I have an '87 Iroc 305 TPI, factory. Putting in carbed 355. I have a 1969 shortblock that has just been rebuilt. I have a set of Vortec heads to set on top, but I am lost on my valvetrain. There is so much information and differences I just keep getting confused. Flat Tappet, Roller, solid, hydraulic, mechanical. 1.5 rockers vs 1.6. Please just tell me what I need.

 

Ok lets start off with the basics.

Your '69 shortblock will be a flat tappet cam (non roller) block. It can be hyd. or solid. But to swap it over to a roller cam you would need to buy a retrofit roller cam swap kit with the link bar type lifters. This runs about $700-1,000 and imho not worth it. If you want roller it's cheaper/better to start with a factory roller block.

Solid and mechanical means the same when it comes to cams.

Do you have a cam in the engine yet? If so what is it? If not then what is your compression (and not just the compression the pistons said in the ad), the real measured volume of parts compression.

Was the block decked/milled/shaved at the machine shop? If so, how much?

What are the details on your vortec heads? Are they just factory 96-00 truck vortec heads, or aftermarket, or screw in studs, guide plates, etc added?

All of those questions needs answers to be able to tell you what all you need for your valve train.

If guide plates have been added or will be added you need the older style rocker arms for the 1955-86 V8... If no guide plates then you need the newer style self aligning rocker arms for 1987-2000 V8

If stock vortec heads, the valve springs will need to be changed, but can't say to which springs until we know the cam that will be used.

 

The heads are factory GM 906 castings. To my knowledge are completely factory. The block, I don't know a whole lot about, it was given to me by my father. It has been bored .30 over and is freshly machined, never installed. There is no cam in the block at this time.

 

Tappets and Lifters are the same thing. There are TWO details needed to describe them. Either Hydraulic or Mechanical/Solid is one. The other is roller or non roller. Hydraulic actually pumps up with oil (hydraulic) and is softer on the valvetrain. Mechanical/solid is just that. Solid. No give. You probably would be better suited for Hydraulic. Either way, you can choose roller or flat. Roller has a little wheel that rolls on the cam lobe. Flat is well....flat! Roller will allow for a more aggressive cam, but obviously that little roller has to stay aligned with the cam lobe. ....and older blocks are not designed to allow for the hardware needed to keep them aligned. Google GM Lifter Spider assembly and you'll see what all later model blocks have. Yours does not have this. As mentioned, you can get expensive lifters with linkbars (I did), but it's not really necessary. If I were you, I'd probably look at a Hydraulic flat tappet lifter/cam.

Pretty sure stock Vortec heads do NOT use guideplates, but DO use self aligning rocker arms as Night Rider said. ....so either use the stock arms or pick up some self aligning arms. 1.5 or 1.6 is the lift ratio. If your cam is ground with .300" lift, with a 1.5 ratio, the final valve lift would be .450". ...as to what you need....again you'd need to pick a cam first. I think most all traditional small blocks came with 1.5 "I think". I have a custom Lunati cam, and when deciding, I told them I wanted a hydraulic roller cam for a given engine, and they suggested "x" specs, using "x" rockers.

...other than that, make sure your cam choice doesn't exceed the capability of the vortec springs, and you should be good. I think lift maxes out around .450 to .475 with stock vortecs.

That's basically to make it all play nice. Remeber...you can change pretty much EVERYTHING in your search for more performance, but each change will typically mean more changes down the road. Doooo research!

 

OK, we're getting somewhere
Sounds like you should stay flat tappet. But cam specs depend on so much....
Flattop pistons? Dished pistons? Deck clearance? What trans? What rear gears? What's the intent for the car? If auto, are you willing to upgrade the TC? Rough car weight w/driver?
In a 355 with around 10:1 CR, start looking at cams like this:
http://www.compcams.com/Company/CC/c...x?csid=85&sb=2

and then adjust upward or downward depending on preferences and answers to all the questions posed.

There are several economical valvespring/retainer kits that permit up to .550" lift without machining the heads.

 

You guys are awesome. Thank you for really dumbing it down for me and taking the time to help me.
The pistons are dished, trans is a 700r4, factory rear end with what should be 2.73 (haven't visually confirmed yet). Intended on changing torque converter if necessary. And weight should be around 3500lbs. Just intend on it being a street car but I like a nasty sounding cam.

 

Your welcome...
You can't have your cake and eat it too. To have good power across the RPM range and have a "nasty" sounding cam, you will need more compression.

This is the #1 mistake people make... Over camming. I don't want to confuse you so I will try to keep this simple as I cam. The nasty sound comes from the cam's overlap. The overlap is the point where both intake and exhaust valves are both opened some at the same time.

The bigger the cam, the more overlap, the more rough sounding lope you get.

However, being both valves are open at the same time, means the compression you are making in that cylinder has a way to get out (through the opened exhaust valve). So the overlap "bleeds" off some of your compression.

If left like that, the engine will have soggy low rpm power and won't make power until higher in the rpm range. To overcome this you rise the compression, or go with a smaller cam.

With dish pistons you are going to be down on compression some, so you will not want to use a cam that can give you that race car sound. You need to know your piston's dish volume or at least piston part #.. Because dish pistons can range from 10cc to 22cc and that can change the compression by 1.14:1

But with the correct setup, you can get a cam that does give it a slight lope where you can tell it's not stock and still keep good power from off idle up to 6000 rpm.

You need to measure your deck height, or how far the pistons sits in the bore with the piston at TDC.

Do at least all 4 corners. Turn crank to get piston to top dead center (TDC) as far up as it will go. Then measure from top of piston to the top of block deck. You can use a dial caliper, feeler gauges and straight edge, or a dial gauge and stand. The measurement can not be done with a std. ruler or tape measure as it will be in range of 0.000" to 0.045"

You want to get your quench height (top of pistons to bottom of heads, including the head gasket thickness) to as close to 0.040" as you can.

Most stock-ish setups with un decked block has the pistons sitting 0.025" in the hole, so .040 - .025 = .015... in that cause you would need 0.015" thick head gaskets.
Fel pro #1094 gaskets.

Factory vortec heads do not have guide plates and uses self aliening rocker arms. They also are lift limited to about .480" lift due to retainer to guide clearance. The stock springs are trash and not good for anything more than a stock cam.


Once we figure out what dish volume pistons you have, then we can move onto what cam size you need