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09-19-2019, 02:40 PM
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#1
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Senior Member
Join Date: May 2019
Posts: 103
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Increasing MPG - 1994 P30 454
Getting around 6 mpg in a 25 foot Itasca Passage (1995) and want to improve this as others in the Uk are getting double this. I'd be happy with 10 so what re the most obvious things tho change/upgrade. I'm looking at Tri-y from Doug Thorley to increase torque but to help with engine and cab temps and I have a manifold gasket leak so its an obvious upgrade.
Look pretty stock as it is and I've changed a fair amount of consumable but I need to look at other options.
Its a 7.4 Chevy big block, HEI. Not really had any experience so any help much appreciated. Seems to run well but ticks under load (which I suspect is the gasket) but is quiet when cruising.
FFG
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09-19-2019, 02:59 PM
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#2
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Senior Member
Join Date: Aug 2015
Location: Phoenix, Oregon
Posts: 2,207
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I would think it should do better without doing anything except possibly a tune up and timing.
We just sold our 454 with TBI powered 26' Flair which averaged 7.5 mpg on several OR to WV and back trips at 70 MPH. Ours had OD and ran at about 2500 RPM at 70 MPH. Gearing can make a difference.
Steve
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1994 30' Monaco Dynasty, 5.9 230 HP Cummins, MD 3060, 1992 Geo Tracker.
1996 Dodge Cummins 2500 with 1996 Lance 945 camper
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09-19-2019, 03:04 PM
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#3
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Senior Member
Country Coach Owners Club Solo Rvers Club iRV2 No Limits Club
Join Date: May 2011
Location: Vancouver, WA
Posts: 37,725
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6 mpg sounds about right for that vintage in a MH.
__________________
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft, HWH Active Air
Charter Good Sam Lifetime Member, FMCA,
RV'ing since 1957, NRA Benefactor Life, towing '21 Jeep JLU Rubicon Ecodiesel
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09-19-2019, 03:12 PM
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#4
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Senior Member
Monaco Owners Club
Join Date: Oct 2014
Location: Rigby, Idaho
Posts: 3,902
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There should be a cold air snorkel bringing air to the air cleaner. If the engine is breathing hot engine compartment air, your power and mileage will decrease. I have the same motor in my 95 Suburban and usually get just under 10mpg with normal around town and highway driving. I have about 275,000 miles on it and it's always been about there. Anyone getting the same 10 mpg or more in a 25' motorhome is a bit unbelievable to me. I'd have to see it to believe it.
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Cheers,
TonyMac
2006 Monaco Safari Cheetah 40PMT
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09-19-2019, 04:07 PM
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#5
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Senior Member
Join Date: Aug 2016
Posts: 1,703
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Quote:
Originally Posted by FFG
Getting around 6 mpg in a 25 foot Itasca Passage (1995) and want to improve this as others in the Uk are getting double this. I'd be happy with 10 so what re the most obvious things tho change/upgrade. I'm looking at Tri-y from Doug Thorley to increase torque but to help with engine and cab temps and I have a manifold gasket leak so its an obvious upgrade.
Look pretty stock as it is and I've changed a fair amount of consumable but I need to look at other options.
Its a 7.4 Chevy big block, HEI. Not really had any experience so any help much appreciated. Seems to run well but ticks under load (which I suspect is the gasket) but is quiet when cruising.
FFG
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Generally I'm getting 8 mpg on the back roads with some stop and go in the towns and villages. On the parkways and expressways closer to 9 mpg at 60-63 mph. On the Hotter days with air conditioner on 'Max" and accompanying alternator drag from the fans cuts that mileage by 1 mpg.
How is your bus running? is it smooth? Black smoke from exhaust? ECM temp sensor is problematic on your engine and tend to make the engine run rich as they fail. I had to change mine. part#15326386 <$25 USD.
__________________
2019 Forest River Sunseeker 2850
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09-19-2019, 10:23 PM
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#6
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Senior Member
Join Date: Aug 2015
Location: Phoenix, Oregon
Posts: 2,207
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I should have also said that the 7.5 average I've gotten over about 35k miles also includes having a tracker in tow, at 70 MPH most of the time.
Steve
__________________
1994 30' Monaco Dynasty, 5.9 230 HP Cummins, MD 3060, 1992 Geo Tracker.
1996 Dodge Cummins 2500 with 1996 Lance 945 camper
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09-20-2019, 12:50 AM
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#7
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Senior Member
Join Date: May 2019
Posts: 103
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I don't drive it hard and its not towing anything, so weight is just over 5,000kg. Speed around 45-50 so not driven hard (it felt like a jelly hence keeping it down but changed shocks, airbags etc since). It runs OK as far as I can see and doesn't shake so pretty smooth. It does smoke on start up but white smoke so may just be burning moisture (always damp here) as its OK when hot. Just need to find someone/somewhere locally who has any idea about these engines as they aren't common in the UK.
