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High elevation, or... learn me on carbs


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18 replies to this topic

#1 KCARNS

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Posted 19 November 2010 - 04:16 PM

Hi everybody.....


I have a hitatchi carbed 86 wagon and am thinking about moving to high up colorado (10,000 ft) for the winter from around 2000 ft. Story short, I am wondering if some of you fuel/air mixture experts could give me some advise. Should I rejet my carb before I leave, do it sometime halfway through, or when I'm all up high?

Secondly, just how do I go about rejetting? Or should I just up and by a weber (although funds are tight right now)

any advise is appreciated,

Thanks

#2 Loyale 2.7 Turbo

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Posted 19 November 2010 - 04:25 PM

If the Carb is OK I don't Believe it would need any Adjustment, but if you can Weberize it, your EA82 Will Perform Much Better.

Kind Regards.

#3 ferox

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Posted 19 November 2010 - 09:36 PM

Sounds like Leadville or Silverton or something. I lived in Durango for a while which is only 6500 feet and even that elevation made a huge difference in performance. I think you will want the Weber with a manual choke, and you might try calling some shops in the area you plan to move to or other high elevation Colorado towns to find somebody that might be able to give you some advice on jetting. It might take a few calls to find someone that knows about carbs, but due to the 4x4 scene I am sure you can find someone.

#4 GeneralDisorder

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Posted 19 November 2010 - 09:42 PM

You can't easily rejet a Hitachi - where would you get jets? It's not like these things are availible in the aftermarket.....

You best bet is a Weber or (even better) fuel injection.

GD

#5 Petersubaru

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Posted 20 November 2010 - 04:24 PM

I just came back from Colorado and was wondering why they sell regular gas starting with 85 octane (mid-range is 87)..does lower octane help in higher elevations...

#6 GeneralDisorder

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Posted 20 November 2010 - 07:01 PM

Lower octane can be run at high elevations because the cylinder pressure's are lower. It's also more volatile and technically contains more BTU's per gallon than high-octane. You should always run the lowest octane your engine can stand without pinging or affecting timing because it is both cheaper and contains more energy and thus will yeild better mileage. It might not accelerate as well due to the inability of the ECU to advance timing without knock but the cruise MPG should go up.

GD

#7 KCARNS

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Posted 21 November 2010 - 03:12 PM

Yep, Leadville.

So at 10,000 feet will my car be even able to move?:grin:

Now the question is do i make the trip with my car as is or slap on a weber to get out there and then rejet it. For those of you who have done to swap is it reliable enough to make a road trip on, i'd be putting one on and heading out within the next week. Probably should have thought of this earlier but thats the way it goes sometimes.

Thanks for the responses

#8 naru

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Posted 21 November 2010 - 03:37 PM

EA-81s operated mainly above 4000' were required to have "high altitude kits" by the EPA. I imagine the same applied to EA-82s.

I think your car will run at 10,000'.Might be a little rich.

Might want to check out TSB #025888 from JAN 88 re high altitude kit.

Edited by naru, 21 November 2010 - 06:24 PM.


#9 GeneralDisorder

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Posted 21 November 2010 - 07:22 PM

*I* could put on a Weber and drive across America the next day - the *Weber* is a wonderfully simple unit and if you use a brand new one or a quality rebuild you are unlikely to have any issues with it directly - however the quality of the *installation* is what creates the "reliability"..... YMMV according to your skill and availibile resources. If all you have is an apartment parking lot and a crescent wrench - might not be a wise move :rolleyes:.

GD

#10 ferox

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Posted 22 November 2010 - 02:31 AM

Yep, Leadville.

So at 10,000 feet will my car be even able to move?:grin:

Barely, but if you are just running to Copper and back you will be fine. You have to go slow in the snow anyway. Not to lecture, but be careful. It's not PNW snow and it can catch you off-guard. It's hard to describe how slippery it is, and a lot of the roads where you are going are just chiseled out of a cliff face with no guard rail. It's a very cool place nonetheless.


Now the question is do i make the trip with my car as is or slap on a weber to get out there and then rejet it. For those of you who have done to swap is it reliable enough to make a road trip on, i'd be putting one on and heading out within the next week. Probably should have thought of this earlier but thats the way it goes sometimes.

Thanks for the responses

It will be frozen in Leadville, so if you have the skills, you should put the Weber on before the trip. But as GD pointed out, if you are not sure of your abilities it might be better to get there and then do the swap. It doesn't sound like you have enough time to get the Weber and do the swap before you leave anyway, so I hope you have a place to work on cars where you are going...preferrably heated.

Make sure you get the manual choke. Warming up your car is a big deal when you are 10,000 feet up in the Rockies in winter.

#11 GeneralDisorder

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Posted 22 November 2010 - 02:41 AM

+1 on the manual choke - I really prefer them on the Weber.

The electric's are alright but seem to want adjustment seasonally and are never quite perfect. I set the electric's a little light (so they pull off quick and don't affect mileage as badly) and then allow them to warm up for 60 seconds or so on the fast idle before driving. Not a huge deal but I still don't like them.

