sti_woody

Hi everyone. I'm a newbie to the LS1 scene, and we have finally purchased our first LS1 powered vehicle. We bought an LS1 powered RX-7 that has a hydro-locked motor. From the teardown we have determined that the pistons, connecting rods and crankshaft are all toast, but valvetrain is intact and healthy.

This may be a simple issue, but I'm a little concerned. We picked up this car to do our first motor build. We ordered an HP kit through flatlander racing and I simply asked for stock specs on all parts(or as close as possible). We were not so concerned with building power at this point, as with making sure the parts in the rotating assembly are high quality in case we do add power in the future.

Well, the pistons flat lander shipped are *not* stock spec, and now I'm concerned we may have a problem with deck height that will result in interference with the head and valves. I did some research and found the equation to determine connecting rod length we can use at the following sites:
https://ls1tech.com/forums/generatio...lanation.html]
https://ls1tech.com/forums/generatio...k-height.html]

Originally we wanted to go with a stock crank size and 6.100" connecting rods, but after looking over the helpful pages above, I'm thinking that may not be an option. Even taking the .006-.007" that the piston rises above the deck height into consideration, we still exceed what seems to be safe limits with a stock crank and stock connecting rods. I am either looking for some suggestions on how to move forward, or some assistance/guidance to the right thread that explains the results of running a smaller stroke crank and the effect it has on hp and torque. Like I said before, at this point we are not concerned with making power, however, I also do not particularly feel like losing power. Sorry if this is a complete noob question, but I'm still trying to learn how all of this works and I don't have the time or money available to order the wrong parts, get everything bolted together and find out we can't start the car without destroying the motor build. In case it is needed, the motor we are using is out of a 2001 WS-6.

The things we already have for the build are:
1. New LS1 block(old one got a rod punched through the side when it hydro locked)
2. Flatlander racing HP rebuild kit. (Pistons are Mahle part# LS1340905F04)
3. The stock 241 designation heads
4. The stock camshaft
5. New, stock length, hardened pushrods

The things we still need to buy for internals are:
1. Crankshaft
2. Connecting rods

I was going to go with the 6.100" Eagle connecting rods and a stock crank, but with a stock crank the equation turns out something like this:

9.240"(deck height)-1.811"(half the crank stroke)-1.340"(piston compression height)=6.089" (rod length)

As you can see, using a stock crank seems to put my connecting rod at shorter than stock. I'm a little miffed that I asked for stock spec parts and they gave me a 1.340 x 3.905 piston, but I guess that's what I get for trusting someone else to find the right parts :-/ Lesson learned. Sorry for being so long winded, but I figure too much info is better than not enough. Any guidance or suggestions are appreciated.

-Woody

KCS

iTrader: (20)

With a 9.240" deck and a 6.10" rod, you should be about .011" out of the hole. With the stock .052" thick gasket, I see no problem whatsoever.

sti_woody

Thanks, KCS. The HP kit came with a gasket, but I'm guessing it isn't the stock gasket thickness(from what I read in one of the threads). I will see if that is stated on the invoice when I get home. If I just buy a stock gasket, will that be sufficient if we go up to 500hp at the crank? I don't anticipate we will ever need more than that, since we plan on doing road course and not drag. As light as the platform is, I think more than 500 would be overkill for handling(if we even go that high). Thanks again.

schnellttz06

They must have assumed you would be honing it out some. The size of the cam will play a significant role as to your clearances, and your rocker ratio. Keep a moderate size cam and , make sure your valvetrain geometry is good and use some putty to check your piston to valve clearance. There is also a tool to cut reliefs in the pistons for added clearance if needed, but I would hate to grind on a new piston.

KCS

iTrader: (20)

The stock MLS gaskets are very good, plenty capable of 500hp.

As for PTV, the Mahles pistons should have valve reliefs, so there should be plenty of room for even relatively big cams, but obviously checking anyways would be a good idea.

sti_woody

Excellent. Thank you schnellttz06 and kcs. Yes, the Mahle pistons already have valve reliefs cut into them, so that *should* be fine. I'll grab a set of MLS gaskets and use the putty method to be sure when we put everything together. I really appreciate the help and peace of mind!

sti_woody

Another related question. How would I determine the head gasket bore. Would it be the same as the piston bore(3.905) and would it hurt to go with a slightly larger bore(say 3.910", since I would presume a smaller bore would be bad).

These are the 2 I am eyeballing on summit right now that I think would meet my needs, but I'm not sure. We haven't had the machine work done yet, and I'm not sure if this is right. Like I said, the piston is 3.905":
http://www.summitracing.com/parts/tf...make/chevrolet
http://www.summitracing.com/parts/cg...make/chevrolet