Need some advice on choosing forged internals for my twin turbo setup.

So after tearing apart my engine this evening I found that I have a chunk missing out of the top of my #1 piston due to some trouble I was having yesterday when under full throttle.

Any how, I had started a thread asking for advice on a motor build back earlier this year before my turbo setup was actually finished and the car was running. Now that I've experienced the behavior of the engine with the setup I would like to start a new thread. Especially since the time has now come.

So provided that there's nothing wrong with any cylinder walls (haven't inspected but one bank of cylinders so far) I'd like to keep the block, and possibly keep the same bore. If any cylinder walls have any scratching then I'll have the block slightly bored.

Well, at just 8 PSI the motor had plenty of low-end before the turbos kicked in, and the turbos kicked in very quickly. I don't want the new setup to have too low of compression for my taste to cause a bit of lag, or lugging-around of the motor. But I do want the motor to be able to support enough boost to make around 900 rwhp through a stalled automatic transmission. The stock engine (with blower cam) currently made 639 rwhp at 8 PSI. So the turbo's seem to be pretty potent. They are Precision "HP Series" 62mm turbos, with .81 A/R.

I'm not looking to spend a fortune on pistons, rings, and rods (and necessary hardware), but I do want some decent stuff. I was thinking maybe Diamond pistons and CompStar rods with ARP rod bolts and head studs. What do you guys think??

I'm not sure particularly sure what pistons I'd need exactly, which I think is where I need the biggest help. I'm also unsure of which heads I'm going to go with but I'll need something that can be afforded on a budget. So if you all can give me your opinions on what I should go with I'd appreciate it a bunch!!

Thanks,
Andrew

clevite h series coated bearings, callie rods, wiseco or mahle pistons (i dislike diamond) with a lower top ring (more meat so you dont chunk a corner again), good moly ring. game on. and i doubt you chipped a piston AND got away with a clean wall and no bent valves. that'd be an act of god to get that chunk out in one clean pass :-D

get stock compression piston, and toss 317s on there to lower it a point or so. a touch lower compression will help you fight predetonation with lower octane fuel, save the c16 and high dollar shit, while shoving a good amount of boost through it. compression is a battle of convenience of fuel types, off throttle response and predet.

i cant bring any insight to an engine build, but for 900+hp dont you have to re-work your fuel set up?

I just dont see a single 255 and 60lb's getting there..

but sorry to hear about your motor!

Quote: Originally Posted by tmbutitta... i cant bring any insight to an engine build, but for 900+hp dont you have to re-work your fuel set up? I just dont see a single 255 and 60lb's getting there.. but sorry to hear about your motor!

I got to 1050HP with nothing but a fuel line routed to my nostrils. Yea, I'm kinda awesome.

Quote: Originally Posted by jcain... clevite h series coated bearings, callie rods, wiseco or mahle pistons (i dislike diamond) with a lower top ring (more meat so you dont chunk a corner again), good moly ring. game on. and i doubt you chipped a piston AND got away with a clean wall and no bent valves. that'd be an act of god to get that chunk out in one clean pass :-D get stock compression piston, and toss 317s on there to lower it a point or so. a touch lower compression will help you fight predetonation with lower octane fuel, save the c16 and high dollar shit, while shoving a good amount of boost through it. compression is a battle of convenience of fuel types, off throttle response and predet.

Why do you dislike Diamond, out of curiousity? I used their pistons on my built '92 Taurus SHO that I used to have and seemed like nice product. Why would you choose Mahle or Wisecor over Diamond? Yeah I'll have to disassemble the valves on that cylinder of the head and see what everything looks like there.

So will stock compression handle enough boost to make 900+ rwhp? And 93 octane is all that's available around here, so I need to be able to get away with using 93 octane on the street. later when I'm ready for more boost I can use racing fuel at the track.

So let's say I'm maybe looking at Mahle pistons..... what pistons of their's would I want for my setup exactly? I'm not sure which ones have a lower top ring, or how to tell which ones do.

Also, as far as 317 heads go... do the 317's use totally different valvetrain hardware than the 243's? Just looking to know what can be transferred, or if anything can be transferred from my current heads to 317's. Do 317's mate up to the LS2 intake manifold? What all mods need to be done, if any, to use 317's on an LS2????

