79 Mustang lean as a bean

Kook

Where are you?

Is that thing tweaked to perfection yet?

The heck, has Holley always owned Mr. Gasket?

Sometimes I hack out my own with plenty of overhang or I've also used a 1/8 spacer plate
between the manifold and spacer that gives a lot more sealing area.

It made by Mr Holley Gasket

On PCM's I have never found an aftermarket gasket that would fit between the intake and spacer always had to use the oem ones

Here's a picture of what the bottom of your spacer might look like.

You need just the right gasket to seal it to the manifold, some aren't quite wide enough like I mentioned above.

Did you change the gasket under the intake spacer (between spacer and intake)

Sometimes those have a nasty habit of leaking if they're not wide enough.

My guess would be that the Holley were big enough and the Mr Gasket aren't big enough to seal right.

Look at the underside of the spacer to see what I mean, there's not a lot of sealing area.

Gary S wrote: Just bought a brand new 450 cfm Holley with a 8.5 in it. Is it possible only the 600's have the 2.5 ? Wonder how they determined a 450 needs a 8.5 and not the 600 too?

Hi Gary

I dug through some carburetor list numbers and found 7 450 cfm marine carburetors with different list numbers and they all had 8.5 power valves as standard equipment. I'm sure there must be more than 7 but that's what I came up with doing a quick check

I suppose somebody at Holley knows, but since it's really just an auxiliary main jet that opens and closes at a certain vacuum setpoint, it must have been part of their calibration process. It puts the fuel in through the power valve channel restrictions in the metering block and they have different sizes in different metering blocks for calibration purposes.And those PVCR holes come in plenty of different sizes in different metering blocks

I figure I'm not saying anything you didn't already know though.

That doesn't really answer your question or our curiosity though

Just bought a brand new 450 cfm Holley with a 8.5 in it. Is it possible only the 600's have the 2.5 ? Wonder how they determined a 450 needs a 8.5 and not the 600 too?

Kook

Here's something I put in another thread yesterday but it pertains to you too

It's power valve info and it'll tell you something about when your power valve opens and closes

A lot of people aren't gonna want to believe what I'm about to say, but if that's the case they can verify some readings for themselves.

You always hear that boats run under constant load and then when a power valve discussion pops up, somebody will say that when you punch it from a dead stop, vacuum goes to zero and quickly recovers.

It don't happen that way though

If you give it full throttle vacuum drops to zero and stays there till you back off the throttle.

If you run the boat at a steady 4000 rpm's vacuum stays steady, it never recovers to a higher vacuum till you back off the throttle.

Same thing at any RPM in a boat that's operating under a constant load.

Here are some representative numbers on a good running 351 that I wrote down a couple of years ago and verified again with a quick boat ride tonight

Full throttle     zero

4000 rpm        2.5 inches vacuum

3000 rpm        7 inches

2000 rpm        9.5 inches

1000 rpm in gear   13 inches

idling in neutral 20 inches

This particular boat has a 6.5 power valve so it's open whenever the boat is going over about 3300 rpm

All these numbers can vary some from what I have depending on engine loading, hull efficiency etc but they'll be steady at whatever reading you have till you move the throttle. It's the concept we're after here. And remember it ain't a car.

Like I said, it's bound to lead to some discussion, but you can check it for yourself easily enough.

You can hook into your PCV line to measure vacuum and use enough hose to get the gauge out where you can see it.

So Kook You'll figure out that your power valve is open a lot of the time adding fuel to the engine. Sounds like you went to an 8.5 so any time your vacuum is less than 8.5 it's gonna open and stay open till you back off the throttle.

summit racing has secondary metering blocks to convert a 4160 to a 4150.    I think you're playing with fire to run too lean like this, detonation could ruin all the work that you have just done to make what sounds like a nice motor.   Jody had some $25 cores a few weeks ago, and sounds like Tim has some he is willing to sell.    That and a carb kit is going to be much cheaper than a motor rebuild if you have a detonation problem or too hot of a burn. you might even have some lookers for that 450 CFM to offset the cost of the core/kit

Or consider a rear metering block conversion kit (uses replaceable jets instead of the fixed plate. I'd still go 600cfm to start with, though. Makes tuning much easier.

Tim and KENO are spot on, best heed

As been said, I would also further encourage reducing the span on the distributor asap, so your not tempted to run too much total advance just to get back the strong off-idle and launch 10btdc provides.

Total advance will have to be reduced if the compression is as high as you say, due to the faster moving flame front and faster peak pressure developed.

To only way do do both, is to reduce the mech advance span, and weights /springs is not equivalent..

Also, a colder plug has to be considered for the right reasons. To make it look like its not lean, is not the right reason. Predetonation, may be one, but the timing has to be spot on and eliminated firstly.
Think of the plug asyour gauge, once one goes changing gauges, things get blurry very quickly.
Something has to be held constant, till the method and evidence is sound.

This thing must sound good with domes and flat-decked.

I'll eventually go up to a 600 but it probably wont be this season unless something happens. When I get a 600 I'm also going to end up porting the heads, gasket matching the exhaust, a little more aggressive cam, running a different prop and so on; but that's more research for a different day.

Right now I finally found my old books and notes on reading spark plugs, but I'm probably going to be in for a new spark plug inspection light, which is fine because I'm going to have to cut these plugs first anyway.

Tomorrow I'm going to gap some new plugs, take it back out to the lake again and make a few more test runs and actually come back with usable data. I'll get my timing set out there first, then get a run to check to see what my fuel looks like, after I get fuel dialed in I'll play with the spark plug heat range. I just want to make it safe for now.

Bore diameter: 4.030in
Stroke: 3in
Cylinder head volume: 57cc
Piston dome volume: +2.7cc
Deck clearance: .01in
Compressed head gasket thickness: .040in (Roughly, this number came from Fel-Pro)

I rebuilt the engine, put new pistons in with GT40p heads, resurfaced the heads, decked the block, CC'ed the heads and came up with about 10:1 compression ratio. This is why I'm messing with carb jetting, plug heat, and timing.

Somebody earlier mentioned octane rating, it's difficult to find above 91 octane here so I've been running 91. Typically on a street SBF build, you don't want to run above 10.5:1 on this fuel if you want to keep it mostly hassle free from detonation, I keep tripping over tuning though because I'm not used to this type of control and I haven't had to read plugs in at least 10 years. I'm very much used to running a wideband anymore. Honestly, it's like I'm pulling my hair out half the time, and loving all of this the other half.

In 1979, probably about 8.3 to 8.5 to 1 or so,