Ford Windsor 408's HP Plateaus @ 5,600

[Joe-71]

Several years ago when this head came out, I was asked to flow test it and give an unbiased report back to them with flow sheet. At first glance, the intake looks good, and with large valve was expecting big numbers. I will have to look for my old records but from memory, it flowed ~287-290 cfm @ .750" intake, and only 180 cfm on the exhaust. I was expecting 210-220 cfm, but the exhaust was dead. Way too big and wrong shape. Joe-71

[PRH]

Here are some numbers for a different SBF Windsor head.

These are a cnc ported import head, supposedly 210cc after porting, had a 2.08” valve.
The advertised flow numbers look(to me) like they’re way to good to be true.

I tested one on my bench @28” on a 4.00” bore and a clay radius....... and frankly the numbers are so far off I don’t know what you could possibly do(as far as the test goes) to get the numbers to change as much as they’d have to, to get them so they are even in the same ballpark.

A- advertised flow
B- observed flow

Lift——— A/B
.200——146/126
.300——207/184
.400——254/232
.500——293/262
.600——315/277
.700——325/286
.800——329/289

However....... even using heads like this one I tested on the OP’s combo..... I would expect it to peak at higher than 5600.

[cab0154]

I am coming up with it only needing about 260 cfm for cylinder demand at 100%VE at 6500 rpm with that cam.

[Tuner]

If this is the head and combustion chamber the engine has, I would be surprised it is happy with 36 degrees total. I have tuned a few SBF with this head and similar heads in the last 10 years or so that were happy with 30 or less .... 26. Too much timing, even if it doesn't knock, will make the engine feel like the brakes are dragging or the car is towing a parachute.

I've found this type of fast-burn SBF head likes an advance curve that creeps about 1 degree per 1000 RPM from about 2500 up to beyond peak.

https://www.flotekheads.com/store/Small ... p131024586

If this is the head and combustion chamber the engine has, I would be surprised it is happy with 36 degrees total. I have tuned a few SBF with this head and similar heads in the last 10 years or so that were happy with 30 or less .... 26. Too much timing, even if it doesn't knock, will make the engine feel like the brakes are dragging or the car is towing a parachute.

This is where I would start, as this is exactly what I’ve seen with the 351w/180cc Pro-maxx head combo in one of my trucks. 10.0-1 compression with a small 264/268@.006” hydraulic roller cam. With 36* total, it seemed lethargic and would just quit pulling at 5300 rpms, but no pinging. Now with 30* total it pulls cleanly to 5800, and is more responsive across the board

I guess I could have expounded on why too much timing can be found to make best power, because the question has been asked, "Is it right to assume that they are running it lean to require a 36 degree total timing on that engine?"

Yes, too lean requires more advance for best power.

The A/F requiring least spark advance is nearly the same as that which makes best power and in the range of 12.5~~12.8 /1.

Leaner or richer A/F than this is slower burning and so requires more ignition lead for best power, this is the reason vacuum advance is used with very lean light-load economy mixtures.

Dyno games can lead down the rabbit hole when starting with incorrect assumptions of timing or A/F. Using an arbitrary ignition timing with too much advance will lead to chasing best power by adjusting A/F toward a leaner (or richer) slower combustion mixture which gives best power for the condition of too much timing.

Conversely, starting with too rich or lean A/F and chasing timing for best power will lead to finding the old 'moahrisbettah' rule is in effect.

And as usual, a blanket statement such as this about internal combustion engines is fraught with exceptions to the rule, because it seems there is always an outlier with its own set of rules, the old "no two engines are the same" caveat.

[Walter R. Malik]

Valve float on the dyno looks like someone pulled half the plug wires off in an instant, it’s that massive a loss.

What lifter collapse looks like, I don’t think I’ve encountered it. I would assume major valvetrain noise with the added lash.

Apples to bowling balls comparison, but personally, I had a 406 Chev on the dyno, 14.5:1, big duration roller cam, ported iron bow tie heads, Vic jr intake produce a very similar dyno graph to this one in terms of hitting a peak and maintaining. It was annoyingly similar to its previous build with 11.5, solid flat tappet, but same heads and intake. (Big $$$ upgrade for no real gains)
Same rotator, same solid roller, same intake, more lift due to rocker ratio, and AFR 245’s, powerband continues to climb rather than plateau, and in fact peaks about 1500 RPM higher than with the iron heads.

I think your heads are the cork, but your results are decent regardless of the early peak.

Chevy to Ford ... now that is really like apples to bowling balls.

[hysteric]

Thanks Tuner.

[PRH]

I’m going to guess the motor in question isn’t going back on the dyno to try and sort out the how’s and why’s of why it was peaking at 5600...... so I suppose it’ll end being another unanswered question in the HP world.

[NewbVetteGuy]

Thanks all!

Appreciated.
I know the engine owner has been tracking the thread.

He’s ordered the higher rpm capable lifters, but has to move on to build a family members Chevy engine before he gets this Windsor motor back in the car to know if they did any good.

He’s going to run what he’s got for now, but I’m hoping we’ll hear back whether the lifters help it rpm a little more or not. (I’m betting the min CSA is the limitation right now.)

Adam