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68 Firebird with a 1976 400. Need Advice


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8 replies to this topic

#1 Franklin68

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  • Year: 1968
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  • Model: Firebird
  • Engine: 400
  • Transmission: Auto

Posted A week ago

Hey need some advice just bought my first Firebird 1968 400, and I did some research and found out it has a 1976 Y9 500557 400 Block. It currently has a 2 BBL carb on it. My questions are #1 is this the original set up for a 1976 400? #2 Should I switch to a 4BBL and new intake? Should I get a new cam while I'm at it? Also I would really appreciate any other advice or recommendations on what to do.  I am looking for performance! As of right now it has an automatic, but that will be changed to a m22 or m21 4 speed. Just got the insurance today on the car and took it out for its first real cruise, and the car definitely has some power but it absolutely needs more. Any suggestions would be greatly appreciated! Thank you!

Franklin M. 



#2 KeyKeeper

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Posted A week ago

What heads are on it?  Sticking a 4bbl carb on a low compression engine isnt going to yield very good results. 

 

Find out what rear gears you have, changing them to higher numerical value will yield the best "seat of the pants" feel/increase in performance.  Especially with a 4spd car.


I prefer to drive short distances....1,320 feet at a time

 

356ci SBC 11.8:1, Eagle rotating assembly, Wiseco .125" dome pistons, Lunati .600/.600 255/263 @ .050 solid roller, HP xp 950, super victor, Dart Pro 1 215cc head 2.08/1.62, all MSD ign, 700R4 3500stall....a work in progress. Est hp 588 thru chambered mufflers


#3 tjs

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Posted A week ago

The block is not a good HI HP block.Run a 4 bbl and drive it.If you want HP you need to start over.Tom



#4 Franklin68

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Posted A week ago

Thanks for the response! I believe they are the stock heads. The car has a 12 bolt posi but I don't know the gear ratio. The front housing is stamped with GM51 and 12346 is stamped on passanger side back housing. I read about the y9 block and how they weren't the greatest block. Not looking for too much HP though, would be very happy with a strong 350hp. Wondering what I could expect from this engine if I changed the Cam, Manifold, Carb, Heads or if you were in my shoes what would you do to the y9 400 Engine to yield the most performance without breaking the bank or breaking the engine lol? Or is this Engine not worth sinking any money into?? Again I appreciate any help, I am new to the firebird world so any knowledge is appreciated! Thank You!



#5 Terriblehondo

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Posted A week ago

You can get the numbers off of the center exhaust ports of the heads.  That will tell you what you heads you have 


The 557 blocks are not good performance blocks they are light weight castings.  


I would think that you could use the block if it is not to High performance.  Someone else could tell you for sure.

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#6 taman76

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Posted A week ago

HP is great on the track, but for average street driving somewhat over rated.    Don't worry about the HP numbers.  Low RPM torque is your friend.

 

Like said, the 557 block isn't the best high HP block but you can still get quite a bit of street fun out of it.   

 

Like Don said, you need to know your gear ratio and what heads are on the engine before any changes can be made.  


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#7 ponyakr

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Posted A week ago

I wouldn't spend any serious $$ on the 557 short block. But, there are things you can do that will work with the next engine you have. A good Q-jet and intake manifold could be used on any Pontiac 350-455. Since you have 6x-8 heads, I'd recommend a 1972 cast iron intake. But, any '76-79" Pontiac 4-barrel intake will work. 

 

Also, an Edelbrock "Performer Pontiac" intake will work just fine, on a mild to moderate 400. No performance increase over an iron intake. But, will keep carb slightly cooler. Will also accept a square bore carb, in case you don't wanna use a Q-jet.

 

A good Q-jet might give you the performance boost you desire. If not, then, as mentioned, numerically higher gears can make a big difference in acceleration. 3.23 & 3.42 gears were the top options, in late 2nd gens. 

 

If this is still not enuff of a performance increase, there are Ram Air Exhaust manifolds,  with 2 1/2" dual exhaust, with low restriction muffs. A word of warning here: MANY times, one or more of the exhaust manifold bolts will break off, rather than coming out, requiring the heads to be pulled & taken to a shop, to have the the broken bolts removed. So far, all these parts will work with your next engine. 

 

If this still doesn't provide the power you seek, then a cam change might do it. The 6x-8 heads only provide aprox 7.6:1 compression. So, you need a "steep ramp" cam, like the Voodoo series. A 256 will increase low rpm response & torque more, and will work good with a stock converter.

 

http://www.lunatipow...id=1774&gid=287

 

But, a 262 will increase mid range & above, more than the 256. Might work better with a converter which stalls a little more than stock--maybe 2200-2400 stall. These Voodoo cams will require stronger valve springs.

 

http://www.lunatipow...ct.aspx?id=1775

 

If you wanna keep the stock valve springs, then an 068 clone cam is about as big as you can use. These 068 cams were used in lots of high compression 400's, and the lower compression 455HO engines. 

 

http://www.ebay.com/...nRYlsIl&vxp=mtr

 

Another way to increase power is to increase compression, by changing heads, or at least having your 6x-8 heads machined down some, to make the chambers smaller. But, keep in mind that increasing compression and performance, on a well used short block, COULD possibly cause blow-by & power loss.   

 

I reckin it all depends on how much you are willing to spend, for more performance, and exactly how much of an increase will be enuff, for now. :yes


Edited by ponyakr, A week ago.


#8 Franklin68

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Posted A week ago

Thank you ALL for taking time and helping me out with my engine situation!  I have alot to look into and consider over the next few days. Im considering starting with the edelbrock pontiac performance manifold and the edelbrock avs 650 carb cfm or cfm 750 q-jet. Any suggestions on the exact model and size of carb would be apprecited.  Also any reccomendations on new Heads would be appreciated as well.  Thank you for all the suggestions and advice!! Please keep it coming! Thank You!!!! 

Franklin 



#9 ponyakr

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Posted A week ago

"... considering starting with the edelbrock pontiac performance manifold..."

 

 

New Performer intakes are now nearly $300. You can usually find a good used one for less than $200. 

 

http://www.jegs.com/...0/2156/10002/-1

 

http://www.ebay.com/...3FZEVWi&vxp=mtr

 

Can probably find one locally a bit cheaper, since there will be no shipping charges. You can also find some on the Pontiac forums, especially the PY forum. But you'll have to ask. Not many guys will advertise 'em, cause they just don't sell very good, since most street guys either use an iron intake or go to an RPM. But, there are probably lots of guys who have an old Performer laying around their shop somewhere.  

 

 

"...Any suggestions on the exact model and size of carb would be apprecited..."

 

 

SMI 800cfm Street Performance Stage 1 Q-jet. They'll build one, based on your engines' specs, and intended use. 

 

http://www.smicarbur...0/productID/840


Edited by ponyakr, A week ago.





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