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Discussion Starter #1 (Edited)
Ok we have been talking a lot about cam, piston, and cylinder head selection in various threads recently. Now to choose a combo you have to choose parts that will work for what you want the car to do and more importantly work properly with each other.

So here is my question. What is the part you select first that you then build the rest of the motor around. For example do I select the heads I want to run and then choose everything to match the heads or do I choose a cam and then select the other parts to match the cam or what?????

I suspect to build a matching combo you must have a starting point on which to taylor the other parts to. Personally I think the starting point is the heads and you match the other components to them.:)
 

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First you have to decide what your engine is going to do:
Street car or trailered race car; road race or drag race.
Then you need performance desired. ET, MPH. Then you need to know weight. From this you can estimate Power,torque, max rpm requirements;
1/4 mile HP = (0.00426 x mph) ^3 x weight

Example: 3,000 lb car @ 120 mph in 1/4 mile requires 400 hp minimum
Higher drag, poor gearing, traction etc. will require more power.

ET = ((Weight / HP)^.333) x 5.825

Our 3,000 lb 400hp strip Nova should be able to go 11.4 in the 1/4 if everything is theoretically perfect. Your results will be less with considering drag, gearing, drivetrain loss and traction.

Once you estimate the power level you need then you can pick VE, SCR and RPM targets. Keep in mind that higher SCR, VE and higher rpm targets often means more money will be spent. You don't get something for nothing.

CID = HP x 792001 / Intake air pressure / SCR / VE / RPM

Note that CID requirements go down if the air pressure, SCR, VE, RPM goes up. Conversely if these parameters are lower the CID needs to be raised to get the same level of power.

From all the above you can rough in the engine specs in this order:
  1. Displacement
  2. Bore and stroke
  3. Rod length and CH
  4. Heads
  5. Compression ratio
  6. Cam

So with for 3,000 lb Nova running 12.0 @ 120 mph with 405 hp @ sea level
you'd need a:
427 CID engine with 85% VE, 10:1 SCR @ 6,000 rpm
355 CID engine with 90% VE, 11:1 SCR @ 6,200 rpm
 

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Discussion Starter #3 (Edited)
"Intake air pressure" is that in an normally aspirated motor just atmopheric pressure?...ie 14.7pounds per square inch?


well I played aroung with the numbers and came up with just over 402ci.

CID = HP x 792001 / Intake air pressure / SCR / VE / RPM

to get that I used the following numbers:

CID=400x792001/14.7/10/.8/6700
which = 402.07cid

Does that sound right?
 

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Yes, but are you going to want to rev a 402 to 6,700 rpm?

Lower the RPM to a big block friendly 6,000 and now you need a 454.

As you play around with the variables you'll see the trade offs and problems.

The larger the displacement, the easier it is to get the power and less rpm is required. Catching on?

The Intake pressure is atmospheric but could also be boost. This is why supercharged engines make power like bigger engines.

A little 283 with 8:1 but 1 atmosphere of boost could easily make 405 hp.
 

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Discussion Starter #5
Paul Wright said:
Yes, but are you going to want to rev a 402 to 6,700 rpm?

As you play around with the variables you'll see the trade offs and problems.

The larger the displacement, the easier it is to get the power. Catching on?

Yes I do, thanks so much Paul for this information. AWESOME stuff
The 427 @ 6000rpm is a much better option :)
 

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69NovaSS said:
Yes I do, thanks so much Paul for this information. AWESOME stuff
The 427 @ 6000rpm is a much better option :)
Bigger is better. You know I don't even own a desk top dyno program? I have a bunch of equations programmed into my HP48 handheld calculator. I can plug in all the variables and solve for "what ifs".

When we were drag racing Jay Leno's tank car against the M1 Abrahams all I brought was my calculator. We already knew the weight of the car and the GPS could give us 1/4 mile speed and ET. I had the HP before he even turned around.
 

