# 99 exhaust heads



## tyrefryer (Nov 8, 2011)

What does the 99 stand for on the side of my exhaust heads (its in the center of the head in cast. Also, what does YU stand for on a 1970 block?
Thanks


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## BearGFR (Aug 25, 2008)

There are several web sites that have this information published. Google things like 'Pontiac engine codes' to find examples. I just used the tools on Wallaceracing.com to find that 99 heads are from a 1971 250hp 400, and will have smaller valves and probably pressed in rocker studs. YU for model year 1970 was a 350, should have block casting number 9799916 on the top passenger side next to the transmission, below the head.

Bear


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## BearGFR (Aug 25, 2008)

There are several web sites that have this information published. Google things like 'Pontiac engine codes' to find examples. I just used the tools on Wallaceracing.com to find that 99 heads are from a 1971 250hp 400, and will have smaller valves and probably pressed in rocker studs. YU for model year 1970 was a 350, should have block casting number 9799916 on the top passenger side next to the transmission, below the head.

Always begin with the 4 character date code to id the model year before you look anything else up. Some codes were used in more than one year and meant different things.

Bear


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## tyrefryer (Nov 8, 2011)

So if its a 350 block and 400 heads is that possible? Can you match up stuff from a 350 to a 400?
Thanks


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## BearGFR (Aug 25, 2008)

Generally, yes. Since all Pontiac blocks are dimensionally the same, you could even put 455 heads on a 326, or vice versa. There are some year model boundaries where some of the water passages changed so it's not universally true (I don't have those boundaries memorized but they're findable on the web). Also, just because something will bolt up and run doesn't necessarily mean it's a good idea though --- variances in combustion chamber size can result in "bad things" such as a small displacement engine with an extremely low compression ratio, or a large displacement engine with way too much compression.

Fr'instance - if we assume your 99's have the factory spec chamber size of 98 cc's (and that's a huge assumption becuase chamber sizes vary a lot on these heads, even untouched), and that your 350 hasn't been overbored, has factory spec head gaskets, and the usual .020 piston deck height, then your static compression ratio works out to be 7.2:1 --- you could probably run this motor on paint thinner and not have to worry about detonation  --- it's also going to be way down on power from what it would be at, say 9:1 or 9.3:1.


Bear


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## tyrefryer (Nov 8, 2011)

Thanks for all the info Bear.
Dave


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## tyrefryer (Nov 8, 2011)

Another question Bear or someone else...

I'll try to explain this the best I can (being a new car peron,lol). On the top of my timing area closes to the top of the block along the canyon, is a bit of water seepage. Now its NOT the water pump seal cause thats in front of the timing and that area is dry, its behing the timing against the block. A friend of mine said it could be the sleeves inside the waterpump/timing area. Is that correct? Have you heard of those seeping at all? Its NOT alot of water but just a bit, nothing on the floor or anything like that. Is that a pretty easy fix if so? Or what do you think it could be? I have checked and tightened all my hoses etc etc.
Thanks again


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## BearGFR (Aug 25, 2008)

Sounds to me like it's most likely leaking at the joint between the back of the timing cover and the front water crossove on the intake. Hot Rod has been dealing with that problem too, check out the conversation on his thread.

Bear


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## tyrefryer (Nov 8, 2011)

I cant figure out how to find the link....what does the replys say? Is it a bad thing or an easy fix? Do I just need to replce the sleeves and put on a new sealer?
Thanks again...


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## BearGFR (Aug 25, 2008)

The thread is here: http://www.gtoforum.com/f50/oy-some-qs-good-people-35418/#post291999

If it's what I think it is, it's not the sleeves. The sleeves are behind the water pump and seal the back side of the pump to the two water passages in the front of the block. They pass through the timing cover. For leakage there to show up where you're seeing it, coolant would be having to climb uphill and also get past either the timing cover gasket or the water pump gasket.

Bear


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## tyrefryer (Nov 8, 2011)

So what would you say it is then? Something major or something a 1st timer could do?
Thanks Bear
Dave


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## tyrefryer (Nov 8, 2011)

Here are a few pics of the leaking area and is highlighted wuth the yellow arrows pointing at the sight where the leak starts.
Thanks for any help...


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## BearGFR (Aug 25, 2008)

Ah hah! You've got a bolt missing. Look at this photo...










Notice very near the top of the water pump, slightly towards the drivers side, there's long skinny bolt through a metal tab that catches on two 'ears' on the timing cover and threads into the front of the intake manifold water crossover. Its function is to squeeze the connection together between the intake manifold crossover and the timing cover. Inside that connection there's a rubber donut that acts as a seal. Your engine doesn't have the bolt at all --- I'm surprised it's not leaking more than it is.

Bear


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## tyrefryer (Nov 8, 2011)

Is this the bolt you think is missing? Maybe it just didnt show up in the pic...Let me know if the yellow arrow is the bolt you are talking about. If its NOT the bolt I cant find a missing one anywhere else.
Thanks for the help Bear
Happy Thanksgiving...


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## tyrefryer (Nov 8, 2011)

Hey Bear, I found the problem. It was a bolt at the very bottom of the alternator/bracket and it was sticking out about an eighth to a quarter inch. I turned it 7-8 times and it finally got nice and snug. I dried off all the top and everything, ran the car up to temp and NO water leaking. So hopefully that was what it was. I would have NEVER looked around there if it was'nt for you. So thank you Bear for the help.....problem solved (I hope, lol).
Dave


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