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I bought a 1970 GTO with a rebuilt 400. The 400 is 72 YT block with 4x heads on it. Is there a lot of difference between a 69 YT block and a 72 YT block besides original heads? Are the 4x heads any good if I'm looking to get somewhere near 400hp or should I be looking for a different header setup? I really haven't dug too deep into the engine with the car being in storage so that's all the info I have on it.
 

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I bought a 1970 GTO with a rebuilt 400. The 400 is 72 YT block with 4x heads on it. Is there a lot of difference between a 69 YT block and a 72 YT block besides original heads? Are the 4x heads any good if I'm looking to get somewhere near 400hp or should I be looking for a different header setup? I really haven't dug too deep into the engine with the car being in storage so that's all the info I have on it.
It appears you have a 1973 engine if it has the 4X heads. '72 engine would have had 7J2 or 7K3 heads.

The book says its a 230 HP 8.0 compression engine. The 4X heads should have screw-in rocker studs, and have the bigger 2.11" intake valves IF they have the screw-in studs. 1.66" exhaust valves. 98CC chambers which kill compression and thus the 8.0 compression.

Basically, the '69 YT and '73 YT short block would be the same. It's the heads that are different in their CC size. '69 heads were 72CC's and pushed the engine to an advertised 10.75 compression -too high on todays pump gas.

That said, do a little searching through the forum topics on assorted rebuild/cam recommendations. You have a good engine to work with and heads can be used with some work. Screw-in studs and 2.11" intakes are a big plus. Get your compression up between 8.5 -9.0 and select the correct matching components. 400HP may be obtainable, but it may require a good roller $$$$ cam and some good head work on the iron heads. Build for torque, not so much for HP with a Pontiac. So, it also depends on your budget.........but don't think an 8.5-9.0 compression engine can't be made to smoke tires and push you back in the seat with the right parts at a reasonable price.:thumbsup:
 

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I'll have to check the date codes on the block but I was going by the guy who rebuilt it telling me it was from a 72 lemans, not sure if he swapped out the heads or not. I do know the engine has got to be above 300hp than the factory 230hp, it roasts the tires pretty well. I know it had a 750 edelbrock carb, edelbrock intake and an accel HEI, but that's about all I know about the engine.
Thanks for the info, I do want to be able to use pump gas so the closer I get to that 9 compression the better.
 

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I bought a 1970 GTO with a rebuilt 400. The 400 is 72 YT block with 4x heads on it. Is there a lot of difference between a 69 YT block and a 72 YT block besides original heads? Are the 4x heads any good if I'm looking to get somewhere near 400hp or should I be looking for a different header setup? I really haven't dug too deep into the engine with the car being in storage so that's all the info I have on it.
Since you note '72 block, ck the block date by the distributor. A June through Dec '72 cast block with 4X's point to an early '73 400. Nearly all 4X heads did not gain screw in studs till late in the '73 model year run. The exception is the 400 3H heads which I've only examined a few original pair and even early dated ones had factory screw in studs. Have literally been through multiple hundreds of pairs of 4x's in yards, many on shelves, easy to ck out.

To ID which version of 4X heads. need to look at the stamped secondary marking. On the exhaust side of each head, there are two projections, bosses, one will be drilled and tapped. the other is flat but stamped with the secondary code. often hard to read while in a parts car. Little scuff with a wire brush, and one can usually see one of he following small stamped codes:

1H....455, 114 or so cc big chambers, 2.11 intake, 1.66 ex valves
.......basically door stop heads unless building a budget turbo 455 build

3H....400 4bbl manual trans, 98-100 cc chambers, 2.11x1.66, screw in studs
........tough to find version, much easier to duplicate out of 4H's or 7H's

4H....400 2bbl, 98-100 cc chambers, 1.92 x 1.66
........very common head core, most 400 LeMans wagons had these

7H....400 4bbl, 98-100 cc chambers, 2.11 x 1.66 valves
........have picked up many 4X 7H's over last 20 years, quite a few as dated pairs
........to closely match dates on '73 & 74 original 455's in customers T/A's and ........GrandAm's

Last, to get near 400 HP out of a 4x headed 400, looking at some serious coin. Most likely going to be using them in some form of mild ported 400 based stroker build to get that level.

