11.5 compression, Iron Head, 91 octane

[Tom68]

Save the thick gaskets for a last resort. Don't use studs and you can change them in the car if you get that desperate.

[Tuner]

Another possibility is if E-85 is available to you it will easily tolerate high compression ratio.

No matter what you do, fast burn heads of any sort, Ford or GM or ?, all respond very favorably to advance curves that are on the sweet spot all the way from lowest to highest RPM, and this may require advancing 1 or 2 degrees or more per 1000 RPM from below the torque peak to the HP peak and beyond.

[Tuner]

Save the thick gaskets for a last resort. Don't use studs and you can change them in the car if you get that desperate.

I would much rather have tight quench and deal with the advance curve. Use a 1/4" thick gasket and run it on kerosene. Thick gasket tricks bring the necessity for correct pushrod length into the picture.

I witnessed the Ford iron N head outrun 18 deg. aluminum Chevy heads when a short track guy entered his oval track car in a road race at SIR against SCCA GT-1 cars, equal weight, displacement, same tires, same carb size (actually I think the Ford had a 750 and the Chevys had 830s) and the Chevys had nothing for him, he was at 180 MPH when they had their tongues hanging out at 175, nevermind he was comfortable drifting ever so slightly at that speed.

[frnkeore]

Tuner, I'm interested in how you got this slope, "20 at 2000 with a slope to 26 at 6000".

What kind of springs did you use for that or what tricks were involved?

[KnightEngines]

By the time you do a decent valve job, blend it into the chambers & do a little unshrouding you'll be where you need to be.

The valve job & chambers are not nice & need doing anyway, why crutch it with the wrong cam or spend $$$ on injection when the valve job & chambers need fixing anyway....

[Tuner]

Tuner, I'm interested in how you got this slope, "20 at 2000 with a slope to 26 at 6000".

What kind of springs did you use for that or what tricks were involved?

First things first, the way to do this is get on a dyno and in 500 or 1000 RPM steady state steps, find the timing for best torque or to avoid knock, plot that data on a graph and then with a pile of springs and some pliers visit a distributor machine. Alternately, you could do like we did, three guys in a 66 Mustang with a timing light, roaring around making 1000 RPM spurts, stop, move the distributor, do it again, and again, and form opinions about what felt the best. Sort of a consensus tuneup. I intended to bring an accelerometer but forgot it. You can use an accelerometer app in your cell phone. Don't be surprised when fast burn heads need a lot less advance than people talk about.

The particular 392 Windsor engine I referred to above has a stock mid-late '70s Ford Motorcraft magnetic distributor. Because those have separate soft primary and strong secondary springs they are easier to manipulate than MSD which uses the Delco type mechanism with the hooked weight acting on a cam shape.

This isn't easy, but it can be done with most any distributor, though it would be tedious without a distributor machine.

In the Delco design (MSD, et al) the shape of the cam on the end of the shaft determines the curve shape, dogleg, slope, or ?, and the springs set the beginning, range and end of travel.

The MSD which has the advance cam welded to the shaft must have the cam shape altered, which I do by winging it and free-hand grinding. In HEI distributors the cam shape piece can be changed and there are I don't know how many different profiles, but the 375 cam is desirable for this and for a template for copying the shape to the welded cams on MSD main shafts.

To avoid friction which will cause the advance to be erratic and inconsistent, the Delco type mechanism must use identical springs with identical preload so the rotating pole piece floats on the grease film on the main shaft. Lop sided spring tension pulls the mechanism off-center and the grease dries out on the side opposite the tighter spring.

In short, it is much easier to use a Motorcraft distributor and either use an original Ford spring package with a stout secondary spring you have been hoarding because you have been setting up distributors for more than 50 years (if you had told me so 50 years ago i wouldn't believe I am saying this), or make a spring from a longer spring from the hardware store.

Clip a section of coils from a spring with the desired coil and wire diameter and bend the end coils to make loops to attach to the advance mechanism. As an example, for a 4 active coil spring, cut 6 coils and bend each end coil to form a loop 90 (or so) degrees to the axis of the spring.

I recall that distributor used a stout primary spring because the initial was so near the 20 at 2000 datum point and did not need a quick ramp up on the low end like 'slow burn' chamber engines, so it was 16 or so initial, start at 14-1500, slope to the 20 @ 2000, then add the secondary spring with .250" coil diameter, .048" wire diameter, 4 active coils. Springs with larger wire diameter and smaller coil diameter are desirable to achieve the long slow advance slope.

The post the spring anchors on adjusted so as to catch the second spring at 2000, where the tension of both springs combines to make the slope range to the datum point 26 @ 6000 and continue toward the end of the advance travel near 28 @ 8000. The advance needs to continue beyond the engine's operating range so instead of hitting a mechanical limit stop the spring is driving the trigger and isolates the timing from engine torsional noise.

In Ford and Mopar distributors the range of advance is usually best limited by moving up the start (fully retarded) end, sometimes done by adding material by welding or brazing to shorten the slot, so as to provide a more favorable angle tangent to the radius of rotation for the spring ends to restrain advance motion of the trigger pole piece.

I hope this ramble makes any sense at all, I got dizzy proofreading.

[travis]

Just thinking out loud...
Aren't the N351 heads 64cc stock? Wouldn't milling them that far (12cc) not only weaken the decks, but also cause other issues?

[Topsp33d]

E85 is a possibility, there’s a pump 3 miles from my house, but something about being tied to a specific location bothers me.

So far we have:

Keep the quench
Blend chambers/ valve job
Dialed timing
Cold air


What about the ivc? Is it of no consequence? I have smaller cams, one I like is 66* (seat ivc). What if I retard that 4 degrees?

Also I never heard back about the 114lsa, was that a joke I missed or is there something to moving the exhaust around? Interested to hear the reasoning

Regarding the deck height I know these heads were meant to be modified so they have extra material in lots of places. I may have to do something for the manifold to line up.

[cab0154]

Save the thick gaskets for a last resort. Don't use studs and you can change them in the car if you get that desperate.

with the hex heads in the top of the ARP studs, ive gotten them in and out in the car and then pulled the heads. not too big of a deal usually.

[cab0154]

E85 is a possibility, there’s a pump 3 miles from my house, but something about being tied to a specific location bothers me.

So far we have:

Keep the quench
Blend chambers/ valve job
Dialed timing
Cold air


What about the ivc? Is it of no consequence? I have smaller cams, one I like is 66* (seat ivc). What if I retard that 4 degrees?

Also I never heard back about the 114lsa, was that a joke I missed or is there something to moving the exhaust around? Interested to hear the reasoning

Regarding the deck height I know these heads were meant to be modified so they have extra material in lots of places. I may have to do something for the manifold to line up.

just test the fuel, and if its gonna sit put stabil 360 in it. you can easily have a second carb as a back up.

[Stan Weiss]

What about the ivc? Is it of no consequence? I have smaller cams, one I like is 66* (seat ivc). What if I retard that 4 degrees?

66* ivc retard that 4 degrees is 70 ivc, which should raise your DCR about .3 of a point.

Stan