#1  
Old 06-12-2020, 02:27 AM
Maloner Maloner is offline
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Default Pontiac 400 twin turbo build

Hey all,

I just signed up to this forum after very high praise from a much respected family member who has been a die hard pontiac fanatic since they started turning wrenches. I'm sure there's info on the forum for this topic, but I'm still figuring out how to navigate and where to look! Any links to helpful content would be much appreciated. Google search has proven to be a little watered down and gets a little broad. I suppose there's not very many turbo'd pontiac 400 builds?

That being said, I've finally decided to kick off my 1970 firebird twin turbo build and I'm running into road blocks left and right. Ultimately at this point I need help finding the right turbos for my build. I'm having trouble finding things like the required air flow for a pontiac 400 engine and required boost pressure ratios so I can disect turbo maps.

Helpful info for opinions would be that I'll be converting the engine to EFI with a coil near plug ignition system and electronic dizzy. I'll have a stand alone ECU system to fine tune ratios, the engine will have ARP everything with metal headgaskets along with forged internals, upgraded valvetrain, flat top pistons and a roller cam (which I'm not sure if I need to figure out the right cam before deciding on turbos or vice versa). I'll be boring the block .30 over and keeping the stroke the same. The purpose of the car will be to casually auto cross and run quarters, but more so to be a fun weekend warrior.

At this point I haven't found any parts I'd be comfortable to click "buy" on because I still don't know exactly what's right for the set up I'm aiming for. Help!!

Anyways. Any sort of direction to help my build would be much appreciated. I look forward to seeing what this community has to offer.

Cheers,
- Maloner

  #2  
Old 06-12-2020, 06:38 AM
roylee62 roylee62 is offline
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While you’re waiting for the smart guys to show up, here is the “reading compression maps for dummies” as I understand it …..
You need to decide the max power level based on the limitations of your engine/drivetrain/traction etc.
Say for example you have a goal of 600hp, and you build the motor (naturally aspirated) something like a R/A III 350hp. (EFI will not increase or decrease power).
To make 600hp, the motor will need 60lb/min of air. Or 30 for each turbo.
For each 1psi of boost, you increase power by 7%.
So to get from 350hp to 600, you’ll need 10psi of boost. (10psi*7%/psi=70%. 70% of 350hp = 245hp)
That’s a pressure ratio of (10+14.5)/14.5 = 1.7. You need to push 70% more air than atmospheric to get to 600hp. Since an engine is basically an air pump, power level is proportional to air intake.
So when you read the compression map, you’ll want the point at pressure ratio 1.7 and lb/min=30 to be inside the most efficient island.
The Borg Warner website has an excellent tool for sizing turbos, with real-time efficiencies at various rpm levels. They also have the turbine (hot side) maps. I just discussed the compression side above.

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  #3  
Old 06-12-2020, 07:01 PM
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Tom Vaught Tom Vaught is offline
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Very Good Post, roylee62. and welcome maloner.

Think you have a very slight typo error with a couple of names (example: Compressor Maps vs compression maps), but the info posted is rock solid otherwise.

Your math is right on the money.

Your mention of the Borg Warner website "matchbot" has a really long link if you do a search on that program.
This link is much shorter.
https://www.borgwarner.com/go/NMY4HT
then at the top where it says "visit" click on that and you should be there.

A few members have made over 700 hp at 13 psi of boost pressure with a belt driven compressor and a turbo system will not have the belt/compressor HP losses.

Welcome to the board.

Tom Vaught

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  #4  
Old 06-22-2020, 11:17 PM
Evil68 Evil68 is offline
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Default Turbo set up for your car

I have a running 68 Gto with a boosted 400. It’s a single turbo I’ve been running for 3 years and looking to sell car with original matching # motor. So the motor, trans, turbo set up and injection are coming out and will be sold, the motor and trans are for a boosted application and have less than 1000 miles. I have all receipts my turbo set up should fit right in call 732-397-6757

  #5  
Old 10-05-2021, 11:37 AM
rizarefaldi rizarefaldi is offline
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It will need 10psi of boost. (10psi*7%/psi=70%. 70% of 350hp = 245hp)
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  #6  
Old 10-05-2021, 12:22 PM
Tim john Tim john is offline
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Please confirm which engine block casting you plan on using, some are better than others.

Tim john---

  #7  
Old 10-05-2021, 03:10 PM
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turbo69bird turbo69bird is offline
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Single turbos are more efficient if you can achieve the same airflow through one. Usually twins are chosen for packaging more that HP gains

That or pure vanity.

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  #8  
Old 10-06-2021, 08:18 AM
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67Fbird 67Fbird is offline
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Not much input from me other than good luck!. I WANTED to go that route about 10+ yrs ago but there really is not much real estate in the front of an F body for all the packaging. It surely is beyond MY plumbing skill set to achieve the overall goal I WANTED. Unless you are swinging for the fence (800+ hp) you have tripled your cost compared to going with a simple efi and run 700 hp.

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