newbie classic high compression engine question

[Hoyt Clagwell]

Reading the hardened valve seat thread got me thinking about leaded vs unleaded gasolines.

What is the impact of using todays 90+ octane unleaded gas in the older high-compression engines? Are octane booster additives needed for the older high compression engines (351 / 428 / 429 ) ?

Thanks.

 

[D.Hearne]

Reading the hardened valve seat thread got me thinking about leaded vs unleaded gasolines.

What is the impact of using todays 90+ octane unleaded gas in the older high-compression engines? Are octane booster additives needed for the older high compression engines (351 / 428 / 429 ) ?

Thanks.

Extensive use of unleaded will let the valves pound themselves into the seats. I've been running CD2 lead substitute in the gas I run in my 68 Merc's 390 to prevent that. Can't tell you how well it works though, it's been running off and on for two years now ( car is parked currently) without adverse effects. Only pulling the heads off will tell me how well it does work. And I ain't about to do that. As for octane boosters, I've yet to run across one that actually works. Best thing for an engine like that is to swap cams to one that's got more overlap. That's what I did with the Merc's 390, it's got 10.25 to 1 compression and a Crane 272 degree Energizer now and runs fine on 89 octane mixed with CD2 lead substitute. With the stock 10.5 to 1 ratio and the stock cam, it would ping on 93 octane.

 

[HistoricMustang]

 

[rbohm]

agreed

 

[D.Hearne]

HUH? What's that about?

 

[2bav8]

Historic really likes the "tech" question.

 

[Max Power]

Or the answer....

 

[Hoyt Clagwell]

Extensive use of unleaded will let the valves pound themselves into the seats. I've been running CD2 lead substitute in the gas I run in my 68 Merc's 390 to prevent that... As for octane boosters, I've yet to run across one that actually works. Best thing for an engine like that is to swap cams to one that's got more overlap. . With the stock 10.5 to 1 ratio and the stock cam, it would ping on 93 octane.

Thanks for the response - What was the impact on performance with the new cam ?

btw - did I post this in the wrong forum ? Apologies if I did.

 

[HistoricMustang]

2bav8 hit on it, but in todays "politically correct" world it will no longer be used.

We certainly do not want to "piss" anybody off, especially those with chrome wheels.

HistoricMustang
www.historicmustang.com

 

[D.Hearne]

Thanks for the response - What was the impact on performance with the new cam ?

btw - did I post this in the wrong forum ? Apologies if I did.

The performance is fine with the new cam. Idles almost like the stock cam, only when cold, can you hear a hint of "lope". This 4200 lb hunk of iron runs mid 14 sec 1/4's with it. Engine is stock except for the cam and headers. I also added a 428 PI intake and 750 Holley carb. Also swapped the rear gears from 2.75's to 3.70's.