Big Block Chevy 427 questions

[hbps1978]

Hello to all! Has anyone built a 427 chevy big block using a 6.700" connecting rod in a short deck 9.780" deck height block. This would calculate out to be a 1.200" compression height.

With a 1.200" compression height piston in this combination can the piston ring lands be machined down low enough to accomodate a moderate dosage of nitrous oxide from time to time at the drag strip? Would you recommend a different length connecting rod? Should I run pistons with the top and second ring lands made for 1/16" rings or run the top rings at .043" and the second ring at 1/16" and have the pistons gas ported for the .043" top rings?

I'm looking to possibly build a .100" over 427 (447 cu in) engine with an aftermarket 24* degree aluminum cylinder head, flat top piston, solid roller camshaft valve train, and a single four intake manifold in a heavy car (3300 - 3500 pds.) I will use a powerglide transmission also.

What 24* degree aftermarket cylinder head (and intake runner volume) would you suggest for this combo? This engine will probably run in the 6800 - 7400 rpm range.

Any thoughts or recommendations from previous experience would be greatly appreciated. Thanks to all in advance.

[Dave Koehler]

You are going to need a dome.
Using your specs you only come out with 7.7:1 compression. (3.76 stroke, 4.35 bore, 0 deck, .040 gasket, .120 cc, .300 down ring, 1.2 CH, 5cc valve relief)

No need to use a rod that long. .250 long will be fine.
Too lazy this morning to figure the ring stack.

Since you are limited to using a flat tappet cam, 3500 lbs and 7400 rpm I would think that an off the shelf 1/16, 1/16, 3/16 ring package would be sufficient.

[hbps1978]

Dave, what dome should I use for this combo? Thanks for your help.

[SupStk]

hbps,
You need to help Dave out here. What comprsssion ratio are you wanting to run? Also what is the head CC's, are you running out of the box or angle mill ect?

[crazycuda]

I am wondering why you would want to use a longer rod in a 427 bbc. I understand the reasoning on a longer rod to keep the piston dewlling at tdc a little longer and also reduce side wall friction.
In the past I used the longer rods in tall deck truck blocks so you could use an off the shelf 427 piston. At one time the shop I worked in built 2 identical 427 / .060 motors the only diference was one was a tall deck and the other was std deck, Both had TRW forged domb pistons (can't rhember the pn off hand ) The same 074 alum heads (box stock) and an old edelbrock intake( the one that had the turned holley flang) and the old l88 cam. There was almost no power difference between both motors according to the dyno results. (this was back in the 80's) In my opion the factory rod ratio is not to bad. Especially if you compair it to the 454's rod ratio which I would definatly use a longer rod in.

[hbps1978]

Thanks again to all who have posted on this subject.

Crazycuda, as far as the rod length, the long rod (6.700") was an idea to cut down on skirt to cylinder wall friction/wear but not a necessary evil. By the way, you never stated in your response what length connecting rods the short deck and tall deck 427 engines you tested had in them. I assume that they probably both had 6.135" rods? I would like to run a 6.535" rod though in this engine I'm thinking about building.

SupStk & Dave, I had thought about running a flat top piston or short dome and angle mill the heads to get the compression ratio that I will want and/or need. What is your opinion on dynamic compression in a nitrous oxide engine?

Dave, I plan on running a solid roller camshaft, not a flat tappet as I am not limited to what I can run in this engine. This is something that I may build to just have some fun with at the track for a little while to help me learn to tune a nitrous setup.

Any suggestions or thoughts on cylinder heads from anyone? I'm going to run an aftermarket 24* conventional style head on this setup. How about the Canfield heads vs. Pro Topline. How about running a set of AFR 290cc CNC ported oval port heads on this engine?

Thanks again to all!

[crazycuda]

Thanks again to all who have posted on this subject.

Crazycuda, as far as the rod length, the long rod (6.700") was an idea to cut down on skirt to cylinder wall friction/wear but not a necessary evil. By the way, you never stated in your response what length connecting rods the short deck and tall deck 427 engines you tested had in them. I assume that they probably both had 6.135" rods? I would like to run a 6.535" rod though in this engine I'm thinking about building.

Thanks again to all!

sorry about that, the std deck used stock length and the tall deck had the longer rods.

[ZEROMAN91]

I've had good response from angle milling the big blocks I've built, I think any thing you can do to keep the dome size down is good.

[hbps1978]

Zeroman91, thanks for your reply. How many degrees do you angle mill your big block heads? Most heads I have angle milled have only been a maximum of 2* degrees.