Thoughts/help on fueling for a 68 w/454 block - Chevelle Tech
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post #1 of 27 (permalink) Old Jun 29th, 20, 2:17 PM Thread Starter
James
 
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Thoughts/help on fueling for a 68 w/454 block

I hope everyone is well!

I have a 68 that I bought a few months ago and have been slowly chipping away at my list. Car is in great shape but did not come with a ton of history other than being in Colorado for a large part of it's life. When it came to me, I decoded block and heads as a transplant 454 block and heads from a 73 Chevelle and it has a super T-10 with a 76-78 date code (cant' remember right now). But it has obviously been worked over with nice comp roller rockers (solid lifters), ARP hardware, and assuming a reasonable cam based on the idle lope. Assuming no one would be foolish enough to put a short crank in it to make it a "396" and that it has been worked over at least once in its life, at minimum i'm assuming it is in the 460s on displacement. It came with an Eddie Torkker II and an Eddie 750 on it that had stock jets and rods, and the way the original plugs looked along with the soot rich tailpipes, it was hella rich. Figured with the altitude change, a stock 750 might work here in SC altitude. Car felt a touch down on power and would have a huge transition between about 80-90% throttle and WOT when the secondaries would pop open. I dropped a touch smaller rod in it to give it a richer mixture (number 11 combo on the 1411 adjustment chart), also I threw a 1 inch 4 hole phenolic spacer on it. It definitely liked the rod and spacer, but I still feel like i'm leaving some on the table. The WOT transition from 80% throttle is better, but transition to wot just makes it literally jump to life.

This is where I need some thoughts and opinions. Am I reaching the point where the Eddie 750 is tapping out? Is it worth bumping up to another smaller rod to give it another 4%? What are folks running on similar setups? Seems like a bunch of y'all are running 850s. Pics below are the new plugs running on the smaller rod and spacer, definitely not rich and no soot at all down as far as I can see on the ceramic; all plugs looked almost identical. Appreciate your time and thoughts!
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post #2 of 27 (permalink) Old Jun 29th, 20, 2:58 PM
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Re: Thoughts/help on fueling for a 68 w/454 block

what does it have for timing? at idle (with vacuum advance disconnected) and at 3,000 rpm ?


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post #3 of 27 (permalink) Old Jun 29th, 20, 3:59 PM
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Re: Thoughts/help on fueling for a 68 w/454 block

Plugs look perfect.

Chas

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post #4 of 27 (permalink) Old Jun 29th, 20, 7:34 PM Thread Starter
James
 
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Re: Thoughts/help on fueling for a 68 w/454 block

Quote:
Originally Posted by mr 4 speed View Post
what does it have for timing? at idle (with vacuum advance disconnected) and at 3,000 rpm ?
16 idle and 34-35 at 3k. PO had it at 6 idle 26 at 3k... Forgot to add that in the OP. Timing did a lot to wake it up too

Quote:
Originally Posted by chasmalo View Post
Plugs look perfect.

Chas

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They do man, thats why i'm on the fence if there is a little more to squeak out of it or if this is the maximized combo. The throttle transition from 80-90 to WOT has me wondering if the fuel curve is where it needs to be. It'll haul the mail at 80-90% throttle, but then that last 10% is seriously different
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post #5 of 27 (permalink) Old Jun 29th, 20, 8:11 PM
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Kerry
 
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Re: Thoughts/help on fueling for a 68 w/454 block

What is the timing at full advance? Revving to 3000 rpm, a stock distributor is rarely at full advance. You need to rev it until it stops advancing to know the true total. How many inches vacuum does it make at idle? Running vacuum advance connected to full manifold vacuum?
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post #6 of 27 (permalink) Old Jun 29th, 20, 9:48 PM Thread Starter
James
 
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Quote:
Originally Posted by pockets View Post
What is the timing at full advance? Revving to 3000 rpm, a stock distributor is rarely at full advance. You need to rev it until it stops advancing to know the true total. How many inches vacuum does it make at idle? Running vacuum advance connected to full manifold vacuum?
Full advance is 35-36 with no vac advance on it going up to at least 5k. I just said 3k since that’s what we talking about in the reply. I’m trying to remember from tuning idle mixture on the carb, but I want to say it was 13-15. I can re-check tomorrow
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post #7 of 27 (permalink) Old Jun 30th, 20, 12:21 AM
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Re: Thoughts/help on fueling for a 68 w/454 block

Quote:
Originally Posted by JasBass View Post
Full advance is 35-36 with no vac advance on it going up to at least 5k. I just said 3k since that’s what we talking about in the reply. I’m trying to remember from tuning idle mixture on the carb, but I want to say it was 13-15. I can re-check tomorrow

How many inches vacuum at idle?

Put in the plain silver step up springs, and pull the top of the carb and check the float adjustment. Rarely are they correct.
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post #8 of 27 (permalink) Old Jun 30th, 20, 6:14 AM
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Re: Thoughts/help on fueling for a 68 w/454 block

A short crank would make it 427 - 440 cid.
Do you have a clue how long the engine has been together?
Sounds like a 750 Holley type might fit you good. Should give you nice response. Some run larger.
HEI has limitations in factory form.
Have you adjusted the lifters?
I ran a 750 dp, accel ignition, old torquer II, same trans on a 440 cid and it ran mid to low 11's.
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post #9 of 27 (permalink) Old Jun 30th, 20, 6:54 AM
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Re: Thoughts/help on fueling for a 68 w/454 block

I did the math on carburetor size. At 460 cubic inches, if you're spinning it to 6,000 RPM, it needs 798.6 CFM at 100% volumetric efficiency.
The 750 Edelbrock is choking it up.
And...with good heads Volumetric Efficiency can go over 100% at peak RPM!
If you're going to change the carb, an 850 Holley should work well.
> Do you have a buddy you could borrow one from?
> 850 CFM jetted correctly and 36 degrees of peak timing - all in by 2500 - 3000 RPM- you might find another 50 Horsepower.
> My assumption for 36 degrees of max timing assumes good gasoline.
> What's the compression ratio?
Keep us posted.

