Tatra 813 related jabbering - go-faster mods & engine ident

[FridgeF]

I thought I'd start a new thread rather than clog up someone else's... I'm getting tantalisingly close to buying an 813, and there are a couple of things that are niggling at me that I'm trying to get to the bottom of.

First one is top speed - 80km/h isn't terrible but it's not fantastic, 100km/h would be far nicer.

Thanks (I think) to John C, a contact who knows about upping the top speed of these trucks has come back and told me that it's done by making the engine rev to 2400rpm, which involves a rebuild (in Czech as apparently only they have the skills) with uprated bearings & bolting some turbos on. Frankly, that sounds rather expensive and over the top.

I'm wondering about swapping gears in either the transfer box or main gearbox - if possible doing something like sticking a pair of 4th gear cogs in the place of 5th gear, but the opposite way round so they give a higher ratio, not lower.

A final option is putting an extra gearbox in between the engine & the main gearbox (perhaps a cut-up gearbox from another truck) to give an added overdrive or splitter box. I've seen it done with Land Rovers using just 3rd & 4th in a cut-down gearbox bolted to the front of the normal box. There are some off-road trucks which have separate transfer cases (input & output by propshafts) so one of these could perhaps be used. It would mean more levers & buttons to play with, but hey ho!

Second thing is multi-fuel capability of the engine - if I can run it even partially on contaminated fuel or Russian 10p/litre 62-octane junk then running costs go down drastically which is always welcome at 5mpg :mrgreen:

Going through some previous correspondence with a guy at Tatra he seems to suggest ALL "true" military Kolos were multi-fuel, which Wikipedia kind of backs up. However, elsewhere on the net it's suggested that only the later 19L engines were multi-fuel, and the law of sod dictates that all the trucks I've found are 17L. Plus, no-one can tell me how to identify a 17L versus 19L engine and whether either of them is multi-fuel. Again, chappy at Tatra suggests he can tell me from a picture of the engine, but hasn't so far explained what's different so that I can look for it myself. Answers on a postcard

[Abrs]

Hi mate

Re. Speed. I think personally I would be hesitant to alter gearing to gain more speed, the 813 is about as good as it can be with its present ratios, if you were to alter the final ratio you would probably find it would make the truck somewhat annoying to drive due to lack of engine power & the need to change down gear often. I can see how the engine tuning route would be advantageous here but again I can see it is not without its problems; more heat for the engine to cope with which may considerably shorten its life, higher fuel consumption , and a great deal more noise and vibration which may not be tolerable on a long journey, in fact as they are they’re not exactly what I would call pleasant to drive anyway! And you would also need better tyres for higher speeds on road.

Multi-fuel. Not all Kolos are multi-fuel, in fact only a very small percentage of the exported trucks were, predominantly it was only the Czech military models that were required to be so. Anyway, sorry to ask but I’m just wondering how much use this capability would be to you though? Diesel is as far as I know pretty much the same the world over, even in Russia, but its cost should be somewhat lower over there? So if the diesel itself is going to pretty cheap anyway would it even be worth adding the petrol etc to it to make it cheaper with all the risks you may be running? - Don’t forget the multi-fuel capability was only intended as a back up in case of a lack of regular fuel, they are not intended to be used continuously running on it as I’ve mentioned before.

Engines; The 19L V12 engine which is basically the same as the 17L V12, however it was only fitted to the last of the 813’s, but was also seen in some of the early 815’s before they moved on to the new V8 lump, all V12 engines in the Tatra 813 are of the T-930 model regardless of their size, there are however different variants of it; turbo, non turbo, diesel & multi-fuel. A distinguishing feature of most 19L lumps is that they are fitted with turbos and an oil filtering canister in place of the old centrifugal unit. You will also be able to tell which variant it is by the engine number, particularly by the suffix in part of the number, i.e. T-930 ‘K’ ‘M’ etc.

An alternative solution to your problem could be to get an engine and box out of a later truck, I’ve been researching the possibility of using the V8 out of the later 815 and so far have not found any evidence that suggests it can’t be done, well apart from the cost! The later V8 engine is a totally different beast, much quieter, more power, better on juice & is also lot more reliable – But saying all this the rest of the 815 would also not be a bad idea .


Regards

[FridgeF]

if you were to alter the final ratio you would probably find it would make the truck somewhat annoying to drive due to lack of engine power & the need to change down gear often.

