small low end motor.

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bikesndbugs
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small low end motor.

Post by bikesndbugs » Wed Jul 26, 2017 8:57 pm

So im wanting to build a small motor that has some good low end torque.
i have around 1500 to spend

Ive got some dual kadrons that i can use.
im thinking single port heads. (already have them) use a old stock intake to make sp kad intakes.

Id like to get a bit more displacement either stroke or bore. not sure. whats cheaper and more usable for low end grunt

with a low end motor like this i dont think counter-weighting or hd spings and all that wouldnt be super necessary.
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Re: small low end motor.

Post by petew » Thu Jul 27, 2017 5:02 pm

As much capacity as you can afford. Ie, 94mm pots and a 74mm stroker or similar. Stock twin port heads and a single Zenith carb. I believe Leatherneck (offroad forum) had something like this for years in his buggy. Very responsive, very torquey.

Torque is about long intake runners and I think you'll find the Kads will be worse not better, until less you have really long manifolds.

P.s. balancing the motor is a good idea just for saving the block and making it run smoother.

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Re: small low end motor.

Post by Marc » Thu Jul 27, 2017 6:21 pm

If your SP heads are sound, I'd be inclined to go 1775 with a stock crank and flywheel (although I strongly recommend having them 8-dowelled). 1915 is a bit much for stock heater boxes, and claims to the contrary aside they DO have rather thin walls and also require removing a lot from the case & heads. A compromise would be AA's "thickwall" 92s which can be had in 96mm case register (the heads will still need to be opened up to the ~101.1mm "94" size but the wider seating surface of the 92 cylinders will allow enough of a seal). SP Kad manifolds exist but are hard to find, hopefully you can make some decent manifolds as planned (don't forget to incorporate fittings for a balance tube between LH & RH sides); that's a lot of mass to be perching atop the heads held only by some m6x1.0 studs so you'll want to add some form of support to limit the carbs from swinging about and causing the intake manifold gaskets to start to leak. Even something as rudimentary as an arched strap over the shroud which attaches under the aircleaner nuts will help, or you can fab supports which connect to the shroud - that'll cut the effects of any relative differences over temperature cycling roughly in half. A slightly larger-than-stock cam would be justified to aid in filling the larger displacement, but keep it mild (Engle W-100 or something equivalent) if you're leaving the valvetrain stock. You could also build an 1800 using 88mm bore (AA's "thickwall/slip-ins" don't need any machinework to the case, although the heads must be opened up to 98mm) and a 74mm stroke. That crank will come counterweighted & 8-dowelled (it's a bit of a challenge to properly match a flywheel to an already-8-dowelled crank but it can be done; then you'd want to lighten the flywheel a bit (say, ~13½ lbs) to compensate for the inertia of the crank counterweights. Theoretically the 88x74 combo would provide a little more grunt than 90.5x69 or 92x69, but I seriously doubt there'd really be enough difference to justify the extra cost & assembly complications.

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Re: small low end motor.

Post by bikesndbugs » Sun Jul 30, 2017 10:27 pm

im more interested in stroking it than a bigger bore. i feel more comfortable not having a high revving motor as a low end grunt motor theoretically lasts longer.

I was thinking get the biggest stroke possible with stock bore. with either single port or dual port heads. i have both. singleports are in great condition. and dual ports are on the car currently.

what im thinking is try to keep stock cam and vaulvetrain for money. do crank, pistons, jugs, and rods. then get the carbs on it.
74mm is common but if i went a little bigger i could run the b type pistons. and keep width and deck height.

im not suree what combo would do this though.
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Re: small low end motor.

Post by petew » Mon Jul 31, 2017 2:23 am

I'm still kinda thinking on this. It still seems to me that what you're seeking to build is a very lazy motor with a limited top end. Which BTW, is fine and every petrol truck/tractor motor in the world was built on these principles. ;)

I am thinking however, that btw the time you put a big crank in your case, you're more than half way into the sort of machine work involved in going bigger stroke. AND, barrels/cylinders are almost the same cost wise right up to 94mm. So, the bigger you go, the more torque you'll have down low. The 2.5l subaru I had in a buggy years back was kinda like this. Big, lazy and super torquey. As long as you change the oil regularly, you'll never kill it. The only thing being the SP heads/stock exhaust will limit that power at a lower and lower RPM depending on how big the motor is. On Marc's advice, I'd still say, thick wall 92s + biggest crank you can do.

