The difference between an 840 and a 291 head is?
 

Someone just sent me one of each and said they came from the same car. They told me they were both 840's and then I get this 921. I looked around and on one site it said the chamber was 1 cc different. On another it said they were the same. Does anyone know what the difference between these are? I can't see how they even look different...help please

Re: The difference between an 840 and a 291 head is?
 

Minor chamber difference..106.8 on the 840 and 109 on the 291. Exhaust valve size was increased to 1.88. Most 291 heads will also use the small 5/8 taperd seat spark plugs.

wilma

Re: The difference between an 840 and a 291 head is?
 

Tom;

I *believe* with the 291 heads, the L78 head still got the 1.72 valve where the LS6 head got the 1.88. I have a pair of `70 dated 291's that are going on my project engine and they're set up for 2.19 / 1.72 valves.

I don't remember off the top of my head, are the 291's drilled for a temp sender hole?

Eric

Re: The difference between an 840 and a 291 head is?
 

There is a temp sending hole on the drivers side head. I have looked at a lot of these heads and think they all had the 1.88 valves..but then again???? Perhaps other techy folks can offer some input.

wilma https://www.yenko.net/ubbthreads/imag...ins/3gears.gif

ps. what size spark plugs do your heads have??

Re: The difference between an 840 and a 291 head is?
 

Not sure on the spark plug size, the heads are still @ the machine shop right now.

I hope to be going by there any day now to drop off a set of pistons so they can get my block work done, and I'll check the plug machining then. I'll grab the dates also.

(I can't wait to hear this thing make noise on the dyno https://www.yenko.net/ubbthreads/imag...ns/naughty.gif )

Eric

Since they have different numbers
 

I put them up for sale no reserve http://cgi.ebay.com/ebaymotors/ws/eBayIS...E%3AIT&rd=1

Re: Since they have different numbers
 

I had a set of 840 & 291 heads that were produced the same week...and believe it or not, the 840s were *cast* for the 1.88 exhaust vavles. The machine shop were the ones to catch it, as I told them to just put a seat of seats and 1.72s in it...but they called and said the heads had never had seats in them (which I knew, they were virgin heads) but that they were made to accept 1.88s...I called Colvin a few times about it, and he confirmed my thoughts...there's an old thread around here with all the ins/outs of the 840s & 291s.