[Brant]

I hate to add an additional Small block Head posting but I need to. Over the past 6 months I've read every posting, artical, magazine, dealing with these heads. It's actually quite simple to understand once you learn to trust one source. I have a few questions, as I am about to make a decision between a few pairs.

This is what I understand

2531894 340 1968-70 2.02/1.60 (‘X’ heads)
3418915 340/TA 1970 2.02/1.60 (many have ‘O’ & ‘J’ stampings)
3418915 340 1971-72 1.88/1.60 (many have ‘J’, ‘U’, ‘O’ stamps)
3671587 340 1973 1.88/1.60
3418915 360 1970-72 1.88/1.60

Now, I was looking at a pair of heads yesterday. Casting #3418915 B with an ‘O’ stamping. Measuring - 2.02/1.60 valves. Came off a 1972 engine.

Is it safe to say that if they are 72's, they were opened up at some time. Once doing so, there is no difference in flow as any other 2.02 head listed above? Is ‘Smog Tubes’, a term for the 1.88 heads - meaning the runners are being obstructed by small valves - Only? No other difference.

Through research I've found a few people owning TA heads. The casting was #3418915 B with ‘O’ stamps. Is it possible these are TA heads. How will I tell without seeing the cast date? These require offset rockers, so I should look the other way.

This information will aid in my head choice. thank you greatly!

[dave-r]

I think "smog tubes" might refer to some late heads that had small holes next to the exhaust ports. Something to do with emissions control I think and you have to tap and plug them for performance use?

I can't comment on any of the above heads. If they are stock they will flow stock and there will not be much difference between them.

I wouldn't waste my time with any of them. I would fit a pair of Edelbrock heads or a pair of ported iron heads from a good company that specialises in porting heads.
The level of porting needs to match the cam and compression you are using.

However I realise not everyone has the spare cash to go that option so if it HAS to be stock heads get a pair from 1968-72 with as big an intake valve as possible. Watch out for valve guide wear when looking at used heads.

[mysticwarrior]

Smog tubes are indeed small ports that are under the exhaust ports that inject air into the exhaust. Tap 'em and use 1/4" 20 stainless allen screws and you will not have a problem. I run a set of 1975 heads on my 1971 340 challenger. The intakes were opened up to 2.02" three angle valve job, pollished and port matched. The exhaust side was polished ,as it already has the hardend seats installed by mopar. I then milled the head to reduce the combustion chamber to 64cc's This was way cheaper than trying to fix up a set of rusty old 'X' heads. The amount of performance obtained from this was eye opening as the 340 was always a little week off the line
( as compared to a big block anyway) and dispite me running a 9.5:1 CR
it pull nice and strong from idle to redline.

[Brant]

Thanks a million for that guy's. I'll now know what to look for. Doesn't seem much work to plug those bad boy'z. In comparison to a Three angle valve job ($), what's it cost to put hardened seats in? If I'm correct, no J's, O's, U's, etc came with hardened seats.