BadRiggins

I have found and will be buying a '99 Vortec 350 engine out of a Tahoe for $100. The plan is to bore and stroke it out to a 383. I have the plans, know a shop, and know where I am getting the internals from. It will be completely forged too. I'm fine with keeping the Vortec heads for now, but I know that I will want something better later down the road. I want something like 68cc or 70cc heads when I twin turbo the engine. So will 68cc LS3 heads work? They pulled up when I was searching for Vortec heads. Also, how difference will 6in rods make compared to the stock length 5.7in rods? I have to pick which ones to get before I order the rebuild/stroker kits.

Thanks, Bradley.

MoJoe

iTrader: (5)

The "Vortec 350" is the good-old, 1955 based Small Block Chevy, with some of the best factory SBC heads. Parts are NOT interchangeable in any way with the new-for-1997 LS series of engines... LS1, LS2, LS3, LS7, LSA, etc.

The "Vortec" label has been applies to many engines, of many different, non-interchangeable families... http://en.wikipedia.org/wiki/General_Motors_Vortec_engine...

As for upgrading heads, you can't go wrong with AFR 195s. There's a number of options, such as here at Summit.

Swapping for 5.7" rods to 6.0" helps the rod angle with the longer stroke. As you may have noticed, the piston height is correspondingly 0.3" shorter.

BadRiggins

So the 6in rods will give me higher compression? Do you know about how much difference?

BadRiggins

Also, a little off topic, but would the 6.0l LQ4 do too much better than the 383 Vortec? I found one, buy it's 4x the price for the block. Thanks.

MoJoe

iTrader: (5)

Nope. The length of rods has nothing to do with compression. (Well, almost nothing.) The size of the chamber, and how close the piston gets to the head, measured around 0.040" including the head gasket thickness, is what will determine your CR.

If you take your 0.040" deck+gasket, and buy pistons for 6" rods, and use 5.7" rods, your deck+gasket is now 0.340", and your 10.8:1 CR turns into 6.5:1 CR.

Going the other way, buy pistons for 5.7" rods on 6" rods, and your pistons are going to stick out of the block by 0.300", which if somehow assembled and cranked means broken pistons, bend or broken rods and a pile of junk.

This is basic information on building an engine. Search anywhere and everywhere to educate yourself. Here are the basics:

1. For best quench, detonation resistance and power potential, optimum piston to head clearance is 0.035" to 0.045". (0.045" or more if using aluminum rods or loose/forged pistons).
2. Quench is the combination of head gasket compressed thickness + how far down in the bore the piston stops, also called deck clearance.
3. Head gaskets can be had in 0.015" to 0.045".
4. Piston depth, or deck clearance, can range from as much as 0.045" with cheap rebuilder pistons (poor performance), 0.025" stock, or as little as 0.000" for a "zero decked" assembly.
5. An original, stock, uncut block measures 9.025" from crank center to deck.
6. Rebuilding an engine may require the deck to be machined flat. This will make the block less than 9.025".
7. Add up all the measurements of crank (1/2 stroke) plus rods plus piston height. That total should be close (0.000" to 0.025") to the finish machined height of your block.
8. How close will determine, or be determine by, which head gasket you are going to use.

You say you want to build a 383 (3.75" stroke and 4.030" bore), and question 5.7 or 6.0" rods...
1/2 of 3.75 is 1.875".
Add your rod length, 5.7" or 6.0", and you get 7.575" or 7.875", leaving 1.425" (5.7) or 1.125" (6.0) for piston height.

Looking at Summit for pistons, you can find...
1.425" pistons w/ 5.7 rods = 9.000"
1.430" pistons w/ 5.7 rods = 9.005"
1.443" pistons w/ 5.7 rods = 9.018"... giving 0.007" deck clearance on a stock 9.025" block. Or 0" clearance on a block decked 0.007" to 9.018".
... or...
1.125" + 6" rods + 1.875" 1/2 stroke = 9.000"
1.130" pistons => 9.005"
1.133" pistons => 9.008"

Side note: The original 383ci came from using a 400 crank in a 350 block. If you went with original rods from a 400ci engine, those are 5.565", and you would use 1.560" pistons to get 9.000".

MoJoe

iTrader: (5)

BTW, While forged pistons are denser, and will withstand more power and abuse than cast or hypereutetic pistons, forged also expands more from room temp to operating temps. That means the cold, forged piston will fit looser in the bore than cast or hyper. A short forged piston for a 6" rod will rock more, will make more noise when cold, and will need a tad more quench clearance (say 0.045"-0.050") to make sure the cold, rocking, short piston doesn't kiss the head.

So... for forged pistons, you may want to stick with 5.7" rods. For hyper pistons, using 6" rods will not need extra clearance (you could run piston-to-head as tight as 0.035").

MoJoe

iTrader: (5)

The LQ4 is a member of the LSx family. Same concepts apply, but most measurement will now be in metric. The LS engine design is more efficient than the SBC, so has more power potential. It is the current popular engine, so many more parts and shops are dealing with them.

6.0L = 366ci
iron block ... Con=less of a weight benefit than LS1. Pro=iron block better for boosted power than AL block.

Since the LQ4 is a family change from the SBC, you will need: engine mounts, exhaust/headers, different trans (bellhousing bolt pattern is different), trans crossmember, throttle cable, fuel lines, etc, etc, and a major wiring swap if staying with electronics.

It can be done. How much skill, money, and/or wheeling-dealing do you have?

Night rider327

iTrader: (13)

A vortec 350/355 or 383 can make 375 to 450 HP with the vortec heads.

Better heads with the correct cam and compression can have that 383 at over 500 HP.

For other heads look at Brodix IK heads, AFR, Dart, Profiler, etc. in the range of 190 to 210cc intake runner.

BadRiggins

I was looking into a comp cam for a turbo/blower.. Is that the best choice for me since I want to twin turbo it later on? I'm looking to build the engine for boost now, so when I get the turbos I can just install them without having to do another rebuild. I've rebuilt a '71 355, but I don't really understand the cam specs, so I don't know how to choose them. I'm a little better with the heads, but not too much.

cosmick

There are 2 different alloys of forged pistons. 2618 and 4032. 2618 is max race, and has more thermal expansion. It's more plastic when things go badly wrong, and may reduce damage to other engine parts. 4032 is more like Hypereutectics, good for daily drivers. Stronger, but at their own higher-than-hypers limit, they're more brittle than like plastic.
And the old TRW "forged" production pistons were really just pressure-cast. Last seen in the '92 Ford 5.0L Mustangs.