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How much HP can the CRF230 handle?

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Hello, 

As you guys know I am in the process of building a turbocharged crf230. I am still thinking about the amount of boost that the 230 can handle. The turbo has a maximum boost of 15 psi which will double the absolute pressure meaning roughly double the hp. I don't know if the engine can handle that. How much hp can the engine handle? I am talking about the rod, crankshaft, transmission... etc. Will they break at lets say 40 hp? 50 hp? I know that what breaks motors is the torque so how much torque? Does anyone sell high strength low end?

Thanks! 

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Edited by Q47
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Hello, 

As you guys know I am in the process of building a turbocharged crf230. I am still thinking about the amount of boost that the 230 can handle. The turbo has a maximum boost of 15 psi which will double the absolute pressure meaning roughly double the hp. I don't know if the engine can handle that. How much hp can the engine handle? I am talking about the rod, crankshaft, transmission... etc. Will they break at lets say 40 hp? 50 hp? I know that what breaks motors is the torque so how much torque? Does anyone sell high strength low end?

Thanks! 

No worry's with crf230 with 40/50hp.You will have plenty,of clutch slipping.Hope nothing breaks.

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It sounds like a fun project but is there an advantage over a 250 2T or 450 4T?  You're in PA.  I would put the turbo onto a Chevy LS motor like the sloppy mechanic. Easy six to eight hundred HP at the tire.

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Crank should hold BUT the connecting rod is pretty flimsy on these. Very similar in size to a cb125s where a XR200R upgraded to a "446" rod over previous "437" rod. The 446 is substantially stronger.  I could check to see if a carillo or Falicon rod is possible for these. As far as trans, on street it should hold up fine. Offroad it will depend on rider.

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It sounds like a fun project but is there an advantage over a 250 2T or 450 4T?  You're in PA.  I would put the turbo onto a Chevy LS motor like the sloppy mechanic. Easy six to eight hundred HP at the tire.

non really, I just love my 230. I should've bought a 450 4t long time ago but got intimidated by the height. I am 5'7". Now I am so in love with this small air cooled beauty. These air cooled engines have something about them that makes them so lovable.

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He is going for 15 psi lol, his engine is going to go pop-pop-boom. Also fuel injection by itself would take him a month to set up correctly. Draw through carburetor set up is the way to go. 5 psi, let the oil leak so it smokes like a 2t who cares. refill and have fun.

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He is going for 15 psi lol, his engine is going to go pop-pop-boom. Also fuel injection by itself would take him a month to set up correctly. Draw through carburetor set up is the way to go. 5 psi, let the oil leak so it smokes like a 2t who cares. refill and have fun.

 

OK, so share your infinite wisdom with him.

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Crank should hold BUT the connecting rod is pretty flimsy on these. Very similar in size to a cb125s where a XR200R upgraded to a "446" rod over previous "437" rod. The 446 is substantially stronger.  I could check to see if a carillo or Falicon rod is possible for these. As far as trans, on street it should hold up fine. Offroad it will depend on rider.

Thanks for the info, this is helpful. I heard Mike Coe's crf is pushing 30+ hp, did he have to change his rod? Any stories of rods breaking?

Edited by Q47

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I have one crank that "chicken-headed" the rod. That is the wristpin end separating from rod. Frank said he has seen another like that. Most likely caused from excessive rpm. If I pull out camera I will photo and measure rods so you can see how light duty the original 230 rod is. Have new Wossner and it appears to be of good casting and materials. The Pro-X rod is a little beefier than stock also. If I was to be beating these things to 30 HP and above I would most definitely be looking for a upgrade. Crank itself is not a issue

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30 RWHP from this old two-valve engine is just an insane amount of power.  According to his builders our two 1984 Al Baker XR265Rs were making RWHP in the low 30s.  These were the big-bore, short stroke engines with two 24mm carbs.  They had everything done to them including 11.5:1 Arias pistons, ported and polished heads, special valve and clutch springs, and the biggest cam Mugen made at the time.  They made very little low-end torque and had to be ridden like a 2T with lots of engine speed and clutch work.  You had to be in the right gear at the right time and the engine lived between 8,000 and 12,000 RPM most of the day.  Al Baker's builders told us to wear earplugs and not to shift until the engine quit pulling which, according to them, was at about 12,000 RPM.  I can assure you these engines went all the way.  The faster they spun the more power they made.

 

My XR265 could stay side by side with my buddy's 1991 XR600 from a dead stop until 50-60 MPH.  His XR600 had a Rob Muzzy pipe with opened airbox and proper jetting.  That is no joke my friends.  When ridden like a 2T these things were insanely fast.  The 84/85 had a tiny chassis which later went on to become the XR200 chassis.  It was basically the same size as our CRF230s with less weight and almost twice the power.  The top-end power the two XR265 engines made was downright scary and silly.  Riding these bikes was literally hair-raising at times.  We used to give the 2T guys fits, especially the KDX riders.  Compared to the stock 1986+ XR250s of the time these two bikes were in a different universe.

 

So using our two 1984 Al Baker engines as a comparison 30 RWHP from this old two-valve engine is a lot!  I just can not imagine it.

 

All that being said the CRF230 engine is far better suited to the type of riding we do today.  My mildly-built engine makes so much power over such a broad range I still find it hard to believe.  My engine is so forgiving it just makes everything seem easy.  Far less effort on the part of the rider.  Is it anywhere near as fast in a straight line?  Hell no!  Not even close!  Is it just as fast in the slow short tight technical areas we now ride?  Yes.  And then some.  I'll bet the CRF230 would walk away from the old Al Baker XR265R where we ride now.

