V8 compression ratio and supercharging a 3.2
#1
10-22-2011, 05:15 PM
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Posts: n/a
V8 compression ratio and supercharging a 3.2
Hi. 
Hoping someone can help out a bit here. I've done some Googling and even asked on another forum but not found the exact answers I'm looking for.
1. Does anyone know the compression ratio of the 3.2 litre AJV8 engine?
2. What compression ratio did the 4.0 supercharged XJR (x308) have?
3. Is it possible (in theory) or has anyone done this: fitted the intake manifold and supercharger off of an XJR to a 3.2 AJV8 engine?
The main question I'm asking is, how easy/possible is it to supercharge the 3.2 litre engine using off the shelf XJR parts?
I know some will want to know why and why not buy an XJR engine. Well I'm planning on maybe using the engine in a different car. An ebay purchase has made me the proud owner of a 1985 Ford Thunderbird, quite a rare car in the UK. Sadly the previous owner had pilfered the 5.0 Ford V8 engine out of the T-Bird for his Capri project. And I'm having trouble finding a Ford 302ci for sensible money.
So I'm considering alternatives.
The 3.2 Jag V8 seems plentiful and good value for money, it also makes more power than the stock 5.0 Ford unit did.
However I might find I'd want more power later on down the line, so I'm looking at the feasibility of supercharging it.
The reason for not going 4.0 or supercharged straight off is cost and availability. The 4.0 litre engine is easily double the cost of the 3.2 to buy and around 3 - 4 times more for a supercharged on.
I wouldn't be after huge power, just 300-320hp would be fine.
I know plenty of guys run 5-7psi supercharged setups on Chevy LS1 motors and they run 10.1:1 CR stock. So I'm hoping the Jag 3.2 would accept a similar amount of boost with stock internals and superunleaded (98 RON) fuel.
Thanks.
Hoping someone can help out a bit here. I've done some Googling and even asked on another forum but not found the exact answers I'm looking for.
1. Does anyone know the compression ratio of the 3.2 litre AJV8 engine?
2. What compression ratio did the 4.0 supercharged XJR (x308) have?
3. Is it possible (in theory) or has anyone done this: fitted the intake manifold and supercharger off of an XJR to a 3.2 AJV8 engine?
The main question I'm asking is, how easy/possible is it to supercharge the 3.2 litre engine using off the shelf XJR parts?
I know some will want to know why and why not buy an XJR engine. Well I'm planning on maybe using the engine in a different car. An ebay purchase has made me the proud owner of a 1985 Ford Thunderbird, quite a rare car in the UK. Sadly the previous owner had pilfered the 5.0 Ford V8 engine out of the T-Bird for his Capri project. And I'm having trouble finding a Ford 302ci for sensible money.
So I'm considering alternatives.
The 3.2 Jag V8 seems plentiful and good value for money, it also makes more power than the stock 5.0 Ford unit did.
However I might find I'd want more power later on down the line, so I'm looking at the feasibility of supercharging it.
The reason for not going 4.0 or supercharged straight off is cost and availability. The 4.0 litre engine is easily double the cost of the 3.2 to buy and around 3 - 4 times more for a supercharged on.
I wouldn't be after huge power, just 300-320hp would be fine.
I know plenty of guys run 5-7psi supercharged setups on Chevy LS1 motors and they run 10.1:1 CR stock. So I'm hoping the Jag 3.2 would accept a similar amount of boost with stock internals and superunleaded (98 RON) fuel.
Thanks.
#2
12-27-2011, 12:49 AM
Senior Member
Hello 300 Bhp/ton- welcome from Pistonheads.
The 3.2 litre engine is pretty stout- it has a castiron crank just like the 4 litre and 4.2 but being of a shorter stroke it is inherently stronger.
The compression ratio for the 3.2 is about 11:1- which is a tad high for a boosted engine. The oversquare nature of the 3.2 means you should target a slightly higher ratio than the stock 4 litre Supercharged engine, say 9.5:1 but this would involve custom pistons.
You say that a stock super charged 4 litre engine is more expensive but you would need the supercharger intercoolers that are part of the manifold of the larger boosted engine. If you don't have these you would have to custom build and that is really expensive. With custom pistons and intercooling you'd end up already above the price of a 4 litre AJ27 supercharged unit.
Then, ideally you should change the cam profiles/timings. Ideally you'd optimise them to your application but this isn't possible without sophisticated simulation software and/or extensive testing. A good place to start would be to use the fixed MOP 4 or 4.2 litre supercharged cams.
Again.
You see the problem?
Let me know if you have any further questions
Marquis Rex
The 3.2 litre engine is pretty stout- it has a castiron crank just like the 4 litre and 4.2 but being of a shorter stroke it is inherently stronger.
The compression ratio for the 3.2 is about 11:1- which is a tad high for a boosted engine. The oversquare nature of the 3.2 means you should target a slightly higher ratio than the stock 4 litre Supercharged engine, say 9.5:1 but this would involve custom pistons.
You say that a stock super charged 4 litre engine is more expensive but you would need the supercharger intercoolers that are part of the manifold of the larger boosted engine. If you don't have these you would have to custom build and that is really expensive. With custom pistons and intercooling you'd end up already above the price of a 4 litre AJ27 supercharged unit.
Then, ideally you should change the cam profiles/timings. Ideally you'd optimise them to your application but this isn't possible without sophisticated simulation software and/or extensive testing. A good place to start would be to use the fixed MOP 4 or 4.2 litre supercharged cams.
Again.
You see the problem?
Let me know if you have any further questions
Marquis Rex
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