Starter Question

[toolmakeron]

I see starters advertised in Ft Lb of Torque, Then I see them listed in H.P. How do I find out the strongest starter, for a hi comp engine.I'm sure there has to be a conversion or chart to learn from. Any help is appreciated, Thanks Guys

[Hectori]

I thing that you need RPM or Time variable to be able to compare apples to apples. But many manufacturers tell the maximum CR that should be used. MSD DynaForce startes say 18:1 and Powermaster Ultra Torque 15:1 for example.

[amc fan]

Horsepower & torque relationship: T=HPX63025/RPM ....HP=T X RPM/63025 T=torque in (lb-in).......T=HPX5252/RPM HP=T X RPM/5252 Torque in(lb-ft

[governor]

Buy the best gear reduction unit your budget will allow.

Gov

[toolmakeron]

Has anyone ever seen the RPM mentioned with starters? The formula that amc gave is great, but without RPM, I think you are lost. I bought a MSD awhile ago & I didn't see any RPM info. Can someone prove me wrong? I think the RPM will depend on the battery condition. Thanks Guys

[Hectori]

Has anyone ever seen the RPM mentioned with starters?

I have never seen RPM mentioned, and i think that it because electric motors have full torque from the start. so you can try to compare hp and torque with low RPM`s. Just a thought thou, i am not electrical engineer.

But for accurate comparing of torque and HP, you need either Time or RPM factor. That means like ft·lbf/sec Or RPM.

[barnym17]

All you need is watts, it directly converts to h.p.

[Warpspeed]

Buy the best gear reduction unit your budget will allow.
Gov

+1

[BCjohnny]

There are two distinct phases that the starter has to overcome in starting an engine.

The first, and most crucial, is the starter's ability to get the engine moving from rest, or breakaway torque. A DC motor exhibits it's greatest torque output, thus amp draw, at the point just before it stalls. This is where geared starters excel.

Secondly as the starter speed builds its torque output falls, as does amp draw, the back EMF being generated within the motor opposing the current draw. Horsepower is increasing. At some point an equilibrium is reached where the power/gearing is matched by engine load and you have cranking speed. This is where the HP rating comes in, and how starters are conveniently rated.

What's it all mean? The hardest thing a starter has to do is the breakaway torque phase so if it can achieve this in any given application, the rest pretty much looks after itself. A geared starter around 2.2kw will start almost any automotive petrol V8 and the space envelope and weight are so minimal compared to one of around 1.4kw it doesn't usually make much sense to pick the smaller unit, certainly when you get to around 6 litres or more.

Construction, design and country of origin deserve more consideration. PMGRs are often lighter for any given rating, but have drawbacks. A new or even rebuilt OE unit is usually far better than a copy, but some OE units are better suited to harsher enviroments than others

[af2]

There are two distinct phases that the starter has to overcome in starting an engine.

The first, and most crucial, is the starter's ability to get the engine moving from rest, or breakaway torque. A DC motor exhibits it's greatest torque output, thus amp draw, at the point just before it stalls. This is where geared starters excel.

Secondly as the starter speed builds its torque output falls, as does amp draw, the back EMF being generated within the motor opposing the current draw. Horsepower is increasing. At some point an equilibrium is reached where the power/gearing is matched by engine load and you have cranking speed. This is where the HP rating comes in, and how starters are conveniently rated.

What's it all mean? The hardest thing a starter has to do is the breakaway torque phase so if it can achieve this in any given application, the rest pretty much looks after itself. A geared starter around 2.2kw will start almost any automotive petrol V8 and the space envelope and weight are so minimal compared to one of around 1.4kw it doesn't usually make much sense to pick the smaller unit, certainly when you get to around 6 litres or more.

Construction, design and country of origin deserve more consideration. PMGRs are often lighter for any given rating, but have drawbacks. A new or even rebuilt OE unit is usually far better than a copy, but some OE units are better suited to harsher enviroments than others

I could not have explained it better!! Very good post!!

[Krooser]

Great subject.

[BCjohnny]

I could not have explained it better!! Very good post!!

Thanks...... I spent most of the nineties, before I sold up, designing and manufacturing high performance starter applications, so it's one of the very few things I actually do understand, lol. I learnt a lot, and curiously for someone over here, a fair chunk of it was getting 510/540 BBCs to light off almost regardless. If I can help with anything, ask.

[toolmakeron]

Here's another follow up question,the choice I'm looking at is, 180 ft. lbs torque, OR 3 h.p.( is this all just marketing hype) The 3 h.p. sounds high to me , but the seller swears to it. Opinions, advice, or any input to this one??? Thanks guys

[af2]

Here's another follow up question,the choice I'm looking at is, 180 ft. lbs torque, OR 3 h.p.( is this all just marketing hype) The 3 h.p. sounds high to me , but the seller swears to it. Opinions, advice, or any input to this one??? Thanks guys

If it draws 2.2 KW on the start it will be around 2.95 HP.....

[BCjohnny]

Here's another follow up question,the choice I'm looking at is, 180 ft. lbs torque, OR 3 h.p.( is this all just marketing hype) The 3 h.p. sounds high to me , but the seller swears to it. Opinions, advice, or any input to this one??? Thanks guys

If it draws 2.2 KW on the start it will be around 2.95 HP.....

No it's not hype, I was doing 3hp 12v stuff more than twenty years ago. If you've room to fit, it's a good choice, and as said will get most things going. It's based on a 'diesel' motor. I'm moving back into this field and one product I am currently working on has motors in the 4hp+ range. Bit overkill, but too much is never enough.