# How does a '72 YS 400 compare to other years?



## mrvandermey (Jun 15, 2011)

Hey everyone, I have questions regarding engines. I just picked up what appears to be a decent engine and tranny. 

I was told by the seller that the engine is a 1968 Pontiac 400 and the tranny is a Turbo 400 (it came out of his '68 GTO).

I saw that the casting date says A282, which I believe means it was made January 28, 1972.

The block casting number is 481988, which I believe is the casting number for 1970-74 Pontiac 400.

The code on the front of the engine states "YS".

So apparently this is a 1972 Pontiac 400 and not a 1968 Pontiac 400. Now, again, if I am not mistaken, the "YS" is the round-the-mill Pontiac 400 (335 HP gross or 250 HP net or something close); and the YS was available on ALL Pontiacs in 1972. But the price seemed pretty good, so I went ahead and bought it. 

Now, my questions are:
1) How does the performance or horsepower of a 1972 Pontiac YS 400 compare to any other year, specifically 1968 or 1969?
2) How do I tell for sure whether the transmission is indeed a Turbo 400 as opposed to a TH 350 (is a TH350 the same as a Turbo 350)?
3) I paid $900 for the set and it is complete (minus plug wires, throttle cable, and air filter) and it came out of a running car (I admit I took the seller's word that the engine does not smoke, leak, ratle, knock, etc, and do not specificaly know for sure if it still runs). Good deal?

Any advice would be highly appreciated.


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## Rukee (Feb 8, 2007)

The TH 350 has a kick down cable coming from the front passenger side going to the carb, the TH 400 uses an electrical spade connection on the drivers side just above the pan for the kick down.


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## jetstang (Nov 5, 2008)

Also, the Turbo 350 has a square pan with a corner cut off, while the turbo 400 has a cross shaped pan. Hopefully it runs good, sounds like a good deal, hopefully it runs good.


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## mrvandermey (Jun 15, 2011)

Is there a huge difference in actual horsepower between a 1972 YS 400 and pre 1970 YS 400? I know 1970 and before used gross horsepower ratings while 1972 used net horsepower ratings, so the numbers could look significantly different. But in reality, is there a huge difference?


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## mrvandermey (Jun 15, 2011)

So on transmissions, a TH400 is the same thing as a Turbo 400 and a TH350 is the same thing as a Turbo 350? 

Is a TH400 a better transmission than a TH350?


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## Rukee (Feb 8, 2007)

yes yes and yes.


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## geeteeohguy (Feb 2, 2008)

You actually lucked out with the engine year a bit. In '71, the compression ratio was lowered but the blocks in '71 and '72 are just as strong as the earlier block. (not so with the mid '70's blocks). If you had a '70 or earlier, you would have a tough time running it on today's fuel. So, with a decent cam (stock is usually fine...those engineers really _did_ know their stuff) and a sharp tune, it ought to run pretty well. So, you've got an engine you can _actually use _on today's poor gas. Win-win, IMO!


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> You actually lucked out with the engine year a bit. In '71, the compression ratio was lowered but the blocks in '71 and '72 are just as strong as the earlier block. (not so with the mid '70's blocks). If you had a '70 or earlier, you would have a tough time running it on today's fuel. So, with a decent cam (stock is usually fine...those engineers really _did_ know their stuff) and a sharp tune, it ought to run pretty well. So, you've got an engine you can _actually use _on today's poor gas. Win-win, IMO!


:agree Yep. 72 model year will be lower (probably much lower) compression so you could probably run the thing on lighter fluid... Which heads are on it? That's one of the key questions. You've got a good strong block to use for whatever you might decided you want to build. Depedning on what you want to spend and the condition of the engine as it sits, you could do pretty much anything. You done good.

Bear


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## mrvandermey (Jun 15, 2011)

Rukee said:


> The TH 350 has a kick down cable coming from the front passenger side going to the carb, the TH 400 uses an electrical spade connection on the drivers side just above the pan for the kick down.





jetstang said:


> Also, the Turbo 350 has a square pan with a corner cut off, while the turbo 400 has a cross shaped pan. Hopefully it runs good, sounds like a good deal, hopefully it runs good.


Here are pics of the transmission. Based on the descriptions you gave me, it looks to me like a TH350 (I mean the seller was wrong about the year). What do you guys think?


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## mrvandermey (Jun 15, 2011)

BearGFR said:


> :agree Yep. 72 model year will be lower (probably much lower) compression so you could probably run the thing on lighter fluid... Which heads are on it? That's one of the key questions. You've got a good strong block to use for whatever you might decided you want to build. Depedning on what you want to spend and the condition of the engine as it sits, you could do pretty much anything. You done good.
> 
> Bear


The heads have "7K3" on center exhaust port.


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## BearGFR (Aug 25, 2008)

That's actually not bad! 7k3's have a nominal chamber volume of 96 cc's. They should also already have the large valves (2.11 / 1.77) as well as screw in studs and guide plates. 7K3's are also 1972 only -- so that sort of confirms what you saw on the engine date code.