With the manual I just set it, start it, maybe add a fine adjustment, and I'm off. No fuss. Plus the installation is easier and they fit better - not at all close to the distributor cap on the EA81's and don't interfere with the PS on the EA82's. All around a cleaner, easier option.

GD

#12 jdemaris

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Posted 22 November 2010 - 09:46 AM

Hi everybody.....


I have a hitatchi carbed 86 wagon and am thinking about moving to high up colorado (10,000 ft) for the winter from around 2000 ft. Story short, any advise is appreciated,

Thanks


Any engine that is not turbocharged loses 1% power and efficiency for every 328 feet above sea level. So that gives you a 30% power loss, if you compare it to driving somewhere AT sea level. Most controls that auto makers put into high-altitude engines simply retard timing. You still lose power.

Only fix is to put up with it, or get a turbocharged car. Back in the 50s, high altitude engines got fixed with #1 - "altitude compensators" that are now called "turbochargers", or #2 special high altitude pistons. But, if you had those pistons - you could damage the car if you drove it back down into low country.

Rejetting your carb won't gain you any power, but it can prevent some waste.

#13 naru

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Posted 22 November 2010 - 11:54 AM

Most controls that auto makers put into high-altitude engines simply retard timing.


This is backwards.If anything,timing will be advanced at higher altitudes.
For instance,an 84 ea-81t will advance timing 5 degrees above 4600'.
Carbed cars will lean the mixture if they are altitude compensated.

If swapping carbs,I would be concerned about the lack of carb pre-heat that comes w/the hokey weber airfilters.

#14 GeneralDisorder

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Posted 22 November 2010 - 12:11 PM

If swapping carbs,I would be concerned about the lack of carb pre-heat that comes w/the hokey weber airfilters.


Some members have had issues with that at higher altitudes and low temps. There are ways to mitigate it though.

GD

#15 NV Zeno

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Posted 22 November 2010 - 06:37 PM

Some members have had issues with that at higher altitudes and low temps. There are ways to mitigate it though.

GD


JAFO...:popcorn:

#16 zyewdall

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Posted 22 November 2010 - 07:09 PM

I've run stock (Hitachi) EA81's at 9,000+ feet quite a bit (I live at 9,300 myself) and they run fine.... I have no idea if mine were jetted for high elevation or not from the facotry, but I never noticed any issues with running with mine. I think the highest I ever had mine was around 12,500 or so, over trail ridge road through rocky mountain national park... still ran fine, up hills and all.

On the other hand, it does reduce the power. A LOT... A stock EA81 at 12,000 feet makes an EA-81 at sea level seem quite peppy, which in turns makes almost any other vehicle ever made seem peppy:grin: If you're not in a hurry... no problem. If you are okay taking 10 minutes to achieve 55mph..... It won't stop or anything... but it might annoy the guy behind you in his 500HP supercharged range rover. The water heated throat on the hitachi's do seem to be quite immune from icing, compared to some other carbs. I've never had issues with them starting in the cold either (assuming everything else is good, of course)

#17 jdemaris

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Posted 23 November 2010 - 09:04 AM

This is backwards.If anything,timing will be advanced at higher altitudes.
For instance,an 84 ea-81t will advance timing 5 degrees above 4600'.
Carbed cars will lean the mixture if they are altitude compensated.


I said "most", not "all" and my comments are not Subaru-specific. They are specific to gas engines with carbs - and diesels with mechanical injection. Most of them that I have specs for, do several things when elevation goes over 4000 feet IF they have a high-altitude package. Timing gets more advanced at cold starts, less adancced when warm at higher RPMs, and exhaust gasses to the EGR are reduced via high-altitude control solenoids. Also, some diesels have altitude-sensing fuel solenoids that cut back on fuel delivery as a vehicle climbs. I suspect newer gas engines with electronic fuel injection do the same.

Subaru is often a bit "different" then ofther makes, so it may well be that they met emmissions laws differently then other compnanies. The high altitude packages, for the most part in the USA, were to meet emmissions regs and not necessarily make the cars/trucks run better. Considering Subaru made the last legal cars in the USA with carbs (1989 I believe), and the first with OBII in 1994 or 95, it's obvious they don't always follow trends.

Regardless of all that, without raising ether the mechanical compression ratio - or raising the "effective" compression ratio with a turbo - the engine is going to lose a lot power as it goes up.

#18 naru

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Posted 23 November 2010 - 09:32 AM

I said....Timing gets.... less adancced when warm at higher RPMs


This is illogical.
Can you provide an example/theoretical support?

#19 naru

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Posted 23 November 2010 - 10:04 AM

I am starting to believe that some motors do superimpose a high rpm timing retard on the otherwise advanced high altitude timing.The theory is a little obtuse,though.

Timing advance is part of most high altitude mods.
Any motor w/high altitude high rpm timing retard also has high altitude timing advance.Not vice versa,IMO.

Still interested to hear of some examples/theory.




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