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Discussion Starter #7
Paul Wright said:
Bigger is better. You know I don't even own a desk top dyno program? I have a bunch of equations programmed into my HP48 handheld calculator. I can plug in all the variables and solve for "what ifs".

just one more question on these what if's are they talking rwhp or flywheel hp?
 

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That's pretty funny. I did the same thing with my TI-83 for passing the time while in one of my "useful" general education classes. It seems that my 307 has some distinct disadvantages:(.

Kev (Thus... 350 time!)
 

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Wow...I got lost all of the mathematical equasional stuff.

Wonder what it would take to push a 3700 lb Chevelle into the low 12's/high 11's with a 402 big block? 450 fwhp?
 

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Discussion Starter #10 (Edited)
ok here goes.

You would need 494.28HP under ideal conditions to get your car to 120MPH

NOW with a 402ci you will need 12.0 to 1 SCR
.85 VE and reving it to 6500RPM. to make 494HP or at least that is what I think it comes out too.

Or you could build a 400HP motor and buy a 100shot NOS kit. that should get you there too :)

You could make 400HP with your 402 with a SCR of 10.5 a VE of .85 and an RPM of 6000. much better rpm for that motor. ;)

I think these numbers are right.
 

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69NovaSS said:
just one more question on these what if's are they talking rwhp or flywheel hp?
It's neither and both. Confused? If you look at the equation it doesn't take into account driveline drag so it must be flywheel. However it also doesn't take into account wind drag so above a certain speed the answer will be more like wheel horsepower. At real fast trap speed (150-200 mph) the air drag is so great the answer is flat out wrong. If you have a car that goes over 150 mph you don't need my help.

This equation is only for figuring estimated horsepower and is most accurate around 100 mph trap speed. It increasingly under estimates hp over 100 mph and over estimates under 100 mph.

The purpose was to show the relationship of the variables NOT give some incredibally accurate and free desktop dyno. The whole series of equations are much more complicated the more accurate you want to be.

I should put a caveat "for educational purposes only" but I wanted to see if someone started posting this on "other" web pages like they thought it up.
 

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Discussion Starter #12
well that is cool, it was very "educational" in my book and it was fun playing around with the various "what if's" :)
 

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Discussion Starter #13
BTW is this simular to the moroso speed/hp slide calculators?
 

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OK Paul, with that known now, how do you determine what will get you to the desired VE? Is this a whole new equation?

Randy
 

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Discussion Starter #15 (Edited)
72GreenRally said:
OK Paul, with that known now, how do you determine what will get you to the desired VE? Is this a whole new equation?

Randy
Ya I was wondering that too, for example how do I guarentee that I get 85% VE for a given combination?
 

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VE questions

that'll have to wait for another day. It's 5 o'clock on a Friday and it's nice out.
 

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Paul Wright said:
that'll have to wait for another day. It's 5 o'clock on a Friday and it's nice out.
Aw, now that's not fair. It's 2:00 here, and it's crappy out!

Have fun in the sun Paul!

Randy
 

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69NovaSS said:
ok here goes.

You would need 494.28HP under ideal conditions to get your car to 120MPH

NOW with a 402ci you will need 12.0 to 1 SCR
.85 VE and reving it to 6500RPM. to make 494HP or at least that is what I think it comes out too.

Or you could build a 400HP motor and buy a 100shot NOS kit. that should get you there too :)

You could make 400HP with your 402 with a SCR of 10.5 a VE of .85 and an RPM of 6000. much better rpm for that motor. ;)

I think these numbers are right.
120 mph? Is that what's estimated my car will be travelling to stop the clocks at the high 11/low 12 second time I posted?
 

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Discussion Starter #19 (Edited)
Dawg said:
120 mph? Is that what's estimated my car will be travelling to stop the clocks at the high 11/low 12 second time I posted?

Should be in the ball park of upper 11's under ideal circumstances :) ie. 11.89
 
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