 

And as a testament to Al Baker's builds mine is still running and running well.  The man knew how to build engines to stay together.

Edited by VortecCPI
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IMO:

On a 230, the intake port is the HP limiting factor.

Properly ported and a really well designed cam is the key to achieving those higher HP #'s

No experience personally but:

I have spoken to one of the masters of two valve air cooled Honda engine performance (Terry Miller) and it was mentioned that prolonged really high rpm on a built 230, on the street does break rods. Terry Miller states the Wossner rod is far superior to a stock honda rod.

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Polaco Motos in Brazil http://polacopreparacoes.com.br/kit-crf-230/are building 35HP 300CC kits for the 230F. They are running MX with them and killing the competition. Worth checking out. Going to need a page translater. Tip, CV (Cavalli) =HP (Horsepower) just in case you want to read the number.

I can see they have another connecting rod. That says something about how much the stock connecting rod can take. It seems like it can't take more than 30 hp. Thanks for the link!

Conclusion: If you are going for 30+ hp you better throw away the stock rod and get a forged rod.

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I suspect that Mike Coe always used a stock rod.

Yes they say there kits are 300cc but the only stroke the crank 4mm

Bore 73.5

Stroke 70

297cc = a lot of case welding to the oil pressure galley then redirecting it.

What do you do with the cylinder studs?

What do you use for a head gasket?

How thick is the sleeve?

The big end of the rod hits third gear main shaft with 4mm stroke.

IMO

There not really 300 cc

They never state piston diameter or stroke increase.

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I suspect that Mike Coe always used a stock rod.

Yes they say there kits are 300cc but the only stroke the crank 4mm

Bore 73.5

Stroke 70

297cc = a lot of case welding to the oil pressure galley then redirecting it.

What do you do with the cylinder studs?

What do you use for a head gasket?

How thick is the sleeve?

The big end of the rod hits third gear main shaft with 4mm stroke.

IMO

There not really 300 cc

They never state piston diameter or stroke increase.

Yeah, I see on my big bore that if it's bored anymore then the bore would go into the studs. 

Bore and Stroke: 65.5mm x 66.2mm for stock gives = pi x 6.62 x (0.5 x 6.55) ^2 = 223 cc

Calculating bore for 247.54cc, bore = 2 * (247.54 / pi * 6.62)^1/2 = 6.90 cm = 69 mm

so for a 247.54 the bore is 69mm, assuming that you cant bore the cylinder anymore.

stroke for 300cc and 69 mm bore, stroke = 300 / (pi * (0.5 * 6.9)^2 ) = 8.023 cm = 80.2 mm stroke

so for 300cc no cutting you need a borexstroke of 69x80.2 mm, and you can't have a stroke longer than 70.2mm. So there is no escaping cutting and welding oil passages. you are right.

 

EDIT: they are maybe using the Chinese way of measuring the displacement, by adding the volume of the head. long stroke and big bore gives 

(70mm x 70mm) it displace 269. with CR of 11:1 you have 293.5 cc if you include the volume of the head.

Edited by Q47
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70mm bore is easy and has been done

72mm stroke is more difficult (big end of rod interferes with 3rd gear main shaft) and has been done

277.2cc

IMO

I suspect those Brazil kits are really only 70X70

Edited by adnohguy
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72mm is max I will stroke crank. Literally any bigger and no web left on crank to hold crank pin in. Of course there is more than one way to skin a cat so to speak. We could reduce diameter of crankpin, therefore allowing more stroke due to reduced big end of rod and pin diameter. Honda used a 26mm pin in early 100's vs 30mm of later 100-230's. That would allow additional 8mm of stoke for 80mm with a special rod. Crazy stuff but doable. 70mm is most bore allowed without stud relocation.

 

By the way took some measurements of rod from XR200 vs CRF230. 

.155  vs 230's .115      This is wall thickness on wristpin boss at end of rod

.375 vs .355   for width of beam under wristpin looking at rod edgewise

.613 vs .559   width of rod looking fro "I" beam s

.115 vs .095   width of edge of "I" beam

198 grams vs 186 and this is with a XR rod being a full 6.5mm shorter!!!!!!

 

Interstingly most 230 measurements are similar to light duty XL125S 437 rod except for length.

Edited by teamrude
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72mm is max I will stroke crank. Literally any bigger and no web left on crank to hold crank pin in. Of course there is more than one way to skin a cat so to speak. We could reduce diameter of crankpin, therefore allowing more stroke due to reduced big end of rod and pin diameter. Honda used a 26mm pin in early 100's vs 30mm of later 100-230's. That would allow additional 8mm of stoke for 80mm with a special rod. Crazy stuff but doable. 70mm is most bore allowed without stud relocation.

 

By the way took some measurements of rod from XR200 vs CRF230. 

.155  vs 230's .115      This is wall thickness on wristpin boss at end of rod

.375 vs .355   for width of beam under wristpin looking at rod edgewise

.613 vs .559   width of rod looking fro "I" beam s

.115 vs .095   width of edge of "I" beam

198 grams vs 186 and this is with a XR rod being a full 6.5mm shorter!!!!!!

 

Interstingly most 230 measurements are similar to light duty XL125S 437 rod except for length.

Interesting, thanks for the numbers. Since there is no crank pin included in their kit I would assume their kit is 70x70 269cc, and they included the volume of the head pocket into the displacement getting 294 if their compression ratio was 11:1. That's the chinese standard for measuring displacement. They probably rounded 293.45 to 300 the same way honda rounds 223 to 230. 

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