Small Block vs Big Block Speed Difference? What is Better?

SquidBonez

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It seems like every Honda clone powered machine on YouTube (be it go kart, mini bike, or mini buggy) runs a small block if they want to really go fast. At least from what I've seen online - by and large - built small blocks are faster than most big blocks. There are tons of videos of people hitting 70+ on small block mini bikes, but very few videos on people hitting high speeds on big blocks. Does anyone here have experience with big block engines? How do they compare to small blocks on the old "butt-dyno"? I would think that the extra power and torque from big blocks would make it no contest - even with the added weight. I know speed is overall determined by gear ratio & RPM, and that big blocks don't rev as high, but you can gear a big block more aggressively than a small block thanks to the extra power & torque they provide. Torque converter options are also more limited for big blocks (there's no "Juggernaut 30 series" equivalent for big block engines...maybe the 780?).

Ultimately, I'm just trying to decide if I should go big block or small block on a lightweight mini buggy I'm building. I currently have the parts to build a Stage 2 Predator 212 coming in, but I'm just wondering if I should stick with a small block or pay the extra money and upgrade to a big block. I'm looking for something that will do well at high speed (rally-style) driving on dirt roads and grass fields. Would it be better to use a lighter, less powerful, but higher revving small block, or a heavier, more powerful, but lower revving big block? I already have a Juggernaut torque converter for my 212, but if I go big block I will change out to a 40 series.
 

Joe-405

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I always say there isn’t a replacement for displacement. I have a small block and multiple big blocks. I won’t ever use a small block unless I have to for space savings or rules for my race classes
 

SquidBonez

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I always say there isn’t a replacement for displacement. I have a small block and multiple big blocks. I won’t ever use a small block unless I have to for space savings or rules for my race classes
But is a build big block is usually faster than a built small block? I already have the parts for a Stage 2 Predator 212 that I'll be running on my current kart as sort of a "test mule". If I'm satisfied with it I'll swap it over once I build my buggy, but if not I'll be going big block. Just hope a Comet 40 series handles a modified big block as well as the Juggernaut handles the modified small block.
 

65ShelbyClone

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Yes. Much faster.

You see built 212s a lot more than built 390s/420s/etc because the smallblocks cost about half as much to buy and build. Bigblocks can make twice the power or more though. I mean a fully done pump gas 212 might be in the high teens power range whereas a "stage 1" GX390 already makes upwards of 16hp.
 

Joe-405

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The big blocks always have more torque and the small blocks more rpm if that helps.

so the big block gets you there faster

and the small block has more top end and rpm.
 

SquidBonez

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Yes. Much faster.

You see built 212s a lot more than built 390s/420s/etc because the smallblocks cost about half as much to buy and build. Bigblocks can make twice the power or more though. I mean a fully done pump gas 212 might be in the high teens power range whereas a "stage 1" GX390 already makes upwards of 16hp.
How does the Comet 40 series hold up to built big blocks? I know Cars and Cameras ran one on a 50-ish horsepower 670 for quite some time before it gave out (and I wouldn't be making anywhere near that much power).
The big blocks always have more torque and the small blocks more rpm if that helps.

so the big block gets you there faster

and the small block has more top end and rpm.
Here's an interesting question: what would give you better acceleration? A low torque, high RPM engine geared way down, or a high torque, low RPM engine with longer gearing?
 

65ShelbyClone

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How does the Comet 40 series hold up to built big blocks? I know Cars and Cameras ran one on a 50-ish horsepower 670 for quite some time before it gave out (and I wouldn't be making anywhere near that much power).

That's hard to say. They're rated up to 18hp, so they'll at least last as long as they're designed to at that power level.

Here's an interesting question: what would give you better acceleration? A low torque, high RPM engine geared way down, or a high torque, low RPM engine with longer gearing?

That's a complicated question. Conceivably they would be equal if both make the same power and are kept at the peak power RPM with an ideal torque converter.
 

Kartorbust

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If you're going to run a high HP build, a 94c Duster will work for you up to 40hp on a 4 stroke build. RBG is running a Polaris clutch or CVTech setup (he's not clear) on his 670 build. The 700 (770, 780, 790) series do not hold up to high power for long term very well.
 

SquidBonez

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If you're going to run a high HP build, a 94c Duster will work for you up to 40hp on a 4 stroke build. RBG is running a Polaris clutch or CVTech setup (he's not clear) on his 670 build. The 700 (770, 780, 790) series do not hold up to high power for long term very well.
I wouldn't be making anywhere near the amount of power as his built 670 build. Likely under 25 horsepower at most. Standard Stage 1 kit (bored stock carb, not mikuni), billet internals, timing advance, maybe a mild cam. That's it.
 
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chimmike

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So i'd be better off doing a stage 1 gx390 at this point than going all-in on a 212 (cam, springs, fw, carb)?
I have both, but don't have a TC for the 390. Still so damn conflicted. Looking to get more top speed than current but not looking to get 45mph on a Manco kart.
 

