engine performance help

[tgus3]

hello all, im back from a short break from karting.
So im finally getting ready to build a predator and I have some questions on the parts. ill list em below with the questions. Thanks

aluminum flywheel
22lb valve springs (should I get anything else for the valves or head?)
arc con rod(shall I get a longer one or same size?
flat top piston(prob)
cam(what kind, mod2?
some kind of carb maybe mikuni, I found a bored stock one on ebay that sposed to give 2 more hp
https://www.ebay.com/itm/Predator-2...=item1a5a994902:g:W-cAAOSwAyJbapMd:rk:13:pf:0

Also ill see if I can shave and port the head



EDIT-Im sure that bob or someone made a thread with a list of parts but I cant find it

 

[65ShelbyClone]

22lb valve springs (should I get anything else for the valves or head?)
cam(what kind, mod2?

The cam will determine what springs are needed and whether the valves or retainers need to be upgraded.

arc con rod(shall I get a longer one or same size?
flat top piston(prob)

You need to measure deck clearance with the piston you plan to use before you'll know how much longer the rod can be.

some kind of carb maybe mikuni, I found a bored stock one on ebay that sposed to give 2 more hp

Bored stock carbs are for stock-appearing kart classes. They are inferior to a slide carb in every way but fitment.

 

[tgus3]

thanks
So what cam and spring combo are best?

and I guess ill get a flattop piston and put it in then measure for a rod


would this be the mikuni to get https://www.gopowersports.com/26mm-mikuni-carburetor-performance-kit-chinese/

 

[J.S.@SMS]

It depends on which cam you want. A mod 2 is a stock lift added duration cam that requires 18 lb springs and is built for 7000 rpm, however a 262 cam has more lift than stock, requires 22 lb valve springs and is built for 7500 rpm.

And no, that is not the carburetor that the engine will need. It is too big, and you loose performance using it. The 22 mm mikuni will work much better with those mods, and can be found here:
https://www.gopowersports.com/22mm-mikuni-carburetor-performance-kit/

And I would order a flat top piston if you have a non-hemi. But if its a hemi then I think that you already have a flat top piston, so check to see if it is a flat top piston.

 

[tgus3]

ok thankyou ill get that but what adapter size do I need to get,48mm?

---------- Post added at 01:14 PM ---------- Previous post was at 12:20 PM ----------

I might just get a stage 3 kit from hotrod minibikes and the get a mikuni

 

[J.S.@SMS]

That sounds like a good plan, and you'll have the filter and filter adapter to use on another engine. And the actual bore and hole spacing remains the same for the 48 and 65 millimeter adapters, the difference is the length. The 48mm adapter will provide better flow and as a result will increase the max rpm of the engine as well as the power. The 65mm adapter will restrict the air a little more, compared to the 48mm, That will decrease the amount of peak power that you have and will cut down the max rpm a bit, but it will increase the amount of torque in the lower rpm range which provides a better launch. But both of them will work just fine, and on engines this small the effects may not even be noticeable.

 

[bob58o]

Tell me if it’s a hemi or non hemi. Picture of the valve cover will work.
I’ve got a few extra carb kits laying around. Some Chinese clones of PWK Flat slides. 24mm. It works great on my 212. Some claim Chinese clone carbs are a pain to tune, but mine works great.

Intake manifold with gasket and bolts.
Silicone sleeve with hose clamps.
24mm Slide Carb.
Air screen with hose clamp.
Idle jet kit.
Main jet kit.
Needle shim.
Offset flywheel key.
Barrel end for throttle cable. (To make a cable of correct length)

 

[tgus3]

Its a nonhemi. would one of those work as good as a genuine Mikuni 22?

 

[tgus3]

I would like this to be a pretty good build hopefully making almost 20hp. ive thot about getting rockers idk tho….so many parts with so many choices....how much better are 26lb over 22pb springs?

---------- Post added at 10:25 AM ---------- Previous post was at 10:03 AM ----------

maybe you can just give me a list of parts thatll get to around 20 hp

 

[KartFab]

if you want to make 20 hp, you need a big valve race head, 24 or 28mm flatslide mikuni, a .310 cam with 1.2 ratio rockers. Aim for 12.5 or more compression. This will legitimately make more than 20 hp.

The 28 mikuni will suffer some loss of torque on the low end but make more hp on the top end, and the 24mm mikuni will make more torque on the low end and lose some top end hp.

If you just want an all around good performing engine, dont worry about hp numbers and build something that you will enjoy riding. High hp means nothing if you are start/stop type of driving and 90% of the time you stay below 5000 rpm. A good cam would be the .275 cam by dynocams or the 280 cam by NR racing. They are just solid performers overall, and you dont have to go crazy with compression ratios so you can use a 10.5:1 on premium pump gas and be just fine.

A good all around build would be the .308 cam with the 24mm flatslide and the gopowersports 28/25 head. IF you want a bit more top end and mid range power you can use ratio rockers. That head will put you about 12.5:1 compression so you will have to use 110+ octane gas. You can just get a geniuine mikuni and put a 140 main and 20 pilot in it and be good with gas.

 

[bob58o]

Its a nonhemi. would one of those work as good as a genuine Mikuni 22?

