SBC Rocker Arm Ratio

[plym49]

Originally Posted by roflwaffle

Well then you're as set as set can be IMO and I think you may see some benefit from less lift. Maybe not. It'll certainly be interesting to try. Just outa curiosity, what kinda mileage do you see round trip cruising at ~60mph?

I have made a lot of changes over the years for various reasons, so it is tough to select the right baseline. But for purposes of this thread, I'd say 19 plus.

[plym49]

Originally Posted by s2man

Why didn't I think of that?!



My Cav has the 2.2L I4 OHV. They say it has the same lobe profiles as the SBC, so anyone who grinds SBC cams could regrind my cam. But since they can only remove material from the existing lobes, I have question how much of a difference they could make from the stock lobes. As you said, cam swaps take a lot of time and money, and I'm not sure I want to put that effort into a project with unknown results.

Advancing my cam will still take a lot of labor; Probably half that of a full swap. But the cost will be minimal, and I know it will move give the FE tuning I'm seeking. Moving the power band into a lower rpm range (via the cam advance) and going with higher gearing will probably be the best thing I can to with this engine/trannie combo.

But enough about my car. I can't wait to see the results if you do the rocker swap. Make sure you get us some good before/after numbers. With tables, and charts, and grapshs!

I don't know your engine. But GM likes to not reinvent the wheel. Are you sure that you don't have the same stamped steel rockers as on a SBC?

If so I can buy a set of 16 1.3 rockers and sell you four.

[plym49]

Originally Posted by malibuguy

you'd prolly gain much more in all directions switching out to roller rockers, or even just roller-tip rockers

any 2, non-canted valve engine is pretty much undervalved...so reducing the lift & duration of the intake valve will just multiply that, plus now your potentially dropping power, which can make the engine work harder, thus using the more fuel, to move the car the same as it would with a stock ratio rocker

if you are really despirate...look here www.hotrocker.com

The whole idea is to reduce power (reference point same rpm and same throttle opening). So to generate the same power (IOW what is needed at that point), you have to open the throttle more so volumetric efficiency goes up. Maybe.

There is no such thing as working harder. Power is power.

[plym49]

Originally Posted by oldschool

to Plym49, #8:

my truck with the antipumpup lifters got around 20 -21 mpg at highway speeds driving for economy, that with a 3 speed manual.

Sounds right. Mine is a 4x4 so it carries more weight, plus the A/C is usually on, etc etc.

[s2man]

I'll have to disagree too, malibuguy. While that blanket statement may be true when searching for maximum HP, the FE goal is to increase torque at lower rpm's. The link you supplied to hotrocker.com (nice link BTW) shows they got max torque up to 2000rpm using only a 1.1:1 rocker ratio. That would drop a stock lift of 0.414 to a mere 0.304. And all the economy SBC cams which I can find specs for, have reduced lift and duration. So 'undervavleing' seems to be the way to go for FE.

plym49 - another trip back to j-body.org, for spec's on my rockers, shows that not only does my 2.2L have a SBC profile cam, it uses the SBC rockers too! Sweet. If your experiment works out, perhaps you'll sell me four of your unused rockers

oldschool - any clacking at low rpm with your anti pump up lifters?

[plym49]

Originally Posted by s2man

I'll have to disagree too, malibuguy. While that blanket statement may be true when searching for maximum HP, the FE goal is to increase torque at lower rpm's. The link you supplied to hotrocker.com (nice link BTW) shows they got max torque up to 2000rpm using only a 1.1:1 rocker ratio. That would drop a stock lift of 0.414 to a mere 0.304. And all the economy SBC cams which I can find specs for, have reduced lift and duration. So 'undervavleing' seems to be the way to go for FE.

plym49 - another trip back to j-body.org, for spec's on my rockers, shows that not only does my 2.2L have a SBC profile cam, it uses the SBC rockers too! Sweet. If your experiment works out, perhaps you'll sell me four of your unused rockers

oldschool - any clacking at low rpm with your anti pump up lifters?

OK. If I do this I will let you know. I think that a set of 1.3 break-in rockers is about US $100, and I believe that they are only sold in sets of 16.

[DAN]

you guys are re-inventing muller cycle industrial motors. they have work scene the 1920. the hot gas still have expansion when the valve opens. muller cut back on the intake charge. this cut down on the hot waste gas going out. if really big motors were used with muller motors you would have slower reving motors with more tork and more efficacy. come to think of it a high line mazda used this with superchargers instead of a bigger motor.