Who’s a fan of low compression?

Totally normal JBOT /

MEEEE!

125psi on a kitted dual variated bike with good .7-.8mm squish is so baller. Dropped from 145psi down to 125 today by cutting the dome. Runs so easy, takes such little to effort to spin the engine so spin it does and makes great power. You can have nice normal timing and even push it a bit without gaining excess heat running on 87 octane

My pinball hobbit had the same low compression and it’s a dream to ride, so I switched my other hobbit to the low compression club (LCC)

I think that the extra compression past 125psi is just pointless on most variated bikes. Just builds up heat and beats components up. You’re welcome

335CE8AA-FE9D-43E4-B8B8-19CD553C49FD.jpeg

(edited)

Re: Who’s a fan of low compression?

Ah man I just wrote this on that thread about the eurokit, then I was like 'nobody wants to hear an old man ranting about low compression' so I didn't post it.

Yeah especially on big over square setups, I don't really have a good reason to explain it but I'll think about it. It seems like on the hobbit and v1 especially, with the 47+ mm kits, letting them get through the lower rpm with lower load and bmep.

It's always better for the combustion process to get an earlier spark event and have everything fully burn, I think the short stroke makes things happen faster, and it takes longer to propagate the flame front across a bigger bore, so lower compression kinda softens things up. Makes it so it's not so violent when it does hit, so instead of putting all that extra heat into the piston and head and detonation, it's pushing the piston down. You can kinda feel it like smoothly building pressure on each hit rather than slamming hard, maybe? Maybe I'm nuts? I don't know.

Big dome, tight narrow squish, like less than 40%, push the timing as hard as you can and pound fuel to the fucker, sure to blast.

Re: Who’s a fan of low compression?

Totally normal JBOT /

Yeah exactly.

Most will just space the head or cyl to get that less compression but then you have garbage squish. Best way is to hog out the dome once you set a proper squish distance.

Graham Motzing wrote:

> -------------------------------------------------------

> Ah man I just wrote this on that thread about the eurokit, then I was

> like 'nobody wants to hear an old man ranting about low compression' so

> I didn't post it.

>

> Yeah especially on big over square setups, I don't really have a good

> reason to explain it but I'll think about it. It seems like on the

> hobbit and v1 especially, with the 47+ mm kits, letting them get through

> the lower rpm with lower load and bmep.

>

> It's always better for the combustion process to get an earlier spark

> event and have everything fully burn, I think the short stroke makes

> things happen faster, and it takes longer to propagate the flame front

> across a bigger bore, so lower compression kinda softens things up.

> Makes it so it's not so violent when it does hit, so instead of putting

> all that extra heat into the piston and head and detonation, it's

> pushing the piston down. You can kinda feel it like smoothly building

> pressure on each hit rather than slamming hard, maybe? Maybe I'm nuts? I

> don't know.

>

> Big dome, tight narrow squish, like less than 40%, push the timing as

> hard as you can and pound fuel to the fucker, sure to blast.

Re: Who’s a fan of low compression?

🇮🇹💦 Of the Loin /

just wick the heat same achievement

Re: Who’s a fan of low compression?

Totally normal JBOT /

> 🇮🇹💦 Of the Loin wrote:

> -------------------------------------------------------

> just wick the heat same achievement

Nope. Low compression spins easier, spools up faster, just plain better all around. Wc or ac it’s just so nice

Re: Who’s a fan of low compression?

Yeah heat= power, you can get rid of it faster but you're just getting rid of more energy that should be pushing your piston down.

Gotta keep as much heat as you can inside the power cylinder and prevent it from escaping until it's done it's job.

Re: Who’s a fan of low compression?

I like it low.

cheap gas, advanced timing…

Leaving power behind for easy riding is fine with me. I still feel like a “man” because I know how to tune better and choose to take it easy.

I don’t wanna be a slave to temps and worrying about lean detonation if I WOT on a hill or something.

Re: Who’s a fan of low compression?

🇮🇹💦 Of the Loin /

Meh, you aren't a giant windsail the low compression setups never get me where I need to be

Re: Who’s a fan of low compression?

