Ford Muscle Cars Tech Forum banner

1 - 3 of 3 Posts

·
Registered
Joined
·
15 Posts
Discussion Starter #1
The spec sheet says this cam kit makes power to 5500 RPM and valve float occurs at 6500 RPM, so where do you set the rev limit?

Here's the build-up:
302W bored 0.030 9.6:1 comp. estimated
Stock cast iron heads(ported, gasket matched)
Hypro.Piston(Fed.Mogal, valve relief,flattop)
Edelbrock Performer 289 intake(re-using)
Holley 600cfm 4160(choke&horn removed)
Reconditioned con. rods. w/hvy dty bolts
Tri-Y headers
Scorpion Roller Rockers
Now for the cam:
CraneCams PowerMax H-288 Hydraulic flat tap.
Specs are:
3200-3600 cruise RPM
Basic RPM 2500-5500
Gross Lift Int./Exh. .488
Degrees Duration @ .050 Int./Exh. 226 deg.
Degrees Advertised Int./Exh. 288 deg.
Lobe Separation 108 deg.
Intake Open/Close at .050" 10/36
Exhaust Open/Close at .050" 46/0

gearhead
67 Fastback
 

·
Premium Member
Joined
·
2,216 Posts
Well you don't want to run it until the valves float. What it will really pull you would either have to find on a dyno or just by feel. Starting at 5500 for a top end keep turning it up in 200 rpm increments until it quits consistently speeding up but stop below 6500. If its all put together fairly well it should pull 500 rpms over spec on the drag strip so that puts you shifting at around 6 grand. Make sure you actually do pull it before 6500 because that small amount of time between eye sees tack and arm pulls shifter can cause you to over rev it.
 

·
Registered
Joined
·
46 Posts
With the rest of your combo, depending on your valve springs and accuracy of rocker arm geometry blueprinting, it is likely that you can spin this engine up to around 6200 rpm before significant valve bounce and valve train component separation begins.

However, there's probably no point in doing so. With your ported stock iron heads and a Performer manifold, the engine will be past its power peak probably by 5500 rpm, if not sooner. It won't go any quicker if you rev it higher, so why put the additional strain and wear on the engine? I'd set the rev limiter around 5700 rpm and plan to shift sooner than that.

The ideal rpm to shift depends on the shape of your torque curve. What you want to accomplish is to keep the maximum AXLE torque applied while accelerating. This is the combined function of your engine's output and the overall gearing to which it's coupled. That can mean shifting at different RPMs in different gears, depending on the percent of retained rpm after the shift in each gear.

I wrote a (rather long...probably boring to some) technical explanation of how to figure optimum shift points (along with explaining the related math) in a message reply on this forum, perhaps a month ago. It was under a topic, like, "What rpm should I shift," or something to that effect. If you're really interested in getting maximum performance with whatever combo you're running...it might be worth a read.

Although less glamorous than passionate opinions and less exciting than some of the "black magic" myths that we all (myself included) tend to cling to sometimes, simple physics applied with sound engineering math doesn't lie. (That's how we got all the wonderful factory performance cars that exist today, don't ya' know)!

Steve
 
1 - 3 of 3 Posts
Top