Dan,

Just the gas mixing or did you bump the timing up too?

Similarly, the Vette always runs better, etc, everything you mention when I add good gas. When I add some "other" fuel I have increased the timing for even more power.
I know you are not racing it but the old add fuel til it slows down technique still works or time for O2 sensors. I'm not sure what others will say here re jetting and the better fuel.

 

gas mixing was the only change. Timing is 18/38
The jets are box stock Holley 800.

 

Slower burn of the higher octane is helping with the higher compression. I usually run a little fatter with the higher compression which seems to run better when using pump gas but when I mix in some good stuff, it's very noticable.

Guess I've never been bright enough to build a low comprssion bruiser that doesn't run any better with good fuel.

I know when I try and run a bit cleaner, on the lean side, my cars with the higher compression hate it and start getting a weird smell (not a rich smell) and don't run worth a crap

 

So maybe she IS looking for more fuel on pump gas?

 

what is the jetting? so many 800dp versions

in the past I have run a bit on the rich side to cool the mix a tad as an anti-detonation thing. mixed results.

 

I'm gonna look @ the choke horn Sunday am.
I wanna say its a 4780-3 but not sure.

George,what jets are you running in yours?

I think mine are 72/80

 

from several sites...dunno how accurate...not the Holley site

4780 800 (F)72,(R)76 6.5,8.5 4150
4780-1 800 (F)70,(R)76 6.5,8.5 4150
4780-2 800 (F)70,(R)85 6.5 4150
4780-3 800 (F)71,(R)85 6.5 4150
4780-4 800 (F)71,(R)85 6.5 4150

 

I'll look tomorrow,Thanks George.

 

unless your carb was bought new, who knows what the jetting could be.
mine was a basic - nothing, straight-up 4780...quite a few changes to it.

 

yup bought new in sealed box---never been apart I only changed the squirters 35/37

 

Ah, squirters, I'm running heavy squirters in both too. I think I'm running 74-83 jets in my 800 but running more compression than yours. Been a while, maybe Kevin remembers what it has in it.

It's on James's 355 right now.

 

Does James leave his choke on like Matt?

 

No choke to leave on. Horn is gone

 

i like to run huge jets and leave the choke on, roll smoke baby!

 

I was running 75/80 on in my 800 on the 427. I think Darryls was a little richer in the secondaries.

 

Here is a very long, but quite informative article/FAQ about fuel, octane, CR, timing, etc.

http://faqs.cs.uu.nl/na-dir/autos/gasoline-faq/part3.html

Our non-managed carbed engines are tossed into the discussion at various points.
About halfway down the page this is presented:

"7.2 What is the effect of Compression ratio?

Most people know that an increase in Compression Ratio will require an
increase in fuel octane for the same engine design. Increasing the
compression ratio increases the theoretical thermodynamic efficiency of an
engine according to the standard equation

Efficiency = 1 - (1/compression ratio)^gamma-1

where gamma = ratio of specific heats at constant pressure and constant
volume of the working fluid ( for most purposes air is the working fluid,
and is treated as an ideal gas ). There are indications that thermal
efficiency reaches a maximum at a compression ratio of about 17:1 for
gasoline fuels in an SI engine [23].

The efficiency gains are best when the engine is at incipient knock, that's
why knock sensors ( actually vibration sensors ) are used. Low compression
ratio engines are less efficient because they can not deliver as much of the
ideal combustion power to the flywheel. For a typical carburetted engine,
without engine management [27,38]:-

Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 30 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %

Modern engines have improved significantly on this, and the changing fuel
specifications and engine design should see more improvements, but
significant gains may have to await improved engine materials and fuels."

More info on changing other parameters (timing, A/F, etc) is presented in the '7' section.
Worth the time to read, IMHO.
Dan

 

84/84 here on a 800dp with both powervalves blocked off. Can't recall what squirters though.

 

well the carb is a 4780-4,so by the charts here & the ones I have, the jets are 71/85
so I may need to go up to 75 in front. Maybe more once the headers are on.

The car runs so good that I'm afraid to 'knobdick' with it!


I learned from my many years of racing that when a car runs alot better out of no where...........its about to blow

That was a high revvin' 400 small block
short 400 rods & 7200 rpm shifts with 150shot.:thumbsup:

 

...I learned from my many years of racing that when a car runs alot better out of no where...........its about to blow

I'll definitely be remembering that little tidbit of information.

 

here is my set

frt 76/74 35 squirter 6.5 pv
rear 80/79 35 squirter blocked

 

What's the reason for the stagger jetting, George ?

Enlighten me, please.

 

matching jets weren't in the "budget" for the "budget" build.

 

That makes sense.

Thanks Greg. I thought I might have been missing out on some secret tune concept.

 

Actually someone did some tweakin' with staggered jetting and there was supposed to be some advantage. George will be back with the long version soon. :yes:

 

stagger jetting:
Actually someone did some tweakin' with staggered jetting and there was supposed to be some advantage. George will be back with the long version soon.


Why: Divided plenum hi-rise, different runner lengths in the BBC heads.

I have to tone down the explanation to make this short and simple enough to understand . The BBC archicture is almost like having two engines at work if you are using a divided plenum intake; small and big runners need different fuel amounts. The stagger jet helps with this. Modern intakes like the RPM have the plenum divider cut down so far less common now to stagger jet. Carb Spacers of large size would also negate any stagger jetting gains

MC71454 did numerous dyno passes with his similar engine, same cam...30-40 gain. You can also find this stagger jetting in the Classic "How to Hotrod Your BBC"
I have my jetting set based on MC71454's findings. Seems to work....