Is my Briggs 5hp to Predator 420 Swap a Good Idea?

[Mrbirmi]

Hey guys,

Thinking of swapping out my 5hp Briggs with a predator 420cc. Ive looked at some of the threads related to moving up in hp, and i believe my frame can handle it. I don't know much about these streaker brand carts but it seemed as though it was made for a larger engine and someone at some point installed the smaller Briggs. The biggest detractor is having to switch torque converters, but I really like the idea of more power plus electric start.

So, is there anything else I should consider?

Is it Stupid to replace the stock exahust and air filter on a predator 420 with aftermarket, but keep the governor installed and functioning?

Here are some pictures of it as is, and any advise or wisdom would be greatly appreciated!

Thanks,

Matt

 

[landuse]

Have you considered that you will have to get a comet 40 series TC to handle that engine. They run at about $300

 

[KartFab]

bigger block, will it fit?

 

[machinist@large]

Wait a minute.......

I've got a Predator 420 on the bench that I bit on because the store manager flat out wanted to move it (haven't had the spare change to do anything with it yet), and I can tell you it is big. I've also got a 5hp Briggs on a trash pump; swapping for the 420 will not be a plug & play slam dunk.

At the very least, the entire engine mount will have to be moved rearwards, both to clear the block itself and make space for the starter and switch box. Just how much I don't know, and it wouldn't surprise me to find out there are even more things that will need to be addressed.....

 

[OzFab]

As Pat (M@L) pointed out, it's not a simple case of "drop & bolt", the frame will need some serious mods... if it will even fit between the seat & the rear cage bar...

Is it Stupid to replace the stock exahust and air filter on a predator 420 with aftermarket, but keep the governor installed and functioning?

No, not at all; removing the governor provides a few more RPM, giving you a few more MPH of top speed; replacing the "breathing aparatus" will gain you a bucketload of low end torque which will give you better/faster acceleration... which translates to "more power where/when you need it!"

 

[Mrbirmi]

Have you considered that you will have to get a comet 40 series TC to handle that engine. They run at about $300

Yes, I mentioned that in the op. Thanks though!

 

[Mrbirmi]

bigger block, will it fit?

I made a special trip to HF yesterday just to take a look and it is big. I think it will physically fit if i make a few adjustments.

 

[Mrbirmi]

I've got a Predator 420 on the bench that I bit on because the store manager flat out wanted to move it (haven't had the spare change to do anything with it yet), and I can tell you it is big. I've also got a 5hp Briggs on a trash pump; swapping for the 420 will not be a plug & play slam dunk.

At the very least, the entire engine mount will have to be moved rearwards, both to clear the block itself and make space for the starter and switch box. Just how much I don't know, and it wouldn't surprise me to find out there are even more things that will need to be addressed.....

Thanks for the feedback! I was kinda thinking of removing the gas tank and relocating it somewhere else. Not sure yet where, because I don't think i want it between my legs lol. I was also thinking of removing the electric start and fabbing up a switch panel at the drivers seat with a push button start

Big thing is I can cut things apart all day long but i don't have a welder to put them back together. Looking at that motor mount again i think it will needed to at least be modified.

 

[Mrbirmi]

As Pat (M@L) pointed out, it's not a simple case of "drop & bolt", the frame will need some serious mods... if it will even fit between the seat & the rear cage bar...



No, not at all; removing the governor provides a few more RPM, giving you a few more MPH of top speed; replacing the "breathing aparatus" will gain you a bucketload of low end torque which will give you better/faster acceleration... which translates to "more power where/when you need it!"

Good to know about the engine mods. .. I know the aftermarket intake and exahust looked cool but didn't want to blow money if they weren't going to gain me anything. Thanks!

 

[KartFab]

So if I were you, and couldnt weld. I would first figure out how you were going to set up your jackshaft and motor mount provided that the engine will fit. The jackshaft placement is going to be a BIG DEAL as you need to find the center to center distance. and make sure the driven wont rub on anything as well as the engine being a little higher so the driven wont rub on the engine block itself.

They sell plates for the GX390's on ebay that have the holes pre-drilled, which is the same block pattern as the predator. If you did all the cutting/drilling and worked out how you were going to set up your jackshaft, I am sure you could get a welder to just lay a bead or two to get the plate all welded on, but the jackshaft is something that needs some thought.

Worse case scenario you would need a hacksaw and buy some additional 14 ga. sq tubing, 3/16" plate, and two bolt on pillow block bearings to make kind of a rectangular motor mount that the top bolts to the motor, and the bottom bolts to the kart allowing the rectangular mount and the motor to move as a single unit to provide the right chain tension/be adjustable.... then pay someone $40 to put it all together after you figured out what and how to cut and did a dry fit. Welders love it when they dont have to remove paint or cut, just weld! If i had to do somethign like this for a guy and had to do cutting etc, i would charge like $200.

Also I did the same thing on a little kart of mine, if i remember i had to get 7/16th inch bolts for the motor mount. They were a perfect fit (much better than the 3/8" that a lot of people use).

 

[MancoGX390]

I bolted my motor mount together! Two 30mm box sections, original Manco TC plate ontop and then a sideways adjust plate then boom engine! Is perfectly good! Centre to centre deistance is 190mm on mine which is about perfect for using all of the driver clutch.

 

[OzFab]

Mrbirmi, do you see the "+ button to the right of the "Quote" button? That's the multiquote button; click that button in as many posts as you like then, click "Quote" on the last post & you can have all the quotes in one post as opposed to the 4 you have above...