Re reducing my maximum rpm

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Re reducing my maximum rpm

September 02, 2025, 04:13:49 am

Hya everyone, is it possible to limit my rpm on my 1990 villa, I've booked in for a test on 1st of October and the only thing I'm worried about really is the emmisions test, so I would like to drop the rpm down say approx 1000 rpm lower than it normally goes, now behind my accelerator pedal on the floor is something which I've took a photo of and not sure what it does, could that be some sort of stop sothe pedal doesn't go down as far, as it is at the moment when I have full throttle the back of the pedal dosent touch this piece, but was wondering if it can be adjusted up to prevent the pedal going as far, it may be nothing to do with the pedal, maybe there is an adjustment on the fuel governer like a screw to prevent full revs, the main question is by knocking of a 1000 rpm would I find it difficult going up hill or would it just go up slower than normal thanks kev

Re: Re reducing my maximum rpm

Reply #1 – September 02, 2025, 07:42:08 am

You have emissions on a 35 year old vehicle?

Re: Re reducing my maximum rpm

Reply #2 – September 02, 2025, 08:35:18 am

When my daughter was about 4 she wanted to drive the golf cart around the property, so I added a crash bar across the front and a block that she slid on to the accelerator pedal which limited the speed the cart would go, as she aged the "Rachel Block" was cut down increasing the speed,
Kevi0000 use heavy duty Velcro and temporally attach a piece of thick plastic, steel or wood to the back of the pedal where it will not be seen, thick enough to limit the travel, reducing the revs to your desired max, drive there normally, reach down, attack the block and smile .

Re: Re reducing my maximum rpm

Reply #3 – September 02, 2025, 09:15:56 am

Quote from: kevo0000 – September 02, 2025, 04:13:49 am

...so I would like to drop the rpm down say approx 1000 rpm lower than it normally goes...

Diesels generally have a somewhat limited operating RPM range. What is the normal max RPM that you see when driving your coach, like when it makes a full throttle upshift? I would think that cutting 1000 RPM off your engine's RPM range would greatly impact its operation. But, I don't know anything about the Detroit Diesel, so could be completely wrong.

Would the people conducting the test be familiar with your engine specs? Would they notice the abnormal (reduced) RPM range?

How do they conduct the test? Do they drive your coach, or put it on a dyno, or test it with stationary equipment? Do they "sniff" the tailpipe? What part of the test has you worried?

Just curious.

Re: Re reducing my maximum rpm

Reply #4 – September 02, 2025, 09:49:37 am

If they are performing the max acceleration test with no load decreasing the max rpm by limiting throttle travel will help but you will find that it would be difficult to drive if you left it limited. There is a way to reduce the max rpm within the governor that would only trim fuel at rated rpm to decrease HP. This probably would not be noticed during testing??? You are already limited by the price of fuel in your area. There are fuel additives that probably would help more than limiting the amount of fuel delivered also. May want to look into that. Im also not familiar with your engine but know that injection pump timing may also be advantageous to reducing acceleration smoke. Ive never used

Rymax Lubricants | Diesel Smoke Reducer

Re: Re reducing my maximum rpm

Reply #5 – September 02, 2025, 09:55:57 am

Search for. " turn up the fuel " for your engine. Then turn it down a click or two before test.
In my case the 3208 has a pump housing that can be rotated to change the fuel to throttle ratio .

Re: Re reducing my maximum rpm

Reply #6 – September 02, 2025, 12:22:42 pm

In addition to limiting throttle to help reduce tailpipe black exhaust, more important is to FULLY warm up engine by going for a long drive, before heading to emissions test site. What State is your motorhome registered in?

Re: Re reducing my maximum rpm

Reply #7 – September 02, 2025, 12:38:10 pm

I'm with Mike turn down the fuel rather than turn down the RPM as it is the amount of fuel that is affected
into the engine will make the difference. Just google turn up your fuel for a 3208 cat.
As Barry said heat up your engine. Hot engines burn cleaner.

Re: Re reducing my maximum rpm

Reply #8 – September 02, 2025, 12:54:56 pm

Quote from: Barry & Cindy – September 02, 2025, 12:22:42 pm

What State is your motorhome registered in?

Kev resides in or near the lovely hamlet of Grumbla, Penzance, Cornwall, England, UK. It is a rural area situated to the west of Sancreed Beacon and lies within the Cornwall Area of Outstanding Natural Beauty.

