OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews

OS 21VZ-B(P) V-Spec 20 gallons Long Term Test

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OS 21VZ-B(P) V-Spec 20 gallons Long Term Test


Words: Orhan Isvan
Photos: Senol Sarihan

OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews


This is the story of my OS .21 V-Spec (blue head) engine which I had bought in May 2007. It propelled my Hellfire SS truggy during the 2007 season and my Jammin X1-CR Pro Buggy in 2008. After burning 20+ US gallons (76 litres) of fuel, I assumed that it was finally at the end of its useful life but the engine proved me wrong. It is now propelling my Thunder Tiger ER-1 Rally car and it appears to be capable of doing so for a long time.

Break – In

Starting this engine for the first time was a great challenge for my starter box, even if the engine was pre-heated to 200°F (≈ 93°C). I had to loosen the glow plug for being able to crank it and tighten once the engine started. I let it idle at 200°F (≈ 93°C) for two tanks; stopped, cooled down to room temp, pre-heated again and re-started several times for heat cycling.

I also pre-heated it on the track before every start, until the metal to metal pinch near the top dead centre turned out to be a smooth compression with high resistance. This happened at about 1 gallon (≈ 3.8 litres). Thus far, I kept its operating temperature at 200 – 210°F (93 – 99°C) by running it slightly rich and by being relatively gentle with the throttle. I applied more throttle gradually, until I race tuned it.

Operation / Performance

Most of the time, it ran at 220 – 240°F (≈105 – 115°C) with occasional 260°F (127°C) when the tank was empty. I never let it stop due to dry tank at speed, though. I always stopped the car before the last drop and waited for the engine to stop at idle. I applied after run oil after every day of running, even if I knew that I would run it the next day.

I used OS T-2060 SC pipe and OS P3 glow plug all the time. I tried the P6 plug once, in a very hot day, but the engine refused to idle and ran erratically. I always used the largest carb restrictor, the blue one.

Propelling a heavy truggy like the Hellfire SS is rather a .28 engine task than .21. I know that racers tend to prefer .21 for fuel economy but the .21 engines in question must have more bottom-end power with at least the same top end, if not faster. The V-Spec was not purpose built for truggy applications so I kept my expectations at a reasonable level. What mattered for me was its ease of operation and reliability. It was quite satisfactory in this respect. It required only minor changes in tune due to different weather conditions. It started easily. Head temp was always as I stated above. It was not very easy for the V-Spec to accelerate the Hellfire out of slow corners but top speed was quite fast. I set my clutch for relatively high RPM engagement and ran my Hellfire all season without any engine trouble.

It propelled the truck during the entire 2007 season, pitting at every 10 minutes and consuming a total of about 10 US gallons (≈ 38 litres) of Roktan S20 fuel (20% nitro and 15% synthetic lubricant). It was interesting for me to compute that the distance the Hellfire travelled with this fuel was about 1230 km (≈ 764 miles)*. The engine was in tip-top condition at the end of the season. Or, so I thought!

In April 2008, the V-Spec left the Hellfire to an OS .28 ZX. Its new duty was propelling my new Jammin X1- CR Pro buggy. It did so during the 2008 season, pitting at every 9 minutes and consuming another 10+ US gallons of Byron Gen 2 20% Race Formula fuel. The distance the buggy travelled with this fuel was about 1440 km (≈ 895 miles)*. The buggy was naturally much easier for the engine to accelerate. It was a lot quicker out of the turns and top speed was fairly fast. The buggy did not make a difference in head temp.

*Read mileage calculation at the bottom of the page.

Towards the end of the 2008 season, the engine was no longer in tip-top condition. The front bearing was leaking. This means an air leak (dusty air, of course) and a considerable one. It could not hold its tune like it used to be. I was assuming that the engine was at the end of its useful life because; I would not buy a new piston/sleeve set, a new conrod and new bearings. Buying a new engine would cost only a little more than replacing all these parts.

Therefore, my V-Spec became the subject of my experiments. Besides, the engine had faced challenge from two new buggies, one with an RB C6 and the other with an OS .21 Speed Tuned V-Spec (black head). My old engine could not cope with them neither out of the corners nor on the main straight. Experimenting with it appeared to be a good idea to me. I added one head shim and shifted to 30% Byron Race fuel, in addition to increasing the clutch bell size from 13 to 15T. After a short break-in period (not heat cycling, just being easy on the throttle) my buggy became a lot quicker out of the corners and much faster on the straight. Then, I tried a 16T clutch bell. Acceleration suffered. Top speed would be even faster if the straight was longer but the straight was what it is (70 metres or 230 feet). No matter what, the old V-Spec was no match for these higher end engines running with 20% nitro, especially during acceleration on the straight.