Probably not as good as a genuine Mikuni, but the carbs I get are less than $30. I use this carb on a head with 28.5mm intake and 25mm exhaust and 11:1 Compression ratio. I’ve got this 285 series (285-0211) camshaft in that engine.
https://www.nrracing.com/category-s/2683.htm

 

[tgus3]

is this the carb your talking about bob?
https://www.ebay.com/itm/24mm-Carbu...=item214a195bcf:g:fC0AAOSw831bxZt2:rk:12:pf:0

 

[bob58o]

is this the carb your talking about bob?
https://www.ebay.com/itm/24mm-Carbu...=item214a195bcf:g:fC0AAOSw831bxZt2:rk:12:pf:0

Yessir.

 

[tgus3]

Does this list of parts look good?

24mm carb

.280 cam

billet flywheel

.020 billet rod

billet lifter set

flattop piston(70mm .570 compression height)

22lb springs

chromoly pushrods

shave and port head(prob use Honda on)

 

[Flyinhillbilly]

if you want to make 20 hp, you need a big valve race head, 24 or 28mm flatslide mikuni, a .310 cam with 1.2 ratio rockers. Aim for 12.5 or more compression. This will legitimately make more than 20 hp.

The 28 mikuni will suffer some loss of torque on the low end but make more hp on the top end, and the 24mm mikuni will make more torque on the low end and lose some top end hp.

If you just want an all around good performing engine, dont worry about hp numbers and build something that you will enjoy riding. High hp means nothing if you are start/stop type of driving and 90% of the time you stay below 5000 rpm. A good cam would be the .275 cam by dynocams or the 280 cam by NR racing. They are just solid performers overall, and you dont have to go crazy with compression ratios so you can use a 10.5:1 on premium pump gas and be just fine.

A good all around build would be the .308 cam with the 24mm flatslide and the gopowersports 28/25 head. IF you want a bit more top end and mid range power you can use ratio rockers. That head will put you about 12.5:1 compression so you will have to use 110+ octane gas. You can just get a geniuine mikuni and put a 140 main and 20 pilot in it and be good with gas.

^^^this^^^
Big numbers sound cool and all, but you have to consider the power curve and longevity if you’re doing something other than just racing it.

 

[tgus3]

yes I do want a reliable engine but I also want a lot of power 15-20hp
I don't race but I my revs are way up there 75% of the time

 

[bob58o]

Alright, when I build a motor, I consider where I’ll be driving it. If I’ll be cruising from stop sign to stop sign then I understand that I'll under 40 mph most of the time. If my camshaft is designed to make peak HP at 7,000 rpm, then I’ll try to gear so that I make peak HP at 40 mph or under.

 

[Nosandwich]

yes I do want a reliable engine but I also want a lot of power 15-20hp
I don't race but I my revs are way up there 75% of the time

Yeppers, with a stock engine????

Point being, you are going to MAGNIFY that response considerably. Sooo, as mentioned... you may not want ( or need), a high revving engine.

Just saying..... there is no magic cam. The best way to think of it is as a stack of cash. You have to decide if you want groceries or bar hopping. You can do either, but not both. That's how cams work. They tailor what RPM's the engine makes it's most power.

 

[bob58o]

Does this list of parts look good?

24mm carb

.280 cam

billet flywheel

.020 billet rod

billet lifter set

flattop piston(70mm .570 compression height)

22lb springs

chromoly pushrods

shave and port head(prob use Honda on)

If using a hemi flattop piston in a non hemi, you’ll probably want the +0.040” connecting rod. Non Hemis usually start off around .040” in the hole. A flat top piston has a 0.020” shorter compression height which would put you around 0.060” in the hole. The +0.040” rod would bring you to 0.020” in the hole. Use a 0.009” / 0.010” head gasket to give you the ~0.030” piston to head clearance that is commonly recommended.

Edit: Or you can use the 0.570 flattop piston with the +0.020” rod, but I’d rather use a lighter piston. It seems to me that the 0.570” piston would weigh more than the 0.550” piston.

Before you buy the rod, you should measure how far down in the hole you piston sits at top dead center. These engines tend to vary. I said non-Hemis usually sit around 0.040” in the hole, but each engine should be measured.

280 series camshaft asks for 26lb valve springs. With 26lb springs, you’ll probably want reinforced rocker arms.
http://www.nrracing.com/product-p/rerockhd.htm

 

[tgus3]

If using a hemi flattop piston in a non hemi, you’ll probably want the +0.040” connecting rod. Non Hemis usually start off around .040” in the hole. A flat top piston has a 0.020” shorter compression height which would put you around 0.060” in the hole. The +0.040” rod would bring you to 0.020” in the hole. Use a 0.009” / 0.010” head gasket to give you the ~0.030” piston to head clearance that is commonly recommended.

Edit: Or you can use the 0.570 flattop piston with the +0.020” rod, but I’d rather use a lighter piston. It seems to me that the 0.570” piston would weigh more than the 0.550” piston.

Before you buy the rod, you should measure how far down in the hole you piston sits at top dead center. These engines tend to vary. I said non-Hemis usually sit around 0.040” in the hole, but each engine should be measured.

280 series camshaft asks for 26lb valve springs. With 26lb springs, you’ll probably want reinforced rocker arms.
http://www.nrracing.com/product-p/rerockhd.htm

Thanks I was wondering about that. so I quess I obviously need to measuer to the highest point on the piston, the outer ledge? because to the middle measures .097 and that's ob not right.

the edge of the piston at tdc measure .037 in the hole.

So yes I guess ill get a 40thou rod with a regular length hemi head.

whats the best way to get springs compressed? American ingenuity?
my friend has 22s and he said thos are really hard so that's what im worried about with 26 lb springs.