For the guys living in the Rockies.......

Orionn

Vehicular Packrat
City
Ann Arbor/Ypsilanti
State
Mi
#1
Could you please tell mewhat R&P gear rotios are that your running, and what your engineis.


I am trying to decide what ratio I want to run with 35" tires and a SBC (carburated).
I want to attend the SOA event and the Scrambles event, so I NEED to get decent mileage or I just wont be able to afford the fuel.
Not to mention, also being able to perform well at the different altitudes.

My axle have 3.55 gear and I am looking at 3.73 gears beings I have a a nv4500 trans (granny low) to make up for the pavement frindly ratio.

I'd like 4.10's, but I am afraid that the engine rpms will be too high on the highway for decent mileage.

I need some input guys, I'm running out of time :eek:

BTW, This is a REALLY NICE Gear Calculator

Oh, and how's your carbed engines running at altitude? any ideas on how much I need to lean the carb to compesate for the thinner air up there?
:thumbsup:
 
Last edited:

Kane

CJ-8 Member
CJ-8.com Member
City
Berlin
State
ct
#2
4.10 for 35's with an OD tranny sounds pretty good. Have you thought of getting a small CFM carb for the trip there and back? If you can get your hands on a small Edelbrock four barrel. They are spread bore so the primaries are smaller and sip fuel when cruising. I switch from a Holley truck avenger to this carb for the street and I gained almost 3mpg for the same sized carb. Just a thought.

Oh and don't forget. That big of an altitude change you will need to bring some jets with you. I would guess you would need to drop 2 jet sizes to run right. I moved to Utah in the 90's and I dropped to jets sizes while living there.
 
City
Reno
State
NV
#3
If i'm correct... the NV4500 has an overdrive with 0.73 ratio?

with 4.10s and 35" tires you'd be running 1870rpms at 65mph

That's pretty low rpms! I'd even consider 4.56s with that overdrive

What engine are you running? Cause if your engine's up for it run the 4.10s! You'll get awesome mileage!
 
Last edited:

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#4
I'll tell you what I know: 258 with an MC2150. T4 tranny and 31" tires. I don't know what my axles are geared at, never checked...I suppose it's something I should consider doing sometime. I operate mainly between 5-7K and have had no issues with my set-up.

I will say that the MC2150 should make the altitude changes idiot proof as far as the carb is concerned. I can't remember - do you know if you have an altitude grounding wire in your engine bay? (Altitude jumper info) Are you Nuttered? Either way, timing will have to be adjusted, too, either manually or possibly with the grounding wire.
 
Last edited:

Orionn

Vehicular Packrat
City
Ann Arbor/Ypsilanti
State
Mi
#5
4.10 for 35's with an OD tranny sounds pretty good. Have you thought of getting a small CFM carb for the trip there and back? If you can get your hands on a small Edelbrock four barrel. They are spread bore so the primaries are smaller and sip fuel when cruising. I switch from a Holley truck avenger to this carb for the street and I gained almost 3mpg for the same sized carb. Just a thought.

Oh and don't forget. That big of an altitude change you will need to bring some jets with you. I would guess you would need to drop 2 jet sizes to run right. I moved to Utah in the 90's and I dropped to jets sizes while living there.
I am running a SBC 350 V8, and I already have a 600 cfm Eidelbrock carb on it, though its in desperate need of a overhaul from sitting.
I'll have to bring a set of jets with me, then. Thanks for the heads up. I forgot all about rejetting for altitude.

If i'm correct... the NV4500 has an overdrive with 0.73 ratio?
with 4.10s and 35" tires you'd be running 1870rpms at 65mph
That's pretty low rpms! I'd even consider 4.56s with that overdrive

What engine are you running? Cause if your engine's up for it run the 4.10s! You'll get awesome mileage!
I have a 'Stock', rebuilt SBC 350 V8. By stock I mean its a replacement egine the previous owner got from Auto Zone or something like that.
So it was rebuilt to the Stock Factory specs for a 1970 4x4 Blazer, 4 bolt main, unknown cam, I think its bored .010 over. What I don't know is where the RPM 'Sweet Spot' is for the Chevy 350, I am shooting for 1800- 1900 rpm assuming this is where I will get the best comprimise of power, performance, and economy. I figure that engine should have the torque to turn the lower gears on the highway. but I also know that lugging the engine is not good for mileage or longevity of the engine. Offroad, I know that the engine will turn the granny low transmison with no problems. Even now, running badly from a dirty carb it can smoke the 35 MTr's on dry pavement in 2nd gear. Its got plenty of power :drool:


I'll tell you what I know: 258 with an MC2150. T4 tranny and 31" tires. I don't know what my axles are geared at, never checked...I suppose it's something I should consider doing sometime. I operate mainly between 5-7K and have had no issues with my set-up.

