How To Get 500+ More RPM, Without Changing Cam Options

[motorvated]

2.0 Liter Four. Doing a top end refresh and not planning on splitting the cases or changing the cam. Would stiffer valve springs and beefier pushrods get me there. I'm a little confused when looking at aftermarket springs, as the European Motorworks Single HD springs are rated at 135 psi seat pressure, and stock springs are rated at about 175 psi. Also thinking that chromoly pushrods set at zero clearance cold don't let the valves open fully when hot due to the lower expansion of the pushrod, plus they are a lot heavier than aluminum pushrods. So what can I use to get those elusive extra 500+ rpm? My old stock 1.8 floated valves up near 6,000, which wasn't bad, but I'd like a little more with the 2.0 liter. I'm racing the car in Vintage. Any suggestions.

[Dave_Darling]

Stiffer springs should get you there, but it won't help. Power drops off like a rock above 5000 RPM, so going up to 6K is pretty much a waste of time. The heads/cam/valves just don't breathe at that RPM.

Not sure what the deal is with the HD versus stock spring pressures listed, but I wouldn't be surprised if they were measured in a different way. (Such as spring relaxed for the one versus compressed to a specific height for the other.)

--DD

[wndsrfr]

Stiffer springs should get you there, but it won't help. Power drops off like a rock above 5000 RPM, so going up to 6K is pretty much a waste of time. The heads/cam/valves just don't breathe at that RPM.

Not sure what the deal is with the HD versus stock spring pressures listed, but I wouldn't be surprised if they were measured in a different way. (Such as spring relaxed for the one versus compressed to a specific height for the other.)

--DD

Dave's right on...the cam is going to dictate where your power is, but what you want to pay attention to is the torque curve--dyno your car then do a bit of choosing which size rear wheel/tire combination will gear you down or up depending on the track. You can also consider doing the transmission flip of 3rd & 5th and put in an "S" 4th to get AFKaSZ gearing--I love mine....

[motorvated]

Stiffer springs should get you there, but it won't help. Power drops off like a rock above 5000 RPM, so going up to 6K is pretty much a waste of time. The heads/cam/valves just don't breathe at that RPM.

Not sure what the deal is with the HD versus stock spring pressures listed, but I wouldn't be surprised if they were measured in a different way. (Such as spring relaxed for the one versus compressed to a specific height for the other.)

--DD

Dave's right on...the cam is going to dictate where your power is, but what you want to pay attention to is the torque curve--dyno your car then do a bit of choosing which size rear wheel/tire combination will gear you down or up depending on the track. You can also consider doing the transmission flip of 3rd & 5th and put in an "S" 4th to get AFKaSZ gearing--I love mine....

You guys are absolutely right. I guess if the torque drops off that dramatically from 5,000 rpm up, then the best shift point from one gear to the next is at the rpm in the shorter gear that corresponds to the same torque at the lower rpm of the longer gear that you're shifting into. Shift at too low an rpm and the torque in the longer gear is too low and you lose power. Also if you you hold the shorter gear to achieve too high a rpm, the torque in the shorter gear drops off too much before you shift and even though the rpm in the longer gear and the associated torque is higher, you've wasted too much time at too low a torque in the shorter gear and lost too much power there. I'd love to see a bunch of torque curves for the engine loaded up in all five standard gears.