Disassembly / Renewal

I disassembled the engine just for taking the piston and conrod for using them as a key ring. It was visible from outside that the front bearing was wrecked. The rubber shield was coming out and I was pushing it back into place! I was certain that the rear bearing would not be in good condition either because dusty air was obviously penetrating into the crankcase through the front bearing. I was a little curious about how the engine still had compression under these conditions, especially when dust was in the crankcase.

I must say that I was not only surprised but also, I felt respect for this engine when I saw its piston/sleeve. So, I decided to revive it. I replaced just its bearings and conrod. It is running great, now. I think the pictures show that the engine deserved this treatment, rather than being thrown away.

Pic 1 and 2 show how far the piston can be pushed up in the sleeve. If they were totally worn out, the piston would reach the top of the sleeve. The distance in the pictures show that the piston/sleeve set still have a lot of useful life. The scratches on the top of the piston are my work! I cleaned the carbon build-up with a sharp tool (but I was careful enough for not scratching the sides of the piston).

OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 1
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 2

Pic 3 shows the piston after 20+ gallons. The conrod is new. I used an OS Speed conrod. Pic 4 and 5 show the condition of the sleeve. If the piston or the sleeve were scratched, they would loose compression and they would not be usable despite the good distance at pictures 1 and 2.

OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 3
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 4
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 5

Pic 6 shows the conrod and the bearings that I have replaced while pics 7 and 8 show how much the conrod can play when it is connected to the crankshaft journal. Without play, the conrod would remain between the blue lines. Even new conrods have some play and this amount of play may still be acceptable but if I did not replace it now, I would have to disassemble the engine later, just for replacing the conrod.

OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 6
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 7
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 8

Pics 9 and 10 show the new ceramic bearings I have installed. The rear bearing is from TKO and the front one is a double shielded ceramic bearing from Power Save Racing.

OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 9

OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews

Pics 11, 12, 13 and 14 show various components after 20+ gallons. I had removed the back plate a few times. It was not scratched like on pic 14. Worn bearings or conrod must have enabled the bottom of the conrod to contact the back plate. I did not replace it though. Pic 15 shows the actual state of the engine.

OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 11
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 12
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 13
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 14
OS 21VZ-B(P) V-Spec 20 gallons Long Term Test Reviews
Picture 15

It is common knowledge that bearings do not last as long as the other moving components in nitro engines. I should have replaced at least the front bearing at the end of the first season. This would prevent dust penetration into the crankcase so the engine would not be subject to such an abrasion during the second season. Therefore, the rear bearing, the conrod and the piston/sleeve would be in better condition after the second season.

Despite the dust abrasion, it was still not too late for replacing the rear bearing and the conrod and the piston/sleeve were exemplary. I whish I had not neglected the front bearing issue.

After 2670 km (1656 miles) of screaming on different cars and with different fuel, including nitro percentage variations, the V-Spec left the buggy to a Sirio S21 CL7B STI Tuned engine and started its 3rd season, this time on a Thunder Tiger ER-1 Rally car.


The V-Spec is a good performer. However, it is not in the contemporary premiere league where drilled, epoxy filled, coated and balanced crankshafts, ceramic rear bearings, longer strokes, sleeves that are machined and/or hand crafted from outside, etc., are now common practice.

In terms of longevity, its piston/sleeve impressed me, even if its bearings, especially the front one did not. I see no reason why the new ceramic bearings and the new OS Speed conrod wear out before another 10 gallons or so. Will the old piston/sleeve last so much? I don’t know but in view of their actual condition, all I can say is “why not?” Only time will say.

As for value, the V-Spec was in a very good position when I bought it but nowadays, the above mentioned state of the art Italian engines are becoming more and more affordable. Neither a little price reduction of the V-Spec nor the hefty (if not exaggerated) price tag of its “Speed Tuned” version seems to place OS Engines in a favourable position in terms of value for money.