It's hard for me to understand if that will all cost US$1500 from I am.

P.s. If you do build all those cubes into it, you could swap the heads or add a turbo later on and have a pretty amazing motor. ;)

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Re: small low end motor.

Post by bikesndbugs » Mon Jul 31, 2017 11:44 am

I don't wanna pay for all that machine work but I do figure bigger the only downside is mpg and I do daily it.
But bigger costs the same.
My uncle said he had a cammed 1835 that lasted 10 years

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Re: small low end motor.

Post by petew » Mon Jul 31, 2017 4:38 pm

How far are you driving and in what conditions? I ask because, if you're doing lots of hwy revs a smaller motor might make sense. If you're just cruising along at 40-50mph, a bigger motor shouldn't make a lot of difference. It'll be all down to the way you tune it and drive it.

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Re: small low end motor.

Post by bikesndbugs » Mon Jul 31, 2017 5:28 pm

i drive 15 to 20 miles half highway other half is 45mph road.
i was thinking low end just because i struggle os much on the freeway to push 31s
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Re: small low end motor.

Post by petew » Mon Jul 31, 2017 8:14 pm

This is a baja right? You better tell us what trans/motor you're using at the moment.

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Re: small low end motor.

Post by bikesndbugs » Mon Jul 31, 2017 9:07 pm

currently i have a basic 1600 dual port. with a stock swing tranny. 4.12 rp.
i plan to go to irs and hopefully do a lower ring and pinion. 31 inch tires.
so i should maybe just build a more high rev motor as long run id enjoy it more. and would be usefully with the future plans more than the low rev motor.
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Re: small low end motor.

Post by bikesndbugs » Mon Jul 31, 2017 10:54 pm

https://aapistons.com/collections/high- ... engine-kit

i did come across this seams like a good deal.

im not sure what exactly id go with

a 1904? maybe thick wall 1835.
probably add a mild cam too
why are there so many options
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Re: small low end motor.

Post by petew » Mon Jul 31, 2017 11:06 pm

bikesndbugs wrote:
Mon Jul 31, 2017 9:07 pm
currently i have a basic 1600 dual port. with a stock swing tranny. 4.12 rp.
i plan to go to irs and hopefully do a lower ring and pinion. 31 inch tires.
so i should maybe just build a more high rev motor as long run id enjoy it more. and would be usefully with the future plans more than the low rev motor.
Honestly, if your current motor is good, I'd spend the money on an IRS conversion and bus trans. A 002 5rib or 091 would be ideal. It will also make the car much more useful offroad.

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Re: small low end motor.

Post by bikesndbugs » Tue Aug 01, 2017 1:28 pm

The current motor works its just really tired. A whole lot of blow by. I guess I could just do rings. And a hone.

I was holding off on the irs conversion as I dont have the space in my garage at the moment. i planned on trying that next year. and dking motor now.



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Re: small low end motor.

Post by Ol'fogasaurus » Tue Aug 01, 2017 5:59 pm

Travis, I agree with both Pete and you but would go one step farther: Check the cylinders, pistons and mike the crank for their condition then, if good; re-ring, change the bearings, do the valves and new oil pump (I am leery of reusing some parts with the oil pump being one of them). You might be able to get by with a small cam but not too big.

My engine is one step above what you have as it is a DP, 1776 and I had a camshaft reground for it: higher lift and shorter duration for more bottom end (torque. The engine will do 5K RPMS but I try to keep it under that.). Don't go with a light flywheel as you lose energy storage you might need that way. A good quality clutch disc and maybe you can even get by with a stock clutch cover.

My opinion for what it is worth.

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Re: small low end motor.

Post by bikesndbugs » Tue Aug 01, 2017 9:56 pm

if i split the case i wanna do a full rebuild. im leaning towards rings and rebuild the heads now. get the doghouse setup complete. and the good carbs.

is there a quick way to check engine condition bottom end?
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