10"1 compresson+pump gas=?????

[1968-coupe]

I have been looking into crate engines, I am deeply lusting after the Ford Racing 521 ci. But it has 10:1 compression, I wasnt worried about it until someone (who knows a LOT about these things) told me that in hot weather with high grade pump gas (93) it would still knock. Is this true?

 

[D.Hearne]

Not true. I'm running a 10.4 to 1 331 on 93 octane and previously ran a 10.25 to 1 390 on 89 gas.

 

[htwheelz67]

if the engine has modern aluminum heads even 11-1 is usually no problem on 93 octane

 

[1968-coupe]

Its a 521 with Ford Racings new aluminum SCJ heads. Its the engine I WANT (key word)

 

[iskwezm]

A buddy of mine has the Ford Racing 514 in his 53' Ford F100 and he drives it year round hot or cold without problems.

 

[rbohm]

one nice thing about the 385 series ford big blocks is that they tend to be less prone to detonation at higher compression ratios. also what cam is in the engine? depending on the duration and valve overlap, that will also help reduce the incidence of detonation.

 

[1968-coupe]

Good thing you brought that up! I got to reading through the information and aparently Imissed something:

"Mechanical roller camshaft, M-6250-A514 Not sutable for street use"

I called and had a nice long chat with Ford Racing and it seems the 521 would need e cam change to be completely street freindly. But he called my attention to Ford Racing's new 427 small block:

535 hp 545 ft/lb of torque
Aluminum of cast iron block
Forged internals
Street friendly
Z304P high flow heads
Roller cam
$8,800 for the iron block.

 

[65ShelbyClone]

10:1 compression really isn't that high for an aluminum-headed engine on pump gas IMO. There are many more factors that determine octane sensitivity,but I wouldn't be uncomfortable feeding that engine the 91 gas we have here. The ignition timing has a large effect here as well.

My 302 only has 9.1:1 and I feed it 87. The next engine I put in my '68 is likely going to have 10.0-10.5:1 and get 91, although EFI with full 3D ignition mapping is also a likelihood.

 

[brianj5600]

That cam does not seem that bad. I ran bigger in a street 306.

 

[rebel65]

my 392 is 10.5: 1 and i run 91 octane as 93 isn't popular in california. i also have aluminum heads.

 

[1968-coupe]

I was told If I kept the cam that comes in the 521 it s reccommended to change the valve springs every 2,000 miles. Or I could go with a less radical cam with a slight hp loss. They said the 427 would handle much better as it is designed for street rods and it would also get better fuel mileage.