It's always a risk. The current idea is stick a transfer box between the engine & gearbox so that I can select "straight-through" (1:1 gearing) or increased (something like 1.5:1). As long as it can pull the higher gearing from standstill (eg low 1st isn't too high) then I can live with having to waggle the stick a bit more often. It won't be anywhere near heavily laden (the payload is 22T, towing is 65T, if we have more than 5T on the back it'll be rare).

I'm figuring that since it has a transfer case/overdrive that is ~0.6:1 (~+40%), if I can only find something that bumps the gearing up by 2:1 then I just drive the truck with the overdrive disengaged (so +100%, - 40% = +60% total, or 20% higher than when the overdrive is in). Hope that makes sense! :shock:

If the gearing is too high I can always disengage the extra transfer box and drive the truck in its normal gear, we're only really worried about the top speed on long hauls on tarmac.

they’re not exactly what I would call pleasant to drive anyway! And you would also need better tyres for higher speeds on road.

You've clearly not been in my Land Rover then :lol: the Kolos is not a lot louder, and is smoother over the bumps. I think with a decent silencer and a leaf or two out of the rear spring pack it will be OK. The big tyres and heavy weight help to ride smoothly (as does the long wheelbase). It also means I don't have a car that is full floor to ceiling with spares, tools, camping gear, and people.

Multi-fuel. Not all Kolos are multi-fuel, in fact only a very small percentage of the exported trucks were, predominantly it was only the Czech military models that were required to be so.

That's handy, the one I'm looking at is ex-Czech military

Anyway, sorry to ask but I’m just wondering how much use this capability would be to you though?

If it will burn anything then we can run it on contaminated fuel, which is free - so saves quite a bit of money at 42l/100km :shock: it means we can stick a 2000L fuel tank on the back, fill it for free and drive to Russia and back for less money than taking the Land Rover. Even if we have to pour some clean engine oil into the fuel to keep things happy, it's still cheap motoring.

I've looked at engine swaps, that would be one for the future (once my bank balance has recovered), the later engines are indeed more advanced, and there are others such as Magirus aircooled out there which are similar style. With the engine divorced from the gearbox it does make engine swaps a matter of a few mounts and a propshaft. I think the 17L unit is not too bad though - I'll trade simplicity and reliability for a few litres of diesel any day. I looked into the engine bay of a MAN KAT recently, no way would I want to fix that thing in the middle of a forest! :shock:

[paulob1]

crikey, sounds like a lot of work, I am off to see some military 815's...should I get some photos and prices for everyone...

[FridgeF]

crikey, sounds like a lot of work, I am off to see some military 815's...should I get some photos and prices for everyone...

My bank balance says no but my head says yes :lol: although there's very little chance I'll be affording an 815.

[Abrs]

All good things come to those who wait - I'm sure you would find a good one eventually for a decent price if you look hard enough.

Only problem I can think of with your additional splitter box idea is that there isn't a lot of room, you would need to modify/fabricate the cabin floor and engine covers to accommodate it, I think you would be better off having a box made to fit rather than trying to find one that will go in and have the appropriate gear ratios - this way you could also retain the original ratio which could be selected if desired, in effect this system would give you 30 gears to play with But if you are going down this route I would suggest increasing engine power a bit somehow, perhaps turbos and larger injectors for starters as driving in normal top gear is frustraiting enough anyway.

On another note; would there be any problems in carrying large quantities of fuel through the boarders? I know U.K. law is very strict, maybe similar in other countries to?

[FridgeF]

All good things come to those who wait - I'm sure you would find a good one eventually for a decent price if you look hard enough.

Well I think I've found a pretty good 813, off to view it this weekend with a bit of luck.

Only problem I can think of with your additional splitter box idea is that there isn't a lot of room, you would need to modify/fabricate the cabin floor and engine covers to accommodate it,

Having had a poke round I think there's enough room for the initial idea of a "small" 4x4 transfer box such as G-Wagen or Land Rover, I can pick a Land Rover one up and I make Mr Muscle look butch :lol:

I think you would be better off having a box made to fit rather than trying to find one that will go in and have the appropriate gear ratios - this way you could also retain the original ratio which could be selected if desired,

Transfer boxes usually do have two speeds - high and low - one of which is usually close to 1:1. Land Rover LT230's come in 1:1, 1.2:1, 1.4:1 and 1.6:1 but low range is around 3:1 which is too steep shame because we know they will live with 500bhp and a lead foot
The G-Wagen one is 1:1 and 2:1, and is made by Germans so is very strong - my friend who suggested this has been trying to break his for a year now and failed.

