Adamsquirrel

Hi everyone, can you help me plan? I have specific questions at the end. The rest is context. Thanks!

Well I joined this forum a while back when I started shopping for my LS motor. I decided to go with a 5.3 L33 (flat-top piston, LS6 cam, aluminum block, 9.9:1 compression, 799/243 heads). This will mate up to a Tremec TR6060 manual transmission I just got out of a 2015 Camaro (the MM6 transmission, not the M10). The goal is to have a bit more power (between 600 and 650hp on 89 or 91) but nothing over 700 because I don't want to start breaking other components that can't handle anything over 700. All this will go in a late 60's corvette with a modified frame to fit the LS and transmission. This car will only see spirited canyon, and freeway street driving (no drag strip).

Things I want: Between 600 and 650 Wheel HP (with at least 450 in the 3000RPM range), gas mileage at least 25mpg when driving conservatively, and virtually NA responsiveness from the motor (in other words, a smooth power curve with not huge jumps or dips).

In order to achieve my desired power output from this motor, I'm wanting to go with turbo(s). A fast, practically NA fast, spooling turbo setup.

The plan so far...
1. From watching all the Richard Holdener videos related to the subject, it seems clear that increasing low end torque helps spooling speed. So I'll be putting a BTR Truck Norris cam in the motor and valve springs to suit it as well of course.
2. I'll be running a LS6 intake manifold because I need the space in the car.
3. I'll be using stock exhaust manifolds either from a C5 corvette or the original L33 truck manifolds.

Questions:
1. Regarding compound turbo sizing- My initial thought was to start with a GT35, into a GT45 (budget matters for turbos, so inexpensive ($500 and less per turbo) turbos are the only things I'm considering). Richard Holdener does a good job saying "make sure you pick the right turbo sizes for your engine displacement and application" but that is where the road ends. How do I research what will be optimal for my setup? I'm not sure where to start.
2. To further increase the heat going to the turbo's (which runs them up), wouldn't having the outside of the headers and exhaust (including tubing throughout the turbo system) ceramic coated, help trap some of that heat inside? Aiding me in my response quest?
3. Is using a GT35, into a GT45, a bad idea overall if I'm only looking to get 650 max wheel horsepower? Will that just be too LITTLE boost per unit, causing issues with exhaust flow?
4. Finally, ring gap for this plan. Maybe 25 top ring 28 second ring?

Thank you for the wisdom and guidance on my journey. :-)

TrendSetter

Why are you compounding? You can make 650whp with a traditional setup much easier.

Adamsquirrel

Good question... as I mentioned in the initial post one of my goals is to have as smooth of a power curve as I can get. From what I understand reading online about compound turbo setups, the smaller turbo helps spool the power and influences the power curve more on the low end of the RPM range, and as you move higher in the rpm range, the larger turbo influences the curve more. Again from more that I have read, it seems the entire point of the compound turbo setup is to smoothen out this overall power curve. But doing this properly is what my first questions was about. How do you size them properly (then at what boost level) for my 5.3? I have no idea about how to calculate those things, so I'm hoping someone has some idea of where to point me.

G Atsma

I think this is much ado about relatively very little possible benefit.
Build the engine for a strong bottom and midrange, then size the hairdryer to pick up the ball to raise the curve smoothly but very effectively.
Watch some Richard Holdener videos. He loves boost and knows what it takes to use it effectively.

TrendSetter

I’m not sure you can size compound turbos correctly to make 650hp on a 5.3. Each turbo would only need to make like 5 psi so they would be way out of their efficiency range. Compound turbos are more for efficiently making very high boost numbers.
Your goals and planned path forward are not compatible.

gametech

iTrader: (1)

OP needs to ditch the 5.3 in favor of a K20, or ditch the idea of compound turbos. Pretty sure in a classic vette, the compound idea is the one to get rid of.

Adamsquirrel

Ah ok. Yes I've watched his videos as I mentioned in the original post. That's what brought on my inquire to begin with here. Are you suggesting a single GT35 with a higher boost? 12? Or a GT45 with a bit less boost? 10?

Adamsquirrel

My previous post was meant for you. Forgot to include the quote.

Adamsquirrel

Got it. What is a typical efficiency range?

Adamsquirrel

Definitely not doing a K20, but others have mentioned it's probably better to go single turbo. :-)

G Atsma

I'm really not the one to ask about turbo spec'ing. Plenty of guys here can do that quite well from my observations.

gametech

iTrader: (1)

Search in the forced induction section for threads by username "customblackbird". He did testing with a 5.3 of a variety of turbos complete with info regarding spool time and backpressure. There is one 5 page thread in particular that has his testing, as well as many comments from others with more info.

LS1Formulation

iTrader: (13)

Here's your turbo: https://turbo4less.com/product/vsr-6...illet-t4-96ar/

It's going to spool fast and give you great midrange power, but it'll be out of steam at the top end of the RPM range. However, if all you're looking for is 600-650 RWHP, it should be able to handle that just fine.

Adamsquirrel

Thanks for that! I'm looking through his posts now.

Adamsquirrel

Sweet! Thanks for that recommendation! I'll do some homework on it. Seems like the right size. :-)

LS1Formulation

iTrader: (13)

One thing to keep in mind is, they have different exhaust housings that can improve response at the expense of top end power, or vice versa. For that turbo, it looks like they have a .81 A/R and a .96 A/R. Given that it's pretty small, I would go with the .96 A/R and if the response isn't what you'd hoped for, purchase the .81 A/R and swap it on. I did the exact opposite recently, bought a 1.25 A/R housing to replace my .96 A/R on my 78/75 because I was worried that I wouldn't hit my power goals ( 800 +) with the .96 A/R. Cost me $169 and I had it swapped in under 5 minutes.

TrendSetter

did you test it or just kept you up at night?

LS1Formulation

iTrader: (13)

It was just from doing research on it, and from what other people were using in their combos. I'd only purchased the .96 A/R in the first place because my Huronspeed kit had a 3" downpipe and I wouldn't have been able to use the 1.25 A/R because it has a 4" outlet. Turned out that the Huronspeed downpipe won't fit due to my UMI K-member, so I'm doing a clean sheet 4" dump pipe with a boost activated cutout, and a 3" downpipe fishmouthed in. Possibly smaller if needed, the exhaust will only be there to quiet it down under normal street driving. If it does turn out to be too laggy on the street, I still have the .96, so I'll just have my fab guy make me an adapter to go from 3" to the 4" dump pipe.