People are saying they are getting 14-15 but I don't buy it. I'm sure I can do better but nearer 10 I'd be happy, and when we retire and do some european trips I'll go lpg.
FFG
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09-20-2019, 01:42 AM
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#8
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Senior Member
Join Date: May 2019
Posts: 103
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09-20-2019, 04:16 AM
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#9
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Senior Member
Join Date: Aug 2016
Posts: 1,703
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Quote:
Originally Posted by FFG
People are saying they are getting 14-15 but I don't buy it. I'm sure I can do better but nearer 10 I'd be happy, and when we retire and do some european trips I'll go lpg.
FFG
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They might be getting that on some of the diesels. But not in gasoline motorhomes. My 4.3 liter 2500kg van would barely get more than 15mpg
__________________
2019 Forest River Sunseeker 2850
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09-20-2019, 08:38 AM
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#10
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Senior Member
Join Date: Nov 2009
Posts: 1,152
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I had a 1988 Itasca 454 towing a Tracker that was averaging about the same as yours. Had the carb rebuilt, tuned it up, new tires, etc. Changed very little.
I installed a vacuum gauge in the dash hooked to the intake manifold and if I watched it and tried very hard to maintain the highest vacuum the mileage could go as high as 9 mpg while towing.
The gauge helped me also identify at what speed the mileage was best. Two mph could make a difference in the fuel mileage.
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09-20-2019, 08:45 AM
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#11
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Senior Member
Winnebago Owners Club
Join Date: Dec 2015
Location: Jacksonville, Fl
Posts: 3,542
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I think that consistently getting 10 miles per U.S. gallon with that engine isn't likely to happen. 6 to 8 seems to be the range I hear the most for those, and what I used to get on mine. WHERE it's being driven makes a big difference too. If much of your driving is in town the the mileage will go down, if mostly cruising on the highway then it should be towards the high end of the range.
If it hasn't had a tune-up recently, do that. But if it's going to take 10mpg to make you happy, I'm afraid you're destined to be unhappy...
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2013 Winnebago Sightseer 36V
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09-20-2019, 10:57 AM
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#12
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Senior Member
Join Date: May 2019
Posts: 103
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I didn't say if I don't get 10mpg or I'll give up, just wanted nearer 10. The UK gallon is 25% more than a US gallon so 6-8 US should be 7.5-10 UK. Its mainly been motorway and taking it easy as its a new driving experience being so long, heavy, wide, LHD, and the wife screaming constantly that I'm on or over the line. Combined with piss poor handling, especially when lorries (big rigs) overtake, its been pretty scary. Lots of things been changed now and spending some money and giving TLC so looking at options to make it better. If 6mpg is it and its running sweet with no issue so be it, but I don't believe that is the case and close to 10 is achievable and anything spent will be worthwhile in future lower fuel spend. I may then look at LPG but want it running sweet first.
I've just changed the leaf spring U bolts as one had broken and it failed its annual test and the rear brakes were imbalance so its going in for a re-test and a full check over underneath. Then got some new tyres to fit for the new season and hopefully reap the rewards of all my recent efforts.
FFG
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09-21-2019, 06:53 AM
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#13
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Senior Member
Join Date: Aug 2016
Posts: 1,703
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Quote:
Originally Posted by FFG
I didn't say if I don't get 10mpg or I'll give up, just wanted nearer 10. The UK gallon is 25% more than a US gallon so 6-8 US should be 7.5-10 UK. Its mainly been motorway and taking it easy as its a new driving experience being so long, heavy, wide, LHD, and the wife screaming constantly that I'm on or over the line. Combined with piss poor handling, especially when lorries (big rigs) overtake, its been pretty scary. Lots of things been changed now and spending some money and giving TLC so looking at options to make it better. If 6mpg is it and its running sweet with no issue so be it, but I don't believe that is the case and close to 10 is achievable and anything spent will be worthwhile in future lower fuel spend. I may then look at LPG but want it running sweet first.
I've just changed the leaf spring U bolts as one had broken and it failed its annual test and the rear brakes were imbalance so its going in for a re-test and a full check over underneath. Then got some new tyres to fit for the new season and hopefully reap the rewards of all my recent efforts.
FFG
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Get the front end re-aligned to Super Steer Specs and it should handle much better. Check your anti-sway bar bushings to make sure they are still pliable not cracked or missing. Koni FSD front shocks (PN # 8805 1006) made a significant improvement in the ride and handling on mine.
__________________
2019 Forest River Sunseeker 2850
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09-21-2019, 08:54 AM
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#14
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Senior Member
Join Date: May 2019
Posts: 103
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Rick, I,ve changed the front shock (Bilstein 24-xxx898). The sway bar bushes have been changed to poly before I bought it. airbags new (50 psi) and just changed rear shocks (Bilstein 24-015875 - know that one off the top of my head) so will ask the garage to look at the alignment while it is in. Many thanks.
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