I would suggest increasing engine power a bit somehow, perhaps turbos and larger injectors for starters as driving in normal top gear is frustrating enough anyway.

I'm a bit wary of too much tuning as it does have an effect on reliability, I don't know how much "slack" there is in the Tatra engine for tweaking (some old lumps are horrifically detuned, Land Rover deliberately do this) and how running on poor fuel would affect it. Has anyone tried pulling out the cold start enrichment knob for a bit of extra go, or does it not work like that?

On another note; would there be any problems in carrying large quantities of fuel through the boarders? I know U.K. law is very strict, maybe similar in other countries to?

I'd be getting a receipt to show I'd taken a tankfull of contaminated, you don't want VOSA dipping the tank and getting funny. The Russian border is a bit special as the Finns nip over & bring back cheap fuel & booze so they're quite hot on that if you're Finnish. We've never had problems, and the fuel tank wouldn't be on display. Coupled with a piece of paper saying where all the fuel came from, I think the border guards should be happy. The Ruskies love bits of paper, especially with rubber stamps on.

[les ward]

fridge (john) i guess the tatra is for lagoda trips then? carrying all jez,s spares for his heavy
right foot :lol: all the best les

[FridgeF]

fridge (john) i guess the tatra is for lagoda trips then?

Blimey Les, are you on every forum on the net? :lol: Or just stalking me? :shock:

That's the broad plan for it, yes. Just need to make sure it can get to camp in reasonable time.

[Abrs]

Transfer boxes usually do have two speeds - high and low - one of which is usually close to 1:1. Land Rover LT230's come in 1:1, 1.2:1, 1.4:1 and 1.6:1 but low range is around 3:1 which is too steep shame because we know they will live with 500bhp and a lead foot
The G-Wagen one is 1:1 and 2:1, and is made by Germans so is very strong - my friend who suggested this has been trying to break his for a year now and failed.

Do you not think that a gearbox this size is a little too lite for the job? I think it's the torque not hp that matters, the Tatra engine is probably physically eight times the weight of most 4x4 engines which will incur a much grater load especially as you are not as likely to unload it at the wheels which a lighter vehicle can as it can break traction easier - i.e. wheel spin when you boot it etc. If you perform a quick getaway in the Tatra you will be exerting nearly 800ft.lb of torque through that little 4X4 box which I think will make it spit its brains out - If you were to have a box made you could at least build it using proper helical gears (not the crappy star wheels they use in 4x4 boxes these days) and heavy shafts which will cope with the forces involved, you could also make it a 'flat' box meaning you won't lose any room in the cab.

Engine wise I think you can easily get a little more power out of it, the 19L version of the engine which is basically the same but is around 2000CC bigger puts out anything up to 350hp = 100hp more than the 17L but it normally has twin turbos fitted This engine also has applications in trams where they're even beefed up further to 400hp, so I think you could at least get another 60-70hp just by fitting turbos and bigger injectors to a 17L - this is without over revving the engine which I would not be entirely happy with - I think heat might start to be a problem but an extra oil cooler might help a bit.

The cold start increases fuel delivery pressure by altering the position of the rack in the injection pump - it alows it to travel further than it would normaly so more fuel is deliverd, this does give you a tad more power but it also makes the engine smoke badly under load and they drink fuel.

Good luck with the truck you're going to see

[Eastblock]

Once you've made it go faster you need to look at the brakes - will they be up to the job? Will the insurance company like the modifications? If you double the speed you quadruple the wind resistance. A Tatra is not the most aerodynamically efficient thing in the world. Fuel consumption is likely to increase drastically.

I think I would leave things the way they are and leave a couple of hours earlier.

[Abrs]

One thing the Tatra does have is good brakes - guess they would need to with the weights they would be expected to carry/tow.

I don't think the insurance would be any the wiser regarding the extra box as long as it didn't look like a complete bodge job. The most likely problem will be getting done for speeding which is a big deal for HGV's with big penalties involved. VOSA are the only people who are likely to notice any mods, and anyway that's only if they have a good reason to look through the truck.

[FridgeF]

Eastblock - we're not building a racing car and we're certainly not after doubling the top speed. The truck will be used to travel long distances (trips to Russia @ 2000km each way) so anything that can be done to make cruising a bit more leisurely is welcomed.

