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Discussion Starter · #1 ·
A 2 HP per CI Chevy (or other traditional brand ) naturally aspirated engine is a race only engine. Prostocks were at that level not too long ago

This 1985 Yamaha was a "hot rod" + it produced 2 Hp per CI. It would idle, cruise and act civil.


Question: Why is one civil, and the other is not.

What (if anything) can be done to make them par?

Thanks

Alex
 

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Peak HP is at 9000rpm and peak torque is at 7500rpm... you wouldn't want to drive a 3500 lb car on the street with that kind of power band.
 

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that MC engine was high tech and had 4-valves per cylinder for airflow
also the redline operating range allowed for the high power production at high rpm
 

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the smaller cubic inch the easier it is to have higher volumetric efficiency and flow I mean with bigger motors comes more volume to fill therefore needing a higher cylinder fill/charge which also comes with needing more duration, longer stroke, / combination of running the stroke at a higher rpm to allow even greater powerband also comes with the inability to drive smoothly you can't have both once you reach a certain point that point is really opinion based on if it is streetable until it comes to a point of not at all streetable
 

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What Spencer said. Remember the rave about the S2000 having like 120 hp/L N/A? Since it was only 2.0L it was attainable. You won't get 120 hp/L out of a typical 7.4L 454 ci BBC, but I'd take 500+ horsepower and 500+ ft-lbs over a 240 hp 2L Inline 4.
 

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how about a destroked LS say something down to 290 to 300 CI with the 6.2 or larger heads and a decent cam. drop it in a T bucket or a vega with 4.56 gears? jim
 

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I was almost going to buy a 1.87 hp/ci LS but then went big block with more HP but definitely less hp/ci.

Talking to about 6-7 big builders around the country that would build an LS or BBC every single one of them said BBC and cubes over the smaller LS for similar power. Most said the bbc could be a one time build, but getting close to that 2hp per ci is pushing it for the smaller cid.

These were all NA builds, boost is on a different level of reliability (better) when moderate. So that 1.87 is not high when you add boost.
 

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Rpm are needed for 2hp per cube NA. Not cost effective as boost. More cubes will always win. What happens when all things are equal for example 402 small block, 402 big block and a 402 LS 🤔 for dyno Queen I guess it would boil down to what heads would flow the most and engine would hold together at the highest RPM.
 

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Discussion Starter · #9 · (Edited)
I read all the replies, thank you

Yes the MC makes peak power at a very high RPM, but it can idle and drive at 2K RPM too.

I still do not know what sets it apart. I do not think VE , or dual valves are going to make that much of a difference, but I can be mistaken

Thanks for the replies gents, reading and learning here. Looking for statistical facts more than theory

Alex
 

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Rpm are needed for 2hp per cube NA. Not cost effective as boost. More cubes will always win. What happens when all things are equal for example 402 small block, 402 big block and a 402 LS 🤔 for dyno Queen I guess it would boil down to what heads would flow the most and engine would hold together at the highest RPM.
BBC all the way, I don’t think there are any LS heads that come close to the the biggest BBC’s. Rpm shouldn’t be a factor because they will all spin the same if you have enough money.
 

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I read all the replies, thank you

Yes the MC makes peak power at a very high RPM, but it can idle and drive at 2K RPM too.

I still do not know what sets it apart. I do not think VE , or dual valves are going to make that much of a difference, but I can be mistaken

Thanks for the replies gents, reading and learning here. Looking for statistical facts more than theory

Alex
You can build a bbc or Ls NA at 2hp/ci sure. It will also drive around at 2000 rpm

You will need about $50k + and the right builder.
It won’t last forever.
And honestly this isn’t top shelf by a landslide plus not even 8000 rpm.

 

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Discussion Starter · #12 ·
16 to 1 compression BBC is NOT a street car.

I am going to drop this topic and try to find an engineer who can explain it.

Thanks all

A
 

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You really can't compare motorcycle engines with car / truck engines. It's easy to make a small engine driveable with over 2hp/ci when you're only hauling around 800 lbs. Vmax is about 600 lbs + 200 lbs for a rider with gear. Doesn't take much low speed torque to get that weight moving. My KTM 450cc dirt bike makes around 2hp/ci and it can lug down at idle on the tight trails. It weighs about 220 lbs + rider. In my case that's around 440 lbs total.
Now take the average Chevelle at around 3600 lbs. It takes much more torque to get that weight moving. Car engines need the power lower in the powerband to get that weight moving. An engine that makes 2hp/ci is not going to have the low speed torque needed to be driveable. It's just physics and math.
 

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16 to 1 compression BBC is NOT a street car.

I am going to drop this topic and try to find an engineer who can explain it.

Thanks all

A
Good luck wasting his or her time.

Some people do not understand numbers.....or what some numbers really mean....or don't mean.
Total power is a measurable, meaningful number.
Total power per cubic inch is, in many ways, an almost meaningless number. (This was referenced above when someone correctly pointed that this "stat" is skewed towards smaller motors.)
It's quantifiable.....but it doesn't necessarily mean much.
Some may say you're measuring efficiency that way....which is often true.
But you're still just trying to make as much power as you can. You're just taking the size of the motor and sticking it into the denominator of a fraction. But the real, meaningful number is the numerator. In this case....power.
People in Finance often misunderstand ROI and people in retail often misunderstand the Sales or Revenue per Cubic Foot metric. In all of these cases, the numerator is all that really matters. The denominator is often some fixed number that means......squat.
Put another way, torque and horsepower move your car or motorcycle. TQ per cubic and HP per cubic inch do NOT. They simply "tell" you how many inches it took to do that.
But regardless of your cubic inch total, you're still likely trying to make as much power as possible.....so lose the meaningless fraction.
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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A 635 HP 400 lb 377 cu. in. N/A LS3 or a 635 HP N/A BBC....which will move a 3500 lb car faster? A little off or ? Topic
 

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A 635 HP 400 lb 377 cu. in. N/A LS3 or a 635 HP N/A BBC....which will move a 3500 lb car faster? A little off or ? Topic
The aluminum BBC with more torque.

A lot of the LS guys forgot that an alumimum BBC is only 125 lbs.

And the big power guys are running very heavy aftermarket iron LS blocks @227lbs. Std Ls is 115-127 lbs. When I was pricing an 800 hp LS from one of the guys above and said it wasn’t an all out race car they HIGHLY suggested the dart Next block.
 

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I am only up to 1.25 hp per cuin on my hot rod. But I did see some 800 hp street drive dyno curves last week....
 

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