miss fire at high RPM

[Gene M.]

Re: miss fire at high RPM

Just raising post to top to see if the problem is solved.

[Mark E.]

Re: miss fire at high RPM

Gene,

Check Bruce's 7/17 post. It was the spark plugs.

[Duke W.]

Re: miss fire at high RPM

Hey Mark,
Thanks for your help. as it turns out it was the plugs!! Funny thing is that the plugs looked fine?Just goes to show you looks can be deceiving
Bruce

You should be using AC heat range "5" or equivalent in another brand. Colder plugs like the OE 44 have more tendency to foul in normal driving. Heat range selection should be based on driving conditions, particularly average load. Since Corvettes are light cars with big engines average load in normal road driving is very low, so they need relatively hot plugs. If the car is run in track events a colder range plug should be used since the engine is operating at full load most of the time, so AC heat range 2 or three or equivalent in another brand should be installed.

AC heat range "5" equivalent is best for normal road driving, including long freeway trips, for all Corvette engines, both small and big block, regardless of the horsepower rating.

Duke

[Bruce W.]

Re: miss fire at high RPM

Thanks Duke, I run ac45. no problem. I also run sunoco 110. Do think this gas causes plugs to burn out?
Bruce

[Patrick H.]

Re: miss fire at high RPM

AC heat range "5" equivalent is best for normal road driving, including long freeway trips, for all Corvette engines, both small and big block, regardless of the horsepower rating.

Duke

FYI, 45s are too cold for my 70 Cutlass. It's an original, non-rebuilt 350/310hp.

I could not figure out why it had incessant run-on and pinging which would only go away with use of at least 50% high octane (race) gas mixed with 91-93 octane pump gas.
Swapped the plugs to Champions similar to 44s in heat range (no AC in 44) a couple of weeks ago, and so far it is running better than it has in several years.

Spent a lot less on new plugs than another 5 gal of race gas.

[Gene M.]

Re: miss fire at high RPM

FYI, 45s are too cold for my 70 Cutlass. It's an original, non-rebuilt 350/310hp.

I could not figure out why it had incessant run-on and pinging which would only go away with use of at least 50% high octane (race) gas mixed with 91-93 octane pump gas.
Swapped the plugs to Champions similar to 44s in heat range (no AC in 44) a couple of weeks ago, and so far it is running better than it has in several years.

Spent a lot less on new plugs than another 5 gal of race gas.

Colder plugs (AC44) run great at higher RPM’s and highway cruise (talking Chevy small blocks). These (AC44) were the original equipment on most SB chevy from the factory. No idea what Olds uses. So unless the engine has issues they should run fine.

Too hot a plug will do exactly as you described.

[Duke W.]

Re: miss fire at high RPM

Thanks Duke, I run ac45. no problem. I also run sunoco 110. Do think this gas causes plugs to burn out?
Bruce

If it's unleaded it will have no effect on fouling. Leaded fuel will increase the possibility of fouling.

Duke

[Duke W.]

Re: miss fire at high RPM

FYI, 45s are too cold for my 70 Cutlass. It's an original, non-rebuilt 350/310hp.

I could not figure out why it had incessant run-on and pinging which would only go away with use of at least 50% high octane (race) gas mixed with 91-93 octane pump gas.
Swapped the plugs to Champions similar to 44s in heat range (no AC in 44) a couple of weeks ago, and so far it is running better than it has in several years.

Spent a lot less on new plugs than another 5 gal of race gas.

I assume your '70 Olds has a real "rocket V-8" and is not one of those "Chevymobiles" that I don't think showed up until the mid-seventies.

Differences in detail design could affect the heat transfer path from the plugs to the cooling jacket, so Chevy heat range may not be a good guideline. What was the OE AC plug number?

I recall that GM settled a class action lawsuit by Olds owners over the fact that some had Chevrolet SB engines, and that GM paid each of those owners 200 bucks. I think it also lead to the GM "corporate blue" engine color and a statement in marketing literature that engines are made by various GM divisions and the installed engine may not be from the same division as the car nameplate or something along that line.

Personally I think the Chevy small block is a better engine. It was designed later and for sure is a good deal lighter than the Olds design, which dates to 1948 and was the first OHV V-8 available in any GM car. Cadillac's OHV V-8 did not come along until the 1949 model year.

Duke

[Bruce W.]

Re: miss fire at high RPM

Duke, Sunoco racing fuel is leaded. Well with a fuelie I guess I will have to change plugs more often. Thanks for your help
Bruce

[Mark E.]

Re: miss fire at high RPM

Personally I think the Chevy small block is a better engine. It was designed later and for sure is a good deal lighter than the Olds design, which dates to 1948 and was the first OHV V-8 available in any GM car. Cadillac's OHV V-8 did not come along until the 1949 model year.

Duke

I believe Olds and Cad OHV V8s both debuted for MY1949. Both went through two or three generations, including a new design for Olds in 1964(?), which included the 350, 400, 425, 455 family. I heard this generation was among GM's most efficient and clean burning V8 for its time. Unlike many other designs, they typically didn't need a smog pump in the '70s to pass emissions. This may be why Olds engines were also used by Pontiac and Cadillac.

I had several 1970s vintage Olds V8s and found them reliable, smooth and fairly powerful. They also have a unique sound, in part because they rotate in the opposite direction. As a DIYer, I appreciated the spark plug access- much better than Chevy SB.

I don't know how they compare exactly, but I believe the Chevy SB's main advantages are size, weight, cost, and plethora of "off road" factory parts- not so much reliability or power.