*Method of calculation

10 min pits ≈ 150 ml/10 min
18 sec/lap = 33,33 laps/10 min = 33,33 laps/150 ml.
146 meter laps x 33,33 laps = 4.866 meters / tank = 4.866 meters / 150 ml
3.800 ml (≈ 1 gallon) / 150 ml = 25,33 tanks
25,33 tank x 4.866metres/tank = 123.256 meters/gallon = 123,25 km/gallon
123,25 x 10 gallon = 1.232,5 km

9 min pits ≈ 125 ml /9 min
16,6 sec/lap = 32,53 laps / 9 min = 32,53 laps/125 ml
146 meter laps x 32,53 laps = 4.749 meters/tank = 4.749 meters / 125 ml
3.800 ml (≈ 1 gallon) /125 ml = 30.4 tanks
30,4 tank x 4749 meters/tank = 144.369 meters /gallon = 144,37 km/gallon
144,37 x 10 gallon = 1.443,7 km


Sylvain Lafrance

Sylvain Lafrance

Hello, my name is Sylvain Lafrance and I am the man behind MyRCBox.com. I have bought my first hobby grade RC in the early 90s. With years, what that started as a simple hobby, quickly became a strong passion. I am so much passionate about R/C that I have created MyRCBox.com in 2006 to share my experiences with R/C products that I use for racing and bashing. Follow me !

View all posts by Sylvain Lafrance →

24 thoughts on “OS 21VZ-B(P) V-Spec 20 gallons Long Term Test

  1. Really good review and very informative I really enjoyed reading the article. I know which engine/motor to get next..

  2. Great absolutely great article. It sure would be nice if the Car mags had long term articles like this where they really dissected the engines. Great photos, thanks for sharing.

    I’m new at this but have an OFNA DM1 1/7 scale on road car.
    In your article you right about the sophisticated engines with the balanced shafts and ceramic bearings ectera on the market now that are more powerful, what would you suggest and why.



  3. I don’t really agree with the Authors Opinion regarding the V-spec not being “in the contemporary premiere league” of engines I’ve been running Vspecs for 3 years now and i’ve also tried other “newer engines” like the Tuned GRP and the Novarossi Plus4, and honestly the O.S is still competitive and in a lot of cases better than many newer engines in terms of power and run time.
    Many will agree with me.

  4. Thank you all, for your kind words. I am so pleased that you enjoyed my article.

    Jim, I don’t have a DM1 but it is my favorite shaft driven on-road car. What about helping you for choosing an engine rather than suggesting a particular one? First, let me know if you have a starter box or if you are willing to buy one. Then, what are your intentions? If you will race, you must have some limitations like displacement, etc (the DM1 would not be allowed in all sanctioned races. If you will not race, you may not need one of the highest level competition engines.

    Paul, what I meant was that the “OS Speed” is in the premiere league.

  5. Thank you for the reply Orhan,and thanks for the continued help.

    I have a starter box for it already and it works great. It’s an OFNA dual motor box. I really just want the car to be as fast as it can be around a track. I plan on trying to organize some 1/8th, 1/7 on road racing for the DM1 pro which I have and the spec class.

    I am a retired engineer by trade so I thirst for technical information on engines, drive trains, suspensions etc. Any reference material you could recommend would be appreciated it.

    Thanks again

  6. Jim, on-road cars are more efficient than off-road cars in making use of the available power due to their 2 speed transmissions. Therefore, on-road engines lack the low-end grunt of off-road engines but in return, they produce more top end power at higher RPM. The transmission compensates for the low-end.

    Most on-road engines, if not all, have smaller cooling heads because Lola type bodies allow better cooling. If the DM1 body will allow sufficient cooling (if you will allow racers to cut large openings on the body), an on-road engine would be the ultimate performer. They are very expensive engines, though.

    If cooling or budget are limiting factors, one can go with off-road engines with the DM1. There are .21, .24 and .28 engines in this category; aimed at buggies, truggies and monster trucks, respectively.

    Tell me which way you want to go. On or off-road engine? If off-road, which displacement? I would suggest .21 even for off-road engines but this would leave DM1 RTR engines out. If you allow larger engines, people would run racing .28 engines. This would probably render the DM1 uncontrollable because already excessive low-end power would be further amplified by the transmission.

    Determine the engine category first, then I will help you choosing one within that category.


  7. Hello again and thank you again for taking the time.

    First and this is just for my knowledge why are the .21 on road engines so expensive compared to the .28 buggy engines?

    That aside most of the people running will not cut the heck out of the buggies so lets look at it basically that way and consider off road engines.

