~10.6 Compression, CJ Heads, Pump Gas

[CV355]

I am curious how reliable my current engine build is.  Earlier in the year I was contemplating swapping heads but was advised it may make some of the conditions worse.  I have a '69 Mach 1 with a 428CJ.  Bore is 0.030" over, decked 0.005".  I haven't checked compression yet, but calculations are pointing at a near-stock 10.6:1 static.  Dynamic, we assume the cam is a Lunati 10503, still set up as flat tappet.  It runs to a ~2800 stall TC, C6, and 4.11 rears (so, drivetrain is somewhat loose).  The previous owner said it ran fine on 91 + a gas station shelf octane booster.  Thankfully I have 93 around here and that's all I run in our vehicles.  I drove the car three times in cold weather and had no issues with pinging, but we don't get many 50 degree days in SC.   

I've been stuck trying to figure out what I really want to do with this thing- my goal is just a fun, reliable cruiser car for maybe 500 miles a year.  Period correct is ideal, concourse not.  After hitting a few snags I decided to leave the original heads on it if the compression ratio isn't too high for modern pump gas. 

Before I send it to the carb tuning guys and zip the thing up for a while, is there anything I should consider doing?  I'd like to avoid a cam swap if I can.

I do appreciate all of the help and input you guys have given me along the way.  I'm looking forward to actually being able to drive this car in the Fall.  2 years of lifts and jack stands is a sad existence for this car...

[427LX]

What is the timing set at and have driven it in 80+ temps. yet? I would think 10.6 if your figures are correct would be pushing it for 93 pump gas with iron heads. Cam duration and Lobe Separation Angle will also determine cylinder pressures.

Have you done a Cranking Compression test yet?

[CV355]

What is the timing set at and have driven it in 80+ temps. yet? I would think 10.6 if your figures are correct would be pushing it for 93 pump gas with iron heads. Cam duration and Lobe Separation Angle will also determine cylinder pressures.

Have you done a Cranking Compression test yet?

At the risk of sounding unprepared, I am unsure what timing is set at.  I've had everything disassembled for 99% of my ownership of the car, and I've only cranked the engine 3 times in the last 16 months.  I'm looking at having the timing checked and cranking compression test done at a local (trusted) performance/resto shop next week.  10503 cam is 224-232-114 I believe, but that's still speculation.  *edit* Hey my memory served me right https://www.jegs.com/InstallationInstructions/600/638/638-10503.pdf

I have never run the car in weather over 50 degrees.  It's a calculated risk right now- if we think that the current build is "tune-able" for 93, then I still have to invest a chunk of money getting the intake machined to match the head plane, plus reassembly.  If there is ample concern with this setup, then I don't want to waste my time and money machining the intake.  Right now there is a substantial step between the intake and head plane where the valve cover seats and it was the cause of an oil leak. 

If I swap heads, most aftermarket heads appear to have a smaller combustion chamber.  72cc vs 68cc I believe?  That pushes me into thinking I may have to tear it down and get the pistons swapped, which really gets into territory I was trying to avoid.  Scope creep from hell. 

[jayb]

I have a close combination in my 68 Mustang daily driver, 30 over 428CJ, stock cast iron CJ heads, 10.5:1 compression ratio, a Comp 294S solid cam, FPA headers, and one of my intake adapters with an Edelbrock Torker intake and a Holley double pumper carb.   I run 12 degrees initial timing and 36 total, all in by 3000 RPM.  4.11 gears and a T-56 Magnum transmission.  Coolant temperature always stays in the 170-180 degree range, and no fresh air induction, so it does get pretty hot under the hood.  I do have an electric fuel pump with a return style fuel system, which solves a lot of the hot weather problems.

I only get 91 octane here, 10% ethanol, and the car runs fine on that fuel with no octane boosters, in weather up to 90 degrees (which is about as hot as it gets here). No pinging or any other fuel related problems.  I don't know your cam specs, but as long as its not a super mild cam, and you have a good solution for fuel delivery that will keep the fuel cool, I think you should be fine on 93 octane.

[CV355]

I have a close combination in my 68 Mustang daily driver, 30 over 428CJ, stock cast iron CJ heads, 10.5:1 compression ratio, a Comp 294S solid cam, FPA headers, and one of my intake adapters with an Edelbrock Torker intake and a Holley double pumper carb.   I run 12 degrees initial timing and 36 total, all in by 3000 RPM.  4.11 gears and a T-56 Magnum transmission.  Coolant temperature always stays in the 170-180 degree range, and no fresh air induction, so it does get pretty hot under the hood.  I do have an electric fuel pump with a return style fuel system, which solves a lot of the hot weather problems.

I only get 91 octane here, 10% ethanol, and the car runs fine on that fuel with no octane boosters, in weather up to 90 degrees (which is about as hot as it gets here). No pinging or any other fuel related problems.  I don't know your cam specs, but as long as its not a super mild cam, and you have a good solution for fuel delivery that will keep the fuel cool, I think you should be fine on 93 octane.

That is encouraging.  I'll have to verify compression ratio then before I commit to anything.  The cam sounds relatively rough for a supposed "stock class cheater cam." Plus the loose converter and high rear gear ratio will help keep the engine under lighter load with most conditions. 

