact word for it)
Thanks

[CarstenKujanek]

OK..
Set the timing on 4° at 1000, but in P (park) not D .Does that make a difference ?
Put it all together , but i think it does not accelerate as good as before !? Starts a little heavier , too.
Should i check it again with gearbox put in D ? Rpm drops to 800 when i put it in D. I think it may be better to get it up to 1000 rpm when it is in D position .
I think i will try to check these things out tomorrow.
Did i forget anything ?
Greets , Carsten

[coolchevy]

I do it usually the following way with an unknown cam.

Most, if not 95% of all SBC run best at a total timing of 36-38 degrees, all in at around 3000 rpm. If I can not play with different advance springs or stops, I turn the dissy until I get those numbers and whatever the static advance is at idle is fine for me - as long as it doesn't ping and starts relatively easy.

I disconnect vacuum advance on dissy as that is for girls only, I treat that the same way as any cam which is not a solid roller - girls stuff

always check those settings in gear, it is of no use if you have perfect idle in park or neutral but car bogs or stalls everytime you put it into gear

[CarstenKujanek]

Grins... Sag mal , könntest Du das mal auf deutsch schreiben ? Alles kriege ich in englisch doch nicht auf die Reihe.. ;-)
Danke ...

[LUV Truck]

This is why I originally asked...

Original von LUV Truck
Are you trying to get the stock timing settings?

Sounded like he was asking about timing settings for a stock "vette" motor with cylinderheads that weren't offered during that build year. For optimal performance, do as Coolchevy states and let the initial (without vacuum advance hooked up) fall where it may.

I do have to disagree with the vacuum advance comment. If you drive the car on the street/road/highway the vacuum advance will do nothing put help you, your motor, your gas mileage and your wallet. Non-vacuum advance distributors are for race cars only and people that 'think' the loss of the vacuum canister will give them more HP or make them cooler.

Ranks up there with:
1. Cams too big engine combination/performance goals
2. Valvetrain too exotic for engine combination/performance goals
3. Fuel system too large for engine combination/performance goals
4. Carb too big for engine combination/performance goals