DIY Ram Air

Would adding a funnel and hose to the air intake on my go kart engine have the same effect as ram air? Would I have to do anything special to my carb after doing this? Would I see a big increase in power? Thanks - andrew

im guessing your go cart doesnt go much faster than 40mph and at that low of a speed you would probably not feel an improvement.

i think you should try though cause the whole thing wont cost you more than a few dollars

I professionally raced go-karts for a few years...what kinda kart and engine? what size? 4/2 stroke? where'd you get it? is it made for racing or recreation? ALL this makes a BIG difference.....

im thinking of going down to walmart and buying a chepo breather and crappy $9 air filter to see if there is any difference at all...i think moving the air intake away from the engine and using a larger diameter tube will give more of an improvement than ram air...but if you do try it (hell its cheap why not) get a K&N filter that replaces an OEM square filter...then build a box to hold it and have it facing forward....more flat surface area=more pressue so that may actually work....ways of giving your go-kart performance are...Removing the govenor, adjusting idle speed to a high RPM, adjusting top end speed to a high RPM, taking your head off and smoothing out the "sharp edges around the intake/exaust side of the cylender (prevents hot spots) giving it beter spark advance (if using a magneto this is wasy...just adjust the flywheel a few degrees) and running a high compression and using ethynl instead of gasoline... but just remember your 5 or 8HP briggs and stratton isnt made to spin at 6,000 RPM or run a 9:1 compression....so it will be very highmantainence... but i have see nwhere the little 150cc 5hp 4stroke briggs make 15-20HP and 18-25ft/lbs of torque....also using a Jr. Drag carbrator (larger bore) and intake manifold (also larger bore) will give very large performance increases (as much as 2 HP...but when you are talking about an 8HP engine that is a 25% increase)....

Its a briggs and Stratton and its 3hp, 8cubic inches its a 4 stroke , not sure if its for racing or recreation , but i'd say recreation. I havnt built the frame yet. Another question , is 3 hp enough power for a guy that weighs 190 to get around in? I'm thinking most likely not and a 5 or 6 hp would be a lot better engine to get, correct?

if you buy new...get the 12hp or the horizontal V-Twin OHC...hella lot more HP...3HP will move more htna you think...just not at any high rate of speed...you may be able to get 8hp out of it if you want to do the MODS...kart engines are very basic engines so if you know the basis of a 4 stroke you can get yourself around...

I dont have the kind of money to buy a 12hp. My friend has a 6hp and it goes REALLY fast with him driving and me riding on the back.

Really fast as in acceleration or top end... i can switch out some gears on mine and make it go 50 where as right now it iwll only go 40 but i will be chokeing my acceleration...or i can swich some out and only alow it to go 30 and accelrate there very quickly...i have found just about the right balence on my kart...just enough to where i can get a lil squeak on cement or some rooster tailon dirt when i want to...but no so much that (since i dont have a diferential...just a soling bar as an axle) when i go to turn and i get on the gas too soon i spin out because i have too much torque to the wheels...i have a torque-A-Verter...its a variable diameter pulley that changes pulle ratios based on load and speed...so this allows me to go up steep hills and throught the mudd and water but also get failry decent speed on pavement even with me only having and over all diameter tire size of 8.5"...they are kinda expensive but well worth it since you have a pretty small engine...i think mine was 150 for an 8HP... its basicly a cyntrifical pulley clutch and a variable diameter pulley that in turn goes through a shaft to a sprket which then transfers energy yo another sprket via chain thich then gives the wheels their torque... i have dual band brakes on mine...they will lock up even with me and a fat firned on the kart on dry pavement....and i have no suspension on my kart so dirfting is easy and fun...untill i hit a pot hole are roll over only having lap belts....

Around here at like princess auto and such, a 6hp honda engine is 399 candian. Or it might have been 5, but around there. there are some that are like 15hp that are about 1200 bucks.

your could also go down to a junk yard and find a small engien with a horizontal shaft that isnt seized....dont buy honda...stick with briggs or techumpsen (i know i spelt that way wrong)

Whats wrong with the honda engines? MY friend baught a 6hp honda engine and it works great.

hook up a blow dryer to it, forced induction for ya lol

ok, here's some mod's for ya, from a pro kart racer...

