Soon I will be getting a 67 428 that I presume will have a bit more then 10 to 1 compression that will probably not like todays gas,what I need to know is the compression due to the pistons or the combustion chambers in the heads.
If you decide to change heads remember 360 pickup heads come with hardened valve seats for unleaded gas.
Is it completely as it left the factory after all this time? If not, it's guessing. This shows https://over-drive-magazine.com/2025/02/06/1967-ford-full-size-cars-fact-sheet/ 345 and 360 HP has Compression ratio: 10.5:1. This shows https://www.ultimatespecs.com/car-specs/Ford/20828/Ford-Mustang-(MY-67)-428-Cobra-Jet.html 335 HP has compression ratio 10.60 Same here which is 68 up. https://www.carmemories.com/ford-engine-specifications/428-engine-specs.html You will probably need to get the head casting numbers to ID what you have as far as chamber volume and what other options are. Cams can change dynamic compression and of course a head gasket can drop it a bit.
Will today's premium work with 10 .5 to one compression,it's been over 30 years since I had a engine with that much.
Leave it alone at get advice from a cam grinder. There are other little tricks like Cometic MLS head gaskets Cometic make them up to .120" compressed thickness [this adds 19cc over a standard .030" crush] And they are reusable
I’d sooner spend the rest of my life buying octane booster every time I filled the tank than to buy a 428 equipped motor and neutering it.
If it will run good on premium that is available I will leave it alone but if it needs av gas then it will not go in a good weather old car I was planning on driving very frequently..
I bought a 351W long block a while back, and we figure the CR is between 10.5 and 10.8. I spoke with a recommended cam company, and will be installing cam with LSA of 110, and am thinking of retarding cam timing to help reduce dynamic compression. I too hope to run premium pump gas.
Let’s not forget the pistons, I don’t know when it happened but a lot of stock high compression pistons are not made to stock deck height and are actually low compression. So you need to actually measure your compression ratio of the parts you have you can’t ***ume anything.
The pistons could be .020-.030-.040 in the hole. Best to take some measurements and calculate what the ratio actually is rather than what’s advertised.
I saw an article sometime recently (I should have book-marked it...) that discussed that current gasoline apparently has a slower burn rate than what it used to have, a characteristic of fuel performance when octane goes up, although supposedly it didn't. The gist of the story was that you can run more initial timing than you think on modern fuels, as much as 8 degrees more. I do know that static compression ratios as high as 11.5:1 are pretty common on new motors, even some that use 'regular' grade. Yeah, I know electronic trickery has more than a little to do with that, but it does make you wonder... FWIW, when discussing compression ratio for my 445" FE stroker with aluminum heads build, 9.6:1 was the recommended max, with 30 degrees total timing.
Well no good solution is going to be cheap or inexpensive. Swapping heads isn't cheap unless you already have the heads but that is probably the best solution in the long run., Swapping on a set of the right lower compression heads and prepping and storing the original heads away to stay with the car.
My Bud built a Cobra , used 65 427 dual quad it was fresh , not one issue with todays premium gas . I suspect it has enough cam overlap and fuel running through it to keep cylinders a bit cooler
I am getting the whole car so I will be able to drive it some before the drivetrain goes in another,like I said before its been years since I had a engine with more then a 9.1 compression ratio and when I did the gas seemed better. I want to use this engine in a car that I want to almost daily drive in nice weather but I have been wanting to build a car for the track so that engine could be a starting point.
I’d run a compression test on it. If it’s a 60 year old engine, it’s likely lost some ring and valve sealing, and the timing chain will have some slack. If you’re below 170psi cranking (dynamic cylinder pressure), you can run pump gas without any issues as long as you aren’t going crazy with ignition timing and rpm.
Plans for the engine is to be in a Galaxie with tall gears for highway cruising,I want this engine for its torque and I doubt it will ever see 4000 rpms.
Compression test. Your rough dynamic compression during that test is the result, divided by atmospheric pressure where you are. Sea level mean is 14.7psi. If your cylinders are 147psi, at sea level, you have 10:1 compression. My Falcon-6 has cylinders that average 165psi, and I am just a few feet above sea level. That equates to 11.25:1. And yes, it runs fine on 91 octane (R+M/2). It was built with a target of 11.5:1. No, this is not an exact method of calculating, as it can be affected my a wide variety of mechanical variables, and even the weather patterns, but it will get you a ballpark number.
You will want less compression if using tall highway gears, that kinda of low rpm pulling can make a lot of detonation, especially in a heavy car.
I reckon you'll be fine on 93 octane. You may want to limit your vacuum advance to about 10 degrees if you plan to run it. If you're really worried about it, jet up a couple sizes in your carb. Ethanol blends are actually more resistant to detonation than non-ethanol. The higher the ethanol content, the more resistant the fuel is.
Planning on 3.00 gears and could go to 2.75 depending on what the car has and the engine is in a heavy car (Thunderbird} now,I want to use this engine for the torque.
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