Quote: Originally Posted by tmbutitta... i cant bring any insight to an engine build, but for 900+hp dont you have to re-work your fuel set up? I just dont see a single 255 and 60lb's getting there.. but sorry to hear about your motor!

Thanks, and yeah I do plan on doing a whole new fuel system when the time comes for fore boost and horsepower. Just want to make sure that the new motor setup can safely support that kind of power for the future. In the meantime things will stay at low boost.

Quote: Originally Posted by 8ball... I got to 1050HP with nothing but a fuel line routed to my nostrils. Yea, I'm kinda awesome.

Brian, "kinda awesome" is an understatement. Haha. Or maybe you just meant "kinda rediculous" lol. So yeah, you're not going to drive down and help me build the new motor?????? Hahaha.

I would count on boring the cylinders. I don't know the mileage, but a used motor alone will generally mean boring even without a piston letting go. Don't buy pitons until you get the machine shop to inspect your block.

I personally think diamond pistons are ok, but so are Wiseco or Mahle like was mentioned. Whatever you get, make sure they are forged. For a boosted motor, consider getting a steel top ring. Callie CompStar rods with ARP bolts are right on the mark.

There are two ways to drop the compression ratio, dished pistons or heads with a larger compression chamber (ok, 3 ways if you play around with head gasket thickness). I would pick which heads you plan to run first and then choose pistions to match the desired CR. Dropping a point of CR will allow you to run more boost in the future of course. I'd be tempted to get L92 heads, if this was my project. But, that will require more swapping of parts. The simpliest is to have your current heads ported (if they are undamaged) and then pick the appropriate piston.

Quote: Originally Posted by batboy... I would count on boring the cylinders. I don't know the mileage, but a used motor alone will generally mean boring even without a piston letting go. Don't buy pitons until you get the machine shop to inspect your block. I personally think diamond pistons are ok, but so are Wiseco or Mahle like was mentioned. Whatever you get, make sure they are forged. For a boosted motor, consider getting a steel top ring. Callie CompStar rods with ARP bolts are right on the mark. There are two ways to drop the compression ratio, dished pistons or heads with a larger compression chamber (ok, 3 ways if you play around with head gasket thickness). I would pick which heads you plan to run first and then choose pistions to match the desired CR. Dropping a point of CR will allow you to run more boost in the future of course. I'd be tempted to get L92 heads, if this was my project. But, that will require more swapping of parts. The simpliest is to have your current heads ported (if they are undamaged) and then pick the appropriate piston.

Thanks for the info! Yeah the block only has 22k miles. Shouldn't I be able to get away with just a fresh hone if the walls aren't scratched?? I definitely won't buy the pistons until the a machinist can determine what we can do with the current block. That's ALWAYS good advice though man.

So how do I decide how many cc of a dish I want in my piston to get an appropriate compression ratio? And how do I determine how much boost a certain cc dish can handle?

And back to the heads... what's the difference between the L92 heads and 317's? What all needs to be done to get each set of heads to work on this this motor? I would definitely go the route of just porting the stock 243's, but since the 243's don't have a thick deck I think I was previously told that they're not a good choice for boosted setups. Is that correct?

With low pampered miles, you might be able to get away with just a hone. You'll need your machinist to mic the bore and make that determination. Personally, I would want a fresh bore if I'm going to the expense and trouble of installing forged pistons. Don't skimp on important stuff like proper ring seating when you plan to boost that bad boy.

As for calculating the compression ratio, your machine shop should be able to do that or use a CR calculator like this one:

http://www.csgnetwork.com/compcalc.html

Heads: the 317 casting is used in low compression trucks. They are similar to your current 243 except they have larger chambers. I would not go that route. Either use the 243 and get the pistons with the right dish for your target CR or invest in better flowing heads.

What CR should you run? I'm not a forced induction expert, but I would probably drop down to about 9.5 CR (give or take). Do some more research in this regard.

