What's your enjoyable HWY cruising RPM?

DocDirk · #1 (**permalink**) 04-15-2009, 07:59 PM

I have a 2.75 rear end in my West Coast which allows 65MPH cruising at about 2250 RPM, and my 533 BB seems not to mind at all. Low end response isn't what I'd like it to be so I'm thinking of a 3.33 which would put me at about 2750 RPM in top gear, 1:1, and I bet it would give me a lot more low end streetdriving seat of the pants fun. Not sure if 2750 would get old after a while as my car is new, shorter test drives are all I've done so far but planning a long Route 66 trip for this summer.

What RPM do you like to cruise at?

Thanks!

Dirk

CHANMADD · #2 (**permalink**) 04-15-2009, 08:06 PM

I can tell you after owning my car for 20 yrs I went from a 3.33 to a 3.07 to a 2.88 and I still use the overdrive on the freeway, with all the power I need in the lower gears. Unless youare trying to win some drag racing championship the high rpms get old very soon on the freeway,,, that is of course assuming that you are going to use the car as a car and not a trailer queen..in which case it would'nt make any difference!

patrickt · #3 (**permalink**) 04-15-2009, 08:20 PM

Quote:

Originally Posted by CHANMADD

Unless youare trying to win some drag racing championship the high rpms get old very soon on the freeway,,,

I agree, and that's exactly why I went with the .64 fifth gear with my TKO. 70mph is just a hair over 2000rpm and I can actually chat with my passenger -- the wind noise is louder than the pipes. And for a quick blast up to triple digits you just drop it to third. And if you really want to show off, you put it in third, rev it to 6000, and then pop the clutch....

undy · #4 (**permalink**) 04-16-2009, 03:59 AM

Quote:

Originally Posted by patrickt

the wind noise is louder than the pipes.

Then yo pipes tain't loud 'nuf..

I like around 2200 rpm.. The 482's not in her power band but she's also not in her buck 'n studder band either. A quick downshift will put me where I want to be. I have a TKO600 with a 3.25. I too have the .64 OD but am wishing I had a .82 now. I got the .64 when I had the 3.73s and it was fine. Fast forward to the 3.25s and the .64 is a little tall for the local 55 mph freeways. It's not a long trip car (thus far) and it only sees local freeway duty, say 65 max. It's not enough of a bummer though to cause me to change it.

Oh! .. and btw, I can ALWAYS hear my pipes

trularin · #5 (**permalink**) 04-16-2009, 06:25 AM

We long trip once in a while. I am at 2700 ( or there abouts ) with a TKO600 with a .64 final.

I like the .64. I get decent millage when I am on the HWY and I can still down shift and put my foot into it if I want to.

patrickt · #6 (**permalink**) 04-16-2009, 07:44 AM

Quote:

Originally Posted by trularin

.. and I can still down shift and put my foot into it if I want to.

You should try dumping the clutch at highway speeds. Take it from me, nothing brings out the grins and 'thumbs-up" from the troopers like a quick bit of wheel spin at highway speeds.

Slick61 · #7 (**permalink**) 04-16-2009, 08:45 AM

I'm running the 0.82 overdrive & a 3.73 rear end. I've got a snotty cam which is NOT happy below about 2400 rpm. I turn about 3k on the freeway at 75 mph... is just right... engine's in the sweet spot, and it sounds WONDERFUL!

jhv48 · #8 (**permalink**) 04-16-2009, 09:58 AM

I keep going back and forth between the .82 and .64 fifth gear ratios.

With my 3.73 rear end, and a moderately cammed engine, I can cruise at 75 mph on the freeway (with the .64 fifth gear) and still hear myself think. Mileage is good and the noise is kept to a minimum, somewhat. Need power, downshift and go.

HOWEVER, when flying on mountain roads, fifth gear is all but worthless on those long straightaways. Too big an rpm dropoff.

Wish there was a .73 fifth gear ratio so I could go somewhere in the middle.

patrickt · #9 (**permalink**) 04-16-2009, 10:13 AM

Quote:

Originally Posted by jhv48

With my 3.73 rear end, and a moderately cammed engine, I can cruise at 75 mph on the freeway (with the .64 fifth gear) and still hear myself think. Mileage is good and the noise is kept to a minimum, somewhat. Need power, downshift and go.

