455.......rebuild info

....I just wanted to get some opinions on a build I am doing.......have a block decked and punched 30 over......with 6x heads number 8....I want to go to 1.77 exhaust valves...1 piece stainless.....I am thinking about running a comp cams xe 274 h....cam.....should I go with roller tip rockers with this set up.....and is this a good cam or should I go with another thanks  

Not worth the effort and expense to add 1.77 for a mild street 455. As for the cam, what kind of car? What trans, converter, gears and other mods are you considering? Roller tips are fine, full rollers are better of course, depends on the rest of the build.
Steve  
A little help... 'cause we don't all have to learn the hard way!

Going into a 78 Trans am......automatic and can't remember my gears I think there close too 3.73.....2000 torque converter with ram manifolds......  

Hello

I see you are a new member by your join date so welcome to the site.

Answers to the following questions would be helpful info for members to know to best answer your questions.

What is your intended use of the vehicle ie mild street, street/strip, all out tire burner or auto cross etc.

How would you like it to idle ie, mild lope, noticeable moderate lope, aggressive lope?

Have you considered pistons, rods and intake, cylinder head porting or aluminum heads etc, or do you want suggestions for those items also?

If you want suggestions for the items above and cost is a factor, what is your max budget for all items total including exhaust?

Do you have power brakes and if so do you want to maintain your existing level of brake performance without needing to add an additional vacuum canister to supplement the potential loss of low speed brake performance caused by some of the low vacuum numbers created by some of the “larger” cams?

Do plan to do mostly fwy and part street driving or mostly street with slower fwy driving?

Without additional info I personally can only offer you the following info on the cam you are interested in based upon my own personal experience with it in various builds I have done. Others opinions or experiences may be different.

CAM - The xe274h comp cam in an engine of around 400 ci with around 9.0 static compression will have a moderate idle with just enough vacuum to keep the power brakes working decently. It is a very popular “style’ of cam and duration. Lunati voodoo is another popular cam. It will run  very strong with this cam but you should use high rpm style lifters.

TORQUE CONVERTER - Comp recommends one with a mild "stall". I use a 2200 with this cam anything higher in your case might be a bit too high.  

Street and maybe a little strip.....have stock crank forged rods with arp bolts forged flat top pistons......block 0 decked heads 6x....mild porting......I need suggestions on the heads and valve train....running stock brakes in a 78 Trans am so I am kind of worried vacuum....I have no intake yet but have the stock carb  I want to run re-jetted.....I just want a aggressive lope but I also need it to idle ok......thanks for your help  

Hello ta78

Thanks for the info, it helps a lot.

Nice stuff you have there. .

Just curious, what type of head info are you looking for? You said you were going to port the heads so I would think that as long as you have screw in studs that's all you need. I would run stock valves on a build like this and simply back cut them to improve flow and run new springs designed for your cam. I personally would not run hardened seats. The they will last longer than stock but stock seats should run 100k miles with mild springs with unleadd gas. I have personally seen this on several occasions on these older motors. I would consider seats only if you knew a shop with a good reputation for doing them so they don't fall out. This has also happened to me before more than once.

CAM SIZE VS VACUUM - My experience is mainly with comp cams but another brand with similar specs will act similar. After reading your new post I would still say you made a great choice for you parameters and it will act as I mentioned above. A lunati 10510703 would be my second choice it should have slightly more vacuum and a decent lope.

INTAKE - Everyone seems to run the Edelbrock performer RPM. I would go with that also.

CARB - I would go up 3 sizes on the main and start there or start from stock and if you have flat spots on acceleration jet up untill they no longer improve. If it's still flat immediately off idle after increasing jet sizes to the optimum for acceleration from around 30 mph then respring lighter however you will probably have to drill at this point. You may need a slightly lighter jet needle spring and may need to drill out the idle circuit air bleeds one size larger with a "number" drill. This is all easy stuff. It shoUld work great when it's done however I personally would put a square bore mechanical secondary holley on it.  

Does anyone use the Summit 2801 or 2802 camshafts, for the price I think they run as well as the 274XE.  I had one in my 71 gto, then when I rebuilt the motor I went to the 274 XE. I didn't notice much of a difference, but I also went from a #15 head with 87cc's to the original 96 heads with 96 cc's. It my cruiser car with 3.31 gears and a manual 3 speed.  It will roast the tires, but If you want to save a few bucks I think the summit kit is the way to go.  I built a 67 400 motor, with 48 heads, that I ported by hand a little, and got rid of the sharp edges in the combustion chambers, had my machinist open up the area under that valves, but nothing major, had a tight 10" ATI converter and 4.10 gears, that car ripped, for a simple combo it dipped into the 11's on a cold night.  But But But...I had to mix 116 fuel with it at the track and it pinged like crazy even on 93 octane.  it was .040 over with a flat top keith black pistons, zero deck.  I sold the car to a buddy of mine, still runs strong, he still complains about the pinging...and has to run octane boost in it.  Im thinking the summit cam may help the ping with the 114 lobe centers.  We are gonna try it in his 69 firebird, but wish us luck, the rebuilt block he bought has domes pistons, and the choice of heads we have to use will have 96cc's or 87 cc's....  

70 bird the 6x head are 76 to 79 and will have hardened seats.

i would put the 1.77s in if your having the heads rebuilt and need valves.  
76 455/4spd TRANS AM
69 GRAND PRIX 406/5SPD

Hello ta78

Rowsley's comment prompted me re-read my post. In hopes of eliminating any confusion it may cause I would reword the first part of it to read, "I personally would not arbitrarily replace any valve seats [ie with hardened ones] unless the existing ones were beyond repair." I would also correct "The they" to simply read "They".


"I personally would not run hardened seats. The they will last longer than stock but stock seats should run 100k miles with mild springs with unleaded gas. I have personally seen this on several occasions on these older motors. I would consider seats only if you knew a shop with a good reputation for doing them so they don't fall out. This has also happened to me before more than once."


"70 bird the 6x head are 76 to 79 and will have hardened seats."


Rowsley, thanks for mentioning that. I actually did know that post 73 [or so] most if not all mfg's went to flame hardened sets due to the unleaded gas requirements however I might not have so I appreciate your info just the same. Better to be sure than assume. Your comment was still beneficial because I did not like the vagueness in my comment so I corrected it.

Thanks  

70 bird i wasn't sure you new what year the 6x's were made.  
76 455/4spd TRANS AM
69 GRAND PRIX 406/5SPD

Hello Rowsley

As I said no problem I am grateful for all info, never hesitate or fear to offer any info or correct any errors I make. As long as it's done in a "friendly" constructive way like your always seems to do it, I'm quite happy about it. I can assure you, and as you can see from some of my posts, I certainly still have a lot to learn.


Thanks