2.5/3.0hp B&S performance parts?

[Boomstick]

Howdy hey again,

Anyway, I've settled on using the 2.50hp engine I have (circa 1968) for a board-track racer inspired bike (to be run as a really fun moped!). That being said, I can't seem to find any real performance parts for either the 2.5's or 3.0hp powerplants.

My goal is to not produce mondo HP numbers, but build something that is virtually bulletproof for a second board-track racer I plan on building (one for gentle cruising, & one for a different kind of fun :smile: ). I plan on going with a forged connecting rod, forged piston, better bearings, & installing much stiffer valve springs (including lapping them into their seats). And yes, the flywheel will be replaced with a proper performance unit (if one is available for these smaller engines to prevent a kaboom. Both units have cast iron bore liners & very, very low hours.

My question is, would a 2.50hp or 3.0hp engine with a stock crank (I'm not sure where to find performance cranks) hold up to extreme revs (6000+)?

I've been bitten by the B&S performance bug. A friend of mine was kind enough to lend me his Animal powered minibike, and it is a legitimate monster. Way more fun than I should have had on 6'' wheels. :thumbsup:

Thanks in advance!
Boomstick

 

[5horsebriggs]

Theres realy no upgrades for those engines do ure self a favor and get a five hp or and predator

 

[creia]

"I've been bitten by the by the B & S PERFORMANCE bug." (emphasis added).
Stop wasting your time and $$$ with 2-3 HP:thumbdown:, and get a 5HP.:thumbsup:
Michael

 

[MoTo-BunnY]

Yeah, the 2-3.5HP engines are great and all for small mini bikes but you can't find any performance parts for them.

The 5HP Briggs & Stratton were the big kart racing engine for many years and there are performance parts galore for them. If you want to tinker with a B & S engine, the 5HP is the only way to go among flathead engines. :thumbsup:

 

[nigel]

someones gota make them. thats all you can fit in small bikes like skat cat, im tryin to build one with an aluminum 2.5horse

 

[joshua. c.]

theres plenty you can do for power with that engine but as far as high revs go there are no parts to be found to make it safe. you can port the engine, send the cam out to be re ground for more lift, try fitting a larger 5hp carb to the 3 hp tank and get a header made for it. iv herd once you hit 7000 rpms with that engine the dipper brakes and a lack of oil fuses the rod to the crank. so try not to over rev it.

 

[Boomstick]

I wouldn't want to try a 7000rpm pull on the cast rod & the iron flywheel (more-so the flywheel!).

I thought there were billet rods for these? If that was the case, a nice, peppy 4500rpm-ish build would be cool to do.

 

[briggsraptor]

I agree with everyone else. The 5 horse is the way to go! If it's to fast add a restrictor plate. :thumbsup:

 

[CarPlayLB]

Is the smaller diameter flywheel that the Jr Drag guys use the same taper as the small Briggs? I see them listed as 3HP flywheels. I guess what I am trying to say is, are the tapers on both the smaller Briggs and the 5HP Briggs the same?

6603 ARC Billet Flywheel, Adj. 3HP Diam. Jr Dragster

That would hep ya get closer! Now just go spend a ton of money on a billet rod and you are there!

 

[creia]

iv herd once you hit 7000 rpms with that engine the dipper brakes and a lack of oil fuses the rod to the crank. so try not to over rev it.

A stock Briggs 3 Hp will never come anywhere close to reaching 7,000 rpm. At around 5,000 rpm it will start to float the valves.
Michael

 

[joshua. c.]

if the engine cant reach the 7000rpm braking point, it sounds like you will be ok. i havent seen or herd of to many built up 3hp briggs. if you do mod it let us know how it goes, it woold make a cool build thred.

 

[Boomstick]

5000rpm's is probably stretching it by a fair margin to be honest with all of you. I sincerely doubt the flywheel is a danger at 5k, but the stock rod is probably not going to like it.

I have a really nice low hour '71 3hp that might respond nicely to a small mikuni, a header, port & head work. I'd figure limited exposure at 4500 or 4000rpms would be safe & bring a little life into these engines.



The original reason I asked was because I'm really surprised there's virtually NO performance parts for these... and there's zillions of the things everywhere. You'd think by now someone would throw their hat into the ring (hello ARC) and make billet rods along with other goodies for them.

Small block power!

 

[CarPlayLB]

What makes the rod come apart? Is it lack of oil? Stress from combustion? If the rod was stress relieved, would that help?

I have made an intake that takes a small PZ style carb, I think it's 16mm, and I plan to make it work.

'Nother question. Raptor engines use a cast iron flywheel and live at 7K RPM. What is different about those than a standard flywheel? I can't believe Briggs made two different ones.

 

[Briggster]

Ask the guys on 4cycle.com I remember reading a build thread on a 3hp someone did. I recall he machined and installed 5hp intake and exhaust valves. The tillotson style intakes for a 5hp will fit your 3hp and the 3hp billet briggs flywheel arc sells fits your 3hp. Cant help with a rod though. You might talk to tim isky, imsure he has done 3hp cams before.

 

[onebadslingshot]

There is plenty of basic things you can do..first ditch the point set up so you can use an offset keyway to advance your timing.A little port work.A free flowing exhaust (Header) A stiffer set of valve spring`s and switch over to a 5hp Tech. carb....and if that isn`t enough power you can do a carb redrill to E85 or a little bigger and run Methanol or 20% nitro like i run...

 

[oldfatguy]

you can stress releve the stock rod to holp it hold up a little better. That consists of polishing the casting seam off of it. does it do anything ? who knows for sure but it makes it look nicer. If you search this site there are several good posts on how to get more performance out of the 3hp briggs . Most don't cost anything to do. porting, mill the head, eyebrow the valves, fire groove the head. polish the piston. cut the compression release off of the cam. Even with all that done it still isn't a 5hp briggs. most of those mods will help the bottom end power. don't try to push the RPMS too much because they weren't ever designed to spin too fast. I mean it's a lawn mower engine for Gods sakes. LOL