HOWEVER, when flying on mountain roads, fifth gear is all but worthless on those long straightaways. Too big an rpm dropoff.

Yes, it's important for those on the fence post with the TKO's fifth gear to look at their rear end ratio, tire size, and engine's behavior in the low 2000's before making a final decision and then realize that the .64 is only for pleasant cruising (and the occasional visit to the salt flats

).

Bob In Ct · #10 (**permalink**) 04-16-2009, 06:48 AM

I've got a 0.68 OD in front of a 3.73 rear. With the 275/60-15s I'm running I turn about 2,200 RPM at 70 MPH (I get a power stroke about every 8 inches I go down the road). This allows me to keep up with the guys on Long Island whenever we join them for a ride. If I need to go, I can drop down to 4th and be 1:1.

Bob

Tony Aprile · #11 (**permalink**) 04-16-2009, 07:42 AM

I have a .82 OD with 3.27 gears. Rear tires are 275/60-15s and turning 2,500 RPM's at 75 MPH.

I had the same combo as Bob in CT but changed to a TKO600...now with a 2.87 first gear it's a bit more usable and no 1000 rpm drop from 4th to 5th gear...

...and Bob if you don't want to bring your cobra over on the ferry...my passenger seat is usually vacant.

joyridin' · #12 (**permalink**) 04-16-2009, 02:15 PM

I have 4.56's in the rear and a .56 O/D. Cruises at just about 2300 at 70 mph. The 4.56's are about to be gone and 3.90's installed. That should drop it another 300 RPM at 70.

jhv48 · #13 (**permalink**) 04-16-2009, 02:28 PM

Maybe he thinks he has a 4 speed tranny and never used fifth!

YerDugliness · #14 (**permalink**) 04-16-2009, 03:02 PM

I know he knows it's a 5 speed. When I emailed him, mentioning how much higher RPM he was claiming than most report, he responded thus:

"Doug,

I rarely take the Cobra out on the highway, so my estimation was a guess."

I'm feeling much better about this all the time, with numbers like those reported by Joyridin' I'm sure my contact must be mistaken. According to my calculations, our final drive ratios would be in the same general range (his 4.56 X .56 OD = 2.55 final ratio, my 3.70 X .68 OD = 2.51 final ratio), so I'm expecting numbers pretty close to those reported in Joyridin's post above.

Thanks, guys!

Dugly

jhv48 · #15 (**permalink**) 04-16-2009, 03:13 PM

Obviously driven very sanely then.

In my car I know exactly how many rpm's I'm turning and what speed I'm going when I hair out and back off of the throttle!

YerDugliness · #16 (**permalink**) 04-16-2009, 03:25 PM

Looking forward to that experience

!!

Dugly

jhv48 · #17 (**permalink**) 04-16-2009, 03:39 PM

You'll love it!

patrickt · #18 (**permalink**) 04-16-2009, 04:08 PM

YerDugliness -- as a general rule, most owners of Cobras kinda know their car, and know things like RPMs at different speeds, and even take it out on the highway.

Remember, not everybody tells the truth when selling a used Cobra. Sooooo, keep you eyes open and don't get swept away by the allure of the deal. There are plenty of Cobras out there and if you start to feel like you're not getting the full scoop, then you're probably not.

DocDirk · #19 (**permalink**) 04-16-2009, 10:06 PM

Well yep thanks for all the inputs, I'll keep my 2.75 rear end and work on improving engine breathing in/out to improve that response...my wiffie and I are planning some leisurely long travels and she ALREADY thinks my car is too lound even with the restrictive baffles (that I'm going to enlarge)....what price a noise cancelling set of BOSE earphones for her??

Thanks again!

Dirk

jhv48 · #20 (**permalink**) 04-16-2009, 10:27 PM

Quote:

Originally Posted by DocDirk

Well yep thanks for all the inputs, I'll keep my 2.75 rear end and work on improving engine breathing in/out to improve that response...my wiffie and I are planning some leisurely long travels and she ALREADY thinks my car is too lound even with the restrictive baffles (that I'm going to enlarge)....what price a noise cancelling set of BOSE earphones for her??

Thanks again!

Dirk

About $300, and well worth it!