High rev 318

[Tim_K]

What's a safe rpm to keep a 318 at for 15-20 miles of highway driving? Stock engine, or modified?

I have a stock 318-2 in my '72 Dart 4 door daily driver. I'm going to put a 3.21 geared axle in it in place of the 2.76 axle, and might have it revved up pretty high on the way to work. I'm thinking of 3500 for a sustained 15-20 mile cruise is a safe limit, with maybe some 4000 rpm bursts now and then.

It will eventually get some engine work, to include:

Bored out oil passages, stock volume / pressure pump, hardened oil pump driveshaft.
Full groove tri-metal bearings.
Double roller timing chain
Mild cam (210-216 at 50)
Ported 318 heads and 3" single exhaust from stock manifolds.
Holley 600-650 4 bbl.
New stock or ARP rod bolts.
Moly rings.

I know headers would be better for power, but don't want the hassle of them on a daily driver A body. As long as I get 200-225 Net HP, I'm happy. I think the above oil system mods will make it ok for 3500-4000 rpm cruising speeds.

[72Challenger]

Tim, since you didn't give us all the info I need to figure road speed, I made some assumptions. With 26" diameter tires and an automatic with a fairly loose converter (8% slip), at 3500 RPM you will be going 78 MPH. That burst to 4000 will have you doing 89 MPH. Sounds just like me driving to work! The engine will withstand those levels for a long time, as long as you keep the right amount of clean oil in it, with adequate pressure, don't overheat, and it's not worn out already.

[1972roadrunner]

3.21 gears and 3500 rpm on the highway?!

thats what my roadrunner runs with 4.10's in the rearend....what kind of tranny does it have? it's gotta have some torky gears to turn 2.71's....oy!

[rumblefish360]

DO NOTHING TO THE OIL PASSAGES!
You don't need it. Just a hi-volume pump and thats it. Your done!
A safe RPM is under 3000 RPM.
Keep it mild and she'll last for years. Cam sounds good.

[1972roadrunner]

my back tires are M+S P295/50R15 105S and are about 26 1/4" tall. i have a 727HD tranny with a stock SIZE 3rd and 4.10's in the rearend. at 70 mph, i'm running almost 4,000 rmp. 65 mph is about 3500 rpm... my bands are all racing bands, i have a TCI Street Fighter t/q which stalls at about 3200-3800 rpm. my second gear is 5.1" and the rest are stock sizes...

my brothers car has 3.56's in the rear, and runs about 2500 at 65, his tires are about 27" tall... his 440 has more than enuff torqe to turn the tires. he also has a stock 727.

[72Challenger]

roadrunner - you've mentioned several times that your second gear is 5.1" - just what the heck does that mean?!? I've always heard of gears being expressed as their ratio, your second should be 1.45:1. Are you sure you're not talking about a 5:1 ratio kickdown lever for the downshift into second?

[1972roadrunner]

no, my tranny guy said thats how tall the second gear actually is...i'm not sure what he meant but i can get one hell of a bark when it hits second! it wouldn't do that before, and i also noticed my speed is a little different in second, according to my tach (i don't trust my speedometer all that much so i use my tach to calculate speed....1st gear at 2,000 rpm is about 20 mph, 2nd gear 2,000 rpm is about 32 mph, and 3rd gear (D) 2,000 rpm is about 40 mph.) its really hard to miss my tach so i use it all the time. go to http://tmezz.mezzweb.com/completecar.html and scroll all the way down to see it...

[rumblefish360]

I believe he means that when in second gear, the new ratio is like 5.1. Where as in drive, the know ratio's are 1.1 in the tranny and the rear is 4.10. It = 4.10 in drive.
I think that 1.45 x 4.10 = 5.945 is the correct ratio your thinking of there 72RR. Second gear = 5.9

[Tim_K]

The 72 Dart has a 727 transmission with a stock (2000) stall converter, That part will pretty much stay the same. The tires are 195/75/14's. It may get some 205/75's to raise the effective gear a little bit.

I think 3500 is ok for a 20 mile run. I used to have a 224,000 mile Slant Six in my '71 Valiant, and would run it in the 3000-3200 range for long highway runs. And this was normal for the 114,000 miles I put on that engine.

My normal cruising speed is 70-75, and I want to run it to over 90 sometimes, just to show all the new cars on the road that this old Dart can beat their cars! And of course the occasional run up over 100 if someone wants to try and outrun me.

[72Challenger]

Tim,

Your current tire size works out to about 25 1/2 inches diameter. With 205s you'd be barely over 26. Your converter probably doesn't slip any more than 5%. Using these numbers you should get:


Tire Rpm Speed
195 3500 79
195 4000 90
195 4500 101
195 5000 112
195 5500 124

205 3500 81
205 4000 92
205 4500 104
205 5000 115
205 5500 127

So normally you should be just under 3500 with either tire. And if you do go crazy, well, let's just say the potential's there. I hope you plan on doing a brake upgrade as well!

[1972roadrunner]

ok, that sounds better...thanx for clearing that up...


sounds like my dads truck, it has the go! but the WHOA is being worked on!