[JedWele]

I have a 77 Trans am 400 4 speed with 6 x-4 heads, It is all stock except for headers. I really like the low end on it, but it runs out of breath shortly after 3500 rpm I was thinking of throwing in a bigger cam or seeing if 1.65 will give me a little boost keeping the stock cam. I know a lot of times you have to enlongate the pushrod holes with the higher ratio. But I have been told that with the mild stock cam and the 6x heads I shouldn't have too. I was wondering if anyone has got away without having to pull the heads of and elongating the pushrod holes with a stock cam and this set up? Thanks guys!

[JedWele]

I have a 77 Trans am 400 4 speed with 6 x-4 heads, It is all stock except for headers. I really like the low end on it, but it runs out of breath shortly after 3500 rpm I was thinking of throwing in a bigger cam or seeing if 1.65 will give me a little boost keeping the stock cam. I know a lot of times you have to enlongate the pushrod holes with the higher ratio. But I have been told that with the mild stock cam and the 6x heads I shouldn't have too. I was wondering if anyone has got away without having to pull the heads of and elongating the pushrod holes with a stock cam and this set up? Thanks guys!

[Ollie]

Dosent matter what cam you run. You have to elongate the push rod hole when you use 1.65 rockers

Its ok to giggle and snicker, Dont laugh and point

[b-man]

You can usually get away with running the 1.65 rockers on a stock cam without pushrod clearance issues. Some have reported slight interference, while others (myself included, stock 068 cam and '71 #66 455 heads) have used stock cams and 1.65s without having to do any pushrod clearancing on the heads.

Just be sure to look for the pushrods rubbing the heads when you install the 1.65s.

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Some say the glass is half full, others say the glass is half empty...I say 'Are you gonna drink that?'
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[JedWele]

Thanks for the responses guys! I guess I will just have to order some and try it out to know for sure.

[JedWele]

Oh , and B-Man when you changed to the 1.65 rockers did you notice much performance gain?

[Will]

I *really* think a different cam would be a much more productive use of your hard earned money. Adding the 1.65 rockers to your existing cam will only add a couple degrees of effective duration and about 10% lift at the valve. Your engine is running out of breath at 3500 because your cam has too little duration. Adding a couple of degrees of duration is not going to get the job done and the extra lift isn't going to amount to much either.

I am currently running a Comp 270 magnum cam (because it was in a core motor I bought and in good condition) in my '73 4-speed 'bird, which is a stock '71 400 bottom end with 6X-4 heads that have been milled .030". Even with stock exhaust manifolds this cam runs quite well in this low compression engine and there's power to 5000 RPM. I know installing headers and a good exhaust would also help a lot. The idle's a bit lumpy but plenty of vacuum and I do have 3.73 gears, not sure what you're working with.

Not that I'm recommending that cam (like I said, it was an unexpected bonus in a core motor), just an example that a significantly larger than stock cam can be used even with low compression.

I don't know what gears you're running or whether you're prepared to change valvesprings, but I'd take a good, hard look at the following cams: Comp XE262 or Crower 60918 for more low end and midrange, or Comp XE268 for more midrange and top end at the expense of some bottom end. Any of these cams may be pushing stock valvesprings. Crower makes a set of springs that will swap right in in place of your stock springs but I can't remember the part number... If someone doesn't come up with it, e-mail me and I'll find it.


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'72 Formula 400 Lucerne Blue, Blue Deluxe interior - My first car!
'73 Firebird 400/4-speed Black on Black, mix & match.

[JedWele]

Yea I have been looking at the comp XE 268 there is a package that has matching lifters and valve springs. But before I started tearing my motor down I was curious about the higher ratio rockers as quick performance gain to hold me over.

[PONTIAC DUDE]

Stock cam and springs.

Check for Coil Bind and ..........also the increase in lift and slight duration is sometimes lost or offset in the extra load it takes to open the valve with the additional spring pressure and friction.

I doubt your will pick up any noticable duration increase. The milder the cam the less duration increase you will see with the softer ramps. The more agressive the cam the greater the duration increase up the ramp with higher ratios.

************************************************** ***************************

Build it fast, build it right, build a Pontiac.


http://PontiacDude.cc

[beertracker]

When elongating pushrod holes for 1.6 rockers how much material should I remove (top side of head) to get the hole oval: 1/16", 1/18"?
How deep should I run the cutter down the hole from top side of head: 2"? I know I cut toward the rocker stud.

[70 bird]

Back from the dead.......19yo. thread.

[beertracker]

No reason to post if you don't know the answer or don't want to help. Is it against forum rules to bring back a old post? The information is still relevant today as was earlier. So much for searching for info on this forum so I don't have to start a new post as the info has already been covered. I will f ind another group to post this question in.

[400 Lemans]

Go down to post 8 for HO instructions.https://forums.maxperformanceinc.com...d.php?t=743726

[MatthewKlein]

Originally Posted by 400 Lemans

Go down to post 8 for HO instructions.https://forums.maxperformanceinc.com...d.php?t=743726

Thank you. I've been curious about this myself.

[Skip Fix]

My original 6x-8 heads with stamped 1.65s and a mild 228/228 Cam Dynamics cam did OK. My 6X-4s on the 81 an a Summit 2801 did not even with some grinding I did on the upper 1/2.

[MarkS57]

Might not help much but Paul Spotts (Spotts Performance) used to sell a nice little tool that was made for this. It would mount to the rocker stud and provided a guide hole for a clearancing drill bit. I don't see it on his site anymore. Maybe someone here has one to lend out?

[PONTIAC LARRY]

Originally Posted by JedWele

I have a 77 Trans am 400 4 speed with 6 x-4 heads, It is all stock except for headers. I really like the low end on it, but it runs out of breath shortly after 3500 rpm I was thinking of throwing in a bigger cam or seeing if 1.65 will give me a little boost keeping the stock cam. I know a lot of times you have to enlongate the pushrod holes with the higher ratio. But I have been told that with the mild stock cam and the 6x heads I shouldn't have too. I was wondering if anyone has got away without having to pull the heads of and elongating the pushrod holes with a stock cam and this set up? Thanks guys!

something else is wrong, that thing should easily pull to 5000 rpm with stock W72 camshaft and real dual exhaust but since its been 19 years ........ LOL

[ta man]

Originally Posted by PONTIAC LARRY

something else is wrong, that thing should easily pull to 5000 rpm with stock W72 camshaft and real dual exhaust but since its been 19 years ........ LOL

My thoughts too..19 years ago...at that time I was building my first 455..and hoping to go to the dragstrip...