Best Rpms For An Rb30 Engine In A Small Bus

[busboy]

Hello,

I am going to put a Nissan RB30 in an old Toyota Coaster bus. It seems the best engine for the job, and although I have not yet bought one, I assume I will be fitting something from a late 80s Skyline with the 3 litre EFI motor. (They fit my budget, they will fit in the bus, they seem a nice quiet motor and everything I have heard about them is good so far.)

The bus is currently helped along by a 2.4 carbie motor (a Toyota R22) and it goes ok, but revs it's pants off at 100km/h (4200rpm). The motor is tired, and the gearbox is pretty ordinary too, so I figured I'd just pull the motor and transmission from the Nissan and fit them as a pair. I checked and I can get the tailshaft modded easily enough, which leaves the diff.

There are a heap of ratios to choose from, all the way from the current 6:1 diff (aarrgh!), through to about 3:1 from the diesel model.

The bus is not very hard to push (After all, the current tired 2.4 litre can do 110km/h if you wait a bit), probably a little easier to push than the Nissan Patrol that was fitted with the RB30, but certainly a lot more work than the sedan. The top gear ratios from the current five speed manual and the Nissan's 4 speed auto are about the same, so the 3:1 diff would give me 2100rpm at 100km/h, but somehow I suspect that is a little low.

So, my question is, what engine revs should I aim for at crusing speed? I'd like the engine to be running freely, not lugging, but I don't want it over revving either.

Your thoughts greatly appreciated,

Matthew

[funkymonkey]

Might be of help? Nothing specific on an RB30 though.

http://www.mindspring.com/~jayk3/toyota/swaps.htm

[busboy]

Nothing specific to the RB30, but heaps of other interesting stuff, thanks for the link. A bit of reading to do.

[mad082]

you won't want to have it rev too low as that will then decrease how well the motor pulls the bus (which is why the 2.4L is able to move it, because the diff ratio is as short as hell). considering that the rb30 in a commodore ran a 3.45:1 diff, that is the bare minimum you would want. it comes down to tyre size though. the patrols with the rb30 ran about a 3.9:1 diff to take into account bigger tyres, etc. and that is what i would be more inclined to run, or maybe even to around 4.3, depending on how big the tyres are.

now this may sound a bit odd hearing this on a skyline forum, but i would actually look at putting in a slightly later model commodore v6 or falcon straight 6. you can pick them up reasonably cheap from wreckers. there are 2 mains reasons why i suggest these. 1: parts are much more readily available 2: they both put out more torque than the rb30 (especially the falcon motors) and that is what you really need to lugging around something as heavy as a bus.

[Stinky Rooster]

/\ +1 for the falcon motor. HEAPS more torque, and you could slap in a single rail borg warner box behind it, or even a C6 auto out of the F100 - F150.

If you can find a good alloy headed EFI 250 X flow I would go for that over the later 3.9 / 4lt, although the EF onwards 4tl with the variable length snail shell intake from the EL would be a great goer with a baby towing cam. You could set it up to pull around 2000rpm @ 110km and not worry about clagging up the heads with the high torque loading, and probably use less fuel doing it - eleventy billion taxi drivers cant be wrong

[busboy]

OK, most certainly not the response I was expecting... but really good points.

I do own an EF Fairmont Wagon with the funny intake, and it is the most incredible towing vehicle. The engine is very reliable, it pulls like a beast, but it drinks like a fish and steers like a cow. The stuff like the brakes, suspension and steering are pretty crummy, but I suppose they would not be put in the bus... I just feel like the engine would be almost too big, and the fact that it uses more fuel in the wagon than the bus currently uses makes me just a little nervous of what it would cost to run. Also, those engines have a list of issues a mile long. Each on their own is no big deal, lame head gasket, weak valves, crappy radiator, disposable power steering pump.... but they add up.

My experience of the commodores is only secondhand conversations, but when we did lots of caravan towing (yes, one of THOSE people) I found that the caravan people all stayed away from them. I am told they would crack heads and the transmissions could not handle the load. If you looked around a caravan park a few years ago, it was either Toyota Land Cruisers or Ford Falcons, as far as the eye could see, but this might have changed, it has been a few years.

I have read a lot of good stuff about the RB30, and I FEEL like it would be strong enough. The bus is only 500kg heavier than the patrol, with a much lower rolling resitance and I am unlikely to going much over 90km/h most of the time. I just thought if I got the revs right, it would work. But it seems like you guys have your doubts, and now I am worried.

The Ford solution is so logical, but... so terrrifying from a fuel and maintenance perspective...

[Sarumatix]

nothing wrong with the RB, also there is a diesel variant around which might be an even better choice. RD28 or RD30 which lives in this among other things http://en.wikipedia.org/wiki/Nissan_Cedric_Y31. No idea what they are worth. Guess it all depends on time and money as with all things .

[busboy]

A big thanks to Grigor for your 3000 RPM suggestion and the calculation method also.

I tried to reply but I am too new (not enought posts) to be allowed to PM you back. But I would be keen to hear your thoughts on whether the engine is strong enough for the job also.

(5 more posts to go...)

[busboy]

Oh wow! I had completely forgotten the Cedric! And they were a brilliant car, but oh what a disastrous name... Did the diesel ever make it to Oz? I certainly never saw one...

Diesel is interesting. I started out thinking diesel, but the funny thing was, I had to drive about 100,000km to break even, and that was assuming some pretty conservative cost differences in the conversion.

Big upfront cost, but lots of really nice reliable engines to choose from if you have the money. (An Isuzu 3.4 litre turbo was nice, but at around $11K for engine and transmission, I lost interest really quick!)

