engine and drivetrain Moving the powerband Schrick 292 & Adjustable Sprocket

[Knapmann]

Hi, I'm building an engine with dual 40 Mikuni's 10:1CR and a Schrick 292. I can't find any info on what the powerband is for the 292 but I'm guessing it will be maybe 4000-6000rpm? As I don't particularly care for revving the guts out of my engines I've been thinking about trying to lower the powerband as close as possible to the 2000-4000rpm range.

I understand the band can be changed with an adjustable cam sprocket.

Do I need to retard or advance the sprocket?

When looking from the front of the car which direction is advance and which retard? (clockwise/counter clockwise)

What amount of movement in the band can I expect approx? 500rpm? 1000rpm?

Would it be best to simply adjust the sprocket as far as possible until piston/valve clearance is as small as possible and leave it at that or can I over adjust it in such a way that the clearance is still OK but the engine will run badly?

Are there any negatives to doing this? Reliability, fuel consumption etc

Are there any other adjustments (carb etc) that can help increase lower end power

TIA!

[dubois]

The M10 is an interference engine, turn that sprocket the wrong way and the valves will hit your pistons (I found out the hard way). A lot easier to go with a 284 cam, or leave the 292 and install a 4-2-1 exhaust header, which will lower your power band. Also I believe with dual carbs you will gain torque, so you really won't have to rev your engine that high. My recommendation, stay away from those adjustable sprockets!

[Tommy]

Here's basic info from Macartney restoration guide. I think you should start with basic setting and I believe you'll be happy with it. If you still feel you would want to improve lower end you could try advance the cam slightly.

hth, Tommy

[Guest Anonymous]

The M10 is an interference engine, turn that sprocket the wrong way and the valves will hit your pistons (I found out the hard way). A lot easier to go with a 284 cam, or leave the 292 and install a 4-2-1 exhaust header, which will lower your power band. Also I believe with dual carbs you will gain torque, so you really won't have to rev your engine that high. My recommendation, stay away from those adjustable sprockets!

IMO if you are installing any aftermarket cam you need an adjustable sprocket to get the cam set to the manufacturers specs, from there you can go where you want to. A small change (1 or 2 degrees) can have a significant effect, assuming you have everything else optimized.

As a standard rule, advance the timing (valve opening and closing occurs sooner in the cycle) and the band moves down (earlier), retard (valve events happen later) and it moves up (higher rpm).

My experience has been limited to the 304, 328 and 336 cams on High Compression race motors and getting it right has taken some time for me to develop. IMO Schrick has a horrible way of spec'ing cam events. I have adopted the centerline method and it works for my application.

We changed a valve spring at a race a few years ago and had a crowd watching as we retimed the motor, one guy the owner of a vintage car shop asked if we would come and teach his guys how to do it, imagine that!

A guy like John F (flybmw02) has taken timing of high compression (14:1 - 336 cam) race motors to a whole new level or JohnA could give a class on this stuff - I would pay to attend

Until you get really comfortable please make sure when you make a change you ensure there is enough piston to valve clearance before starting the motor. With a mild cam (up to 292) you should not have an issue 1-3 degrees each way. Not sure what Dubois' problem was but IMO many cams are set up incorrectly. In all likelihood the cam could of been 3-5 degrees out of spec before it was "tweaked".

Good luck

anthony k

calgary, ab

[M3M3]

LOL...i don't get it...

the whole point of sidedrafts, hot cams and high compression so that you CAN and SHOULD rev the engine higher! 4-6k rpm is not reving the piss out of an engine...that is the range you should be in with that setup and if you aren't in that range on a regular basis you are wasting a wonderful experience and sound.

:-)

[Lorin]

^ I agree.

Every mod you mention applying to your engine (except compression) decreases low end torque and raises the RPM where the engine will make power.

You could put a very restrictive exhaust on it to boost low end torque. Also , small chokes in the carbs will do the same thing.

[Knapmann]

I know these mods will create a higher power band but I just want to try and keep it as low down as REASONABLY possibly; as close to the the area I normally drive in as I can. My car is a daily driver, and I don't think many people who use these cars daily also drive about pulling 5-6k rpm all the time. If they do their ears must hurt quite a bit.

I think most people who drive around in this range are probably using it as a weekend toy to blast around windy roads which is fine but just not what I want. I know your gonna say I'm not getting the best out of my engine this way but I don't see the point of having power in a rev range I never use IF I can nudge it down a bit.

Thanks Tommy for that Macartney info. It gives the power band a bit lower than I guessed it would be. Maybe with the adjustable cam I can knock it down to 3-5k.

[Knapmann]

IMO if you are installing any aftermarket cam you need an adjustable sprocket to get the cam set to the manufacturers specs, from there you can go where you want to. A small change (1 or 2 degrees) can have a significant effect, assuming you have everything else optimized.

As a standard rule, advance the timing (valve opening and closing occurs sooner in the cycle) and the band moves down (earlier), retard (valve events happen later) and it moves up (higher rpm).

My experience has been limited to the 304, 328 and 336 cams on High Compression race motors and getting it right has taken some time for me to develop. IMO Schrick has a horrible way of spec'ing cam events. I have adopted the centerline method and it works for my application.

We changed a valve spring at a race a few years ago and had a crowd watching as we retimed the motor, one guy the owner of a vintage car shop asked if we would come and teach his guys how to do it, imagine that!

A guy like John F (flybmw02) has taken timing of high compression (14:1 - 336 cam) race motors to a whole new level or JohnA could give a class on this stuff - I would pay to attend

Until you get really comfortable please make sure when you make a change you ensure there is enough piston to valve clearance before starting the motor. With a mild cam (up to 292) you should not have an issue 1-3 degrees each way. Not sure what Dubois' problem was but IMO many cams are set up incorrectly. In all likelihood the cam could of been 3-5 degrees out of spec before it was "tweaked".

Good luck

anthony k

calgary, ab

I'll probably find the limits of my adjustment when building the engine. Then I'll tune the engine at zero degrees before playing around with the advance within that limit.

Am I right in thinking that to advance the timing I turn the sprocket counter clockwise (looking at the engine from in front of the car)?

Do you have to change the spark timing with each adjustment?

Thanks

Neil

[CLIMBERNYC]

FWIW, just finished a dual weber conversion 8.5/1, flowed head with 292 cam, ie 2 step headers and exhaust. The car has loads of torque down low. Dont forget that the sidedrafts will increase throttle response over a standard carb and also push through more fuel. I dont think you will want for power down low.

[aa/fd]

The adjustable sprocket is necessary to correct the changes in the cam to crankshaft center-lines.

For example if the head is surfaced the centers get closer, same with the block if it is decked or the main line is bored.

All these machining process move the centers closer making the timing chain longer so to speak retarding the cam timing.

Any proper engine build requires a precise "degree" of the camshaft.

Advancing cam timing will make a measurable increase in cranking pressure.

Changing the lobe centers will also make an impact on the "power band"

Cam timing adjustments are not as effective as intake runner length in moving the band up and down. Longer runners = lower speed power band, if I recall 17 to 19 inch was a good area to start. There is a formula available calculate the runner length versus bore and stroke, off the top of my head I don't recall where to find it