Grumbla - Wikipedia

Re: Re reducing my maximum rpm

Reply #9 – September 02, 2025, 02:32:41 pm

God, 3rd time lucky,
Ive been trying to write a reply for last half hr, well I'm at my mum and dad's, there nearly 90, and I get so far with the reply, and then my mum or dad will speak and then il put the phone down to the side and then I don't know what I do, but the message I write has totally disappeared and can't find it, il be back up at grumbla later, can concentrate better on writing tex thanks for inputs, all interesting and il explain later about our emmision tests thanks kev

Re: Re reducing my maximum rpm

Reply #10 – September 02, 2025, 06:06:45 pm

I wish I knew how to go back to these messages I lose this is now the forth attempt, right here we go again basically are emissions you drive in they rev the engine up full revs till it gets to temperature, then they put a probe in and rev it for 5 secs full revs, and it's either a pass or a fail, everyone over here when mot is due worry about their emmisions, the amount of really good cars get scrapped because they have failed their emmisions test , we have crazy laws over here, but yeah after reading a previous comment earlier about not driving it on slow revs but the plan is to get it within 2 mile of the place and just pull in, do an adjustment to slow the revs down, I haven't got any hills to climb once I get that close to the testing station, thing is I got an 11am booking, so really it would best if I turned up at 10.55 with engine nice and hot, but I know what these places are like they do there own trucks first then they do private mots, I have got a full tank of super diesel, and I'm gonna put a gallon of injector cleaner in the tank aswell, it doesn't seem to use any oil, I check it regular and stays same level, I get a bit of grey smoke when I first start it up and after a while of driving back and forth in the yard it seems to get alot less so I think after 50 mile with engine hot it should have had a bit of a clean,, funny actually I've done 48 miles in this over a 5 year period in a small scrap yard, sometimes he has not many scrap cars here and I take advantage of the space, I had all the discs turned and new calipers, so at least once a week I move it back and forth and work the brakes just to stop the surface rust from covering them and also it keeps the pistons nice and free, anyway il read that engine manual and find the governer screw that controls the revs, what would be the correct tick over for my 8.2, it ticks over at around 7000 on start up and then once reasonably warm, it runs at about 8000 tick over, would that be too fast , kev

Re: Re reducing my maximum rpm

Reply #11 – September 02, 2025, 06:10:51 pm

Quote from: kevo0000 – September 02, 2025, 06:06:45 pm

I wish I knew how to go back to these messages I lose this is now the forth attempt, right here we go again basically are emissions you drive in they rev the engine up full revs till it gets to temperature, then they put a probe in and rev it for 5 secs full revs, and it's either a pass or a fail, everyone over here when mot is due worry about their emmisions, the amount of really good cars get scrapped because they have failed their emmisions test , we have crazy laws over here, but yeah after reading a previous comment earlier about not driving it on slow revs but the plan is to get it within 2 mile of the place and just pull in, do an adjustment to slow the revs down, I haven't got any hills to climb once I get that close to the testing station, thing is I got an 11am booking, so really it would best if I turned up at 10.55 with engine nice and hot, but I know what these places are like they do there own trucks first then they do private mots, I have got a full tank of super diesel, and I'm gonna put a gallon of injector cleaner in the tank aswell, it doesn't seem to use any oil, I check it regular and stays same level, I get a bit of grey smoke when I first start it up and after a while of driving back and forth in the yard it seems to get alot less so I think after 50 mile with engine hot it should have had a bit of a clean,, funny actually I've done 48 miles in this over a 5 year period in a small scrap yard, sometimes he has not many scrap cars here and I take advantage of the space, I had all the discs turned and new calipers, so at least once a week I move it back and forth and work the brakes just to stop the surface rust from covering them and also it keeps the pistons nice and free, anyway il read that engine manual and find the governer screw that controls the revs, what would be the correct tick over for my 8.2, it ticks over at around 7000 on start up and then once reasonably warm, it runs at about 8000 tick over, would that be too fast , kev

Oh and also like was said dropping a 1000rpm may be a bit too mutch, so perhaps just knock 500 rpm off it temporarily, what do you think kev

Re: Re reducing my maximum rpm

Reply #12 – September 02, 2025, 06:33:39 pm

Quote from: kevo0000 – September 02, 2025, 06:06:45 pm

what would be the correct tick over for my 8.2, it ticks over at around 7000 on start up and then once reasonably warm, it runs at about 8000 tick over, would that be too fast , kev

Kev,

Are you sure you don't mean 700-800 (like loose the zero)??

If your actual readings were 7000-8000, your tach is WAY off. Idle speed will be under 1,000 RPM. Max RPM likely at or under 3.000.

I don't have the exact numbers for your 8.2 liter DD 4 stroke, but my numbers will be close.

On many applications, the tach is driven off the alternator. That MAY be where these very high numbers come from

Re: Re reducing my maximum rpm

Reply #13 – September 02, 2025, 06:45:59 pm

Kev couldn't possibly be saying his engine IDLES at 7000 to 8000 RPM. That wouldn't make sense to anybody in their right mind.

