Sheppard

Hey everyone, I am kinda new at this, I am a first year apprentice mechanic, and this is my first post, I have an 84 Trans Am, and I recently bought a 400 block, already bored out with new rods, crank and pistons. The guy I bought the motor off told me because of the oversized rods he had installed in the engine, a normal camshaft will not work for me, he said it well hit off the rods, he told me that I need a small oval faced camshaft. Anyone ever hear tell of this before or have any experience with this? Thanks any help will be great.

sofakingdom

iTrader: (1)

Depends on what rods they are.

Never heard of "small oval faced" cam. I have however heard of a "small base circle" cam, which basically makes the cam smaller so there's more clearance to the rods.

YOu can get an idea of how much smaller the lobes can be from this pic of a cam I have. It's a small base circle solid roller.



Some rods actually give MORE clearance to the cam, than stock ones.



Note how much the "corner" is rounded off, where the rod bolt WOULD be if it had one, on these, which are the top-of-the line Eagle forged H-beams, 6" length. Note that they have cap screws instead of bolts, for exactly that reason.

Find out EXACTLY what the rods REALLY are, BY PART NUMBER only please. POs are notoriously unreliable as to accuracy of details like that unless they can supply you with receipts. A pic looking down the cam tunnel with the crank turned to where the #1 or #2 rod bolt is visible looking into it, might also be of value.

Sheppard

Hey thanks, I am going to do some searching to see if I can find out what kind of rods these are, I found a box that one came in and all it tells me is that its a Scat rod, no numbers or anything to be found, and yes small base circle is what I meant, I dont know why I said small oval faced, lol. Any idea on what Scat Rods are like?

InfernalVortex

iTrader: (4)

Scat rods are just regular stock replacement style rods. They'll likely have good ARP rod bolts in them. They're good, but nothing special. I run them in my motor. Hasn't blown up yet... lol.

If they're I-beams I would consider selling them (if theyre new and uninstalled) and getting some H-beam rods. I have mental hangups about running small base circle flat tappet cams. just seems like a bad idea. Flat tappet cams area bad idea, but a roller cam setup will set you back an extra $1000 over a flat tappet one, so most people just run flat tappets for budgetary reasons. Just be well aware of the extra considerations they require and you should be fine.



The left two are I-beams, the right one is an H-beam. They are better for reasons perfectly illustrated by the sofaman already.

Now just to be clear, SCAT does make H-beam rods and various other more expensive rods, but SCAT rods are among the more affordable decent aftermarket I-beam rods with ARP rod bolts in them. They're popular in that range, and due to their popularity at that price point and the popularity of the more exclusive brands above that, PLUS the mention that you will need a small-base circle cam, make me think you have regular scat I-beams.

They could be anything, but I suspect they are some variant of these:

http://www.summitracing.com/parts/SCA-35700P/

They are a budget brand, but they do use ARP waveloc bolts which are nice. They are good insurance and will hold together at higher RPMs than any stock rod bolt could.

When people do budget performance rebuilds I suggest that they either have their stock rods re-machined and have ARP bolts put in them, or get rods just like those SCAT rods. The cost is pretty close so most people just get new rods that already ahve the new bolts.

Sheppard

Thanks alot, judging by the shape they look to be the I Beam rods. They are already installed into the block so I think I am going to keep them. This engine build is not happening right away anyway, as I said earlier I am a first year apprentice and the cash flow is not that high right now lol. I am just trying to gather information right now for when I finally do the build, I know what to look for. My first project is to get my Trans Am in good working order as of now with the 305 in her. Got the car put up for the winter and can not wait to get working on her this spring.

ex-x-fire

Measure the stroke, see if its 3.75 inches.

DAVECS1

iTrader: (2)

Wow talk about timing. I just spent today working on this very problem. First time I have ever run into it, bit it is also the first time I have built a 406. I have Ohio Crankshaft 4340 rods, very similar to SCAT rods. I am using the Wave-loc bolts. I had Ohio clearance the rods when the put together the short block, but unfortunately I still had really tight clearance on the #2 and #6 rods. I am running Comps NX288HR cam, not too crazy but decent size. It is a hydraulic roller. When I was getting ready to degree the cam, I always run the motor through 2 complete rotations and check everything. Thats when I found it, not sure why it was only on those two cylinder. It did not take much at all to make about .40 of clearance. I took the rods out and just touched them with a course 3M scotch pad on a little drum sander. After that everything looked great. If the timing chain evergoes this motor is going to be all over the road though!!!!!



Yes I thought about balance and all, but I really don't believe I took more than a gram or so.

Orr89RocZ

iTrader: (20)

Callies compstar rods in my car with arp 2000 bolts. .400" lobe cam, clears fine on my regular hyd roller cam. I dont believe its a special base circle. My last cam was in my 3.75" stroke 383 with Eagle H beams with arp 8740 bolts. .383" lobe and 1" base circle from what I could measure/determine. Nothing wrong with going with a small circle cam.

izcain

Hyd and solid rollers have a smaller base circle then a standard flat tappet anyways. So you will acually gain clearance if you decide to go this route.

Just about most all the aftermarket rods gain clearance in that area.

I have had to grind a few rods myself to get the clearance I needed!

DAVECS1

iTrader: (2)

Capscrew rods and H-beams rods look to be made for this. I probably should of went H-beam but I dumped alot of money into the pistons and block and these met my strength requirements. Never really thought about cam clearance as I have never had that issue. Another thing I learned is cam timing, duration and LSA make a huge difference. I could actual retard my cam 4 degrees and it cleared, but I did not want to count on that, and that is not how I modeled my engine.

Orr89RocZ

iTrader: (20)

You always should degree the cam in. Also effects piston to valve clearance too.

DAVECS1

iTrader: (2)

Yea THat is the next thing I have to check once I get it togetehr, but it should be good. I had custom pistons made by JE and I gave them my head model and valve model numbers. I have landed the heads to check it out and the valves fit right in the reliefs so as long as they don't hit the piston I should be good