verskel

Okay, last night I got my Chevy by the numbers books and went through all the Big Block engine plants (at least most of them). One book is 1965-1969 and the other is 1970-1975.

According to 'original' stock setups......most Big Blocks (396/402's-427's-454's) were using a Mechanical cam with 0.520 lift intake / 0.520 lift exhaust.

The L-88's were using a 'monster' cam of 0.560 lift intake / 0.580 lift exhaust.
.....and the ZL-1's were even bigger at 0.580 lift intake / 0.620 lift exhaust !
:eek:

Anyways, my question is that what's the most lift you could go with using conventional parts (i.e. - iron heads, 427 /454 block, etc.) ??? What are the valvetrain issues on a Big Block ?

GDaina

Difficult to answer...depends on the valve reliefs in the pistons...the 12:1 piston valve reliefs were deepen than the 11:1 and flat top pistons, or so it appears. Most engine builders like to have a mininum .100-.120 valve to piston clearance, think GM was more conservative and had closer to .250 or higher valve clearance.

The block has no bearing in valve to piston clearance..




[Modified by GDaina, 10:29 AM 3/29/2004]

verskel

Okay, maybe I'm going about this all wrong.....

After more research, the engine that I thought I had isn't what's in my car. :mad ......guess I shouldn't complain since it's still a big block but it'd be nice if it was a 'real' 427. :cuss

Anyways, as it turns out it's a '402' just like this one --> http://www.rebuilt-auto-engines.com/...l?p_prodid=285

So, what are my cam options ?!? .....could I use the 0.520 / 0.520 lift cam from the 375hp Camaro engines ? :confused:

zwede

Also, how will the vehicle be used? For a race setup I've seen well over 0.700 lift with a stock block and the right (aftermarket) pistons. But a valvespring that can handle that kind of lift at a high rpm is not going to live long on the street. It's all a compromise... Longer life->lower performance.

verskel

Street.....I'm not looking for a race setup.

BlueL36

I just went through this thought process. I'll post pics with "what I did this winter" after I get the car home and put some miles on it to give proper feedback. I went with the stock cam/hydraulic lifter replacement kit- gm #12364055. Lift .461/.480, duration at .050 214/218, lobe centerline 115. I wanted to keep it 'mild and driveable.'

Good luck with your decision :seeya

GDaina

I don't know if the flat top pistons have valve reliefs...if they do, then you can use the 435 HP cam, and you can also use the L-88 dual springs without any harm to the cam. I would not use the single spring that the factor used with the 435 cam. When I got my 68, the first thing I did was change over to the dual L-88 springs...that move saved my motor, as I was racing a Hemi and broke one of the valve springs...the inner spring kept the valve from dropping.

verskel

Thanks Gdaina ! Flat-tops with valve reliefs. ;) ....and the dual springs sound :cool: I'm trying to build a street / strip hotrod ~ nothing fancy but very noticeable that there's some power. Not too concerned with driveability as long as it'll idle (can be choppy) and start relatively easy. I'm also using a stock M-21 muncie 4-spd. :thumbs:

zwede

I'm using flat top pistons in my LS5. They have valve reliefs. My cam is a hydraulic roller with 0.573/0.585 lift. I put about 40k miles on it sofar.

Brettmc

Those roller cam setups will cost you some SERIOUS bucks. Stick with a flat tappet setup for budget concerns. Big block valvetrains are heavy....keep it light as possible and use good springs and it'll rev purty good. Somebody will correct me if I'm wrong but I think the 396 block is the same as the 427 block...you can prolly bore it to 427-sized bore. The good thing about the short stroke big blocks is they'll rev. You can find some really good power in them over 6000 if you're brave and if you built the valvetrain right. Chuck Harmon built an L88 clone...do a search to find out how THAT turned out.

Brett :thumbs:

verskel

Hmmmmm.....but it's much cheaper than an engine transplant. What do you engine guys think of this ?!?

http://www.iskycams.com/partnum_temp...ler=no&x=7&y=6 :reddevil :D

442olds

What heads do you have. You should be looking at that as well as the cam. If you have the heads in that engine rebuildlers picture, your never going to be able to support that Isky cam. Your getting into large oval port 290cc or better or you may as well just jump up to a small Rect Port head 300 to 315cc. The heads shown in the engine rebuilders picture are close to peanut port if they aren't already.

verskel

Guess I have the peanut heads.....

#3993820....71......oval...OPEN...402, 113cc chamber, 255/114 ports
#3993820....71-84...oval...OPEN...454 Passenger and Trucks, 113cc chamber, 255/114 ports

Also, I think these have the smaller valves - 2.06 In and 1.72 Ex

zwede

I'm familiar with those castings. Yes, they have the small valves. They are NOT peanut ports, but regular ovals. Intake port about 255 cc or so.

They're actually considered an excellent head if you port them and install the larger valves.

442olds

Those aren't to bad. I have basically ported versions of those. 265cc Int and 116 ex. But I do have lareger valves 2.18/1.88. I'm using a Comp Cams XE282HR which is a hydraulic roller. It works well with similar heads and a single plane with an 850 DP. I still think I need a little more breathing room because when I get a little above 5500 the motor starts to run out of breath. I would say you could get away with a slightly smaller cam in a flat tappet hyd or solid and still be ok.

My plan was to upgrade later but build the bottom end the way I wanted and work with the heads I have till then.