Perhaps, when typing, he was hitting an extra 0 and meant to say it idles at 700 to 800 RPM. That would be much more logical.

But, we'll have to wait till he checks back in to know for sure...

Re: Re reducing my maximum rpm

Reply #14 – September 02, 2025, 07:06:23 pm

Yeah 700 I meant ha ha God I'm terrible with typing, I type very quick with one hand and sometimes even the predictive tex don't predict

Re: Re reducing my maximum rpm

Reply #15 – September 02, 2025, 07:10:58 pm

Kev, this may be helpfull...

Practical Guide To Servicing Your Detroit Diesel 8.2L | Diesel Pro Power

Re: Re reducing my maximum rpm

Reply #16 – September 02, 2025, 07:14:09 pm

Yeah cheers , il have a look at that a minute kev

Re: Re reducing my maximum rpm

Reply #17 – September 02, 2025, 07:19:33 pm

Just had a quick browse there diesel Pro power, I order parts from them a chap called luis Santos, I ordered a couple of spare rocker cover gaskets off them and other bits and pieces Ive needed over the years arrives quickly usually by ups, the fastest I've ever got something was 3 days,

Re: Re reducing my maximum rpm

Reply #18 – September 02, 2025, 07:23:07 pm

Quote from: Protech Racing – September 02, 2025, 09:55:57 am

Search for. " turn up the fuel " for your engine. Then turn it down a click or two before test.
In my case the 3208 has a pump housing that can be rotated to change the fuel to throttle ratio .

Thanks Mike, il try and find that tommorrow, would that be in the 8.2 workshop manual cheers kev

Re: Re reducing my maximum rpm

Reply #19 – September 02, 2025, 07:27:00 pm

Oh I looked at the spec label on rocker cover that you sent, I took a photograph of both my labels years ago, I found them the other day, I'm glad I did, cause the labels have worn away now over the years, you can hardly see them now , but mine is the 225 bhp, it says maximum rpm 2700 rpm , I'm sure when I run on full throttle it goes up past that, il check that in the morning the gauge itself goes up to 3000 rpm, I'm not sure if it does reach that or not , il definately be out with my manualtommorrow

Re: Re reducing my maximum rpm

Reply #20 – September 02, 2025, 07:40:25 pm

I just read that article about rymax, that's handy I wonder if they sold it in larger quantity like 5 ltr, it sounds good stuff , it says to run with regular diesel though, it wouldn't harm the engine would it if I have super diesel in it, the cleaner the better

Re: Re reducing my maximum rpm

Reply #21 – September 02, 2025, 07:52:21 pm

It's normal for a 3208 cat engine to smoke on startup.

Re: Re reducing my maximum rpm

Reply #22 – September 02, 2025, 08:14:57 pm

Quote from: Chuck & Jeannie – September 02, 2025, 12:54:56 pm

Kev resides in or near the lovely hamlet of Grumbla, Penzance, Cornwall, England, UK. It is a rural area situated to the west of Sancreed Beacon and lies within the Cornwall Area of Outstanding Natural Beauty.

Grumbla - Wikipedia

Hi chuck, I looked at that link of Grumbla you posted, if you go onto Google maps satellite View and spin the map around, as your looking at the road going off to the right, spin the map around approx 90° anti clock wise you will see my villa parked there, when I first moved there there were trees up higher than the villa then they chopped them all down cause
they had to build a new wall , so they could get planning permission to build the house behind, well Google don't update their maps for a number of years I think, I've been up there since 2013, but the hedge went a year later, so I've had a nice view all these years but never updated on Google , its only probably within the last 12 months maybe that the Google camera van has been round and updated everything

Re: Re reducing my maximum rpm

Reply #23 – September 02, 2025, 08:50:17 pm

Quote from: oldguy – September 02, 2025, 07:52:21 pm

It's normal for a 3208 cat engine to smoke on startup.

But, Kev has a Detroit Diesel 8.2 liter 4 stroke, not Caterpillar 3208. Very different motors.

Re: Re reducing my maximum rpm

Reply #24 – September 02, 2025, 10:14:20 pm

Quote from: kevo0000 – September 02, 2025, 08:14:57 pm

Hi chuck, if you go onto Google maps satellite View...you will see my villa parked there...

I found it! That's a really clean good looking GV you've got. And what a beautiful place to live! You are close to the coast, and surrounded by all that greenery. About as different as it could be from where we live in dry, brown, desert West TX. I bet you have some great camping destinations to visit nearby. I see you are not far from a place called Land's End, which seems to be appropriately named. Very interesting neighborhood!

For those who might like to see Kev's coach, here is the location: Google Maps

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