Matthew, the point I was trying to make was in fact that proper tuning can make a bigger difference in MPG as well as power than most people think. The article was an example of this. They increased the fuel mixture, and improved MPG/HP at the same time. The biggest fuel concern is for sure going to be how heavy the right foot gets, but if mpg is a real concern, don't underestimate the value of proper tuning. Any time you add or change parts there is almost always more HP/torque, and MPG to be had.
This engine went from 14.3:1(only 24 degrees total spark lead prevented detonation)@WOT to 12.9:1 with improved MPG. You are right, they made a 30+ year old engine w/10.25:1 compression more efficient, and more powerful, and better on gas.
I would be more concerned about gearing as far as MPG rather than compression ratio's. I can't believe that enriching the mixture from say 12.9:1 to 12.4 because of increased compression would make that noticable of a drop in mpg.
Then agian I have never run an engine with 11:1 pistons either.

|UPDATED|6/16/2003 9:26:08 PM|/UPDATED|

As I said I don't have all the details of the Article, but it sounds like some interesting reading. Just from what you have told me, what I see is a major improvement in effiency.

I wouldn't think that the increase in your mixture would cause a major drop either, unless as you stated engine RPM is playing into the formula.

I do know a double pump is going to cause the engine to consume more fuel, just because it has to pump systems and everytime you roll the foot into it both squirters are going to add fuel into the engine. Now at cruise there really should be no difference in fuel consumption, although vacuum secondaries do close down some as they only stay open enough to supply the engine with the minimum air requirements based on engine vacuum.

I'm sorry if I sounded hostile, for some reason my last few post seem to come out like a "know it all", when I'll be the first to say I'm not.

Since you brought up fuel economy, I'll throw out some stats concerning my 454/365 Auto with a Holley 650 double-pumper. If I'm heavy on the foot (which is the case 90% of the time ) I'll see 7-8 MPG. If I'm cruising @ 65mph, I'll see 12MPG at best. Sometimes I think I can hear her chug like a frat boy downing a beer when all barrels are open wide.


|UPDATED|6/18/2003 9:33:21 PM|/UPDATED|

Thats probably pretty close to what it was rated at new Joe, if I were to hazzard a guess. What kind of revs are you turning at 65? I recall looking at an old "new car review on a 68 Hemi Charger and it was getting between 10-12 mpg w/4sp & like 3.90 gears.

PrivateGod, No your not coming off hostile. Were all here to learn from each other. It just sucks sometimes to communicate something clearly or have a complete understanding of something when you don't have all the facts in front of you. Thats why we are all on here is to learn and have a good time.

What drops my jaw, is when I'm talking cars (in general not just Vettes) is when they complain about gas mileage. They alway go and tell me what they have in the engine and I look at them blank faced, because they complain about it. I always tell them if you build it for power its going to suck the gas, you can't have the best of both worlds you have to give and take. I always laugh and say if its costing you more then what you expected then get rid of it, I'm sure theres a Honda dealer down the road that can set you up with a ride home. Lets face it GM did a good job of getting us decent gas mileage right off the assembly line, at least for the technology they had available.

Now as enthusisast if we decide to keep everything as original then we will have similar results as it came from the factory. Now if were willing to look at aftermarket parts, do some home work and apply some late model technology, we can get close to the performance of a C4 and have more performance, better fuel mileage and a C3 that is more fun to drive. We just have to be willing to give up some of the original factory equipment. I personally have no problem doing so. If something needs to be replaced I look for the latest and greatest thing.

Hi Guys,

Thanks for all the detailed discussion, it's definitely helping me decide what will be the best fit for me.

Per After Shark's replies: I do intend on contacting Holley as well but I'm interested in more than a manufacturers opinion. Interesting thoughts on the timing of the accelerator pump to the transmission type. I knew dbl pumpers were ideal for man trans, but I never knew why. As far as fuel economy goes, I'm ok with the 9mpg I'm currently getting. If switching to a dbl pumper (yes, I usually have my foot into it) is going to cost me 1mpg then I'm all for it. If it's going to be more than 3mpg, I'd have to think about whether its the right choice for me.

Joe V: Thanks for throwing your mpg's out there, it does help to see what others are getting. It sounds like you've got a pretty good mileage range which brings us right back to "its all in the foot". I'm hoping to get a handle on the difference in mileage between the dbl pumper and the vacumn secondaries when you are driving with your foot into it.

By the way, what's a "4-corner idle type"?

Thanks again!!

ricknhis69 said: By the way, what's a "4-corner idle type"? Thanks again!!

Those are the holleys with idle adjustments in the primary and secondary metering blocks. Other ones just have a secondary metering plate and no idle passages. Joe