Totally normal JBOT /

> 🇮🇹💦 Of the Loin wrote:

> -------------------------------------------------------

> Meh, you aren't a giant windsail the low compression setups never get me

> where I need to be

You’re a giant who rides a single speed

Duh of course it won’t work meats

Re: Who’s a fan of low compression?

🇮🇹💦 Of the Loin /

Single speed is real moped everything else is just scooters

Plz tell the robots

Re: Who’s a fan of low compression?

I would say anything above 120 psi is “normal compression”, low compression is being able to turn the rotor by hand and start it. I’ve built some +200psi bikes and they just don’t hold together very long to sustained abuse. I feel like if the studs don’t stretch you end up ruining your crank bearings in short order. Squish band not in the equation, anything that is a daily rider should be in the 125-165 psi range.

Re: Who’s a fan of low compression?

🇮🇹💦 Of the Loin /

150 PSI (technically it's 148 or 151 I think) is 10:1 compression ratio

220 PSI is running a 14.6:1 compression ratio.

I've never really measured compression, Angel just kinda showed me how to guesstimate compression one time for the low side so I just use that to eliminate compression when diagnosing a no-start situation

I haven't ever modified a head except for a Batavus Bronco I got from a dump and would sand a puch head down on a cinder block the Scuba Steve way to regain compression when the blown out rings inevitably lost more slowly.

I'd say a Gila on a V1 is generally like 185/190? I think that's a good some but you do need to manage heat in high load situations. Gila does good at surviving heat tho. They do blow head gaskets so there's that

Re: Who’s a fan of low compression?

I have a whole rant in my pocket about how most moped motors run too much compression and that's why so many bikes run bad and seize early. I shoot for 150psi usually around there, less with big pipes and rpms, because you are measuring at idle rpms and at speed they make a lot more. People don't realize that.

Re: Who’s a fan of low compression?

Alan Jackson /

10 years agoi used to run 210 psi for short spells (holed a piston) but then settled on 150psi as my target. 2 years ago i reduced this to 135 and this year im happy with 120 on my moby. (still wont pedal start)

must be an age thing...

wish my blood pressure would come down with age... (edited)

Re: Who’s a fan of low compression?

how are y'all measuring this?

someone please please please link me to a high quality low CC compression tester that isn't from Amazon.

Re: Who’s a fan of low compression?

Totally normal JBOT /

I took a standard long hose compression checker and took off the crimped hose connectors to reveal a hose barb underneath.

Cut hose and then hose clamp. I also don’t use the brass extensions it came with. Schrader right into the jug.

Re: Who’s a fan of low compression?

Dirty30 Dillon /

https://maverickmowersupply.com/752311-compression-tester-

That one is definitely short enough to mitigate hose bulge.

It looks like this other one allows you to mount the threaded couplers directly to the gauge, which would be ideal, if that's the case.

https://www.autotoolworld.com/OTC-Bosch-Automotive-5606-Compression-Tester-Kit_p_162959.html

Re: Who’s a fan of low compression?

Alan Jackson /

i borrowed 4 gauges off a local bike repair shop and tested them alongside my 2.

2 of them read identical and 2 got thrown away. so much difference. the best two were old school gunsons from the 1980's

the newer gunson available on amazon was way out.

Re: Who’s a fan of low compression?

> Totally normal JBOT wrote:

> -------------------------------------------------------

> I took a standard long hose compression checker and took off the crimped

> hose connectors to reveal a hose barb underneath.

>

> Cut hose and then hose clamp. I also don’t use the brass extensions it

> came with. Schrader right into the jug.

I’m going to try this with the hose one I have 🤙🏻 Thanks for the pro tip.

Re: Who’s a fan of low compression?

> EH FCC of the QCB wrote:

> -------------------------------------------------------

> > Totally normal JBOT wrote:

>

> > -------------------------------------------------------

>

> > I took a standard long hose compression checker and took off the

> crimped

>

> > hose connectors to reveal a hose barb underneath.

>

> >

>

> > Cut hose and then hose clamp. I also don’t use the brass extensions it

>

> > came with. Schrader right into the jug.

>

> I’m going to try this with the hose one I have 🤙🏻 Thanks for the pro

> tip.

