Thread: 4TEC vs road car engine
04-02-2015, 12:30 AM #1
- Join Date
- May 2013
4TEC vs road car engine
Why is it that our 4tec engines have a much, much shorter life than a regular road car?
If we look at the differences;
4tec - 1503cc four stroke - max 8000 rpm - wet sump - SC - 260HP/3 cylinder (eqv 350HP in a 4 cylinder as far as stress per cylinder) - rebuild @ 200 to 300 hours (may still run, but compression down etc), definately needs a rebuild by say 500 hours.
Regular european car - 1200cc to 2000cc - gasolene - turbo (a few supercharged) - 100HP to 300HP - max 7500rpm to 8000rpm - rebuild between 130000 miles to 160000, could be up to 200000 miles.
Both applications have similar compression ratios, are built of similar materials, run at the same temperaturs, are water closed loop cooled.
So why the hell does the 4tec engine last only 10% of the life that a car engine does?
Yes, the ski gets a lot of holeshot, zero to WOT, but no more than a car would do over 200000 miles of pulling away sharply or overtaking or goofing around (look at say an Subaru Imprezza WRX or Mitsubishi Evo - both 300 plus HP - 2000cc - massive turbo psi - 4WD - driven by hooligans).
If you look at the data from a CanDoo on engine use of a ski, with 150 hrs on, you'd be surprised that around 75% of its life has been spent between 2000rpm and 5000rpm, about 15% between 5000rpm and 7000 rpm and on around 5% at true WOT. If you think about it, you can often sit for hours cruising, but WOT, on the whole, is only for a very short period of time.
Look also at transmission. On a ski, we have a 3ft drive shaft to final drive. In a car, you have one or maybe two driveshafts, half shafts, a transmission, one or two differentials and possibly four driven wheels even a clutch. Think of all of this rotational resistance the engine has to deal with every time you step on the gas.
Yes, a ski has more drag in water than a car does driving along the road, hence why we see lower MPG, but it's nothing compared to driving off road or up a steep hill dragging a trailer.
One could argue that a race car engine doesn't last very long because it has all the power squeezed out of it, the limits stretched and tolerances so fine. Agree, but then our ski's are hardly so highly tuned and stretched (I'm talking stock ski's here). We're getting only normal amounts of HP out of a relatively large engine, 1500cc, compared with many road cars in Europe.
So why is there a HUGE difference in usable life between the two engine uses?
I'd bet that of a car covering 200000 miles, less than 10% of that time has been at standstill tick-over. Probably 80% has been between 3000rpm to 4500rpm and the remaining 10% 4500rpm to 8000rpm. If you assume an average speed of a car over its life is no more than 25mph (it's harder to average more than this over most journeys - as an average - check out your computer over a week's driving) - then at 200000 miles that car will have clocked up 8000 hours. OK, so take an average of 40mph and 100000 miles, that's still 2500 hours. At very worst case scenario the car still out lives a 4tec by 900%.
Yes, there can be salt water and sea air, but it's not corrosion killing the engine, it's wear.
Oil and filter changes on the 4tec are much, much more frequent than any car. And a million times more often than an abused car, that will still far outlive a 4tec.
The situation changes little, in relative terms if you take a NA 4tec rather than a SC one.
Of course there are exceptions and I'm sure people will claim they knew a ski with x thousand hours on etc, but in the main and generally speaking, we don't get much past 200 or 300 hrs without significant compression loss (whether or not you realise it). All this is assuming that the engine lasts this long (flywheel bolts failing etc).
So I'd welcome your thoughts on why the difference is SO big but the set up, use and materials are the same when all is balanced out.
If I didn't know the capability of the 4tec, I'd gamble all my money on the fact it would outlast a car engine or at least be much closer to a similar life expectancy.
Over to you.
04-02-2015, 01:08 AM #2
- Join Date
- Oct 2007
I think the biggest difference lies in the fact that the machine has a change, try to put your car in first gear and use it as a jet ski, I think it does not have a long life.
04-02-2015, 01:22 AM #3
- Join Date
- May 2013
04-02-2015, 02:50 AM #4
Same could be said for mercruiser V8,s
We run 454 and 502ci big block chevs in Jet boats on tours doing alot of work around the 4000rpm mark and some are lucky to see 1000 hours. Thats stuff all compared to it being in a car?
04-02-2015, 03:01 AM #5
How often do you hold your road car at over 7000 rpm for long periods???
04-02-2015, 03:11 AM #6
- Join Date
- Mar 2006
you have to look at why seadoo 4 techs fail, but just off the top of my head:
clogged up fuel pump from dirty gas cans, cars fill up at the pump, wet exhaust system on the 4 tech-- moisture causes valve seats to rust-- drop in compression (the more time between cycles = more chance of rust = less hours before compression drop-- rolling stone gathers no moss. Do you think the number of hours a seadoo engine would last would go up or down if it was never shut off and it was feed clean fresh gas? When do these motors need a rebuild as the compression is too low?-- after x hours? no.
I personally think these 4 techs are amazing and are very reliable, but I see you are just comparing and asking a question. How about asking the question a little differently, such as-- How long would a 4 tech motor last if installed in a car? Race car or daily driver-- who is driving it?
04-02-2015, 03:39 AM #7
We pulled 1500 total commercial hours on Seadoo GTI jet skis under hire. 1000 with out one hick up.
04-02-2015, 03:45 AM #8
i have got 100 hrs + running a turbo setup at 18psi all day... besides oil and filter changes... compression has stayed the same..
besides the engine breaking driveshafts and shearing blades off props, at stupid boost levels..the engine has been good..
I put it down to the motor being prepped right..
My 2004 rxp which has the snot beaten it out of my kids has 410 hours.. i hate having to even pull the charger out because the turbo sits there needing less maintenance.. the 04 rxp is 215hp stock...
04-02-2015, 07:24 AM #9
Maybe the fact that water is 1000 times more dense than air and it puts alot more strain on a motor to push a ski through water than a car down the road. A typical car requires about 20 hp or so to keep a car at 60 mph takes a whole lot more to go 25 on a jet ski most likely. The other part is rpm, I know you mentioned earlier about it by my ski spends most of its life over 5000 rpm lol rpm will tear stuff apart quick.
04-02-2015, 07:43 AM #10
you also have a 1.5l making the power of most 3l V6s getting the shit shaken out of it and coming unhooked at high RPMs in an extremely wet environment that is loaded with salt 1/2 the time or more. These skis also don't have the sensor arrays of modern cars
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