If dead set on using 4X's, def need to have them magged as 4X's don't have the best rep. National Pontiac engine builder I provided many many 400 cores to through out the 90's and into the 00's wasn't much of a fan of he 4X's, saw many that were cracked. Induction hardening of he ex valve seat was relatively new and the later 5C-9's, and 6X-4's were much more to his likening.
 

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Since you note '72 block, ck the block date by the distributor. A June through Dec '72 cast block with 4X's point to an early '73 400. Nearly all 4X heads did not gain screw in studs till late in the '73 model year run. The exception is the 400 3H heads which I've only examined a few original pair and even early dated ones had factory screw in studs. Have literally been through multiple hundreds of pairs of 4x's in yards, many on shelves, easy to ck out.

To ID which version of 4X heads. need to look at the stamped secondary marking. On the exhaust side of each head, there are two projections, bosses, one will be drilled and tapped. the other is flat but stamped with the secondary code. often hard to read while in a parts car. Little scuff with a wire brush, and one can usually see one of he following small stamped codes:

1H....455, 114 or so cc big chambers, 2.11 intake, 1.66 ex valves
.......basically door stop heads unless building a budget turbo 455 build

3H....400 4bbl manual trans, 98-100 cc chambers, 2.11x1.66, screw in studs
........tough to find version, much easier to duplicate out of 4H's or 7H's

4H....400 2bbl, 98-100 cc chambers, 1.92 x 1.66
........very common head core, most 400 LeMans wagons had these

7H....400 4bbl, 98-100 cc chambers, 2.11 x 1.66 valves
........have picked up many 4X 7H's over last 20 years, quite a few as dated pairs
........to closely match dates on '73 & 74 original 455's in customers T/A's and ........GrandAm's

Last, to get near 400 HP out of a 4x headed 400, looking at some serious coin. Most likely going to be using them in some form of mild ported 400 based stroker build to get that level.

If dead set on using 4X's, def need to have them magged as 4X's don't have the best rep. National Pontiac engine builder I provided many many 400 cores to through out the 90's and into the 00's wasn't much of a fan of he 4X's, saw many that were cracked. Induction hardening of he ex valve seat was relatively new and the later 5C-9's, and 6X-4's were much more to his likening.

I'm definitely not set on keeping the 4x's, I would prefer if I could find another Pontiac head for the engine but not sure which one so I can still use pump gas. Someone told me #64 would be the best but when I looked that up it was for a 455 and I have the 400.
 

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70 casting 64's are tough find and expensive as cores, not the best choice. They are a restoration piece. Built a set up and ran them on a 70 YZ 400 in my '80 T/A nearly 30 years ago. valves were hard to find for them back then, as they are an in between length. Ended up having my machinist do some jockeying with spring heights and slightly longer sealed power 67-70 2.11-1.77's. Today, would look at what Faria has to offer for new valves..Last few nice core pairs of 64's that I have sold went for $800 a pair. Many fellows have sold them for even more. Time one has a pair gone through with new 1 piece stainless valves, new springs, new guides, comp valve job, going to be in at another 600+, that's if you have a reasonably priced machinist who knows Pontiacs. Most of the self proclaimed Pontiac engine builder guru's will charge for more than that, you will almost be in the price of a new pair of alum heads.

Better choice to get near same C/R and save some bucks is buy a good pair of the following much cheaper core heads and have them professionally gone through with new 1 piece stainless valves, correct springs, guides, good valve job,

6x-4's, 5C-4's, 5C-7's, all 94-96 cc as cores:
...........all have screw in studs. 2.11 x 1.66's. Milled .040 to .060 will raise C/R into low to mid ...........9's on .030 or .040 400. That is the recipe, has been since the early 80's. Without ...........porting but with killer valve job and wproper cam selection, make 370-380 gross hp.
...........Street port job and upgrade to 1.77 exhaust, can make a really good street/strip head. ...........Occasionally can find them with all work done, discounted as racers are stepping up.