[funkymonkey]

I don't think the cedric diesel's ever made it to oz... but I think the Nissan Patrols did come in a GQ variant with an RD28T 2.8L Diesel Turbo.

[Mandingo]

Sounds like fun.

Is this gonna have a turbo hangin off the side busboy?

[busboy]

Just looked up the specs on the RD28 (non turbo) and they are almost EXACTLY the same as the current petrol Toyota 22R motor. Not sure how a diesel would enjoy running at 4200 rpm for hours on end... could be messy.

Interestingly, the turbo version has a slight edge on the RB30 for torque, but only a few percent, so overall I would say the RB30 still feels right.

[busboy]

Sounds like fun.

Is this gonna have a turbo hangin off the side busboy?

Not if I can avoid it. Once you add a turbo the whole insurance thing gets tricky. I looked VERY hard at putting a turbo Volvo 740 motor in it (they are a pretty robust motor, I know, mine has 360,000km on it and is still going strong), but the whole parts thing had me worried. Then a bloke at the roads office pointed out the insurance companies would run for miles, so I went back to looking for a good petrol motor. That's when I found the RB30.

[funkymonkey]

what about a 13B? yes I'm being serious. We almost imported a bus for a customer a while back, a Mazda Parkway 28 seater, and it had full log books (as required by the agency) for... wait for it... just over 1 million kms. Still ran the original engine. Needless to say we were bloody impressed.

[busboy]

A recieved a good comment re the RD28 turbo and the cost of getting one right. Yep, for those reading between the lines, this is a price sensitive conversion I am trying for here.

I am wise the fact that by compromising on cost I have to give up some aspect of performance, whether it be speed, reliability, economy etc.

When I looked at what was most important I realised initial outlay had to be low, (which ruled out diesel), then came economy (hence my fear of Ford motors), then came reliability (the RB30 seems to do well here) and finally, speed ( a Ford motor would be better here). So I guess I am resigned to accepting that this little bus is going to be no road burner. Really, if the current 22R motor and gearbox were not so tired, I think I'd happily up the diff ratio a little and live with the performance. But they are pooped, and an RB30 with auto just has to be a better option. Right...?

Two more posts and I can PM!

[busboy]

what about a 13B? yes I'm being serious. We almost imported a bus for a customer a while back, a Mazda Parkway 28 seater, and it had full log books (as required by the agency) for... wait for it... just over 1 million kms. Still ran the original engine. Needless to say we were bloody impressed.

Well, THAT was right out of left field! Nope, I have to admit, I would never have thought of it in a million years.... What's the logic here? Happy to rev at 4200 rpm of course, that would practically idle speed to a rotary.... I don't know much about them for torque etc, time to read a little.

Hmmm.....

Torque seems a little lower than I'd like (except on the turbo version, where it is insane), but then with those sorts of rev ranges maybe torque is not so important. I have never driven one so I can't really imagine how they'd translate.

[Birds]

Falcon or Commodore (Buick 3800) motor IMO...they've been done to death so there's no shortage of knowledge out there regarding conversions. Lots of people have converted Ford Transits to running the 3.8 litre with excellent results...some have even put a T56 behind that for something of a fail safe tow/carry vehicle. It's the Commodore automatic transmission that lets it down as a tow vehicle, they were always a weak item compared to the Ford...that said, my father always towed his speedboats with Commodore company cars and never ever had an issue.

RB30...sure it'll go better than the current engine but if you're spending the money/time on a conversion you might as well do it for a worthwhile increase in low end torque. Not to mention there's so many buick engines around that if anything ever goes wrong or you kill an engine you will always be able to find a spare / parts.

[busboy]

what about a 13B? yes I'm being serious. We almost imported a bus for a customer a while back, a Mazda Parkway 28 seater, and it had full log books (as required by the agency) for... wait for it... just over 1 million kms. Still ran the original engine. Needless to say we were bloody impressed.

Well, THAT was right out of left field! Nope, I have to admit, I would never have thought of it in a million years.... What's the logic here? Happy to rev at 4200 rpm of course, that would practically idle speed to a rotary.... I don't know much about them for torque etc, time to read a little.

Hmmm.....

Torque seems a little lower than I'd like (except on the turbo version, where it is insane), but then with those sorts of rev ranges maybe torque is not so important. I have never driven one so I can't really imagine how they'd translate.

[Birds]

Here ya go, all you need to know about rotaries:

http://www.skylinesaustralia.com/forums/Ro...ck-t287781.html

[busboy]

Falcon or Commodore (Buick 3800) motor IMO...they've been done to death so there's no shortage of knowledge out there regarding conversions. Lots of people have converted Ford Transits to running the 3.8 litre with excellent results...some have even put a T56 behind that for something of a fail safe tow/carry vehicle. It's the Commodore automatic transmission that lets it down as a tow vehicle, they were always a weak item compared to the Ford...that said, my father always towed his speedboats with Commodore company cars and never ever had an issue.

RB30...sure it'll go better than the current engine but if you're spending the money/time on a conversion you might as well do it for a worthwhile increase in low end torque. Not to mention there's so many buick engines around that if anything ever goes wrong or you kill an engine you will always be able to find a spare / parts.

So maybe a manual commodore trans would overcome the main problems with the commodore option? I must say I liked the V6 config as it allowed me to move the C-of-G back a bit further. The bus was designed for a two ton payload on the back axle, and currently it is actually 100kg lighter than when I bought it empty due to removing the seats and doing a VERY lightweight conversion of the interior.

Is there a commodore engine that has a particularly good reputation (except the RB30 VL of course!)

(Good point about not skimping on cost to the point of silliness too.)