Test before and after the 'conversion' .

Post the results , please .m;)

Re: Who’s a fan of low compression?

I just posted on the other thread, theoretically it shouldn't matter but I might be wrong. It will take more revolutions to 'pump up' with a longer hose, but I'm curious for someone to really try it back to back

Re: Who’s a fan of low compression?

Totally normal JBOT /

Duh I already told you. 20% diff approx.

Here’s what I did it’s fine

8A0DB39D-049F-46CA-9881-8A9DCA5F2F79.jpeg

Re: Who’s a fan of low compression?

> Totally normal JBOT wrote:

> -------------------------------------------------------

> Duh I already told you. 20% diff approx.

>

> Here’s what I did it’s fine

Just double checking with a different tester . ;)

Re: Who’s a fan of low compression?

> Totally normal JBOT wrote:

> -------------------------------------------------------

> I took a standard long hose compression checker and took off the crimped

> hose connectors to reveal a hose barb underneath.

>

> Cut hose and then hose clamp. I also don’t use the brass extensions it

> came with. Schrader right into the jug.

I’m going to try this with the hose one I have 🤙🏻 Thanks for the pro tip.

Re: Who’s a fan of low compression?

> EH FCC of the QCB wrote:

> -------------------------------------------------------

> > Totally normal JBOT wrote:

>

> > -------------------------------------------------------

>

> > I took a standard long hose compression checker and took off the

> crimped

>

> > hose connectors to reveal a hose barb underneath.

>

> >

>

> > Cut hose and then hose clamp. I also don’t use the brass extensions it

>

> > came with. Schrader right into the jug.

>

> I’m going to try this with the hose one I have 🤙🏻 Thanks for the pro

> tip.

Again , Test before and after the 'conversion' .

Post the results , please . ;)

Re: Who’s a fan of low compression?

Wtf…odd double post

Re: Who’s a fan of low compression?

> EH FCC of the QCB wrote:

> -------------------------------------------------------

> Wtf…odd double post

Too bad you can't get winning lotto tickets like that^ . ;)

Re: Who’s a fan of low compression?

> Dirty30 Dillon wrote:

> -------------------------------------------------------

> https://maverickmowersupply.com/752311-compression-tester-

>

> That one is definitely short enough to mitigate hose bulge.

>

> It looks like this other one allows you to mount the threaded couplers

> directly to the gauge, which would be ideal, if that's the case.

>

> https://www.autotoolworld.com/OTC-Bosch-Automotive-5606-Compression-Tester-Kit_p_162959.html

I got the stens compression tester coming.

funny it wouldn't work from the link you put up there...maybe it'll work from this one?

https://maverickmowersupply.com/752311-compression-tester-?search=stens%20tester&description=true

anyways, it'd be cool if all the people who did this stuff seriously all got the same tools so we could share results between each other and know that we're all talking the same language, if you know what i mean

Re: Who’s a fan of low compression?

Totally normal JBOT /

> P D wrote:

> -------------------------------------------------------

> > EH FCC of the QCB wrote:

>

> > -------------------------------------------------------

>

> > > Totally normal JBOT wrote:

>

> >

>

> > > -------------------------------------------------------

>

> >

>

> > > I took a standard long hose compression checker and took off the

>

> > crimped

>

> >

>

> > > hose connectors to reveal a hose barb underneath.

>

> >

>

> > >

>

> >

>

> > > Cut hose and then hose clamp. I also don’t use the brass extensions

> it

>

> >

>

> > > came with. Schrader right into the jug.

>

> >

>

> > I’m going to try this with the hose one I have 🤙🏻 Thanks for the pro

>

> > tip.

>

> Again , Test before and after the 'conversion' .

>

> Post the results , please . ;)

Again, I’m giving you the results. Jesus. I tested it years ago. I’ve been using this for like 10 years.

It was about 20% off.

If you want exacts go mod one for fucks sake

Re: Who’s a fan of low compression?

Totally normal JBOT /

Pressure = force/volume.

More volume (longer hose) creates false low reading.

C3A538C8-9E1A-45FD-95D3-DB7FAC87CA39.jpeg

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