We are more than aware of the speed limits in the EU and penalties for breaking them. However, in Russia things are a bit different and when you're race support sometimes you need to be somewhere as quickly as possible.

I would hope a small increase in gearing, with the truck lightly loaded, would not increase the fuel consumption too much or over-gear the drivetrain. The thing is rated to tow 65t and carry 22t, I doubt we'll be carrying more than 10t at the maximum.

[Eastblock]

Eastblock - we're not building a racing car and we're certainly not after doubling the top speed.

I wasn't implying that, I was just trying to state how the physics work around air resistance

I'm a bit sceptical when it comes to trying to make a vehicle something it isn't. Travelling distances like that I would be more concerned with reliability than speed.

[Abrs]

The reliability of the 813 in its basic form is pretty good by all accounts - they used a lot of these in CZ ect during the 70's & 80's for hauling large loads across the more remote areas in eastern Europe, they even made semi-trailer versions and container carriers which performed all the jobs you'd find modern HGV's doing - It's not reliability but more the comfort that would concern me on a long journey, it gets very hot and fumy in the cab after a while, the noise is also a big concern for me; your ears start to ring after only a short while driving. I also find them tiresome to driver after a while as you need to constantly think about what you are doing; especially when changing gear & using the splitter - basically what I'm saying is they aren't the nicest truck to drive on road these days, after all they were designed during the 60's :roll: , now take them off road and then they shine - this is I think were thay are really at home 8)

[Eastblock]

That could be my Gaz69M you just described there I wear earplugs if I'm going to be travelling more than a few miles. The Praga probably won't be any different.

[gaz66chris]

i have to admit (as much as i love them!) praga's must be the noisiest russian trucks i know!! and as for the praga lizard that duncan had at war and piece!!!. trying to sit in the passenger seat and manualy operate the throttle on the injector pump, with no covers on the engine, i had no ear protection with me and i truely belived that my ears were going to bleed!! words cannot explain how loud that thing was!

[Abrs]

The Praga like the 813 uses one of Tatra's air cooled direct injection diesel engines, being air cooled makes them a lot louder than a water cooled engine & being DI also helps increase the noise level a fair bit.

[FridgeF]

It's not reliability but more the comfort that would concern me on a long journey

It's a good point and I'm under no illusions. However, I'm currently doing the trip in a 1978 Land Rover with leaf springs, Volvo axles, and a 4.6 V8 up front with not much silencing

On long journeys it's hot, bumpy and noisy but it's also overloaded with 4 people and a ton of gear in it. By the time we've hooked a trailer on the back with a car on, we're limited to 90-100kph, and doing 10mpg.

The Tatra would solve the loading/space issue at least and, as far as I can tell, doesn't do any worse on the others - even the 5mpg is not so bad if you can carry twice as many people to share the fuel bill. As was proved this year though, we do need the off-road ability, hence why more modern stuff of the same ability is either out of price range (MAN KAT etc.) or is not enough of an improvement overall to be worth spending the money on (Mog, Volvo, Pinz). As I have explained to my mate, all the sensible trucks are too sensible for me :lol: if I'm gonna blow my savings on something big and stupid it's got to be full-fat stupid

I'm confident some stuff with the Tatra can be improved - there's not exactly a lot of sound or heat proofing in the cab, and so far there doesn't seem to be a great deal in the way of exhaust silencing either. A friend made a fibreglass transmission tunnel for my Land Rover which cut down engine & transmission noise massively, I think the same may help for the Tatra. I reckon cab ventilation can be improved too, to keep things a bit cooler.

[FridgeF]

Well I haven't managed to buy one yet, got very close but the world economy jinxed it at the last minute, still saving the pennies though (if you have a cheap 813, PM me :roll: )... and still thinking about this speed issue.

I am now fairly convinced that running a Land Rover LT230 transfer case backwards between the engine & gearbox would give a decent gearing increase (1:1.222 is a commonly available ratio, with 1.211, 1.41, and 1.6 also available) which a lightly-laden 813 should be able to pull without too much stress. The truck I test drove had a wonky gearshift and we accidentally pulled away in a higher gear more than once without drama.

Even in standard spec Land Rovers the LT230 lives behind a 380nm rated gearbox with ~3:1 1st gear, which suggests LR are reasonably confident it will handle over 1000nm of torque. We and others have run them reliably behind engines making double that torque.