JTSpeedDemon

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A few things I'd like to add:
With big blocks, not only are they much more expensive, there's usually more problems with vibration as well, simply because there's one big piston swingin' around in there, and there's usually counterbalance shafts/systems added into the equation, which some people elect to remove.
Then of course there's also the fact that there's less big block parts on the market than for small blocks (less, not none), and what is there is much more expensive. So if you want to put in the extra $$$, I'd say a big block is a lot better for high speed offroad stuff. Otherwise I'd say a small block's flexibility in performance, setup, and powerband can't be beat for on road applications for their size (why else are all the sprint karts running small blocks??)
 

SquidBonez

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A few things I'd like to add:
With big blocks, not only are they much more expensive, there's usually more problems with vibration as well, simply because there's one big piston swingin' around in there, and there's usually counterbalance shafts/systems added into the equation, which some people elect to remove.
Then of course there's also the fact that there's less big block parts on the market than for small blocks (less, not none), and what is there is much more expensive. So if you want to put in the extra $$$, I'd say a big block is a lot better for high speed offroad stuff. Otherwise I'd say a small block's flexibility in performance, setup, and powerband can't be beat for on road applications for their size (why else are all the sprint karts running small blocks??)
I'm definitely leaning small block now simply because I already have the parts coming in (these package delays are killing me though). Here's what mods I'll be doing: PVL flywheel, 4 degree timing key, ARC billet rod, 22lb valve springs, 0.01” head gasket, MOD2 camshaft, header pipe w/ muffler, carb jet, chromoly pushrods, and an Autolite 3910X spark plug. This will be on my Predator 212 hemi. Should be around 15 horsepower, 7000+ RPM. Pair that with a Juggernaut torque converter w/ a yellow driven spring in the 3rd tension setting, and it'll definitely be enough to move around the buggy I'm planning on (which will be designed to be as small and lightweight as possible). I was originally just going to go with a Tillotson 225 but I didn't want to spend a ton on my very first build.
 

Budget GoKart

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My big block yerfdog smokes my small block streaker the streaker has no goveneor and a custom intake and the yerfdog has no goveneor and stockish gearing and a chinese tc
 

Dfish1247

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Theres three ways of making horsepower, displacement, rpms, or forced induction. This assumes the test engines have the same volumetric efficiency ( how good it turns fuel and air into power. ) But, bigger displacement means more torque at lower rpms, but runs out of rpms sooner, given same head, cam, carb,etc.

Torque converter is the way to go for a kart at home. Granny gear to start, and overdrive for top speed.
 

Kartorbust

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Problem is, not all CVT setups offer an overdrive, or at least one that's highly noteworthy. Ones most affordable offer about a 10% overdrive. More expensive ones have around a 30-55% overdrive. For a stock engine setup and a 8:1 or even 10:1 will get you close to 50mph. But for something like that, you are paying about $500-$700. Which could mean engine mod prices to get the same speed. Just food for thought.
 

SquidBonez

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Problem is, not all CVT setups offer an overdrive, or at least one that's highly noteworthy. Ones most affordable offer about a 10% overdrive. More expensive ones have around a 30-55% overdrive. For a stock engine setup and a 8:1 or even 10:1 will get you close to 50mph. But for something like that, you are paying about $500-$700. Which could mean engine mod prices to get the same speed. Just food for thought.
The Juggernaut supposedly doesn't have an overdrive (highest gear is 1:1). That's fine by me, since I'm currently planning on running a 6.7:1 gear ratio (9T/60T). That will be good for low end and top end.
 

Kartorbust

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The Juggernaut supposedly doesn't have an overdrive (highest gear is 1:1). That's fine by me, since I'm currently planning on running a 6.7:1 gear ratio (9T/60T). That will be good for low end and top end.

Fair enough. Snagged a screenshot from the NRRacing 420 Predator they modded and was selling for about $1700. Seems quite impressive, even as it falls off hard around 7200rpm.

Big block or small block, just depends how much weight you want to throw around, ~40lbs vs ~75lbs. Either one can be modded to the moon, just the small block can more than like spin at a higher rpm.
 

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SquidBonez

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Fair enough. Snagged a screenshot from the NRRacing 420 Predator they modded and was selling for about $1700. Seems quite impressive, even as it falls off hard around 7200rpm.

Big block or small block, just depends how much weight you want to throw around, ~40lbs vs ~75lbs. Either one can be modded to the moon, just the small block can more than like spin at a higher rpm.
Considering I want to keep this thing as light as possible (and I'm not trying to spend a small fortune on my first build) I think the small block is the way to go. Plus, like I said before, there seems to be less options available for 1" bore torque converter kits that can reliably handle the power of a built big block. And the few that are available (like the 780) are very expensive.
 

KartFab

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Mild modified big block was floating the valves at 65 mph in under 300 ft, where higher stage small blocks were barely able to hit 55 mph in the 1/8th mile. This was at a drag race a few months ago.
 

SquidBonez

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Mild modified big block was floating the valves at 65 mph in under 300 ft, where higher stage small blocks were barely able to hit 55 mph in the 1/8th mile. This was at a drag race a few months ago.
What do you mean by mild? Like stage 1 with governor removed beating stage 2/3 small blocks? I've seen that GX390 Manco you have and it rips.
 
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