Problem with excessive quench dimension.

[swampbuggy]

I have heard it said that increasing compression ratio is a change that will help the power output across the entire powerband, unlike some other changes will not. who agrees with this thought ?? Mark H.

[pdq67]

I believe that this was a modification to try and improve things.

Stan

ab-jaguar.gif

IMHO, this is an iteration of the old MOPAR Poli- 318 combustion chamber that I think has been dissed through the years.

pdq67

[digger]

I have heard it said that increasing compression ratio is a change that will help the power output across the entire powerband, unlike some other changes will not. who agrees with this thought ?? Mark H.

yes, within normal bounds and below threshold of knock

[Tuner]

Is this what you are talking about?

Stan

Perhaps the Ford "Kent" engine used in Formula Ford.



As a side note, this 1.6L engine in FF tune is another example of if it has the advance curve Ford advised in the old "Muscle Parts" tuneup guide it will be sufficiently superior to "all in at 2500" in straightaway performance it will make the the scrutineers go crazy looking for a cheat in carb and intake air leaks. If it is the only car in the field with the correct advance curve, it will be the only one that can move aside out of the draft and pass on long straights.

[4vpc]

In one of his books from some years back, David Vizard reported on a mildly supercharged SBC. Reducing squish/quench from I think 0.060" to 0.040" made more power at the same boost and allowed a psi or more greater boost (and more power still) at the 'ping threshold'...

Conversely read about his Avenger which had something like 1/4" to make it go.

[digger]

my understanding it is not bout clearance alone its about squish velocity which is a function of squish area and clearance as that's what generates the turbulence in the chamber. with a big band loose clearance not as big a deal as with small band and loose clearance

[Tuner]

This type of chamber with the spark plug and exhaust valve in a raised cavity first appeared in the late 1920s or early '30s in 216 Chevy six and some Mercedes, perhaps others. The 216-235 Chevy head looks essentially the same, but of course with siamese intake ports so the swirl characteristic is likely not be the same.

During WW2 when gas was rationed some folks ran cars on Kerosene. Stories abound that the 216 Chevy was more successful at avoiding knock but flathead engines were more prone to knock and how some used water injection to eliminate knock so they didn't have to retard the timing so much the engine lost too much power and ran hot. The Chevy 216 combustion chamber is apparently more tolerant to extremely low octane fuel because it is more compact than a side-valve chamber. Obert's and Taylor's books discuss this chamber shape and squish clearance subject.

[pamotorman]

I remember one time a friend had a FE ford engine that he was told it was a 390 but when he tore it down the piston were at least 1/8" down in the hole and it was a 360. any ford guys here know if this the way they were built or was this just a mix match of parts

[Tuner]

To reduce UHC they gave up squish to reduce quench. They did that by putting the 390 piston in the 360. Until they ran out 40 years ago you could get Ohio or Silv-O-Lite pistons for the 361 Edsel that had zero deck. Same engine 360 and 361, .050" over 352, different nomenclature. In spite of the higher compression ratio the couple of Ford PU engines I rebuilt in the early '70s using Edsel pistons were much better engines, less detonation prone with more power and better mileage.

[fdicrasto]

Got the motor on dyno finally and ran well. Did timing loop starting at 34 degrees, went as high as 36.5 and settled at 33 degrees. Plugs showed no signs of detonation issues, couldn't mess with cam timing and could not find any VP gas so settled for Sunoco maximal. Of course the engine never made a pull starting below 4000 rpm's. Thanks again for advice and info.

[Schurkey]

The Jaguar "HE" "May's Fireball" cylinder head was particularly good for use at "high" (for the time) compression and "lean" fuel mix. This benefited fuel economy, but not emissions.

When emissions regulations forced the use of O2 sensors and therefore stoich fuel ratio, the head was not such an improvement.

[Frankshaft]

Got the motor on dyno finally and ran well. Did timing loop starting at 34 degrees, went as high as 36.5 and settled at 33 degrees. Plugs showed no signs of detonation issues, couldn't mess with cam timing and could not find any VP gas so settled for Sunoco maximal. Of course the engine never made a pull starting below 4000 rpm's. Thanks again for advice and info.

You going to leave us hanging? What did it make? 33 degrees isn't excessive timing for that deal at all.

[Carnut1]

Shaft, lets guess. I say about 755hp.

[fdicrasto]

I am amazed how close Carnut1 came to the number. 753.5 hp @ 7500 and 617 ft lbs at 6000 w/ 4 hole spacer. Didn't take it past 7500 so may have been a couple more there. I'd post the 3 relevant sheets if I could figure out how. I was surprised that the 1" 4 hole and 1" open spacer swap was within a tenth of a hp and 2.5 ft lbs on torque. Vacuum pump only pulled 7" vacuum.

[pdq67]

I believe that this was a modification to try and improve things.

Stan

ab-jaguar.gif

Imho, take this design and tilt the intake and you come up with the old, MOPAR, "Poli-head"..

pdq67