Get a bigger bore carb, it'll cost a little bit. Smooth out ALL rough edges on the inside of the head, EXCEPT the outer rim, where it meets the gasket. Get a superlight piston. a shallower head maybe. K&N makes an airfilter for it, at least the 5hp. Run methanol, used to be $5/gallon, not sure bout now. Advance the timing, do this by pulling off the flywheel, take out the piece of 1/4" stock (the little bar) you can buy a new one or make your own, but it should look like a square S, so that the flywheel is adjusted forward half the width of the stock (or 1/8" at the crank, not sure how many degrees that is). Get an Autolite Platinum plug. Take your pullstart OFF. Only hold it against the engine when starting it, then pull it off (reduces drag against the crank).

Our karts were setup similar to this, although we had 5hp engines and used 3hp flywheels (stronger spark). We had direct drive via Centrifugal Clutch (the clutch was on the crank with a 12 tooth gear chain driven to our choice size gear on axel). Live axel (solid). With a 68 tooth gear in the rear, we could hit ~55mph on the track (1/8 mile). With a 53 tooth gear on the back, we reached ~110 on the Freeway (paced by friend in car). We also rebuilt our engines weekly and ran synthetic oil with a crankcase breather. We managed 14.7hp out of a 5hp block. A LOT of performance is in your fuel/air mixture.

Take it from a pro and have fun!

*EDIT* - With a 68 tooth on the back, we could stomp on it and spin the rear tires for a while on asphalt. We also had our racing clutches set for a quick grab at low RPM instead of gradual at a higher RPM.

or you could save your pennies and buy an old YZ125 motor...and Jet-Lee you forgot to tell him if running methanol or ethnyl to replace all steel fule fittings in the fileline and carburator with brass fittings as steel will gat all F'd up from the alcohol...

sorry for the SPing im tired as hell...hurricane started flooding the yard agian so i was up till 1 last night pumpin it out and then i had to wake up at 7 this morning to cut up a tree that was blocking the road... :-\

Is the hurricane gone now? And also is there something wrong with the honda engines or do u just not like them? :feedback:

ya the hurricane is gone now... the sun is shining... still a binch of water in my yard and ive been fooling with the damn govenor on my kart for a while trying to get it to run right so i can go muddin' :-P but anyways...there is nothing wrong with honda engines...but the most commonly used kart engine, fram some 7 y/o's firsk kart to a 20 y/o's world calss racer, that it has proven its self time and time agian...on top of there are many books that tell how to make a performance engine out of your briggs and stratton...and Techumpson engines are basicly like honda and acura...except i dont beleive the compaines are one in the same...if you know how to work over a briggs yo ucan work over a techumpson....

Yeah, Briggs and Tecumseh are pretty much the same...and both are really easy to work on...

CB, you're right about the brass/steel deal with methanol, I just didn't think of it because we always ordered ours with brass, so we never had to switch anything out, good point though.

About the original question: A funnel is the exact opposite of what you'd want for ram air. You want a cone where the small side is pointing towards the airflow, big side towards the intake of the engine. A funnel pointing foward will give the air a nice easy path to revert out of the intake and give you little to nothing. A reversed funnel will trap air in, no path to revert, better converting the moving air(well moving intake, same thing) to pressure.

I'm sorry but IMHO, your full of $h!t.

Lol, funniest thing I've seen today. I agree though I think he's full of shit.A regular funnel would be better , not some flipped cone thing, because it would funnel all the air towards the intake correct ?

Yup, but it wouldn't make any noticeable difference unless you were travelling at about 100mph. Get a cone shaped filter. And your funnel idea, make sure the big end is facing forward, the direction you plan to go. I just re-read duplox's post, and it would make sense if the air filter was BEHIND the engine.
In our racing karts, we had cylindrical filters sticking straight up off the carb, higher than the top of the engine, so it would catch all the airflow.

Read Maximum Boost by Corky Bell. Its all in there. I wouldn't say something as fact unless someone much smarter than me said it first.

lol maybe i should start following that rule...lmao...anyways...Jet-Lee, what type of kart racind did you do? Open wheel Dirt Track? or Pavement? or did you drag them? i noticed yo usaid something about a 1/8 mile...

Open wheel dirt and some pavement. I really HATED pavement, because as soon as everyone formed a line, there wasn't much competition, unless someone really screwed up. Not to mention wrecks were A LOT worse. 1/8 Clay tracks were the best, so much fun. They take more skill because you slide around the corners.

Do you guys know where I could get an 8 hp briggs and stratton engine in the lower mainland? The only place I know that sells that type of stuff is Princess Auto, and when I went there I only saw honda and some other brand. THanks- Andrew

BTW, anyone have a rough idea how much it would cost in candian dollars?