46's.....the late '73-73 variety w screw in studs. 86-87 cc chambers, 1.96 x 1.66 valves

4C-5's, seldom seen, cc'ed at 87cc stock in two chambers. 1.96 x 1.66 One pair I have came off a very late 73 built 350 4spd LeMans GT, I parted. As '73 heads have stock screw in studs.Have these on shelf for future 301 turbo block hybrid deal.

'70 model "15" casting. near 87 cc chambers. used to chunk these off '70 YH455's in the trunks ...........in the pick-n-pulls and crusher yards and yank a pair of 6X's. eventually realized, with ............new 2.11x1.77's & screw in studs installed they can make a good street head. Have .............sold last half dozen pairs fairly quickly, wish had more. work great with '70 & earlier ............alt/PS brackets. With 71 up brackets will need to flip long alt bolt around

Hope this helps, other than the 64's and the 6x-4's, most of the above heads can be picked up relatively cheaply.
 

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The casting date codes on your engine may indeed show up as a 1972 engine, but later year 1972 engines would go into 1973 cars due to the time frames when new models come out and hit the dealership.

Any iron head you select needs to be magnafluxed for cracks, as do other major components like your block, crank, rods (if you use them), etc.. Heads can crack around the valve seat and will still run fine, but are not something you want to use.

I just had my 98CC 7K3 heads rebuilt for my 455CI build. My compression with the components I have selected will be 9.0 -right where I wanted. Vatted & magnafluxed them first - $40. I did my own porting, bowl & chamber work, and polishing on them. Then I gave them to my machinist. Everything new. Ferrea SS valves, valve springs, retainers, keepers, bronze guides, teflon seals, re-surfaced, 3 angle valve job, & assembled. It set me back $670.00 for the pair, not each, but a pair (does not include the ARP rocker studs and stamped steel rocker arms). I can't justify a pair of aluminum heads for $2,200-$2,400 as its not in my budget and my iron heads will make the torque & power I am looking for.

Your engine, if never touched, has 230HP, but remember that HP ratings were changed in 1971 and do not have the bigger advertised HP of the previous years. That said, it may indeed feel like "300 HP" and might be IF we used the earlier HP ratings. I had a '72 250 HP 400CI in a '70 Judge (later transplanted into my '67 GTO) and it was a real pulling and tire burning engine. I just had another '72 250HP 400CI in my '68 Lemans with its low 8.2 (and I think a little less) with a Comp Cam to match the low compression and it was a screamer and ran on 87 octane. I was not disappointed. Now building the 455CI for it.

Again, don't be sucked into HP ratings. Don't get hung up on head casting numbers and which is best. Select a chamber CC that fits your build to get you nearer to 9.0 compression for iron heads. It does not take a lot to get a Pontiac head to flow well enough for a good street build and it saves you money over the aluminum heads. Screw-in studs are best because you don't have to have a machine shop do this conversion, so it saves you money and keeps your costs down, but it can be done.:thumbsup:

Ya just gotta have a plan.:biggrin2:
 

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Discussion Starter #8
The casting date codes on your engine may indeed show up as a 1972 engine, but later year 1972 engines would go into 1973 cars due to the time frames when new models come out and hit the dealership.

Any iron head you select needs to be magnafluxed for cracks, as do other major components like your block, crank, rods (if you use them), etc.. Heads can crack around the valve seat and will still run fine, but are not something you want to use.

I just had my 98CC 7K3 heads rebuilt for my 455CI build. My compression with the components I have selected will be 9.0 -right where I wanted. Vatted & magnafluxed them first - $40. I did my own porting, bowl & chamber work, and polishing on them. Then I gave them to my machinist. Everything new. Ferrea SS valves, valve springs, retainers, keepers, bronze guides, teflon seals, re-surfaced, 3 angle valve job, & assembled. It set me back $670.00 for the pair, not each, but a pair (does not include the ARP rocker studs and stamped steel rocker arms). I can't justify a pair of aluminum heads for $2,200-$2,400 as its not in my budget and my iron heads will make the torque & power I am looking for.

