Holley 8007 390 cfm tuning for a 345

I'm working to tune this carb to work well with a warmed over 345. The engine has an early square bore manifold with no smog, headers. The deck was shaved to move the piston crowns from .058 in the hole to .032. The heads are from an early 345e with no smog fittings and were surfaced .009". A .040 head gasket was used and it's running a comp 252 cam. Currently the dizzy is set 15 deg adv and the idle is a bit loppy (which is not expected with this cam) and vacuum is around 15".

To top this fine IH mill a new Holley 8007 390 cmf carb was purchased.

The 51 primary jets were to lean start with so they were replaced with some 52's I already had. It runs much better but still surges a bit on cold days.

The accelerator pump cam screw was move from position 2 to 1 to provide a bigger shot of fuel and this solved most the bog issues.

The secondary spring was changed from plain to the next heavier brown spring with a noticeable improvement in the bog before the secondaries opened.

Today a bung for a sg13 oxygen sensor was welded into the exhaust. The bung was made from an 18mm nut. This sensor is a narrow band unit that puts out 0-1.1vdc. Running .5-.7 v is an ideal mixture. A multi-meter is being use for the readout. It takes a few miles for the sensor, located just after the collector warms enough to read properly.

Took a drive to town and found that the primaries are still lean. The meter rises quickly when the throttle is pressed from shot of fuel. It also looks like the secondaries are Rich too, but we'll deal with that next after the primaries are dialed in.

The plan for this thread is to document what changes are needed to tune a new Holley to get great economy and power in a scoutii.

Things are moving in the right direction. Upped the primary jets from 52's to 54's and it's got a lot better throttle response. Mpg went from 12.75 to 13.2. The 54's still appear to be a bit lean as the meter is reading .25v on a flat road doing 65mph.

A vacuum gauge was also added so I now know that it's pulling 16-17 hg on that same flat road at the same speed.

On a Holley my understanding is that the transfer slots deliver fuel below about 30 mph and the carb seems lean in this range. The next step is to open up the idle fuel restricter's a few thou which should also give it more fuel when adjusting the mixture screws. As it is the screws are way out, still need to check how many turns, and it has barely enough fuel to idle properly.

fdchappie said:

on a Holley my understanding is that the transfer slots deliver fuel below about 30 mph and the carb seems lean in this range.

Click to expand...

That carb should idle perfectly with your setup. I would consider some more timing up to 13* initial with the vac advance disconnected. The cam will appreciate the timing and needs it to make optimum vac. You could be beyond the screws if not.

Screws= till just off idle stop
transition./ pilot jet = throttle position about 1/8- 1/4. Not so much rpm.
Pump shot and main emulsion tube= fills the gap between pilot and main initiation.
Main air corrector initiates the main emulsion so bigger is earlier to fill the gap.

Fuel level effects almost all ranges. I would see if an increase in fuel level helps your lean condition. Don't weight the o2 sensor more than your sense of how it responds to manipulating the pump shot while at a constant speed. If it is that lean you will feel it pick up a tad while fluttering the pedal a bit up and down rapidly. That will supplement the fuel mixture without a significant increase in air flow.

Some good tips there. The advance is already at 15 deg w/no vac and there is an occasional light ping so I plan to back it off a deg or 2.

The builder kept the tolerances pretty tight and as it breaks in the idle keeps getting smoother and it needs to be turned down as the rpm's increase.

I'm also planning on opening up the power valve fuel ports a bit. I've read that 1/2 the dia. Of the jet size is best. There is no detectable enrichment below 6.5 hg when the pcv opens.

Fuel level is right at the test ports and I plan to drop it a bit, as per mayben, to prevent fuel slosh on inclines. I need to extend the vents too which May also affect the ratio. But experience has taught me only 1 change at a time and thoroughly test the results.

If you have those items dialed it should not be lean. Are you sure there is not an air leak meaning excessive pcv flow or booster? Having used that carb on a few applications, they all required no fiddling with idle jets or power valves. All idled perfectly with 1-1/2 - 2 turns out on the idle screws.

I like your approach and conclusions, along with what Robert stated I'll add that if the idle screws are overly out (you mentioned them) it won't leak fuel as most people think. They will become a vacuum leak and the idle ckt will go lean, it is easier to pull air around the screws threads than to pull fuel from the wells.
It don't actually 'pull' fuel or air, it is easier to think of it that way and the result is the same.

Hey Robert, since it sounds like you've used a few of these carbs on similar apps, were they tuned to get the most out of 'em or were they just tuned till they ran good???

If you've "super" tuned one, what mods from stock did you do???...??? I very well realize that when drilling on ports the material can't be put back, so I really don't want to go in the wrong direction.

One of the subjects of interest is power valves and tuning a truck/tow vehicle vs. A car. Some of the info I've read suggested a lean jetting and having the pv open quickly once a load is applied. For example since my cruising vacuum is 16, using this method I'd put a 14 pv in. However IH tuned the similar carb on a 392 with a 2.5 pv which implies a fairly Rich main jet and the pv kicks in only when you're really into it. Comments?