I wouldn't say something as fact unless someone much smarter than me said it first.
I already stated something else as fact....
If you have a cone, with the small end pointed into the wind, aerodynamics are going to force the air AWAY from the opening, thus making you run an EXTREMELY LEAN mixture, which can put a hole in your piston....heres a crappy diagram

-------> /
------> /
------>
------> \
-------> \

Where is most of the air going??? It's hitting the side of the funnel/cone and being deflected AWAY from the carb.

ex. #2

----->\
------>\
------->
------>/
----->/

NOW where is most of the air going??? It's hitting the sides of the funnel/cone and being deflected INTO the carb.

Do you have first hand experience with this stuff?? Have you built 15hp engines out of a 5hp block? Have you ever made an engine so strong it blew the head through your ceiling? (yeah, we had one that we couldn't dyno, because of the girdle it required to keep everything together. We lost two heads) If not, then you can't further this conversation with any useful information. Goodbye.

Artistic, Sorry man, I don't know ANYWHERE to even get stock engines right now. I raced back in Cali, and now I'm in Arkansas, so....yeah....good luck though man. Let me know if you need anything.

Don't take it up with me, take it up with Corky Bell. Don't kill the messanger.
"I already stated something else as fact...."
Are you implying that you're smarter than me, or better yet, Corky Bell? So I should believe your average AF monkey over someone who is smart enough to write the most popular book on turbocharging? Sorry, but if you had the choice of believing a racing legend or someone on AF, what would you choose? Or are you saying that you are repeating what someone smarter than you said? If so, whom?
Now this isn't fact, this is speculation on my part:
I'd imagine you'd get better results with a funnel if the car isn't moving fast enough so the column of air the size of your intake piping isnt flowing as much as your engine is. It probably wouldn't do much better than an open pipe. Go karts probably can't go fast enough to cause the ram-air effect(which is minimal to begin with in all practical car/kart applications). But the question was about ram-air, and I informed him of the correct 'ram air' intake configuration.

But you don't have to believe me about this. Believe the top fuelers, aircraft jet engineers, you know, professionals.
http://www.draglist.com/photoimages/2003/Indy2003/Cooke/prostock/304-Q3-SteveSchmidt.jpg
http://www.draglist.com/photoimages/2003/Indy2003/Cooke/prostock/305-Q3-WarrenJohnson.jpg
http://www.draglist.com/photoimages/2003/Indy2003/Cooke/prostock/307-Q4-BruceAllen.jpg
Their intakes are not funnels, in fact, the opening is the smallest part of the intake.

Or perhaps a ramjet engine would illustrate my point:
http://www.onera.fr/conferences/ramjet-scramjet-pde/images/ramjet-design.gif
This engine will ONLY work if air is being forced into the chamber, since it needs compressed air to function. Yet it does not employ a large funnel on the front, rather, something that more closely resembles the opposite of a funnel. A quote from the website from which that picture came:
"The air inlet/diffuser admits air to the engine, reduces air velocity and develops ram pressure. "

Here is a link to the site:
http://www.onera.fr/conferences/ramjet-scramjet-pde/

About the original question: A funnel is the exact opposite of what you'd want for ram air. You want a cone where the small side is pointing towards the airflow, big side towards the intake of the engine. A funnel pointing foward will give the air a nice easy path to revert out of the intake and give you little to nothing. A reversed funnel will trap air in, no path to revert, better converting the moving air(well moving intake, same thing) to pressure.
Finally someone who have got it!
Don't understand why people always think that a funnel will work. The ram-effect is all about reducing velocity, and thereby decrease dynamic pressure and increase static pressure.

The pressure increase can be calculated based on the reduction in velocity:

(V1-V2)^2/(2*R*T)

To get an increase a significant velocity must be achieved, then the engine power can increase by a few percent.

Designs for supersonic speed can however differ, like for example the ramjet.

Finally someone who have got it!
Certainly seems like the people who've 'got it' about anything somewhat complicated(especially airflow questions) are in the minority, doesn't it? Thanks for the support.

hehehe...duplox you havent been around kart racing very much have you? there are karts with YZ125 engines (6 speed trannies) that will kit in excess of 130mph...there are direct drive karts more than able to reach 70mph (right about where ram air will have noticable effect on a regular car engine) your forgetting that a 5hp briggs block is one cylender... dramaticly less airflow compared to even a VW bug engine...

hehehe...duplox you havent been around kart racing very much have you? there are karts with YZ125 engines (6 speed trannies) that will kit in excess of 130mph...there are direct drive karts more than able to reach 70mph (right about where ram air will have noticable effect on a regular car engine) your forgetting that a 5hp briggs block is one cylender... dramaticly less airflow compared to even a VW bug engine...