Your engine, if never touched, has 230HP, but remember that HP ratings were changed in 1971 and do not have the bigger advertised HP of the previous years. That said, it may indeed feel like "300 HP" and might be IF we used the earlier HP ratings. I had a '72 250 HP 400CI in a '70 Judge (later transplanted into my '67 GTO) and it was a real pulling and tire burning engine. I just had another '72 250HP 400CI in my '68 Lemans with its low 8.2 (and I think a little less) with a Comp Cam to match the low compression and it was a screamer and ran on 87 octane. I was not disappointed. Now building the 455CI for it.

Again, don't be sucked into HP ratings. Don't get hung up on head casting numbers and which is best. Select a chamber CC that fits your build to get you nearer to 9.0 compression for iron heads. It does not take a lot to get a Pontiac head to flow well enough for a good street build and it saves you money over the aluminum heads. Screw-in studs are best because you don't have to have a machine shop do this conversion, so it saves you money and keeps your costs down, but it can be done.:thumbsup:

Ya just gotta have a plan.:biggrin2:
Thanks Jim, that's all I am working on right now is a plan. The work I plan to do won't be started until next winter when I get my 3 car garage for it. What kind of ballpark price am I looking at to have someone port iron heads?
 

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Always start with the date code by the distributor, and the block casting number (down low next to the trans flange, behind the passenger side head). Pontiac sometimes used the same 2-character engine code (YT, YS, etc) in different years to mean different things - sometimes VERY different engines. So you've got to nail down the model year first in order to know how to correctly interpret the other codes.

For a reliable pump-gas friendly (93 octane) cast-iron head engine shoot for a compression ratio between 9:1 and 9.5:1 (or 9.3). Yes, some people have gotten away with "pushing" that envelope some but really, when you look at the difference in power you get by doing that (usually less than 5-10 hp), my opinion is that the reward isn't worth the risk. YMMV

The challenge in using the earlier, smaller chamber heads is in getting the compression ratio down into the safe range without completely destroying the "quench" characteristics.

Bear
 

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Thanks Jim, that's all I am working on right now is a plan. The work I plan to do won't be started until next winter when I get my 3 car garage for it. What kind of ballpark price am I looking at to have someone port iron heads?
I don't know what it would cost to have heads ported/polished, but it is not inexpensive. Most engine building machine shops usually can do this. The assorted Pontiac engine builders found on the internet all do this. But.......

Why not do it yourself. This is half the fun. Not very difficult to do a basic intake gasket port match and smooth out the intake/exhaust runners. Now if you want to open up the bowls or do some combustion chamber work, that is a little more work and skill and you don't want to mess up.

Here is a Youtube video on the basic job you can do. https://www.youtube.com/watch?v=LdSgdX9mprE

You can get a die grinder from Home Depot or Lowe's or any other tool supplier. I use a carbide cutter to remove metal and these can be purchased online or at your local welding supply store or tool store. The sanding rolls can actually be bought in kit form for porting/polishing heads. I bought a kit 30 years ago and still use it. You can usually find sanding rolls locally. Here is a good kit to use that has all the extensions for the sanding rolls. Engine Porting Kit

You can also get the carbide cutters from Eastwood, but to be honest, for a nice basic port/polish you really don't need them. If you get any, it would be to remove any metal at the port openings to match the gasket, but you can most likely use a sanding roll to do this. Now if you port match your heads to the Ram Air IV gaskets, then you would need the cutter as you are raising the roof a fair amount and then blending it back about 1". I did this on my heads. I also used a "snap gauge" to equalize all my port openings by grinding on the pushrod side of the port -just enough to equalize and not break through and then blended everything.

You can do some heavy head work, but it is not for the faint of heart if you have never done this or don't want to chance screwing up and damaging the heads -like in the bowl area. I never did this before and tried it on my heads -very carefully. I'm no expert, but I think they came out good. My machinist was impressed.