If you want to change heads, the L92 heads have 70cc combustion chambers. That should drop CR at least a 1/2 point. The L92 flow better and have bigger valves. Best of all, they are cheap. You will need to use the correct valve train parts to switch to L92 head. This is not a big deal. Plenty of good threads describing everything you need to do for a swap.

As for the 243 not being suited for FI, it's true some other heads are better because they have thicker deck area. That's not to say you can't use 243 heads, it's just that other heads might be a better choice.

Quote: Originally Posted by batboy... With low pampered miles, you might be able to get away with just a hone. You'll need your machinist to mic the bore and make that determination. Personally, I would want a fresh bore if I'm going to the expense and trouble of installing forged pistons. Don't skimp on important stuff like proper ring seating when you plan to boost that bad boy. As for calculating the compression ratio, your machine shop should be able to do that or use a CR calculator like this one: http://www.csgnetwork.com/compcalc.html Heads: the 317 casting is used in low compression trucks. They are similar to your current 243 except they have larger chambers. I would not go that route. Either use the 243 and get the pistons with the right dish for your target CR or invest in better flowing heads. What CR should you run? I'm not a forced induction expert, but I would probably drop down to about 9.5 CR (give or take). Do some more research in this regard. If you want to change heads, the L92 heads have 70cc combustion chambers. That should drop CR at least a 1/2 point. The L92 flow better and have bigger valves. Best of all, they are cheap. You will need to use the correct valve train parts to switch to L92 head. This is not a big deal. Plenty of good threads describing everything you need to do for a swap. As for the 243 not being suited for FI, it's true some other heads are better because they have thicker deck area. That's not to say you can't use 243 heads, it's just that other heads might be a better choice.

i disagree on the piston/head talk. if you choose the piston to the head, you're smurfed for changing compression again later. if you choose a stock cr piston with your stock chamber 243s, you have ~10.9:1. now you can toss 317s on there. and get down to like 9.5:1 or so, just buy swapping heads. if you decide to pull turbo later or sell motor, you slap 243s back on and you have a good n/a motor again. alot easier to swap heads than pistons later.

I think I understand now that keeping the some CR pistons and using lower compression heads will allow for extra power. But will either the 317 heads or the L92 heads allow for enough boost to make 900+ rwhp when used with factory CR forged pistons?

So can any of you guys give me specifics on what's needed to make the 317's or the L92's come together on my motor???

I don't understand why you'd want to put 317 heads on. You gain no better flow over the stock 243. The only thing you get is lower CR. He has to replace pistons anyway. Now if you weren't changing pistons and were on a tight budget, then I can see the logic of going 317. Boosted motors actual benefit from using dished pistons and smaller combustion chambers. If you're going to the trouble and expense to change heads, then get something that will actually flow better. With 70cc heads and a minor dish to the pistons, if you want to return to N/A, just mill the 243 heads a little to bump up the CR again.

OP, if you do go the 317 route, it uses the same exact valvetrain as the 243. If you swap to a bigger cam, you'll need better valve springs and hardened pushrods regardless of what heads you use. If you go with L92/LS3 heads, you'll need to use L92/LS3 head gaskets. You'll also need a LS3 or L76 or FAST 102 intake manifold. Additionally, you'll need L92 rockers and pedestals (LS7 rockers might work too, but double check that first).

If you use the search button and type in L92, you'll find a lot of info. Here are a couple links to get you started.

http://www.ls1gto.com/forums/showpos...22&postcount=7

http://www.ls1gto.com/forums/showthread.php?t=177018

Yeah I'm not sure which heads I'd want to use personally. I mean, is more flow really necessary from the L92's? I'm not sure how much it would cost to gather up the other necessary parts (valvetrain stuff and intake manifold) in order to make the L92's work. I already have upgraded valve springs and pushrods on my 243's, so if I can use that stuff on a set of 317 heads to cut costs then that may be a direction to look, since the 317's can use the LS2 intake manifold.

I mean if the better flow characteristics of the L92's is necessary then that's a different story. But if they're just suggested for the extra horsepower from them then that shouldn't be a big deal because I can always crank the boost up to compensate, right? My twin turbo setup should be able to make some monster power, so as long as 317's can handle the boost necessary to make 900 rwhp or so I think I'll at least consider them. What do you think?