[Falcon67]

Its all in the tune up and how the head chambers work along with the quality of local pump fuel.  I can "drive" the 10.5:1 351C around on 91, but it has a decent sized hydro roller and such.  BUT - at the track, 91 is no-no because it peppers the plugs every pass.  So I pretty much stick to VP110.  If we had 93, that might be OK for cruising.  I have mixed, fuel, but the result is extremely gummed up intake runners.

Note my "street car" is 28" tires, 4.56 with a spool, 4600 stall converter and a decent sized cam, runs high 11s at 3250 lbs, 8 point roll bar, air shifter, etc.  Open the trunk and pump fuel in the fuel cell LOL. 

[CV355]

Its all in the tune up and how the head chambers work along with the quality of local pump fuel.  I can "drive" the 10.5:1 351C around on 91, but it has a decent sized hydro roller and such.  BUT - at the track, 91 is no-no because it peppers the plugs every pass.  So I pretty much stick to VP110.  If we had 93, that might be OK for cruising.  I have mixed, fuel, but the result is extremely gummed up intake runners.

Note my "street car" is 28" tires, 4.56 with a spool, 4600 stall converter and a decent sized cam, runs high 11s at 3250 lbs, 8 point roll bar, air shifter, etc.  Open the trunk and pump fuel in the fuel cell LOL.

Oh I've been there before.  In 2009 I had a street/strip car that was set up far more for strip than street, but I drove it and being younger didn't care about missing the creature comforts.  My mindset has changed since then.  I watch a video of a concourse 428CJ and go "wow, look at how smooth and quiet that engine is!"  I just sold my GT500 recently and I'm missing an angry exhaust and kick in the pants.

It sounds like my plan should be to get the dynamic compression tested then make a decision on whether I want to leave it stock and machine the intake to match, or if I need to do a teardown

In the event that a teardown is necessary, is CR the main variable to play with here?  What is key to getting these FEs running on pump gas without making it a slug in the process?

[blykins]

If the specs are correct, it's a whopping 304/324 degrees advertised duration. 

The reason it sounds good is that it's got overlap for days. 

That long 114 LSA also helps, because the ICL is relatively high as well. 

The DCR calculator shows it should work.   DCR stuff is theoretical though.  In reality, if it doesn't ping, I wouldn't worry. 

I'm curious to see how it operates the power brake booster though.  86 degrees of overlap, if the specs are correct. 

FE's are the same as any other engine when it comes to making them run on pump gas.   It takes a combination of static compression ratio, the right cam, the right timing, etc. 

[CV355]

If the specs are correct, it's a whopping 304/324 degrees advertised duration. 

The reason it sounds good is that it's got overlap for days. 

That long 114 LSA also helps, because the ICL is relatively high as well. 

The DCR calculator shows it should work.   DCR stuff is theoretical though.  In reality, if it doesn't ping, I wouldn't worry. 

I'm curious to see how it operates the power brake booster though.  86 degrees of overlap, if the specs are correct. 

FE's are the same as any other engine when it comes to making them run on pump gas.   It takes a combination of static compression ratio, the right cam, the right timing, etc.

That is also encouraging.  Not sure how much vacuum it pulls at idle, but likely not a considerable amount.  I'm swapping out the booster and master cylinder, and might have to run a vacuum pump.  I've run manual brakes before and really did not care for it. 

[blykins]

From experience, 64-65 degrees of overlap yields about 14-15 inches of vacuum on a well-tuned engine.   You're sitting at 86.  If those specs are correct, I can't see how it would have any vacuum and a reservoir will probably be necessary.

[Falcon67]

>My mindset has changed since then.

LOL, did I mention that I'm 63 and still run 3" bullets on 12" of collector extensions.  I like it loud.  My other car runs methanol, and I'd love to get this one converted over.

[CV355]

From experience, 64-65 degrees of overlap yields about 14-15 inches of vacuum on a well-tuned engine.   You're sitting at 86.  If those specs are correct, I can't see how it would have any vacuum and a reservoir will probably be necessary.

Sounds like a pump and reservoir is what the doctor ordered then.  The few times I did drive the car, the brake pedal felt an awful lot more like my old manual setup than an 8" dual bendix...  This is good info!

>My mindset has changed since then.

LOL, did I mention that I'm 63 and still run 3" bullets on 12" of collector extensions.  I like it loud.  My other car runs methanol, and I'd love to get this one converted over.

That's why I like your generation better than my own age group.   Believe me I like it loud too- I've had plenty of straight-pipe supercharged / turbo cars that you could hear from miles away. 

[blykins]

You don't necessarily need a vacuum pump, but just a reservoir would work. 

[67428GT500]

I am not sure where you came up with 68CC. Factory information shows 72.7-75.7CC on the C80E-N.  Might be a good idea to check compression.

                                                                                                                      -Keith

                                                                                                 

[CV355]

I am not sure where you came up with 68CC. Factory information shows 72.7-75.7CC on the C80E-N.  Might be a good idea to check compression.

                                                                                                                      -Keith

                                                                                         

Aftermarket heads.  TFS has 70cc, Edelbrock has 68 and 70 I believe.  That'd just make my compression issue worse.