A very good video, which I feel is more aimed at the experienced head porting and polishing guy, that shows you some heavy work done on a Pontiac head is by Pete McCarthy. Click on his highlighted name here - Pete McCarthy I have this DVD and it is good info on head flow in general, plus head modifications. He also has his book that every Pontiac nut should have in that it gives you head numbers, block numbers, year by year Pontiac engine info, rod/intake /exhaust manifold info and differences and tons of pictures. This is where I get a lot of my info when someone is looking for it.....like your engine ID for example.

A very good book you want to have in your Pontiac collection is the Pontiac Engine Design & Blueprinting by H-O Racing Specialties sold through Ames and can be found in their on-line catalog. Good drawings & references on port designs, head work, and a good Pontiac 3 angle valve job PLUS a ton of other info on the Pontiac engine.

Jim Hand has a book out that most will recommend and is top notch in modifying the heads, cam selection, intakes, etc., but it is no longer in print at this time and getting a copy used seems to be more than the price of an ounce of gold. Hopefully it will be reprinted at some point.

So, do a little homework, do a lot of reading and watch some of the assorted Youtube clips, and get an idea of what you are getting into and if you feel comfortable doing the work yourself. I think it is easy enough to do the basic port matching and polishing, and then add a good set of the Ferrea SS valves, and a good "Pontiac" 3 angle valve job to get a decent street head that will add to your engines performance short of going the racing route and wanting BIG horsepower numbers.:thumbsup:
 

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of the three books Jim mentioned, if you're going to only buy one, that had a lot of focus on Pontiac engine build, it would be Jim Hands. Have no problem with Pete McCarthy's Pontiac Performance 1955-1979. it is an informative book, that I used to buy 20 at a time & stock and sell, but it is more geared to the history of the traditional Pontiac V8 engine and ID codes.

Jim Hands book is more complete in speaking about head porting. FWiW, there is an art to cast iron head porting. It's one thing to take a pair of big valve Dport heads and get them to flow 225-235 cfm (at .500 lift on the intake side @ 28" pressure drop). it is something else to port a pair and get a great I/E flow ratio, and on heads like the 7k3's, get into the mid 260's on the intake side. Have such a pair of ported 7k3's along with a pair of race ported 4X's and have paid to have many '71 197's flowed as well. Have ran across numerous pairs that the person doing the head porting, w/o a lot of experience, and w/o the aid of a relative cheap Super Flow 110 flow bench, really messed up the I/E ratio. A really good port job will increase airflow at critical mid lift numbers and have a preferable I/E ratio.
 

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" Have such a pair of ported 7k3's along with a pair of race ported 4X's and have paid to have many '71 197's flowed as well. Have ran across numerous pairs that the person doing the head porting, w/o a lot of experience, and w/o the aid of a relative cheap Super Flow 110 flow bench, really messed up the I/E ratio. A really good port job will increase airflow at critical mid lift numbers and have a preferable I/E ratio."




Key word here is "race ported" heads where a tenth of a second means win or lose and heavy metal grinding/shaping to accommodate valve lifts well over .500" as used by racers wanting the 197 round port 455 HO heads -so I agree if we are talking race heads. In stock form, both the 4X and 197 HO head are not that far in flow differences under .500" lift, which is about 6% http://www.wallaceracing.com/ultimateflow.htm and not something you will feel in the seat of your pants. It is the potential they possess in highly modified form that make them desirable for class drag racing.