The airflow of an engine pretty much relates to its output power (3-4 kg/kWh).

To get to speeds above 130 mph you basicly need a superkart, it has a 250cc engine with 70-100 hp. Those engines have service intervals of about 2 hours.

I HAVE BEEN over 100mph in a 5hp Briggs & Stratton engine. Not a superkart, not a shifter kart, my SPRINT KART.

...saab...a yz125 motor is 40-50hp straight off the bike. a bone stock 125 is more than able to reach 85mph...and a yz125 weighs about the same as a race kart. a friend of mine races a yz"85" its been bored an stroked. its 118cc actual displacement. been dynoed at 75hp...he runs Ethnyl and a pretty high compression. we have clocked him to 116mph on the highway. and his bike is set up for dirt track racing.

so your friend took a go-kart on a freeway? okay.......

so your friend took a go-kart on a freeway? okay.......
side road next to the freeway...and it wasn't my friend, it was me and my brother. How do you think we tuned our karts? running them as hard as we can while making the adjustments via remote systems. We've run alongside 99 in Exeter, CA plenty of times. Tuning all depended on the track we were going to race at...Dirt? Clay? Concrete? Asphalt? Sometimes tuning was done while racing (literally, the two of us) around our block (Yes, we got caught by the cops many times, but there really wasn't a law against go-karts in the streets).

so...how would you interpret me saying _I_ have been over 100mph in my kart, as "my friend has drivin a go-kart on the freeway." Are you just not reading everything? If not, READ EVERYTHING.











Yes I'm an ass, I don't care. I get joy from pissing people off.

A superkart has about 80-100 hp, it tops around 250 km/h, or 150 mph. When we talk top speed weight has nothing to do with it, it's all about drag.

With say 80 hp for 150 mph, 100 mph will require about 35 hp and 60 mph around 13 hp. Going twice as fast means four times the power is needed.

118cc and 75 hp... my guess is a lying dynamometer.

An original bike 125cc engine is around 30 hp, enough for around 100 mph.

Saab, I respect your knowledge, and hate to cross you, but how do you explain my speed with my kart? The engines normally dyno'd at around 7hp, give or take 1/2hp. We paced each other (in cars) at about 105-110mph. We did have ONE engine that we dyno'd at 14.7, but it only saw one race, never saw any street action.

hehe..sabb too bad its possible for 600cc NA bike to make 150hp on pump gas...why wouldnt it be possible for 118cc to make 75hp on race gas? and its a 2 stroke at that.

jet-lee, i was refering to frymans comment, not yours.

"a friend of mine races a yz"85" its been bored an stroked. its 118cc actual displacement. been dynoed at 75hp...he runs Ethnyl and a pretty high compression. we have clocked him to 116mph on the highway."

umm, hmm, "a friend of mine", "we have clocked him to 116mph on the highway.", soo.....yeah, thats what i take that as, sorry if im wrong but its right their.

not beleiveing me? ok w/e...lets just say he moved down here from PA last christmas and has a room full of big assed trophies and plaques and is sponsored by Utopia and Fox (as an ammature)

hehe..sabb too bad its possible for 600cc NA bike to make 150hp on pump gas...why wouldnt it be possible for 118cc to make 75hp on race gas? and its a 2 stroke at that.
600cc and 150 hp = 250 hp/litre
75 and 118cc = 635 hp/litre

The most powerful twostrokes, in specific power, that I can think of is MotoGP's 500 cc four cylinder engines, they are said to produce about 250 hp or 500 hp per litre.

Also, I haven't seen any dyno results showing more than 120 hp for a 600 cc engine on pumpgas. To get 150 hp from a 600 cc engine you must take it to 16000 rpm or so.

Hey Johan, I don't mean this as a criticization or anything of the sort, but you got facts down pretty good, and they seem to come right off the top of your head, I admire that, so I was curious what you do for a living or what kind of degrees you have?

Saab, I respect your knowledge, and hate to cross you, but how do you explain my speed with my kart? The engines normally dyno'd at around 7hp, give or take 1/2hp. We paced each other (in cars) at about 105-110mph. We did have ONE engine that we dyno'd at 14.7, but it only saw one race, never saw any street action.

