# 1973 block in my 68



## GTO68convert (Sep 11, 2018)

I just bought a 1968 GTO Convertible and I found out it has a 73 block. Although, it has a 73 block it has the 68 heads. It also has a mild cam with rocker rollers, double roller timing chain, 4 barrel edelbrock carb and aluminum eledbrock intake. With the emissions on the 73 block does all the other upgrades help with horsepower?


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## BLK69JUDGE (Jun 10, 2010)

*Hello*

welcome

drop the top and drive it and enjoy it ...

its only goin' to be as fast as it is ....if its running good leave it alone..

used short block?

rebuilt short block ? whats the history if any ??

compression test ?

tons of variables..... 

welcome ...

1st post always require pictures of said vehicle also ............. just kiddding ... oh no Im not ... yah I am


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## GTO68convert (Sep 11, 2018)

Rebuilt only has about 7000 miles on it. Runs great but was wondering for future reference what was so different about those blocks to only be 170/180 HP.


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## Shake-N-Bake (Jun 16, 2015)

GTO68convert said:


> Rebuilt only has about 7000 miles on it. Runs great but was wondering for future reference what was so different about those blocks to only be 170/180 HP.


In regards to power output, the difference is in the heads and camshaft.....and to a lesser degree, the carb.

Sent from my SM-G930V using Tapatalk


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## Instg8ter (Sep 28, 2010)

Welcome, Nice looking car. i agree if its not broke don't fix it. Top down and drive it like you stole it. The block is the same as your original, like said heads and cam are what provides the power. you can do a compression check on all cylinders to make sure the rings and valves are sealing good. Make sure the temp doesn't get over 220, pontiacs are notorious for overheating if the water pump isn't clearanced right.


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## GTO68convert (Sep 11, 2018)

Thanks guys for the complements!! One other question I have about the car. When I start it up a cloud of white smoke. Did I add to much additive because it only did it after I put gas in it and added some?


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## PontiacJim (Dec 29, 2012)

GTO68convert said:


> Thanks guys for the complements!! One other question I have about the car. When I start it up a cloud of white smoke. Did I add to much additive because it only did it after I put gas in it and added some?


The '73 block is fine as is and emissions related items were not in the block. 

As *Shake-N-Bake* noted, the combustion chambers in the head as measured in CC's, is for the most part how Pontiac lowered compression. So compression was lowered using bigger chamber heads. Also, valve size determines some of that HP. Typically the 2.11" larger intake valve size are used on the higher HP engines, and if your heads are the 1968 #16 heads, you have the good heads. HOWEVER, there is also a small valve #16 head used in 1970, so you want to confirm they have screw-in studs and check the cast date code. And of course, camshaft size provided the HP ratings.

So the answer to your question is "yes", this all adds up to better HP, closer to stock or possibly a touch more with the #16 heads UNLESS the rebuild included pistons that were installed to reduce compression with the #16 heads so you can use pump gas without detonation/pinging.

Keep in mind that in 1971, HP/Torque ratings went from "Gross numbers" to "Net numbers" so the HP/TQ numbers appear to have really dropped, but not so much as you might think. The change in how the HP/TQ was measured is what causes this radical drop.

The smoke could be from the additive if it has oils in it OR the valve seals may be going south on you. Typically when the car sits a bit and then when you fire it up you get some smoke, it can mean valve seals. But since your engine was rebuilt 7,000 miles ago, it should not be the oil seals. So just monitor it and watch the next tank of gas.


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## Cafr119 (Dec 9, 2017)

Nice car, bro !!!!! I agree that 350 will be fine, drive and enjoy !!!


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## BearGFR (Aug 25, 2008)

Nice car! Welcome sir...

Emissions stuff was implemented everywhere EXCEPT the block. The heads, cam, valve train, intake, and exhaust are what give it it's "personality".

Bear


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