I will say that the MC2150 should make the altitude changes idiot proof as far as the carb is concerned. I can't remember - do you know if you have an altitude grounding wire in your engine bay? (Altitude jumper info) Are you Nuttered? Either way, timing will have to be adjusted, too, either manually or possibly with the grounding wire.
As I dont have the AMC 258, so I wont be running the MC2150 carb. I have to agree with you with the MC2150 carb, I had one on my last AMC 304 V8, and it was great.
Also, I have none of the factory harness left under the hood. The previous owner took care of all that (and left me a tangled mess to sort out and clean up)
I am running a factory GM HEI distributer (vacume advance). I have never heard of that having an altitude setting like your describing, but then again, I waas never looking for it either.
I'll have to llook it up and see how GM handled altitude back in the 70's on stock HEI engines.

OH, on a side note, to get a deeper crawl ratio, I am considering a doubler in front of the T-case.

Thanks for your input on this.
Keep the thoughts comming thx everyone! :cheers:

:popcorn:
 
Last edited:

OGRES

Ramblin' Wreck
LIFETIME
City
Suwanee
State
GA
#6
Orionn,

I was running 4.10's with my AMC 304 and 35's...I was around 2,100 to 2,300 RPM's at 65 to 70 mph. I never ran faster than 70 but I could have pushed it. 65 mph was a good point that got me pretty good mileage (for an AMC V8...14 mpg at one 60 100 mile stretch).
 
City
Reno
State
NV
#7
I have a 'Stock', rebuilt SBC 350 V8. By stock I mean its a replacement egine the previous owner got from Auto Zone or something like that.
So it was rebuilt to the Stock Factory specs for a 1970 4x4 Blazer, 4 bolt main, unknown cam, I think its bored .010 over. What I don't know is where the RPM 'Sweet Spot' is for the Chevy 350, I am shooting for 1800- 1900 rpm assuming this is where I will get the best comprimise of power, performance, and economy. I figure that engine should have the torque to turn the lower gears on the highway. but I also know that lugging the engine is not good for mileage or longevity of the engine. Offroad, I know that the engine will turn the granny low transmison with no problems. Even now, running badly from a dirty carb it can smoke the 35 MTr's on dry pavement in 2nd gear. Its got plenty of power :drool:


Thanks for your input on this.
Keep the thoughts comming thx everyone! :cheers:

:popcorn:
In that case go with the 4.10s for sure :thumbsup:

You shouldn't have any problems with lugging. Good luck with the decision :cheers:
 

b.b.chev

Legacy Registered User
City
Black Forest
State
CO
#8
My wifes CJ5 has an AMC 360, t-18 4spd with 4.27 gears and 33 inch tires . At 65 M.P.H it runs about 3000 r.p.m. gettng roughly 15 m.p.g. on the highway. As far as jetting goes I don't think I would mess with it for the short time that you will be here for the event, I would consider bringing a timing light with you though , I generally run a stock engine like yours with about 10 to 12 degrees advance here .
 

Kane

CJ-8 Member
CJ-8.com Member
City
Berlin
State
ct
#9
You motors sweet spot will be where your distributer makes full mechanical advance. On most older small blocks it is aroung 2200-2400 rpms. When you acheive full mech advance and then the vacuum advance reaches max your motor will be sipping fuel and will have the most complete burn. A stock 350 generally has about 35-38 degrees mechanical advance with about 10 degrees vacuum advance for a 45-48 total. If you take a timing light and check your motor this will help. make sure you pull the vacuum advance hose off so you only get mechanical advance. Rev your motor while watching the timing marks on the balancer. Someone may have to watch your tach. When the advance stops then have that person read your RPMs. That will be where you want to be. If you harmonic balancer does not have the full scale timing marks you can buy a timing tape from Summit or Jegs that you can plce on the balancer.
 

Orionn

Vehicular Packrat
City
Ann Arbor/Ypsilanti
State
Mi
#10
Thanks for the information guys :thumbsup: every little bit will help me.

Kane, What your telling me is EXACTLY the type of information I am looking for.

I'll have to go thrue the HEI disty to be sure its working properly first then, and clean the carb, and fix the exhaust to get a good baseline, then build on that for the gearing.
sounds nuts, :crazy:

If anyone else has information they would like to share, please do.

I wonder if I should just upgrade to a DUI HEI disty?
 
