Old Engines are inefficicent at creating power/torque,WHY? 3

[mechanicat16]

Why do old engines produce such little power for their displacement, for example, the 1968 426(7.2L) hemi produced 425HP.The modern 6.1 L hemi produces about 425 HP, the same as the 7.2! Why is this?

 

[LionelHutz]

Any ideas?

Learn to read...

 

[patprimmer]

Like Rod and Lionel said, plus learn to start your own thread instead of hijacking this one AFTER you do your homework.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[Tmoose]

"The engine was carefully rebuilt with attention to the heads & the entire valve train."

Seems like for lots of projects The focus is on measureable hard parts. Rod bearing clearances controlled within 0.0002 inch, etc.

My old twostroke dirt bikes have patiently explained to me several times there is exciting HP and excellent throttle response still hidden in the small suitcase full of brass jets and aluminum needles.
When Bill "Grumpy" Jenkins first achieved prominence in drag racing it was as a tuner.

 

[evelrod]

Tmoose, I'm a "tuner" by that definition.
I can read plugs, tailpipes...
I can hear what the "heartbeat" is telling me.
I can "sense" what the engine is doing.
Yes sir, I CAN do all these things. I've always been able to do all these things. I have NOT been able to teach others how I do it, not for not trying.
My oldest boy, the painter/artist/mechanic is fair, but misses the little stuff.
My youngest son is a "reader". If it's in a book, he knows all about it. He is, however a very talented race car driver.
My daughter loves cars. She also loves computers, Ipods, cell phones and, is for the most part very intelligent...she is also a space cadet when it comes to cars.
Even my wife, just after we were married enrolled in a basic automotive maintenance course after she graduated high school.
If you want to follow me around, maybe it will rub off a bit. The last of the "black arts"?

Rod

 

[Tmoose]

Here's a not old, relatively "new" 1500 Cee-Cee ( 90 cubic inch ) engine that wheezes out a mere 75.231 lb-feet.

http://www.electrifyingtimes.com/priustechspecs.html

This, despite benefit of such proven power boosting brochure bullet points as:
- 13.5-1 compression ratio
- Fuel injection
- 4 valves per cylinder
- DOHC
- cHaIn DrIveN cams
- Variable valve timing

And, the popular torque enhancing "long stoke."

Might have >>something<< to do with those interesting valve timings.

Pretty good BSFC though.

 

[GregLocock]

Heywood makes the point that 'over expanded' engines such as Prius' pseudo-Atkinson tend to sacrifice max bmep for economy.

Cheers

Greg Locock


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[Tmoose]

Hi Greg,

Yeah, I was just being contrary, providing a new, high tech sounding example of "crumby" HP and torque. Probably cause I'm pretty old and inefficient myself.

I wonder what operating condition triggers The intake closing at 120 ABDC. 50 degrees BTDC. Start compressing when the glass is nearly empty. Just take a quick sip of air.

I used to have some info on Crower's "more complete expansion" kit for Chevy V8s. High compression, skewed valve events. That had to function with a carburetor though.

Dan T

 

[Marquis]

SIDI on its own gives no major fuel economy benefit. It must be carried out with other changes in mind. It's nothing like the huge step change in efficiency you get when going from a pre chamber diesel to a DI diesel.

SIDI or GDi delays the onset of knock at high loads- which means a higher compression ratio can be specified. May be 1-2 ratios higher than a conventional SI engine. For every ratio increase- assume about 3% fuel economy benefit. When you're already at 10:1 it may be less- say 2.5 %. This is a benefit in terms of BMEP and BSFC. GDi alone gives between 3-5 % benefit in terms of Volumetric efficiency and therefore torque. However some of the fuel economy benefit of GDi alone is lost due to the pump drive torque required to inject at 200 bar or so. So the net gain is about the benefit of the CR change alone with a handy BMEP benefit- due to charge cooling and due to the CR change itself.
If the engine is down sized to compensate for the power/torque increase- - while targeting a certain torque/power curve you can get a further slight benefit in fuel efficiency due to lower pumping losses.
The biggest gain with GDi comes when you boost the engine in league with variable cam phasing. You can specify BIG valve overlaps at low engine speeds- for great scavenging- and boost the engine hard, and not worry about short circuting of the injected fuel because being DI you can inject whenever you want in the cycle and thus avoid short circuiting. This gives a HUGE wall of torque at low speeds- and you can therefore, in theory down size your engine further to chase slightly better fuel efficiency.

http://www.auto-scape.com

 

[Marquis]

Evelrod said:"My daughter loves cars. She also loves computers, Ipods, cell phones and, is for the most part very intelligent...she is also a space cadet when it comes to cars."

is she looking for a husband? ;-)

http://www.auto-scape.com

 

[evelrod]

I sure hope so.

Rod

 

[ornerynorsk]

Who said arranged marriages don't work !!!

 

[lawayosh]

Rod -

Practioner of a Black Art indeed. There have always been lots of parts selector/assemblers out there. Some working to very precise tolerances and clean to a fault. But, not many have been able to make every motor they touch the one to beat.

I thought that I was OK at tuning, but would have my partner touch it up before we made a run. Not just to make sure as a lot of times he would make a minor adjustment which made a real difference. Typically, it would be me in the seat fired up and ready to stage, he would nod his head when it felt and sounded right to him. Found it was best not to ask him to explain how he knew what to adjust, just drive the car.

Yosh

 

[TxGat]

If you want to keep the GTO original and up the HP and torque then I recommend balancing and blueprinting the motor, change the pistons to a dish or dome and a thinner head gasket for higher compression, and have the heads fully (re)ported using 21st century tech . These with the original cam spec ought to get you well into into the 400's hp, perhaps into the low 500's with a mild mod on the cam (newer tech again in a place that you can't see looking under the hood). I recommend you go to Comp Cams and download CamQuest 6.0 (it's free on their site) and play with the figures some. Your motor with a carb ought to generate a considerable number of cam options. Then you pick the one you want to live with.