Take that 400, zero deck the block, get some good forged flat-top pistons. CC those heads to find out what the chamber volumes really are. If they're 96, then milling .040 off them ought to put them at 87 cc's. On a zero decked, +0.030 400 running standard head gaskets that'll land you at 9.12:1 compression. Ought to be just fine with 91 octane or better. You might need to mill the intake some to restore the fit. You could also cut the heads a little more - as much as .050 and get a little more compression - up to around 9.3:1, but doing that wouldn't leave you any 'meat' on the heads for future rebuilds/freshening up, so that's up to you. DO cc them first though because chambers can and do vary from the factory numbers by quite a bit sometimes.

Bear


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## mrvandermey (Jun 15, 2011)

BearGFR said:


> That's actually not bad! 7k3's have a nominal chamber volume of 96 cc's. They should also already have the large valves (2.11 / 1.77) as well as screw in studs and guide plates. 7K3's are also 1972 only -- so that sort of confirms what you saw on the engine date code.
> 
> Take that 400, zero deck the block, get some good forged flat-top pistons. CC those heads to find out what the chamber volumes really are. If they're 96, then milling .040 off them ought to put them at 87 cc's. On a zero decked, +0.030 400 running standard head gaskets that'll land you at 9.12:1 compression. Ought to be just fine with 91 octane or better. You might need to mill the intake some to restore the fit. You could also cut the heads a little more - as much as .050 and get a little more compression - up to around 9.3:1, but doing that wouldn't leave you any 'meat' on the heads for future rebuilds/freshening up, so that's up to you. DO cc them first though because chambers can and do vary from the factory numbers by quite a bit sometimes.
> 
> Bear


Well I am glad to hear I found a pretty good find. I still do not know whether this will be my final engine or just my "drive-around" engine. Originally my plan was to purchase this engine just as my drive around engine while I build my "dream engine" as time and money allow for. 

I am building a '68 GTO Convertible and although it is a real 242 GTO, it is not numbers matching, nor is it a factory Ram Air of any kind. So I guess my engine options remain open.

By the way, everyone mentions the use of 91 octane or higher, and although I am from the state with the highest gas prices, the highest octane we have is only 91.


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## geeteeohguy (Feb 2, 2008)

I agree, the 7k3 heads are indeed good heads. I am running 87cc heads (#15) on my '67 GTO with the original block and flat top pistons, and it still wants to ping a little bit on 100 degree days up long grades. I'm stuck with the same poor gas as you are....I need to play with my advance curve a bit, but I'm a pretty sharp tune-up guy. you might want to keep those heads around 90-92cc for added insurance against detonation. I used to get by with the stock heads when leaded 94 octane was available, but those days are long gone.


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## mrvandermey (Jun 15, 2011)

A couple more questions. The carb appears to be a Q-Jet and it looks original to engine. What size is it likely to be? How can I confirm what size it is? Is a Q-Jet the best carb to use on this motor and heads?

With these heads, if I want to use headers, I will need the "L" brackets, correct?


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## BearGFR (Aug 25, 2008)

If you can get the number off the side of the carb, there are sources to ID it. All Qjets though are at least 750 cfm - a few are 800. I'm a big fan of them. My car runs 11's with an 800 cfm version. It's possible on a big inch engine to need more, but it's not something you run into every day, especially on a street engine. There are right ways and wrong ways to set them up, and closet 'experts' who don't know nearly as much as they think they do about them are plentiful so be careful. Are those heads some that don't have the 'end' bolt holes? Instead of headers you might consider a set of the reproduction ram air manifolds. They don't give up a lot in terms of performance compared to a good set of headers, but they fit MUCH better and don't give you clearance headaches. For the best performance though, good headers are the best choice - just be prepared to deal with all the other "issues".

As far as octane, the rule of thumb for iron heads is octane needs to match compression --- 9.1:1 for 91 octane, 9.3:1 for 93 octane, etc. Notice I said 'rule of thumb' though - it's not a hard and fast rule. With careful cam choice, dead-nuts tune up, and a monster cooling system there are people who can and do push those limits successfully - some by a lot. It's not child's play though... 

You've got a good base there for both your drive around and your dream engine. Build it as a 400 with those heads (milled) a decent flat tappet cam and some good rods, and it'll be a nice/fun car. Then when you're ready to get a little more serious, swap in a stroker rotating assembly (you might even be able to reuse the rods), roller valve train, worked aftermarket aluminum heads, and it's play time 

Bear


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## geeteeohguy (Feb 2, 2008)

:agree:agree:agree^^^^


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## mrvandermey (Jun 15, 2011)

Well after a little research, I did discover the transmission is definitely a Turbo 400 and not a TH350, so that is a bit of a relief. I guess I will go ahead and use this engine and tranny set up for at least my "drive around engine" and I may even ending up building this one up.


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