Predator 212 performance issues

[Papapoo]

Hi everybody, I just finished building a Non-Hemi Predator 212 with 26 LB valve springs, billet connecting rod, makuni clone 24 mm carb, .308 cam, velocity stack, trumpet, billet flywheel, 10T “max torque” clutch, and a 40T rear sprocket. All this on a 5” FLR frame. I’ve ran into an issue of only topping out at ~45 MPH, when I thought I’d be going ~55+. Are my expectations too high, or is something wrong with the bike. Please help!

 

[creia]

What RPM are you hitting when you are "topping out at 45 MPH"? It would be helpful if you knew that. If you don't have one, get yourself one of those cheap tachs on Amazon where the signal wire wraps around the spark plug wire.
Michael

 

[Papapoo]

What RPM are you hitting when you are "topping out at 45 MPH"? It would be helpful if you knew that. If you don't have one, get yourself one of those cheap tachs on Amazon where the signal wire wraps around the spark plug wire.
Michael

I do not have a tach, are you able to send me a link for a good, cheap one? If not that’s ay-okay.

 

[ole4]

Amazon.com: Runleader RL-HM011E Digital Hour Meter & Tachometer | Maintenance Reminder for Gasoline-Powered Lawn Mower, Tractor, Generator, ATV & Small Engine Equipment : Automotive

 

[ole4]

What diameter is your rear wheel What has been done to the head besides valve springs? 4to 1 ratio may be more gear than your engine can pull. Try a larger rear sprocket. A 308 dyno cam with the right head and a good intake and exhaust should pull good to 7000 rpm.

 

[Davis]

Geared way too high. You could try going down a big hill.

 

[Papapoo]

What diameter is your rear wheel What has been done to the head besides valve springs? 4to 1 ratio may be more gear than your engine can pull. Try a larger rear sprocket. A 308 dyno cam with the right head and a good intake and exhaust should pull good to 7000 rpm.

You’re saying get a larger rear sprocket? And nothing is done to the head. I was going to hand port it using a Dremel but I misplaced it. And I’m not sure about my rear tire diameter, I’ll get you that info today.

 

[Papapoo]

Geared way too high. You could try going down a big hill.

Lol okay, what would you recommend for a replacement rear sprocket?

 

[sparkwizard]

Try to leave an inch of rubber outside the sprocket. Example: go as tall as you can without scraping the chain on the ground in turns. How tall is your rear tire? Height, not wheel size. What pitch is your chain? (35, 40/41)

 

[Creativehands]

You need to change a few things. A 1.60 ish, or lower gear ratio will put you into the 55- 57 mph range. Hope this helps you.

 

[Papapoo]

Try to leave an inch of rubber outside the sprocket. Example: go as tall as you can without scraping the chain on the ground in turns. How tall is your rear tire? Height, not wheel size. What pitch is your chain? (35, 40/41)

Wouldn’t that make the bike super torque-y and sacrifice top speed? I’ll measure the rear tire soon, as I am busy at the moment. Will get you that info ASAP. And I’m sorry but I’m not sure what “Chain pitch” is, I just have a basic 420 chain.

 

[sparkwizard]

420 was the answer I wanted, thanks.
Torque is produced by your engine, not your gear ratio. Your gear ratio multiplies the torque produced by the engine. What has been suggested above, is that your engine is not producing enough torque to pull the bike any faster with the geaing you have now. You engine is doing the best it can, but it needs to be able to rev higher to take advantage of the cam you have in it. It is a higher RPM cam, and you need to gear the bike to let it rev. Yes, you need more "torque multiplication". It seems like it will kill top speed, you are correct, but it will be much better than riding downhill all the time, and pushing it back to the top, right? There will be a sweet spot where the RPM maxes out at the top speed you want to achieve.
Right now, your gear ratio is 4:1. I would shoot for 5.5:1 if you can find a 55 tooth and it is not too tall for your tire, that would be a good start.

 

[Papapoo]

420 was the answer I wanted, thanks.
Torque is produced by your engine, not your gear ratio. Your gear ratio multiplies the torque produced by the engine. What has been suggested above, is that your engine is not producing enough torque to pull the bike any faster with the geaing you have now. You engine is doing the best it can, but it needs to be able to rev higher to take advantage of the cam you have in it. It is a higher RPM cam, and you need to gear the bike to let it rev. Yes, you need more "torque multiplication". It seems like it will kill top speed, you are correct, but it will be much better than riding downhill all the time, and pushing it back to the top, right? There will be a sweet spot where the RPM maxes out at the top speed you want to achieve.

Thank you very much for explaining that in great detail, where I live and ride is very hilly and there are very little flat areas. In a little while I’m gonna try and do a top speed test going down one of the larger hills nearby, which I have not done yet. With the current gearing the bike pulls really good I just am not satisfied with the top speed, which I assume means it’s torquey? And if I wanted to get the maximum torque I could out of the bike, shouldn’t I get a torque converter vs a clutch?

 

[sparkwizard]

Thank you very much for explaining that in great detail, where I live and ride is very hilly and there are very little flat areas. In a little while I’m gonna try and do a top speed test going down one of the larger hills nearby, which I have not done yet. With the current gearing the bike pulls really good I just am not satisfied with the top speed, which I assume means it’s torquey? And if I wanted to get the maximum torque I could out of the bike, shouldn’t I get a torque converter vs a clutch?

Did you add a billet connecting rod? Without a tach, be careful letting it scream down a hill. It will go!
Edit...never mind I see in your initial post, you did. Be safe and have fun!

 

[Papapoo]

Did you add a billet connecting rod? Without a tach, be careful letting it scream down a hill. It will go!

Yes I did, it was one of the ARC ones that come with bearings off GoPowerSports.

 

[Papapoo]

Did you add a billet connecting rod? Without a tach, be careful letting it scream down a hill. It will go!
Edit...never mind I see in your initial post, you did. Be safe and have fun!

Thank you, I’ll get you all the results of that test in a few.

 

[massacre]

Are you building this bike for top speed?

 

[Papapoo]

Are you building this bike for top speed?

Yes, top speed.

 

[massacre]

Yes, top speed.

Reason i ask, is that a top speed only build will be totally different than most other builds.
Kinda like how cars that race at Bonneville are built totally different than say a top fuel dragster.
This might sound weird but i found that ceramic bearings made a big difference in the rolling resistance on my drag bike.
Once you get your gearing figured out, there are small things you can do to increase top speed, such as good bearings, the right tires, lightweight parts, etc.

 

[Papapoo]

Reason i ask, is that a top speed only build will be totally different than most other builds.
Kinda like how cars that race at Bonneville are built totally different than say a top fuel dragster.
This might sound weird but i found that ceramic bearings made a big difference in the rolling resistance on my drag bike.
Once you get your gearing figured out, there are small things you can do to increase top speed, such as good bearings, the right tires, lightweight parts, etc.

Yeah I totally understand that, I want good acceleration and good top speed as where I live there aren’t very many straights. I just wanna get the main issue figured out and then do all the small things.