I wouldn't expect any other type of kart to have that much less drag than a superkart, superkarts do have wings which adds drag but they are generally lower than other types of karts and do have some bodywork.

With a given power it is impossible to go faster what the drag allows you to, to overcome the drag you need a force and if we take the metric hp as an example, 1 hp = 75 kg lifted one meter in one second, 75 kg equals 735 N (this since g=9.81 m/s^2 and 1 hp is 735W), that means with a drag of 735 Newton you can't go faster than 1 m/s, half the drag and you have twice the speed. If we instead look at the watt it equals one Newton and one meter per second (easier to calculate with).

So, 250 km/h, which a superkart tops at equals 69.4 m/s (divide 250 by 3.6), and with a power of 80 hp (typically 80 to 100 hp) which equals 58800 Watt, a superkart gets a drag of 847 N. The drag increase on the square, so if you just want to go 105 mph, 47 m/s that is, your drag should be around 382 N, that equals 18 kW or 24 hp. Even with half the drag the power of 7 hp isn't enough.

Have you measured the speed correctly by for example using a GPS or a accurate measured distance with an accurate timing device?
Have you driven in both directions within a short time?
If you answer yes on both your engine power is higher than you think, and/or the drag is lower.

We didn't have proper speed measuring devices at the time. Now that those devices are so readily available, I've been out of racing and sold my kart. We'd paced each other, one person in the kart, the other in a car (Beretta) watchin the speedo. The engines were 5hp Briggs & Stratton blocks, bought stock, changed the carb to a bigger bore, Splitfire plugs, 3hp flywheel, burn methanol, and advanced the flywheel 1/8th of an inch at the crank (don't know how many degrees that is). We were told by fellow racers that gave us about 6.5-7.5 hp total, but we never dyno'd those. We only dyno'd our creations, to see if we could stick a high power stock appearing engine on our kart and not get nailed (we raced in the stock classes). What does it sound like to you, we were puttin out through those?

There are several ways to measure power which gives different results. So it can be difficult to say how much power the engine is producing, even if it's stock. The methanol with the ignition advance increase the power, perhaps by 20% or so. A larger carb can both decrease as increase power.

Also, to get a correct top speed measurement one must drive both directions not to get any advantage of wind or by gravity. To measure the speed with a car usually gives an incorrect speed, perhaps 10% or so must be removed to correct it.

We were headed North/NorthEast in central California round about August/September...dunno if there was any type of incline or not...

Sabb's right...well im jsut telling you what the dyno said. may have been a lying dyno as you said. it was a motorcycle dynojet in Daytona, FL. Though We also measured his dads Harley V-Twin to 180Hp, im suspecting that the dyno may have been exagerating by 25-35%...that would put the bike at around 50Hp and the Harley around 130...

50 hp from 118cc sounds better, but even that is quite a lot.

A looked after a some numbers on top speed for different karts, it seems that most karts with 5 hp are said to have top speeds below 100 km/h, 100 km/h is what they ahould have according to my calculations.

Just remember its a 2 stroke, makes its power above 5,000RPM and has something like a 16:1 compression. he also burns 5% nitromethane and 95% ethnyl.

sounds like we got quite the thread goin on small engines....

Just remember its a 2 stroke, makes its power above 5,000RPM and has something like a 16:1 compression. he also burns 5% nitromethane and 95% ethnyl.
I would expect the rpm to be at least around 10,000 rpm, 5,000 rpm isn't much for an engine which likely have a stroke of somewhat above 50 mm.

me no know, of corse the dyno was lying about HP numbers maybe it lies about RPM's too....next time i get a chance ill grab thoes dyno charts and figure out how to post pics.

A superkart engine delivers maximum power somewhat obove 10,000 rpm (two 125cc cylinders). This would equal about 50 hp from an engine half the size at the same engine speed.

choki-dori. saab, you missed the whole arguement over in the engineer technical fourm. with some guy argueing with everyone (including curtis73) about how if an engine is running cooler it is harnessing more energy from its fule and there for running more effiecient and that heat isnt energy but it is and cant be related to a watt of electricity and all this other BS. could have used ya. but we gave up on his mind. by the way what all education do you have in chemistry/physics feild? j/w.

:1:

Jet...looking at your "are you a traceur" site in your siggy, i seem to have found the moves i use while running from cops...lol

lol...they come in handy... :uhoh: :evillol:

My latest vid (http://lee.neptune.com), Yes the camera man sucks, but he was the only person around.