[rborders]

I bought a 79 with a .030 + 400 (406) SBC in it.
I can tell by the idle that it has a mild cam in it but I have no idea about the specs.
By the numbers on the heads I can tell the are from a 400 SBC.
I have no idea what kind of pistons are installed. (Flat top , Domed )

My question is this.

If I want to change to a cam with a more lift how do I make sure it's not going to be too much and cause piston to valve interference ?

 

[steelybill]

I have a 400 with flat top pistons. They have valve reliefs/notches in the tops of the pistons. Mine has around .490 lift. Getting past that can be a problem with the height of the valve guides, when the spring retainers can collide with the tops of the guides. The tops of the guides can be trimmed a bit shorter if the heads are off etc. If you go beyond 280 degrees duration on a cam, the vacuum will fall off, and may be a problem for power brakes and heater/AC controls etc. Also higher duration may need a torque converter with a higher stall speed, because the cam may not have much low RPM torque & power.
If the heads on there are stock type, they are 76 CC combustion chambers. Dished stock type pistons wont work well with a cam of any long duration, and may even loose some power. It's sort of having a combination of parts that will work together.
Finding what type of pistons you have seems like a first step....

 

[JJLT1]

i'd find a hot rod machine shop,,they can build you a cam card in about a hour and check the clearance,,
and probly have a bore scope to look at the pistons,,that wont tell you everything but its way better..

as far as more lift on stock heads,, it probly wont help alot unless there ported..
you would get more change from the duration on the cam..thats what Bill is talking about..

you really need to know where your at,,to get to where you want to be..:texas:

 

[steelybill]

I was going to mention a boroscope, but was not sure if engine shops use them. It's a common tool in aviation. Sure is handy though....

 

[~JM~]

Instead of a cam swap. What about changing the ratio of the Rocker Arms to a higher ratio?

~JM~

 

[JJLT1]

JM swaping to 1.6 rockers will get you about .025 to .030" more lift,,not much..:texas:

 

[JJLT1]

JM also with stock heads youll need to modify the pushrod guide hole with a louis tool,
or the pushrods may rub or bend..:texas: and youll still have to check all clearances..


louis tool
http://www.jegs.com/p/Comp-Cams/Comp-Cams-Louis-Tool/747132/10002/-1

 

[~JM~]

JM also with stock heads youll need to modify the pushrod guide hole with a louis tool,
or the pushrods may rub or bend..:texas: and youll still have to check all clearances..


louis tool
http://www.jegs.com/p/Comp-Cams/Comp-Cams-Louis-Tool/747132/10002/-1

Sounds like its almost as involved as a cam swap. I was thinking that there would be more benefit.

~JM~

 

[JJLT1]

yea kinda a pita for the benefit,,
the intake has to come off to catch all the metal chips from the drilling..

harland sharp makes a 1.65 full roller,, that will get you .045-.050 more lift,,

but the hp gain dosnt come from the lift,,
the heads have to flow better,, if there is no more flow potential in the head,, no big gain..
i think the ads say 15-40 hp?? :dontknow: every motor is a little different..

less friction is there with a full roller rocker,, but still the hp gain is minimal..

but,, if you do 10 things worth 5hp,, it is still 50hp..:texas:

 

[steelybill]

Small block Chevys respond well to a good exhaust system, including headers. That could be one of 10 things to help the power, like JJLT1 mentioned......
Bumping the ignition timing up 3 or 4 degrees more than stock initial timing even helps.