Chas


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post #10 of 27 (permalink) Old Jun 30th, 20, 7:02 AM
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Re: Thoughts/help on fueling for a 68 w/454 block

BTW, at 6500 RPM the airflow requirement (carb size) goes up 865 CFM.

What heads are you using?

Chas

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post #11 of 27 (permalink) Old Jun 30th, 20, 7:25 AM Thread Starter
James
 
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Re: Thoughts/help on fueling for a 68 w/454 block

Quote:
Originally Posted by pockets View Post
How many inches vacuum at idle?

Put in the plain silver step up springs, and pull the top of the carb and check the float adjustment. Rarely are they correct.
13-15 at idle. I can re-check this afternoon, but that's where my memory is taking me. And Yessir, beat you to that one. I pulled it apart when I got it to check floats and clean up anything that needed it. Used the drill bit technique and they were spot on. It's got the stock red/pinkish springs in there now

Quote:
Originally Posted by mrpaticular View Post
A short crank would make it 427 - 440 cid.
Do you have a clue how long the engine has been together?
Sounds like a 750 Holley type might fit you good. Should give you nice response. Some run larger.
HEI has limitations in factory form.
Have you adjusted the lifters?
I ran a 750 dp, accel ignition, old torquer II, same trans on a 440 cid and it ran mid to low 11's.
Definitely don't have an exact date and you know what happens when people assume...so i'm going to assume, based on cleanliness, how the rockers/springs looked, and general feeling about the car, I think this was re-done in the past year or two but not driven much. Between the awkward wiring I re-did, and how loose stuff was, I think someone had a trailer queen put together to take to shows and then unload back in their garage. For lash, I want to say they were mid .02s. Kinda embarrassed I don't remember details from only 3 months ago. Covid brain...

Quote:
Originally Posted by chasmalo View Post
I did the math on carburetor size. At 460 cubic inches, if you're spinning it to 6,000 RPM, it needs 798.6 CFM at 100% volumetric efficiency.
The 750 Edelbrock is chocking it up.
And...with good heads VE can go over 100% at peak RPM!
If you're going to change the carb, an 850 Holley should work well.
> Do you have a buddy you could borrow one from?
> 850 CFM jetted correctly and 36 degrees of peak timing - all in by 2500 - 3000 RPM- you might find another 50 Horsepower.
> My assumption for 36 degrees of max timing assumes good gasoline.
> What's the compression ratio?
Keep us posted.

Chas


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I had a feeling. Thank you for running that math, that will be the next tidbit to learn what the formulas are. I'll poke around in the community here and see if anyone has an 850 out there. Either way, I haven't been a huge fan of the Eddie and was already kicking around the debate of going to a Holley or biting the bullet for the sniper since I drive the car a lot. "Good" gas is thankfully something I have access to here in SC; 93 but with 10% eth blend. Still on the hunt for a no eth station with 93.
I wish I had info on the build like CR, cam, crank, and rods. Realistically, prob in the 9s on CR...another assumption! Heads are the stock irons from a 73 Chevelle 454, I don't have a scope to shoot down the intake to see if they have been worked over or not. Eventually, i'm going to work up a nice build on the engine. But for now, ironing out this fueling and possibly considering an RPM air gap 2 for that dual plane smoothness. She's such a strong runner right now, just can't justify ripping it apart for for the few wrinkles that need to be worked out.

Either way, I know the exhaust is a choke point as well with iron manifolds, but does have 2.5 exhaust with an H pipe.

Threw in an under the hood pic, just cause!
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post #12 of 27 (permalink) Old Jun 30th, 20, 10:38 AM
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Re: Thoughts/help on fueling for a 68 w/454 block

Hook up the vacuum advance to full manifold vacuum, and put in the plain color step up springs. I would also advance the timing a couple more degrees to 38 total.
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post #13 of 27 (permalink) Old Jun 30th, 20, 1:57 PM Thread Starter
James
 
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Re: Thoughts/help on fueling for a 68 w/454 block

Quote:
Originally Posted by pockets View Post
Hook up the vacuum advance to full manifold vacuum, and put in the plain color step up springs. I would also advance the timing a couple more degrees to 38 total.
I'll order a spring set on the way home today, i'll pop for the $11 lol.

Another thought i'm having, I wonder if this is the common vac secondary issue with these Eddies where they don't seem to work well and even at WOT aren't fully open. I feel like this convo is leading down the road to a Holley conversion of some sort
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post #14 of 27 (permalink) Old Jun 30th, 20, 3:54 PM
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Greg.
 
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Re: Thoughts/help on fueling for a 68 w/454 block

Is your Gas Peddle opening the Carb all the way when at/on the Floor

I had that problem and it only showed up because my Mechanic/Pro Racer
said I should be seeing Higher MPH at the end of the 1/4
turned out the Rod on the Gas Peddle Mechanism was not Bent right so it would not interfere with the Air Cleaner
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post #15 of 27 (permalink) Old Jul 1st, 20, 11:02 AM
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Re: Thoughts/help on fueling for a 68 w/454 block

On two different cars I've worked on over the years I found the carburetor was not opening completely with accelerator on the floor. It's always worth checking. Get a friend to stand on it - (engine off ) check that all bbls are fully open.

> Watch out for floor mats that get in the way as well.

Chas

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