Brand new head, preignition as bad, if not worse.

[Anonymous]

Well, after way too much effort to weld the crack in my old 200, head, i sprung for a new casting and swapped my new valves and hardware into the new one. Installed new port divider, reassembled engine, and fired it up. Previous preignition problems were back, maybe even a ,ittle worse. Back to shop, check timing, compression, etc. Timing is set at around 34 total at about 3000 RPM, which should be fine, I thought. Upon checking compression with new head installed, I now have 200lbs. compared to previous 160-170 with old head. New head has C5..... casting #, whereas old head had original C8...#. Anyone know if a 65 casting would have that much smaller combustion chamber? I know that 200lbs. compression is about right for a hi-perf V-8, just wondering what was good in one of these 200s? Cam is stock, only real mods to engine were Hooker header and Pertronix ign. conversion. I am beginning to wonder now if perhaps the new .030 over pistons could possibly be incorrect dome height, whatever, creating too high of a compression ratio
to run properly on todays gas? Still have reman. dual advance distributor with pertronix kit, and when I watch timing advance with light, it looks perfect. I am really beside myself trying to figure this one out. Just wondering if maybe I should try new single advance dist and play with ignition timing some more but at this point I cant help but think I have a bigger problem than just timing. Please.... Someone...H E E LP!!!!

 

[buzzA4]

Papa,
Just a coupla thoughts.

First, stock 200 pistons are dished not domed. That would account for additional compression. Stock measurements with dished, 7cc pistons give a 9:1 compression ratio. Whereas, domed pistons increase the CR to 11.1:1

Second, The balancers are notoriously for slippage and becoming misaligned. The rubber gets old and allows the outer ring where the timing makes are to slip. This makes the timing marks unusable. If your balancer is old, try to check to see if indicated TDC on the balancer is really actual TDC on the #1 piston.


Third, the combustion chamber on a C5 and a C8 200ci head should be the same, unless someone had milled your "new" C8 in it's previous life. The only way to know for sure would be to cc it yourself. If the C8 head isn't a 200ci head but actually a 170 head then you would have a smaller combustion chamber (but only 3-5cc's).

If you have a 170ci C8 head and stock measurements elsewhere except for domed piston, you could have a CR of close to 12:1

I think that could makefor a pre-ignition problem. Unless you start using racing fuel.

That's my $0.02. Compression calc link: http://falconperformance.sundog.net/compcalculator.asp

Good luck, Buzz

 

[addo]

Another fix would be a cam that bleeds off some compression - but then the motor would be pretty hot!

 

[Anonymous]

200# of static compression is very high for pump gas. If you run that much compression you need to retard the timing considerable. I run about 205 on a high perf. Harley -but it has a fully programmable ignition. and has a whole special range on the box for hi-comp. and another range yet for super or turbo chargers. You might try dropping your initial timing down to around 4*-6* BTDC and get your total back in the mid 20's. With that much compression your piston doesn't have time to start the power stroke before to much combustion has taken place. Spark takes place while the piston is still on the compression stroke(BTDC) That is why hi-octane and slower ign. advance is necessary for hi comp engines. The higher the octane the slower the burn --which provides the follow through on the power stroke. Hi compression causes hi cylinder temps which causes gas to burn faster. If timing doesn't help you can try for a thicker head gasket or get the combustion chamber enlarged. Next is a overlapping cam. These suggestions are in order of expense.

 

[grocery getter]

Ford Mustang 200 ci 6 Cylinder

In the middle of 1965 Ford introduced the "peppy" 200 ci 6 cylinder to replace the 170 ci. It was a great little engine and was the stock engine that came with the Mustang in late 1965. From the outside the "new" 200 Six looked much like the earlier 170 ci Six. The valve cover, oil pan, fuel pump, water pump, intake manifold, exhaust manifold, even most of the gaskets interchanged. These days many high performance parts are available for these great little engines. You can find high performance by using our search function and input "200 6".


General Engine Specifications

Model Prefix..............................................................................EFZ

Type....................................................................Inline Six Cylinder

Cubic Inches................................................................................200

Compression Ratio....................................................................9.2:1

Combustion Chamber Volume.......................................48.3-50.3 cc

Brake Horsepower................................................120 @ 4400 RPM

Torque....................................................................190 @ 2400 RPM

Bore & Stroke.................................................................3.68 X 3.126

[size=18]Compression Pressure......................155-195psi @ Cranking Speed[/size]
Taxable Horsepower..................................................................32.50

Firing Order.......................................................................1-5-3-6-2-4

Valve Arrangement-Front to Rear................E-I-I-E-I-E-E-I-E-I-I-E

Engine Manifold Vacuum @ Idle....................................................17

Engine Idle RPM

Manual Transmission.................................................575-600

Automatic Transmission.............................................500-525

Engine Initial Ignition Timing - BTC

Manual Transmission.............................................6 Degrees

Automatic Transmission.......................................10 Degrees

Oil Pressure.........................................................................35-55 PSI

Oil Capacity................................................................4.5 U.S. Quarts

 

[Anonymous]

That's a neat spec sheet- notice the static compression of 155- 195 with initial timing of 4-6* and keep in mind regular LEADED gas was 93 octane in '65. Also lead was a great combustion inhibitor.( and a brain cell growth inhibitor it turns out). As octane declined, compression ratios also fell. In the late 60's early 70's pump gas could be got with well over 100 octane (Sunoco blue comes to mind). The short stroke design of the 200 allows it to accept a little less octane than a long stroke design like the 250. The 200 sounds really good with way too much advance as it really smooths out the idle, but preignition is not your friend and it occurs long before it is audible.

 

[grocery getter]

That's a neat spec sheet- notice the static compression of 155- 195 with initial timing of 4-6* and keep in mind regular LEADED gas was 93 octane in '65. Also lead was a great combustion inhibitor.( and a brain cell growth inhibitor it turns out). As octane declined, compression ratios also fell. In the late 60's early 70's pump gas could be got with well over 100 octane (Sunoco blue comes to mind). The short stroke design of the 200 allows it to accept a little less octane than a long stroke design like the 250. The 200 sounds really good with way too much advance as it really smooths out the idle, but preignition is not your friend and it occurs long before it is audible.

good reply... 93 regular 8)

I had a friend who raced trans-am, close to 700 ponies in a 310 c.i.
His brother thought he would save some$$$ and go with unocal racing instead of sunoco purple. it was a short day at the races

 

[BaldEagleMav]

Hi Papadoc67,

It might be interesting to try water injection on your "high compression" engine before doing anything major like dissassembling the motor to change pistons, etc.

As I understand it, water injection (wi) slows down the burn (much like lead and higher octane fuel) so that you can take advantage of the high compression you have, while running on today's low octane fuel.

I have done a wi set-up on my '73 Mav with the 250 in preparation for decking the block during my next rebuild.

I don't know if this helps in your case, but I have the Holley Weber 5200 carb on my 250. This carb has an extra port vacuum connection (for distributor timing) which allowed me to connect aquarium air line. Then run the air line to a bottle of distilled water (mounted lower than the carb - so that you don't get gravity feed of the water). I am also using a cheap plastic aquarium air line valve to control the feed rate of the water. I haven't had time to adjust the feed rate yet, but I am told I should aim for a 20:1 ratio of fuel to water. This would mean one gallon of water for every 20 gallons of fuel.

People have increased their gas mileage using wi with no other changes to their motor. Who knows, you might solve your preignition problem and get better gas mileage as a side benefit.

Regards,
BaldEagleMav