View Full Version : Turboing a 461ci Pontiac

02-27-2006, 07:21 PM
I'd like to build a single turbod 461ci pontiac motor. Here is the motor I was planning on building. I wasnt looking for anything extravengent or expensive, just something that will work. I was only gonna run like 6-7lbs. I'm new to forced induction so any help would be great. I read the article bout 1 - 1-1/2 years ago in high perf pontiac bout a guy who turbod his 455 for under like $900 using a junkyard turbo and being creative. http://highperformancepontiac.com/tech/0309pon_turbo/ anyone have and good ideas? I was thinking bout getting a turbo off like chevy 6.5L turbo diesel pickup. also how reliable would the stock rods/crank be under about 6lbs of boost? If they would be reliable i'll probably just bore it .030 and use speed pro forged pistons to save money.

Not sure on carb for turbo app
edelbrock performer intake manifold
edelbrock performer 87cc heads
comp cams 51-222-4 cam(rpm:1300-5500 | DUR @ .050: 218/224 | Lift w/ 1.5: .462/.470 | LSA: 110*)
comp cams alum 1.65 roller rockers
comp cams chromemoly pushrods
eagle 461ci stroker kit(forged pistons, forged h beam rods, cast crank)
D Port exhaust manifolds
moroso deep oil pan
not sure on turbo or wastegate or bov

02-27-2006, 09:28 PM
I don't know much about Pontiac motors but with that size, I would DEFINATELY go with 2 of the 6.5 turbos.

02-28-2006, 02:35 PM
I would definitely recommend buying a copy of Corky Bells's book "Maximum Boost". It will address everything you are asking, from layout to fabrication to testing.

Good luck - sounds like fun!


02-28-2006, 02:54 PM
I remember seeing an article awhile back about a compnay that used to make turbo kits for Trans Am's. I think it was HO performance or something like that. It used a small turbo and included cast manifolds and such. I think they had said something about coming back out with it. You might also check at the Performance Years forum or the Pontiac Zone forum you may get some good info there. I know if you were looking at an S/C combo the Ken's speed and machine could help you. Also there is rumor that BOP engineering and Vortech are working on a kit (For an S/C motor).

02-28-2006, 06:47 PM
67bird, you are correct bout reading the article. back in 79 a company called HO Performance did have a turbo kit for the pontiac motors. Anyone have any idea how much boost the stock rods/crank can take? If they can take around 8lbs, I might just bore the 400 out .030 and use stock rods/crank with 6X-8 heads and RA D Port manifolds. Here is a basic(bad) drawing of what I was planning. I'm not too familiar with turbo setups, so if somethings backwards pls lemme know.

Little Bob
03-01-2006, 10:47 AM
I would definitely recommend buying a copy of Corky Bells's book "Maximum Boost". It will address everything you are asking, from layout to fabrication to testing.

Good luck - sounds like fun!


Yeh what he said, and I also would check out www.turbomustangs.com know what your thinking. No It's not just Mustangs. It's probally the most comprehensive collection of information on Turbocharging out there. You can also check out www.pontiaczone.com and www.performanceyears.com/forums. Just do a search on Pontiac Turbo. I'm also planning a turbocharged Pontiac. I have one piece of advice for you, Just remember you get what you pay for. If you want a reliable system with a deciant amount of power. It's going to cost you.

03-01-2006, 11:40 AM
You may have heard of them?


03-01-2006, 02:14 PM
Hey that pic is about what my turbo setup looks like on the vette except my turbos have the intakes facing each other and suck fresh air from the cowl hood. I have seen a few twin 6.5 turbos on small blocks and they work good but they might be too small for that much displacment

John Monnin
03-01-2006, 03:45 PM
Do yourself a favor and buy a kit from a shop or learn how to read turbo compressor flow maps.

For example I the flow map below is from a guy looking for turbos for drag racing a 3.0L twin turbo engine with a 7300RPM redline and I did this quick estimate. Much of this in information is from Jeff Lucius's webpage.

Corky Bell's Book " Maximum Boost" shows you step by step exactly how to calculate the engine demand and read compressor flow maps. The best way to undstand it is to follow along and run the numbers for your car.

The super simplified interpretation, making a LOT of assumptions, like your car is at sea level, the volumetric efficency is always 85%.... This simplifies things a lot,maybe too much, but gives you a decent idea if a turbo is the right size

The Left side of the chart is Pressure ratio, this is (Boost level+ 14.7)/14.7psi
So 15psi of boost has a pressure ratio of (15+14.7)/14.7 = 2.02

The bottom of the chart is how much air your engine needs at a specific RPM and boost level. I used 85% volumetric efficiency for a DOHC engine but an old school Pontiac is probably lower. to simplify the calculation: Use this formula
(Cubic inches x RPMx.5X.85XPressure ratio)/1728.

So for a 183CU(3.0L) engine at 5000RPM the CFM required =
183CIx5000rpmx.5x.85x2.02/1728 = 454CFM,

Since my car has 2 turbos each turbo only has to flow 1/2 as much = 227CFM@5000 RPM

Go to the compressor flow map and draw a horizontal line at a pressure ratio of 2.0, then draw a verticle line at 227CFM.


The two lines intersect on the 76% zone, This means the compressor is 76% efficent at this flow and boost. Jeff used a higher volumetric efficiency for the engine so my calculation is a little off, but not too far off. Usually you will not know the true volumetric efficnecy of the engine so this value is a guess.

The zone in the middle of the flow map is the highest efficency zone. Each ring farther from the middle zone is a little less efficient. The line on the left is called the surge line. If the intersection of these lines is left of the surge line the turbo is not making usable boost. If the intesection gets off the map to the right the turbo can not flow that much air at that boost level.

You want as much of the demand of your engine to be in the center high efficiency zone of the turbo. That is why you look at the boost level at the full range of boost levels and RPMS that you will be running.

Flow maps don't take into account several other issues so don't get too obsessed with them. They do give you a good idea if a turbo is going to be sized right for the RPMS and bost you plan on running, The the compessor flow maps do show how a HUGE turbo that makes massive horsepower can make less horsepower than a smaller turbo at lower RPMS.

P.S. The guy running these turbos was not happy with the performance he had, too much lag and he had to make tons of boost to get to the sweet spot on the turbo. This compressor flow map shows that the turbo was probably too big but he ignored it to his regret later

John Monnin
03-01-2006, 03:49 PM
I calculated that with a custom billet crank I could stroke my engine to 4.1L So I reran the numbers with a 4.1L engine


The SOLID colored lines are a chart of a series of flow calcualtions at differnt RPMS. For example the solid green line is the engine demand at 5000RPM assuming a 96% volumnetic efficiency.

The Dashed lines show the the boost level being ran.
For Example the dashed Yellow line represents 15 psi of boost.

To read the chart find the intersection of the RPM and the boost.

The intesection of the solid green 5000RPM line and the dashed yellow 15psi line is in the middle of the highest efficiency zone of the compressor wheel.

The solid lines

Notice how the demand of the engine drops right in the middle of the compressor flow map. 2 or these turbos shoudl be awesome with a 4.1L engine.

P.S. The volumentirc efficiences are really high on these charts, this was based off of the dyno charts of some highly modified 6G72 engines by guys who are smarter than me so I just use thier numbers.

03-02-2006, 07:57 AM
im probably just gonna stick with a N/A 400. thanx for the info guys, Its too much for me to get into right now.