I am thinking of building a 6" rod 400 motor for my 82 Z28, and was wondering if i would run into any clearance problems. I think i will be using a Wiseco forged dished piston with bushed 6" 4130 Scat "I" beam rods, and Scat cast 3.75" crank. I will be running a comp XR274-12 solid roller cam and some Pro Iron Lighting heads.

Would Scat 4340 "I" beam rods with cap screws be better, as far as clearance problems are concerned?

Is it wise to run bushed rods on the street?

Thanks alot for your help and suggestions.

 

makes me think that you are planning some type of artifical aspiration. If thats the case, I would not go longer than a 5.85" rod on a 3.75 stroke. The oil ring support is needed bc of the short compression height on a 6.0 rod/3.75 stroke combination, and that makes for a less than maximum ring combination (seal and placement) on a boosted build.

Bushed rods are fine, I doubt u will need a reduced basecircle cam. But, I would call comp and see what BC the solid is ground on. If its over 1", it will be very close.

But, the choice of rod length/I beam/capscrew really does not play into the issue of clearance (the clearance at the journal is the same regardless of rod length/rod design and fastener type).

Most H beams are stroker clearanced, very few I beams are.

 

if i were changing rods in any engine to differant length, i'd have a inch or so of grout put in incase i hit water grinding. screw type rods give you alot more clearance then nut/bolt rods. i also guessed you're running power adder, if so i'd look for some other rods and crank.

 

I have Wiseco flat top pistons with 6" rods for my next 400 and the stroke is 3.800 on my nitrous motor. You can see the oil ring is in the pin hole and that not the best thing for oil control but it's needed to keep the top ring down for a power adder. I also have other 6" rod 400s with the rings at the top of the piston that will keep the rings out of the pin hole but just don't run nitrous or a blower on them.

Jerry

 

Great pic!! Im gonna follow thisn one.

 

I'm building my 406 right now and am using 6" H beams. I did have to take out my rod bolts and grind on them to make them fit. Not a big deal. I would rather do that than grind on the block and get shavings in the engine. Also, you WILL need a small base circle cam for these rods. I had a custom one ground from TPIS. I talked to Comp, Lunati, Isky, Crane, and TPIS before I ordered my cam and they all said there would be clearance issues with the cam if I didn't run a small base circle. Also, I am running Probe Pistons and the oil ring are not in the pin hole.

 

I have 6" H-beam rods and a 3.800 stroke crankshaft and can clear any base circle cam. You just stroker style rods.


Jerry

 

Right now i am just building this motor for just natural aspiration. But i am using -20 cc dished forged pistons for the future if i want more power!! The Scat 4340 "I" beam rods have cap screws and therefore should be stroker clearanced.

 

Where do you get stroker style rods? What makes them stroker style? Are the sides on the big end smaller since that is what gets so close to the cam? I wish I had known about these before.

 

Look at the pic above, the right side of the rod has been machined flat compared to the left side, that gives more cam clearance.

 

Exactly. As Smokey Yunick once said, "Use the longest d&mn connecting rod that you can fit in the engine!". Or something to that extent.

 

Eagle and Scat H-beams are both clearanced for stroker apps, but I'm sure there are others. They machine them to where the rod bolts are snuggly up in the rod, so they don't protrude out much towards the bottom of the rod.

Oh yeah Wiseco pistons are great. Best buy on the planet, they come with rings! I've never seen a weak engine running them.

 

That's really cool! I've never seen that before. I'm using the Hawks Racing H-beams that aren't like that.

 

IN fact, the SCAT I beams use more material in the bolt thread area and have less clearance than a GM - bolt/nut OEM style rod.

Take my word for it,, I measured a factory clearanced rod (about .75" from inner journal to outer bolt head clearance). The SCAT I Beams had over .85" of material in that area and would not clear by a long shot.

As I indicated above, almost all H beams come stroker clearanced , but you pay for it with the extra weight.

 

The rods I use are made by a company here in California called Carrillo Ind. In the picture thr right side of the rod is cut for cam clearance. The price is kind of high, The rods in the picture was $1,600 for them direct from Carrillo.

Jerry

 

 

The Scat website says that the 4340 forged I-beams with 7/16 cap screws are stroker clearanced. Plus they are about half the price of the H-beams. Here are some pics

 

H-beams

 

that clears up most of it.. the 4340s with 3/8" cap screws (the ones I got), are not stroker clearanced.. at least they did not used to be.

 

Well I have a 412 (.030 over and 3.8" stroke) and using Scat H Beams (supposed to clear up to a 3.875" stroke) and i am having clearance issues with my 264/272 @.050, 649/649 lift, 107 LSA standard base circle cam. #6 #5 and #2 rods dont clear. Ordered a small base circle cam and let ya know what happens.