For a street build, its not that critical and you are not doing any modifications that will mess up the heads. The basic port and polish is not trying to contour or re-shape any of the factory castings. Instead, you are simply cleaning up and equalizing the intake entry at the gaskets and smooth and blend any irregularities in the intake/exhaust passages for some improved flow. Add a good 3 angle valve job and the better flowing Ferrea valves and you have increased flow above the high dollar stock 197 HO head.:smile2:

The exhaust side of the Pontiac factory heads were problematic in the I/E ratio because of the tight turn the exhaust port takes and is why Pontiac used the split pattern cam by adding additional duration and sometimes more lift on the exhaust valve to compensate. When the I/E balance numbers are made optimal, ie highly modified/high dollar race heads through the use of flow bench testing, you can take advantage of the aftermarket camshafts having the same cam duration numbers. So the imbalance was compensated for by the factory, and aftermarket cams do the same with both duration and lift and thus so many choices -which I assume could be better nailed down through actual flow test numbers to better match your heads. This is also why a much improved exhaust system really helps a Pontiac engine due to the design of the exhaust port.:thumbsup:

Now if I were bent on building a max HP engine for the street where intake flow numbers do dictate HP levels, the factory iron heads would probably fall short for such a build unless I invested high dollars into a set of iron heads to maximize their flow -and that might not be enough. I would simply upgrade to a high flowing CFM aluminum head of better design which is also capable of handling the larger lifts of a matching roller cam.

Just my take on it.:yesnod:
 

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70 casting 64's are tough find and expensive as cores, not the best choice. They are a restoration piece. Built a set up and ran them on a 70 YZ 400 in my '80 T/A nearly 30 years ago. valves were hard to find for them back then, as they are an in between length. Ended up having my machinist do some jockeying with spring heights and slightly longer sealed power 67-70 2.11-1.77's. Today, would look at what Faria has to offer for new valves..Last few nice core pairs of 64's that I have sold went for $800 a pair. Many fellows have sold them for even more. Time one has a pair gone through with new 1 piece stainless valves, new springs, new guides, comp valve job, going to be in at another 600+, that's if you have a reasonably priced machinist who knows Pontiacs. Most of the self proclaimed Pontiac engine builder guru's will charge for more than that, you will almost be in the price of a new pair of alum heads.

Better choice to get near same C/R and save some bucks is buy a good pair of the following much cheaper core heads and have them professionally gone through with new 1 piece stainless valves, correct springs, guides, good valve job,

6x-4's, 5C-4's, 5C-7's, all 94-96 cc as cores:
...........all have screw in studs. 2.11 x 1.66's. Milled .040 to .060 will raise C/R into low to mid ...........9's on .030 or .040 400. That is the recipe, has been since the early 80's. Without ...........porting but with killer valve job and wproper cam selection, make 370-380 gross hp.
...........Street port job and upgrade to 1.77 exhaust, can make a really good street/strip head. ...........Occasionally can find them with all work done, discounted as racers are stepping up.

46's.....the late '73-73 variety w screw in studs. 86-87 cc chambers, 1.96 x 1.66 valves

4C-5's, seldom seen, cc'ed at 87cc stock in two chambers. 1.96 x 1.66 One pair I have came off a very late 73 built 350 4spd LeMans GT, I parted. As '73 heads have stock screw in studs.Have these on shelf for future 301 turbo block hybrid deal.

'70 model "15" casting. near 87 cc chambers. used to chunk these off '70 YH455's in the trunks ...........in the pick-n-pulls and crusher yards and yank a pair of 6X's. eventually realized, with ............new 2.11x1.77's & screw in studs installed they can make a good street head. Have .............sold last half dozen pairs fairly quickly, wish had more. work great with '70 & earlier ............alt/PS brackets. With 71 up brackets will need to flip long alt bolt around