City
White Rock
State
NM
#11
In general you can expect about a 2% decrease in power per 1000' in elevation increase. A couple of tricks for dealing with it would be about a 2* advance in timing/1000ft but not more than about 12-14* advance in initial advance. You can also play with spark plug heat range but it's not worth the trouble for a short visit. As far as the carb, you may want to run your float level a little below normal and be sure you have good fuel pressure, perhaps an electric booster pump even, as vapor lock becomes more of a problem as you go up in altitude as well.

I run 4.10s in my scrambler with the 258, stock carb and with the stock gears, a t5 and 33s I could get a reliable 18 mpg if I was careful, with the 35" and 4.10s gears (and quite a bit more weight) it dropped to about 16-17mpg. Now with the auto and 4.10s, still stock carb, I see 14 mpg plus or minus. I live at ~6500ft and most of the numbers are based on going down hill to Moab or down and back up to Silverton/Ouray.
 

Orionn

Vehicular Packrat
City
Ann Arbor/Ypsilanti
State
Mi
#12
Thx Trust;
Sounds like I wont miss the power loss too much with the altitude untill we hit the passes.

I am already running an electric fuel pump at the tank, so delivery should not be a problem. Thats good info though for other guys still using an engine driven pump.

You know, I am not looking for stellar mileage on the trip, but I woud like better than 12mpg or so. I am hoping for 16mpg or so across the plain states. With prices reaching an estimate of $4+ by July, I need to try for the best I can get.

Thanks again to everyone for the information, y'all rock! :cool:
 

SeeJayAte

CJ-8 Member
CJ-8.com Member
SOA Member
City
Greenfield
State
In
#13
I'm running almost the same combo you are---350SBC, NV4500, 35's, and 4.56gears. I drove this rig back from Denver to Indiana when I bought it and the 4.10 gears would have been better on the highway, but the 4.56's aren't all that bad. My 8 seems to like 55-60 mph as eveything feels good at that speed. Not the best for making a quick trip, but if I'm in a hurry I'd really just rather drive something else anyway!:rotfl: I would recommend the 4.10's for the trip, but the 4.56's once you get there!:shrug: Otherwise, I plan to install a Percy's Ajustajet on the Holley carb(570cfm) so I won't have to do any jet changes in Colorado. Might bump the timing a couple of degrees too before then, if I get any detonation I can always back it off easily enough. I'll be trailering my rig out there, so I don't exactly face the same challenge that you do. If there's anything else I can think of I'll be sure to post it up.

Steve
 

Orionn

Vehicular Packrat
City
Ann Arbor/Ypsilanti
State
Mi
#14
Steve;
Thanks for the info. What kind of mileage you getting with your setup.
just a good estimate if you dont know. It will give me something to shoot for when making changes.

As for changing gears when I get there. I may be able to do that, I made a change of plans, I am running a Ford 9" rear axle now. I could carry an extra 3rd member with the 4.56's already setup in it and just swap out the third member when I get there and swap the other back in for the trip home. Its a fair amount of work, and there is the oil to deal with, but definatly doable and somethng I have thought of. I would set the front up to match the trail gears of course :)


When are you leaving? several of us from the Midwest have talked about a wagon train to the event....safety in numbers and all that in case I break...I mean someone breaks down :rotfl:
 

SeeJayAte

CJ-8 Member
CJ-8.com Member
SOA Member
City
Greenfield
State
In
#15
Sorry for not responding sooner, had a busy week.:banghead: My guess on mileage would be about 15-17 on the road, not great but not bad considering. I've often thought I'd be better off with 4.10's in the axles and 4:1 transfer case gearing but that would be a fairly exspensive switch that I just can't justify right now. I really like your idea of the quick? change rear differential, sounds like something I would do if I had a removable 3rd member axle!:smokin: As far as the Midwest caravan, I don't know yet when I'll be leaving but I am also going to the Colorado Scramble the week before. My plan is to park the tow rig in Loveland or somewhere just on the east edge of the mountains and drive my 8 from there, so I won't have to tow thru the mountains. I figured a RV-storage type place would be good(secure) and not too exspensive for a couple of weeks. I'm certainly open to other suggestions if anyone has some.:thumbsup:

Steve
 

Randyzzz

Blown Budget
LIFETIME
CJ-8.com Member
SOA Member
City
Redmond
State
OR
#16
On the edelbrock carb, check your metering chart. You may be able to get away withg just a rod change, save you the trouble of going too deep into the carb.

The DUI distributor is basically a GM HEI, so I don't see any advantage there. MSD makes a cool variable advance module that allows 15* timing change by twisting a knob...

http://www.summitracing.com/parts/MSD-8680/


But it only works with one of their ign boxes. I had great results with a MSD billet distributior and 6AL Ignition box- pricey but reliable.
 
Top