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Hi All,

what does camshaft cruising RPM means?I have a bbc 427 withcamshaft duration [email protected] and would like to installa 5 speed OD transmission to cruise 75mph at 2200 RPM. Rear gear is 3.42.

A friend of mine told me that engine RPM has to be at least 3000 for cruising. Other guy told me that It is fine to cruise at 2000 RPM.

Current RPM at 75 mph is 3250. When I drive 50 mph at 2000 RPM, car runs perfect.

thoughts
 

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You'll have more drag @ 75mph than 50mph, but with a 427 and that small of a camshaft for the displacement you're not going to load the engine down. Heck even a 350 with that cam should still tolerate 2000rpm @ cruise.
 

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67 Camaro SS/RS L78 M20 Convertible
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thats all gigantic displacement engines. even 396. even a 350 sbc.

Important is that the engine feels good at the rpm you want to cruise.
When it feels good and behaves properly, that means that cylinder filling / torque output / combustion stability is proper.
my engine happily accepts throttle and WOT from 1500 rpm up and thats where i cruise.
 

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If your present setup can accelerate up a steep hill from 2000 rpm in high gear you are probably fine.

Single plane or dual plane intake? Rectangular or oval ported heads?? Compression ratio?? More to this than just cam timing.
 

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My Camaro with a 220/230 hydraulic roller in a 383 SBC would drive through town at 40mph in 6th gear with 3.42's (1000rpm).
Never an issue on the highway at 1500rpm/about 60mph.

You will be fine.
 

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1968 Camaro 1975 camaro
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Cruise RPM is essentially where the engine isn't struggling(with that CI and cam I doubt you'd have any problems).
I have a 489 with a 237/243 duration at 0.050 on a 110 that I can cruise down to 1500rpm, as long as oil pressure is decent and the engine stays cool, I let it eat at that speed. It does seem happiest around 2000 where my timing is all in.
 

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67 Camaro SS/RS L78 M20 Convertible
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Cruise RPM is essentially where the engine isn't struggling(with that CI and cam I doubt you'd have any problems).
I have a 489 with a 237/243 duration at 0.050 on a 110 that I can cruise down to 1500rpm, as long as oil pressure is decent and the engine stays cool, I let it eat at that speed. It does seem happiest around 2000 where my timing is all in.
Similar build here: 496, 238/248 110LSA. Also 1500 upwards its fine.

Off topic but i gotta ask: what is your initial, total timing? all in rpm is 2000 i read from your post?
 

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1968 Camaro 1975 camaro
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Similar build here: 496, 238/248 110LSA. Also 1500 upwards its fine.

Off topic but i gotta ask: what is your initial, total timing? all in rpm is 2000 i read from your post?
My initial is about 20 and all in at 35(aftermarket aluminum heads with nice chambers) at 2000ish with 10 degrees of vacuum advanced.
Now this is a fuel injected set up so I am not limited by springs or weights on when the timing comes in.

I also have overdrive, so if I was cruising at that 1500 before, my timing would be at like 22*. I was just playing with it and tried more timing at the cruise RPM, and it liked it. My cruise RPM temps went from 185/180 to 170 and I have a 185 thermostat. I run 14.7:1 AFR at that cruise speed as well.
I have achieved right at 18 with my old set up with that combination(4.10s with a 250/256 solid flat tappet cam). This new one is still with 4.10s, but with the new roller cam that I think MIGHT be able to hit 19!
 

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My initial is about 20 and all in at 35(aftermarket aluminum heads with nice chambers) at 2000ish with 10 degrees of vacuum advanced.
Now this is a fuel injected set up so I am not limited by springs or weights on when the timing comes in.

I also have overdrive, so if I was cruising at that 1500 before, my timing would be at like 22*. I was just playing with it and tried more timing at the cruise RPM, and it liked it. My cruise RPM temps went from 185/180 to 170 and I have a 185 thermostat. I run 14.7:1 AFR at that cruise speed as well.
I have achieved right at 18 with my old set up with that combination(4.10s with a 250/256 solid flat tappet cam). This new one is still with 4.10s, but with the new roller cam that I think MIGHT be able to hit 19!
To set everything in relation: Whats your CR-Ratio, fuel 87-93?, altitude you drive at?

mine is 9.7:1 iron heads, 93 fuel, sea level.

Your setup is not far from a conventional spring setup.
I am about to install a standalone knock sensor system.
Before that i dont dare squeezing the efficiency out of it.
I aim for 16 initial, 34 total at 2500 rpm with 12° extra vacuum advance.
Driveability is already very good but i can feel i leave efficiency on the table..
 

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To set everything in relation: Whats your CR-Ratio, fuel 87-93?, altitude you drive at?

mine is 9.7:1 iron heads, 93 fuel, sea level.

Your setup is not far from a conventional spring setup.
I am about to install a standalone knock sensor system.
Before that i dont dare squeezing the efficiency out of it.
I aim for 16 initial, 34 total at 2500 rpm with 12° extra vacuum advance.
Driveability is already very good but i can feel i leave efficiency on the table..
Mine is 10.25:1 aluminum heads, 91 octane, about 300ft above sea level.

I agree, it isn't too far off from the lightest springs, but since I have set it, I haven't messed with it. The biggest thing is getting the timing to be there at the cruise RPM and light load. I could probably add fuel and it will pull down to 1300, but at that point it won't be super happy anyway.
I had about 15 initial when I started, but it seemed to like about 20 at idle. I just got it to where it drives well in any condition. I haven't honestly tried more timing, but I am not sure if I need it. It doesn't knock unless the fuel is old, fresh fuel cleans it up without any of my input.
 

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The cam in my 350 is about the same and it cruises easily at around 2000. You’re buddy is wrong about cruising at 3000. If that was the case we would not have much use for OD transmissions.
 
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