    You said if we go .21 it would eliminate DM1 rtr engines, I don’t understand that or what DM1 RTR engines are.
    Based on that what would be the best .21 and which would be the best .28

    A few other questions.
    If I go with a .28 and decrease the ratio between the engine and drive train to reduce torgue wouldn’t that help reduce the high bottom end torgue but still give me more mid range torgue for winning in the corners and short straights?

    Also which are the engines with better useable high rpm capabilility because if I get a high RPM output engine I can gear for less torgue and the combination of that gearing and high rpms will give me crazy top end speed.

    Bet you never thought you were getting inovolved with such a pain.


  8. Take it easy. I wouldn’t be involved if this was a pain:) .21 on-road engines are expensive because they deliver more specific power (power/displacement)than any other RC engine. Power that comes from displacement does not require as much ingenuity, as sophisticated designs, as valuable materials and as delicate machining processes. On-road engines are like the F1 engines of RC.

    The DM RTR has a Force .28 engine. Most high-end .21 engines would outperform this RTR engine but a high end .28 would be too much power for anything lighter than a 1/8 truggy or monster truck. The more so, if the car has a 2 speed transmission like the DM1. Yes, taller gearing will convert this excessive power to excessive speed while maintaining the car’s controllability but this would be viable for very long straights. Longer than most race tracks have.

    A .21 buggy engine seems to be the optimal choice for your case. Since you will use it for on-road duty and since a 2 speed transmission will be at the engine’s disposal, forget about low-end grunt (unlike you would do for choosing a buggy engine) but concentrate on high end power.

    For this, you will be looking for longer stroke and higher number of ports as if you were choosing an on-road engine. There is no direct relation between the number of ports and RPM but usually, higher number of ports are designed for improving top end performance. A longer stroke engine is like a long legged runner. As long as he may make the same number of steps per minute, the long legged runner will be faster than his short legged competitor. If a long stroke engine can rev as high as his shorter stroke competitor, it will be faster. Long stroke enhances torque. Combined with high rev, it delivers more power. Make sure that the engine has a ceramic rear bearing, though. High revving long stroke designs put more stress on the bearing.

    Turbo plugs are also preferable in your case. They make engines a little more powerful at a little higher RPM. They are not necessarily an advantage for off-road but they are for on-road.

    Drilled, epoxy filled and balanced crankshafts would be snappier when accelerating (due to their lower rotating mass) and smoother at high revs (due to being balanced).

    Werks, Sirio, Novarossi and RB are the first ones to come to my mind for having long stroke (16.7 mm or longer), 7 port engines in their product line with lightened and balanced crankshafts but check out others as well. The new Novarossi Toro Nero (the 7 port one) has an unheard of 17.6 mm stroke but the engine is too new for having an opinion about. RB and Novarossi do not use ceramic bearings in their off-road engines but one shouldn’t expect a high wear bearing (or any other high wear material) in them.

    For your case, also prefer high RPM tuned pipes. Unless you will apply EFRA/IFMAR rules, you are looking for a 086 pipe with appropriate (short) header. If these rules will apply, use the factory recommended and branded (aka expensive) pipe.

    I hope this has not been more confusing than helpful.


  9. thanks again for all your help, just kidding about the ‘pain’ thing hope you were not offended.

    Now I must go off and start looking up specs, for the various engines and also the potential tracks that we may run on.


  10. Great write-up!
    Didn’t know that an RC engine can go that long w/o any components being replaced at all!
    My engines have not seen 10gal each, most of the time I get a new one for the new season..
    I have ran the V-Spec before, great engine for the price!
    And now I’m running the Ninja JX21..
    I totally agree on replacing the front bearing every season, anyway they are much cheaper than the rear ones.
    But I’d have to add that you cannot use the OS Speed conrod in the V-Spec.
    The oil lubrication hole on the V-Spec is at the crankshaft pin whereas the oil lubrication hole for the Speed and the Ninja is on the conrod itself.
    Maybe, just maybe you can use the Speed rod in the V-Spec cos you’ll have 2 oil lubrication holes?
    Correct me if I’m on wrong?

  11. No Jim, I am not offended at all. Good luck with your shopping.

    Faizal, thanks. You are right on the lubrication holes but an extra lubrication hole would make no harm.

