How do you tell a know it all he's wrong?

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Chris142

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Jun 5, 2003
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Had a clown come in today. Boy did he get under my skin!

He has a 71 Chevy Chevelle with a 350/350 combo and 3.08 gears in the axle. He says that it uses too much gas so here is his plan.

70's 305 from a junkyard.
Huge rumpity rumpity cam.
Huge hi-rise intake and a hole in the hood for it to fit through.
750 CFM Edelbrock carb with the secondaries tied shut.

700r4 overdrive trans.

Gear vendors overdrive behind the 700r4.
New 2.50 axle gearing.

For some reason he thinks this is going to net him much better MPG!

The 70's 305 was a dawg to begin with. The big cam and stock low compression is going to kill any low rpm power.

Carb is too big as is the hi-rise intake.

Having double overdrive is going to bring the small engine below it's optimum rpm as will the 2.5 axle gears.

All this is going to make the car miserable to drive plus the low vacuum from low rpm, big cam etc is going to make the metering rods in the carb lift up and dump fuel since the carb will be seeing low vacuum all the time.

He thinks he's going to get 30 mpg hwy with this setup.

Of course I'm an idiot when I told him he'd be better off with the 305 heads on the 350(high compression), a set of tri-y headers(scavenge the cyls at lower rpm's), free flowing exhaust and a quadrajet carb.

Serously how well does a car run @ idle and full throttle at the same time?

I swear I can't make this stuff up
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How about putting in a modern fuel injection motor? An lt-1 would be nice and pretty cheap to find..
 
Add 24" rims (with moon spinners for more aero advantage :)) to go along with the double overdrive!!!!!
 
Sometimes people just peg you for someone who doesn't know any better than they do. If that's the case, the best thing to do is to get on their good side and then let them fail. Then you can say "I told you so" and they will listen.

The other possible reason is that the person you're dealing with is just a dogmatic thinker, i.e. they believe first and find reasons later. In that case, it's likely that nothing you can do will convince them, and the best you can do is to make them go away.
 
Originally Posted By: chad8
How about putting in a modern fuel injection motor? An lt-1 would be nice and pretty cheap to find..


You could find a junkyard 4.8L or 5.3L LSx for less money then what building a 305 would cost. That would net great fuel economy and probably make more power then a hopped up old 305.
 
Oh and he's doing all these mods for a trip to the east coast and back. I know the rebuilt 700r4 and gear vendors will cost $3000.

Better off buying a $3000 Saturn, Toyota or Honda for the trip and selling it when he gets back.

The cam and intake are designed for 3000rpm and above. Why does he think that running them lower will give better MPG?

He did mention that the cam will give higher HP and I said it won't at 2000 rpm which made him mad.
 
The factory with millions of dollars couldnt get 30 mpg from a V8 X body,speak nothing of a V8 A body,hence why they were killed off in 1989 in favor of V6/FWD cars (W bodies),so how is a bench racer going to do it with a mishmash of parts? I still laugh at the doltzes that claimed their 1975 Olds 88 with "Rocket 350" could get 28 mpg highway,or their 1957 Chevy V8 got 25 regularly.If cars actually had got that kind of mileage,there would have been no 1970s gas crisis,people selling off their "boats" for new Toyotas and Datsuns,and downsizing cars and engines would have never happened.Tell him to get rid of it,get an Omni Miser,Geo Metro,Rabbit diesel,or 1980s Nissan Sentra,and see what real mpgs are.
 
It takes a certain amount of energy to do a certain amount of work.

Where will the reduction in work occur? Or the increase in thermal efficiency?

Done correctly:

1) no reduction in work here. Same vehicle.
2) Possible increase in efficiency, reduced frictional losses by smaller engine, running lower RPM.
3) Possible increase in efficiency, higher compression.

The only items related to increased efficiency are on the order of a few percent, maximum. So, with proper engineering, his MPG will go from 13 to 14. Yay!

Of course, there are many mis-steps with this approach, including the camshaft. Good thermal efficiency requires extracting as much power as possible at all operating speeds. A camshaft with excessive overlap or lobe timing designed for high speed operation will significantly reduce low speed efficiency. Hence the lump-lump sound of inefficient combustion at low RPM's.
 
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Why do you want to tell him he is wrong? Did he ask your opinion? If it is his money and he's made his decision that this is what he wants to do, then get on with it.
 
I don't even bother unless its going to effect my wallet some how, otherwise i could care less how someone else spends their money and waste their time.

You can turn this your way by telling him your interested in buying it if it doesn't work out, then offer him chump change for the shell.
 
Originally Posted By: Maximus1966
Why do you want to tell him he is wrong? Did he ask your opinion? If it is his money and he's made his decision that this is what he wants to do, then get on with it.
he started in asking how to replace his a6 compressor with an r4 then he told us his plan and and what we thought so. I told him what I thought.
 
Originally Posted By: javacontour
Tell him the only thing he'll hear, "Good luck with that."


And "Please let us know how that works out".

Everyone has a right to their opinions, even if they are in all likelyhood wrong. Probably the most relevent question here is whether you were ticked off by his having a different opinion, or by the attitude he took toward your opinion.

It is always hard to have your opinion disrespected (true for him, also), but in your case you have the voice of experience, which he may not understand. But it also seems you have some trouble communicating technical concepts.

People think and communicate in two distinct ways - Starting with a concept and then looking for facts to support it, or starting with (presumed) facts and looking for a concept which explains them. You might think about which way you communicate vs how your "trouble" customers do and see if you can adapt to their styles.

Your aim should always be a win-win situation, which means that either their point of view, or their right to have it, needs to be validated somewhere in the conversation. It shouldn't be an ego battle between you (and this may not be the case, it may be mostly a problem of conversational dynamics). You can achieve this, and get your points made by saying "I hear what you are saying, but think about this...".

If you are the expert, then you should be secure in that knowledge. If you need it to be validated by people off the street, then that is an insecurity that can get in the way.

And there are indeed people who won't listen to anyone, know matter how conversationally skilled. Be polite, then go on with your life. They aren't worth any distraction you might allow them to cause you (and it is your choice).
 
The 305 only has a smaller bore/valves than the 350, same r/s ratio, so same piston acceleration characteristic. If he wants better FE should have stopped there. As mentioned, the cam will drop his effective cylinder pressure, the lower static compression will drop his torque more than it needs to be dropped and combined with the 2.50 final will, again as mentioned, drop his cruising RPM well out of the efficienct range.

If I were him, I'd keep the 350 and go for the 2.50
or go 305 and keep the 3.08. Either way I'd opt for higher static compression and fuel injection. To keep the bottom end responsive, I'd go with long runner manifolds and perhaps a roller truck cam to enable torquey cruising in OD. But honestly, if FE was my prime concern, I'd swap platforms.
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You don't,

Simply ignore said individual and laugh knowing they will probably come in afterwards saying it is getting WORSE MPG. And who the heck tries to squeeze MPG's out of a 70's 305/350 engine?

Tell him to drop a Honda B motor in there to get slightly better mileage while it tries to haul that heavy chassis around.
 
Really, the best thing for him to do for MPG would be to put a powerplant and drivetrain from a 90s-00s Camaro or Firebird in there.
 
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