Hope this helps, other than the 64's and the 6x-4's, most of the above heads can be picked up relatively cheaply.
Hello!
My name is William Murtaugh. My father and I are rebuilding our 1979 firebirds 400. From the block code and date code we have discovered that it is a 1972 400 and has the 7J2 heads on it that do not have the material to drill and tap end holes to better seal up headers with. We bought some 46 heads for next to nothing that have the valves and springs still. The reason we have taken the engine and trans out is to replace the cam shaft and do a full rebuild on both. The cam had a dead lifter and that wore out the lobe that drove it so we get to replace it with a performance 268 cam from Butler. Our concern is that these 46 heads have 72 cc combustion chambers and the 7J2 heads have 96cc champers so of course this is going to kick our compression ratio up from factory and we are a little worried it will increase it to far for premium pump gas as that is what we intend to use. A few tricks to get the ratio down would be pistons with larger pockets for the valves, someone said that there are thicker head gaskets that could also make up the difference. The 46 heads are off of a 428 and have the small valves I believe and the material to drill and tap end holes for our new headers. We bought the 46 heads for less than what paid for the L brackets that mount up to the side our 7J2 heads so we sent them back... just getting the headers on the engine with those L bracket studs while it was on the stand was a nightmare. Any and all insight to this would be much appreciated. This will be my first full rebuild project and I would very much so like to get it right. I suppose using the 7J2 heads would not bother us to much. Our goal is to have a running Trans Am that when you put your foot down there is no question that it has more than factory power. Nothing crazy but a rough idle and snappy throttle response is desired. We have an 800cfm Edelbrock carburetor as well as a lifted aluminum Edelbrock intake. The 268 cam kit we are getting comes with new springs and lifters as well as retainers a timing chain and both sprockets. Some one told us we would be pushing nearly 10.36:1 with the 46 heads and I am hoping we can get that down to a ratio that we can run pump gas with. Again thank you to anyone that can chime in and give us any advice. Hope you have a great day!
 

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Hello!
My name is William Murtaugh. My father and I are rebuilding our 1979 firebirds 400. From the block code and date code we have discovered that it is a 1972 400 and has the 7J2 heads on it that do not have the material to drill and tap end holes to better seal up headers with. We bought some 46 heads for next to nothing that have the valves and springs still. The reason we have taken the engine and trans out is to replace the cam shaft and do a full rebuild on both. The cam had a dead lifter and that wore out the lobe that drove it so we get to replace it with a performance 268 cam from Butler. Our concern is that these 46 heads have 72 cc combustion chambers and the 7J2 heads have 96cc champers so of course this is going to kick our compression ratio up from factory and we are a little worried it will increase it to far for premium pump gas as that is what we intend to use. A few tricks to get the ratio down would be pistons with larger pockets for the valves, someone said that there are thicker head gaskets that could also make up the difference. The 46 heads are off of a 428 and have the small valves I believe and the material to drill and tap end holes for our new headers. We bought the 46 heads for less than what paid for the L brackets that mount up to the side our 7J2 heads so we sent them back... just getting the headers on the engine with those L bracket studs while it was on the stand was a nightmare. Any and all insight to this would be much appreciated. This will be my first full rebuild project and I would very much so like to get it right. I suppose using the 7J2 heads would not bother us to much. Our goal is to have a running Trans Am that when you put your foot down there is no question that it has more than factory power. Nothing crazy but a rough idle and snappy throttle response is desired. We have an 800cfm Edelbrock carburetor as well as a lifted aluminum Edelbrock intake. The 268 cam kit we are getting comes with new springs and lifters as well as retainers a timing chain and both sprockets. Some one told us we would be pushing nearly 10.36:1 with the 46 heads and I am hoping we can get that down to a ratio that we can run pump gas with. Again thank you to anyone that can chime in and give us any advice. Hope you have a great day!
All you can at this point with the 46 heads is to get a set of dished pistons having the needed CC's to get the compression nearer 9.0 for the street, but higher compression will work if you are willing to use an octane booster or race gas blend IF needed.

The Comp Cams may pose a problem with its 110 LSA. These work better with lower than 9.0 compression as they build additional cylinder pressures - so this can act like increasing compression and you may be back to either using a premium pump gas, octane booster, or race gas blend. An LSA of 112, or 114 may be a better choice. So I would consult Butler on the dished pistons and if the 268 cam will now be an OK choice with the higher compression of 9.0 or so, if you go that route.

With regards to the missing exhaust bolt on those heads, the solution is to use the RA cast iron exhaust manifolds IF they can be used for your body style, or you may be able to drill and tap for a stud.

I found a photo of this done up. Caption said, " fine thread tapped and then you run grade 8 studs not bolts."
 

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