  12. Thanks for such a great article. I enjoyed the read. Having owned 2 standard V-Spec’s a JP Modifyed version, I’m very curious to find out more about the condition of the conrod pin on the crank.
    If you have some time one day, and perhaps a digital vernier caliper, could you very carefully measure the roundness of the actual conrod pin and report the maximum and minimum diametres? They tend to wear in an oval pattern, and become out of round, causing excessive slop that will lead to glow plug consumption and very difficult tuning.
    Please note when measuring that the out of roundness of the pin is rather uneven, meaning that it will be different when closer to the crank as compared towards the end of the pin. Many measurements will be needed.


  13. Thanks, Brian. I did so but unfortunately, I didn’t note my measurements. I have even the pic of the crankshaft and a close up view of the journal (crankshaft pin) but I forgot to send them to MyRCBox. I can send the pics anytime. I didn’t know that, one day, I would write an article on what I did. This article was a bit in a hurry. If I write another one for another engine, you would see a lot of measurements, including the journal.

    However, the angle at my pics 7 and 8 are -partially- due to the combination of the ovalness you have mentioned plus the ovalness of the conrod bushing. Since the conrod bushing must normally have a higher share in this total and since the total is not -very- excessive, I think the conrod journal must have reasonably low wear.

    I whish I had noted my measurements… Maybe next time. On the other hand, even if I had kept notes, do we have a reference on how much ovalness is acceptable? If so, I would be delighted to know.

  14. I am nearly illiterate when it comes to the content but being a scientist I can tell that this is almost a scientific article. It might even be considered peer reviewed with all the great comments you got! I’m so proud of my dad 🙂 Maybe next you’ll write about the first car we built together.


  15. Great review indeed. I have to agree with one of the comments from Paul though. These ‘standard’ V-Specs honestly can keep up with any other engine out there. I strongly believe they are the bench mark of all design as far as model off road engines go. I have had one that is probably a bit older than this one reviewed which I still use, and to this day have never had one flameout. They have as much low – mid – and top end power as engines twice the price, yet the crankshafts and porting are some what basic to other models.

  16. Thanks, Duncan. The V-Spec was, indeed, one of the most powerful engines when it was first introduced. Many years passed since then, though. When I was running the V-Spec on my buggy, an OS Speed outperformed my V-Spec. Then, an RB C6 did. Some other engines also can. In my experience, the Speed is not only a little faster. It is way faster. In fact, if it was not faster, wouldn’t the standard V-Spec have denied the reason of existence of the Speed version?

    I now have a Sirio S21 CL7B STI Tuned engine with the hope of catching the OS Speed. My new project is to compare the performance of these engines on my own track by making use of a lap counter and a radar gun. I will first try to determine the optimal clutch bell size for each engine on the same track and then, try to compare the performance of these engines while they will be equipped with their respective optimal clutch bells.

    I will be as objective as I can. Any suggestions for being more objective is welcome. This project may take some time but at the end, I will share my findings with the RC fans.

    Please let me know the methods of comparison that would make my project more interesting and more credible.


    P.S. My daughter sent a lovely comment. I am also very proud of her. Please rest assured that, I will be more objective towards the engines than she is towards me.

  17. hi all this was a very interesting article on the os v spec .
    i have never in my life been into car racing and the like but was into other things .
    anyway im 49 and have gotten into offroad rc racing and am loving it.
    i bought a second hand xray xb8ec with a os v spec in it and knew nothing about motors .i got told never buy second hand but this thing has been abused by me in tuning stakes from not knowing what i was doing but i do always clean this motor out after using with a mixture of petrol and atf fluid .
    this engine now that ive learnt about tuning and stuff is still going strong and have just put it into my GS team pro truggy and i hope it has more bottom end power than my ws7111 .i think it will as is 3 port engine and with extra heavy xray clutch springs it should go well.
    how much fuel has been through this v spec motor before i got it i have no idea but it looked well used .
    i have put through it in seven months of learning about 5 to 10 liters of fuel i think .well anyway it is a really great motor an lets see how long it goes for.

  18. Gotta love OS. May not be the fastest engine on the track, but it will be the only engine left running after the dust settles. 😀

    the hardest bit of it is that you race yours. Racing is much rougher on an engine than backyard bashing. one wonders how long this engine would last in that position…

  19. Thanks for the great review. I have one of these on my Inferno MP777 WC. I had major difficulties starting the engine for the first time. Actually my starter box batteries (7.4V 5000mAh) were flat by the time I could get it running!

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