Big block turbo sizing

[junior636]

Just dreaming right now but I’ve considered putting twin turbos on my 512. Always wanted a turbo car. Not looking to set the world on fire just get another 200-300hp out of it. I’m not interested in hearing about block strength. What size twins would I be looking at for low boost on an engine this large? Probably just run 7lbs off the waste gate. I’ve built a few turbo set ups and then never finished them . Pics of my current 512 in the orange car and the 440 turbo I built but then sold before getting it going.

 

[MadScientistMat]

I'm using a single Garrett GT40 on a slant six, and it spools up at around 3000 rpm. You have a bit more than twice the displacement and it looks like you are being a bit more aggressive on the motor, so I would say two GT40s ought to be about perfect.

 

[RustyRatRod]

 

[junior636]

View attachment 1716497007

Too small

 

[TT5.9mag]

I run twin 78/75s on 496 inches at low (9psi) boost on gasoline non intercooled.

 

[TT5.9mag]

Probably just run 7lbs off the waste gate.

Good luck with that. That’s what everyone says. Right up until they run 7psi. It’s almost immediately when you think “I wonder what 8psi feels like?”

 

[junior636]

I run twin 78/75s on 496 inches at low (9psi) boost on gasoline non intercooled.

Do they spool up good/quick? I was thinking smaller since I’m not trying to make much power. I’ve done 2 single turbo set ups and the merge is always a pain. That’s why I’m wanting to go with twins.

 

[TT5.9mag]

With a single you make a merge on the hot side. With twins you make a merge on the cold side.

Yes it spools instantantly but it’s in a boat in front of a jet and there is always a ton of load. On the dyno we started the pulls around 3500 and it was in boost right at the hit. The turbos have billet compressor wheels, new gen turbines, and ball bearings, so all the crap to make em spin up fast.

What is your total power goal? And how much power does the engine make NA?

 

[junior636]

With a single you make a merge on the hot side. With twins you make a merge on the cold side.

Yes it spools instantantly but it’s in a boat in front of a jet and there is always a ton of load. On the dyno we started the pulls around 3500 and it was in boost right at the hit. The turbos have billet compressor wheels, new gen turbines, and ball bearings, so all the crap to make em spin up fast.

What is your total power goal? And how much power does the engine make NA?

My guess is 600-650hp right now. 800ish hp would be great until I can get an aftermarket block if I decide to turn it up or go racing. I have the sickness and they just never feel fast enough. Really just a street car not planning a lot of track time. Something very simple, low boost non intercooled with a blow through carb, 5-7 psi.

 

[TT5.9mag]

My guess is 600-650hp right now. 800ish hp would be great until I can get an aftermarket block if I decide to turn it up or go racing. I have the sickness and they just never feel fast enough. Really just a street car not planning a lot of track time. Something very simple, low boost non intercooled with a blow through carb, 5-7 psi.

650 NA plus 7 psi is about 975hp. Blow through carb is good if you’re going to run non intercooled. I wouldn’t worry too much about the block. They can take a lot of power when prepped correctly. @Turbo440Dart just made more than 800 on a stock block and we were hardly leaning on it, and his doesn’t make nearly that much NA. You can use smaller turbos but the way they’re sized you start to run in to back pressure issues with the small hot side. I use twin 67/62s on my W2 magnum at 360 inches. I bet those would spool instantly on 512 inches and backpressure would probably be up near 2:1 at full song with 650na hp. Twin 70s with .96 hot sides would be about as small as I’d recommend on that big of an engine.

 

[Turbo440Dart]

650 NA plus 7 psi is about 975hp. Blow through carb is good if you’re going to run non intercooled. I wouldn’t worry too much about the block. They can take a lot of power when prepped correctly. @Turbo440Dart just made more than 800 on a stock block and we were hardly leaning on it, and his doesn’t make nearly that much NA. You can use smaller turbos but the way they’re sized you start to run in to back pressure issues with the small hot side. I use twin 67/62s on my W2 magnum at 360 inches. I bet those would spool instantly on 512 inches and backpressure would probably be up near 2:1 at full song with 650na hp. Twin 70s with .96 hot sides would be about as small as I’d recommend on that big of an engine.

Judging by his old combo photos me and him have spoken on the facespace a time or two.

His combo should sneeze 800 with a couple pounds to it. Definitely won’t take 7-8 to get there.

 

[junior636]

Judging by his old combo photos me and him have spoken on the facespace a time or two.

His combo should sneeze 800 with a couple pounds to it. Definitely won’t take 7-8 to get there.

Yeah, that’s me. I just can’t be happy until I go turbo lol

 

[TT5.9mag]

Yeah, that’s me. I just can’t be happy until I go turbo lol

Do it!!