Thanks for the links also. I'll check them out here shortly. I found a really good one yesterday afternoon covering great information about the L92 heads, but couldn't find anything in that thread stating what all was need to swap them in. I'll check to see if either of those two links go over the valve train parts needed and all to make the L92's work. Thanks again for all of your help so far!

You do have the advantage of cranking up the boost to compensate, so head flow isn't quite as critical as with N/A applications. Your choice really. It would be much cheaper just staying with your 243 with dished pistons (you have to buy pistons regardless). I know a couple people running forced induction with 243 heads. The main problem they have is finding traction. Picking up a pair of 317 heads and using stock height forged pistons is certainly an option too. I don't see the wisdom of buying another set of heads though if you don't gain any power.

Quote: Originally Posted by MEAN GTO... So after tearing apart my engine this evening I found that I have a chunk missing out of the top of my #1 piston due to some trouble I was having yesterday when under full throttle. Any how, I had started a thread asking for advice on a motor build back earlier this year before my turbo setup was actually finished and the car was running. Now that I've experienced the behavior of the engine with the setup I would like to start a new thread. Especially since the time has now come. So provided that there's nothing wrong with any cylinder walls (haven't inspected but one bank of cylinders so far) I'd like to keep the block, and possibly keep the same bore. If any cylinder walls have any scratching then I'll have the block slightly bored. Well, at just 8 PSI the motor had plenty of low-end before the turbos kicked in, and the turbos kicked in very quickly. I don't want the new setup to have too low of compression for my taste to cause a bit of lag, or lugging-around of the motor. But I do want the motor to be able to support enough boost to make around 900 rwhp through a stalled automatic transmission. The stock engine (with blower cam) currently made 639 rwhp at 8 PSI. So the turbo's seem to be pretty potent. They are Precision "HP Series" 62mm turbos, with .81 A/R. I'm not looking to spend a fortune on pistons, rings, and rods (and necessary hardware), but I do want some decent stuff. I was thinking maybe Diamond pistons and CompStar rods with ARP rod bolts and head studs. What do you guys think?? I'm not sure particularly sure what pistons I'd need exactly, which I think is where I need the biggest help. I'm also unsure of which heads I'm going to go with but I'll need something that can be afforded on a budget. So if you all can give me your opinions on what I should go with I'd appreciate it a bunch!! Thanks, Andrew

We would be happy to help you with a nice rotating assembly. We have been using K1 Crankshafts and Rods with great success. They are very nice quality and the price is great. We use Diamond Pistons for all of our builds. They are very well made and we have used them in many 8 second applications. I would recommend upgrading the Crankshaft vs. just the Rods and Pistons. The bigger the cubes the better. As far as Cylinder Heads, anything beyond 15 psi and you'll be glad to have a thicker deck like the Trickflows or AFRs. Depending on the Crankshaft you're using, I would keep the compression in the 8.5-9.0 range.

Quote: Originally Posted by batboy... You do have the advantage of cranking up the boost to compensate, so head flow isn't quite as critical as with N/A applications. Your choice really. It would be much cheaper just staying with your 243 with dished pistons (you have to buy pistons regardless). I know a couple people running forced induction with 243 heads. The main problem they have is finding traction. Picking up a pair of 317 heads and using stock height forged pistons is certainly an option too. I don't see the wisdom of buying another set of heads though if you don't gain any power.

Yeah I mean back in the day when I was considering staying N/A, and even when I had the Maggie I was all about making more power when it came down to choosing another set of heads. Now that I can make more boost/power just by pushing a button on my controller I don't look at it to be as big of a factor. I mean, if I were to even port 317's for better flow it sounds like it may cost me a bit less than to go the L92 route.

I guess I'm now just concerned about a thicker deck set of heads as well as my budget more than anything. Do either the 317's or the L92's have a thicker deck than the 243's???

The deck thickness of the 243, 317, and L92 heads are probably about the same. Like Seth said, you if plan to build an engine to handle more than 15 psi, you better have deep pockets and spend some bucks. For thick deck heads, look to PRC, Trickflow, or AFR.