In all applications that I have used this Holley, they were small displacement v8's and only mildly modified with cam and compression. Cam specs very similar to the 252 IH grind in lift and duration.
In all of these cases the only things they needed were secondary spring and main jet changes to run perfectly.

Only in very hot engines were air and pilot jet changes necessary and that was not on the 390 cfm unit. These had 238+ intake duration @ .050 where idle vacuum was very low.

I want to give you my take on your engine and how it should be running when I take into account your setup.

The 252 comp cam should give you a solid 18-19+ inches of vacuum especially on a 345. It should have a rock solid smooth idle at 700. With the 390 there is no reason to have any bog issues.

The pv should never be noticed in smooth application of throttle. When driving in say 3rd and at the peak torque rpm range as you move to full primary while watching the vacuum gauge, as you cross the pv opening point you should feel nothing, if it picks up you need to go with a earlier opening pv and or a bigger primary main jet. If you are very good at feeling the tone and acceleration of the engine you May be able to feel the engine start to fade or lay down as you approach the pv point, if you do it's going lean and needs an earlier pv. If it does not laydown but just picks up at the pv point just go up in main jet.

Agreed about the vacuum level and idle quality, which I don't quite have now, but it keeps improving.

On initial start up this carb flooded the secondaries. After removing the needle valve for inspection it behaved fine. Since then I've discovered that the rubber grommet for the fuel transfer tube was cut during assembly. Perhaps a small chunk of that grommet in is in the secondary bowl messing with the idle.

So it looks like I need to pull the carb and check the secondary bowl for debris and see if a proper idle vacuum and smoothness can be achieved. There's less than a 1000 miles on this engine and the idle does seem to be need to be turned down from time to time. The pcv valve was removed from the valve cover and when my thumb was placed over the hole there was no change in idle quality. Haven't checked the brake booster yet, but the engine that came out idled great.

I've been getting right around 12.5 mpg out of this carb, so a base line has now been established. This week the power valve was changed from the 6.5 that came with the carb to a 2.5 which is what IH installed in carbs for this app and what Holley uses in the truck avenger. Main jets were dropped 1 size to #53's.

One thing I discovered is that I was only getting 2/3's throttle! I know that this won't improve the mpg, but what the heck, I want everything it's got when needed. The problem's were caused by the fast idle adjustment arm and the limit on the secondary throttle shaft. This carb as supplied comes with a fixed arm that opens to way below the intake manifold at full throttle, however with carb sitting on an IH manifold it hits the carb mounting surface. Fortunately there is an easy fix, Holley makes a spring loaded arm that does not protrude below the base of the carb. Luckily I had one from a carb that was switched to manual choke. It's a drop in replacement.

The other problem is that there is a lever on the secondary throttle shaft that limits full throttle. Why I don't know as the linkage limits opening already. IH didn't think it was needed either as there is no arm on my 392 carb. So with a few strokes of a hack saw it was gone. Now she set my eyeballs just a bit farther back in the sockets at wot. :d

also per the manual and confirmed via measurement of IH carb. The power valve orifices should be 1/2 the size of the main jets. This nets a 25% enrichment. So with #53 jets the orifices should be .026" this carb comes with .036" orifices. This means when trailering up the mountain it'll be running pig Rich. The plan to correct this issue is to get some 6-32 brass set screws and drill and tap the metering plate. The set screws can be drilled to the correct size and the problem will be corrected.

After seeing all these changes needed, I realize that I really should have spent more time trying to find a factory original Holley for a 392 with the correct internal and external setup.

Well another report. After the changes above the first complete tank of fuel achieved a remarkable 14.94 mpg! If this holds for a few more tanks it looks like the design goal of 15 mpg is a success.

I have the brass set screws, however with such good results I'm afraid to mess with it. The next phase of tuning is about to commence as we'll be towing a 19' rv trailer to the coast this weekend. We'll see how the 2.5pv and secondaries work together under load.

Trailer tow went well, except for loosing the brakes on myers grade. The first observable sign was pinging on regular gas. Added premium and the pinging went away, as it would do with the previous engine.

The carb ran lean on the hills so a conversion kit was purchased to convert it to a 4150. I wanted to go to the next plate size, it would have taken the secondaries from 56 jets to 59, however Holley no longer makes it, hence the change to a metering block.

The carb was converted and setup with 58 main jets and it's still lean. Just switched the 58's out for a set of 60's so we'll see how that does.

The 4150 that comes oem, list #4312, that comes on a 392 has 53 jets and a 2.5 power valve. Now Holley does not make a secondary metering block tapped for a pv so the jets need to be 6-10 sizes larger than stock. The new metering block also comes with larger idle restrictors. The #3 metering plate had a .026 orifice and the new metering block has .031 orifices. This has allowed the idle mixture screws to be adjusted about 1/2 turn in.