Help 427-400

[Tom Bryant]

The reason for the difference is the El used an electric tach and the Corvette used a mechanical tach, which is the more accurate of the 2. It is unlikely that a 454 in 1970 would turn 7000 rpms and hold together for very long. Your 67 was too lean from the factory, and that caused your plug problem.

As to the tach question I really don't know. If I had an electric tach malfuntion it would either quit altogether, stick and jump or lag behind. I have had oem and aftermarket lag behind. Never had one read fast but I suppose it's possible. Also there have been volumes written on the problems associated with mechanical tachs on every Corvette site and in every Corvette magazine.

Since a mechanical tach is basically the same mechanism as a speedometer head it is subject to the same shortcomings as to calibration and maintenance. If the cables and gears are in good shape, lubed properly and and not kinked or worn then it should work as it was intended to by the engineers. Sort of goes back to the statement on the old ignitions. If it's well maintained it will get the job done. One of these days when I'm feeling especially masochistic I need to pull the cluster from the '59 again and send the tach in to be recalibrated. It worked within a tick of my engine tester until it broke then the shop that fixed it got the cable speed wrong when they recalibrated it.

The carb on my '67 was a 780 vac secondary manual choke over the counter Holley. It was the only non-stock part. I always suspected it as being a little too rich for stop and go city driving but it never smoked out of the Hooker side pipes. Realizing that headers tend to lean out an engine I probably should have had it hooked up to a sniffer to be sure.

Tom

 

[67435animal]

I noticed I had made a mistake on purchasing the for mention plugs R43 and R45 are for small blocks, current plugs in car are 43N- I will take John Z suggestion on 45XLS, I have noticed in ZIP catalog they sell 43XLS, with all the great information provided I may opt for 45XLS since it is a hotter plug, again Thanks for the help, I will keep everyone informed. What a great site for infomation!!!!!!!

Thanks again!!!!!

Michael 427

Michael, is your ignition standard or TI? If it is TI, I strongly recommend the NGK plugs:

Spark Plug Part No. Stock No. Plug Gap
Standard BR5ES 4722 .035[font=helvetica, arial, veranda][/font]

I had fouling problems with all the AC's that I tried but these have been great. The car runs smooth and strong and starts easier too.

Bob

 

[Hib Halverson]

here's a pic of an R43 pulled from my misfiring motor:

Here's an R45 from the same motor... no more misfires

There is no question that the above two plugs demonstrate the effects of different heat ranges, but, looking at the 43s, my guess is a mitigating circumstance is oil fouling (or perhaps rich mixture at idle) combined with a stock ignition system not able to fire a 43 in an engine that's burning some oil. So, it might be that the engine in that 65 may not tolerate 43s but that's mainly because of it's oil use and a stock ignition, not that a 43 is too cold for high-performance street use. In an engine which sees no starts without warm-up, has an ignition system in good condition and a low level of oil consumption, the 43 is a good choice if the car gets driven fairly hard.

On the other hand, if the engine uses a little oil, is not driven hard, sees starts without warm-up, then the 45 is a better choice.

 

[Michael 427]

67435animial- I have standard ignition, any thoughts on what number I should use in the brand you mention.



Michael 427

 

[Vref]

Thanks for the pics. I just switched from ND w16s-u to the AC45's. When I pulled out the ND's they were all fouled and oil soaked also. Non TI.

Does anyone know what heat range the ND w16s-u was? I never heard of this plug.

 

[67435animal]

67435animial- I have standard ignition, any thoughts on what number I should use in the brand you mention.

Michael 427

Michael, as far as I know, that plug is good for both standard and TI ignition. It should do the job for yours as well. I will tell you that it crosses to the AC43XLS - ACR45XLS but the XLSs fouled in my car. These do not foul.

Go to http://www.ngksparkplugs.com/apps/car_truck_suv/default.asp?nav=60000&country=

You can buy NGKs at Advance Auto Parts for $1.68 each. Let me give you the exact number I am using on my car. It is the BR5ES. This is the one you want. They've been installed in my car for over 3 years (about 4000 miles) without any fouling or stumbling:

NGK 4722 Spark Plug: Plug No. BR5ES

I pulled #5 from my engine and the plug has no fouling on it and the electrode is a nice light brown.

You may be able to run a slighly hotter plug from NGK...probably the BR6ES

Let me know if you have any other questions.

Bob