"Just go turbo first, that's where you will end up anyway" <-- I should have listened

[Samurai7one]

Guys, I'm pondering a turbo build.  I have many parts to pick from but not sure which route to go. Here's a short list of the parts I have on hand:

 

-My current engine: L28 triple Mukuni, flat top pistons, P90 head (shaved .080") 

-N42 block/N47 head, stock internals, clifford 4BBL intake, Holley Carb

-N42 block/N42 Head, completely stock setup.   

-I have a stock turbo manifold and was gonna acquire a Pro Tunerz Intake & a MS3 setup.

 

I will use stock internals w/ probably some Ross or JE dished forged turbo pistons. N42 block is a given, but which head?  P90 would be a no brainer, but its been shaved.  I can always use a 2mm thick high quality head gasket (e.g. Kameari) to get the compression back down some.  But maybe I should just use the N42 Head. IDK

 

Alternatively, I can run the N42/N47 all stock including pistons with the turbo setup and just see how much boost it can take lol.

 

Thoughts?

 

 

 

[AydinZ71]

3 hours ago, Samurai7one said:

Guys, I'm pondering a turbo build.  I have many parts to pick from but not sure which route to go. Here's a short list of the parts I have on hand:

 

-My current engine: L28 triple Mukuni, flat top pistons, P90 head (shaved .080") 

-N42 block/N47 head, stock internals, clifford 4BBL intake, Holley Carb

-N42 block/N42 Head, completely stock setup.   

-I have a stock turbo manifold and was gonna acquire a Pro Tunerz Intake & a MS3 setup.

 

I will use stock internals w/ probably some Ross or JE dished forged turbo pistons. N42 block is a given, but which head?  P90 would be a no brainer, but its been shaved.  I can always use a 2mm thick high quality head gasket (e.g. Kameari) to get the compression back down some.  But maybe I should just use the N42 Head. IDK

 

Alternatively, I can run the N42/N47 all stock including pistons with the turbo setup and just see how much boost it can take lol.

 

Thoughts?

 

 

 

 

you should CC your head and run the calc to determine your static CR. 8.0-8.5 you can still make decent boost without detonating. Stock is 7.4

[rossman]

9 hours ago, AydinZ71 said:

you should CC your head and run the calc to determine your static CR. 8.0-8.5 you can still make decent boost without detonating. Stock is 7.4

Yep, with that selection of parts, I'd run the n42/p90 and if needed, get custom pistons to get the compression in the range Aydin recommended.

 

I'm running a 3l n42/p90 turbo setup with 8.5 CR at 20 psi of boost. I've never had it dyno'd but it's got more than enough power for the street.

[Samurai7one]

Thanks for the reply guys.  Any suggestions on where to get custom pistons, that won't break the bank?

[AydinZ71]

Unfortunately, if they are worth getting, they will be expensive  minimum $1200. 
 

i would step Back for a second and identify your power/torque goals and budget. We could let you know the steps once that’s figured out. I have never boosted the OEM NA block, so I can’t tell you what the limit of the OEM pistons are. I have an L28et block where the OEM pistons were designed specifically for boost (rings are lower from the crown). The OEM bottom end should do 400ft-lbs of torque and whatever HP your head can flow. 
 

if you want something that is very reliable but staying under 400ft-lbs, I would just consider forged pistons designed specifically for boost. Beyond 400, you need better rods as well. Have not run into someone who broke the crank thus far (exception: poor balancing and machining). It’s way over-designed and heavy. 

with you head, have it CC’d. I doubt any of us have enough experience to know precisely how many CC’s you have left after removing 0.08 (which is a lot). Once you know the CC’s, it’s an easy calc to figure out your CR without a dish, and you can add dish CC’s to get the CR you need.

 

i am oversimplifying since you also need to check your deck clearance, bore, etc. but that’s all easy the check yourself with a caliper. Then head CC’s are the thing most folks don’t have the patience and skill to do right, much machinists do it all the time. 

[Tony D]

On 1/23/2022 at 2:16 AM, Samurai7one said:

Thanks for the reply guys.  Any suggestions on where to get custom pistons, that won't break the bank?

Run the stock build engine and spend your money on porting, polishing, camshaft and EMS along with a properly sized turbo. An all stock L28 at stock compression ratio of 8.5 will run 350hp without anything but be somewhat of a boring ride IMO (see end for why.) 

A bone stock L28 N42/N42 bottom end with a ported, polished, cammed and fuel injected (Now, was blow through mikunis) EMS can make upwards of 450HP at 17psi with a GT35R strapped to it.... And that's limited to under 7,000 rpms. Once you get all that sorted, and are satisfied with your build THEN buy your pistons and retune as you deem necessary.

By that time you will know what you are doing, and breaking the pistons will not break your bank. I know someone who did not listen to this device and spent upwards of $6000 on engine 'refreshes' before he listened, put a stock bottom end under his head and bolt-ons and then blew those pistons three more times before getting it all right. But those pistons and rings only cost him $200-300 a set (ITM off eBay) and he learned that after the Fel Pro Gasket blows three times, likely the pistons are shot...

All those failures on the stock bottom end didn't add up to the costs of ONE refresh of his forged piston built engine. He was mildly annoyed that a stock bottom end ended up besting his 'first generation forged piston' build by some 25 odd horsepower and at only 17psi instead of 30!

Spend your time on fuel delivery and airflow, same as an N/A. Then worry about durability.

You WILL blow up your engine tuning it if you're going after big numbers, and even if you're not clogged injectors can sink your setup at 8psi as spark knock at 30psi. 

I'd never put a MLS head gasket or Forged Pistons in a Boosted Build unless all major tuning is over and I was satisfied with the results to 7,000 and only had 7,000+ left to tune. Even then, I'd keep a Fel Pro Gasket in there for a 'safety valve' in case detonation occurred. Blowing a $50 head gasket is better than sinking the rings on 5 of your cylinders because a fuel filter decided to explode and clogged all your injectors!

Identify your power goals in advance, and work to them. Don't get greedy and make components do something they aren't capable or suited to doing. Under 400HP cast pistons will do just fine unless you want the engine to ACT like an L-Series and pull to 8,000... then you will need forged pistons and woo wheee will it be fun to drive compared to a big boost low-flow setup which will basically be a Boring Big Block Corvette setup. Sell the Z in that case and buy the Vette...

Edited May 10, 2022 by Tony D