Which would give me more HP?

[johncmng]

Which would give me more HP and Tourque over the stock 3.2 motor?

3.2Liter 10.3:1 CR
or
3.5 Liter 7.0:1 CR

Thanks in advance

[beepbeep]

first one in N/A form, second one (much more) in turbocharged form.

7:1 C/R is useless unless you turbocharge. It will allow 1+ bar of boost. Or you can make N/A engine of it and drive it on kerozine

[cstreit]

WHat he said. You didn't mention turbocharging, so why would you go wtih 7.0:1 compression?

[johncmng]

I was thinking about going to 7.0:1 CR and Turbocharging it till I have $$$$.

[beepbeep]

You'll have spanking 130-140 ponnys w/o turbo on 7:1 C/R.

[johncmng]

Even on a 3.5 liter motor!? I thought it would be more.
So what would be a good compromise to rebuild a 3.2 Liter motor in stages. I want to have a least the same amount of HP now. But I want to turbocharge it later.

[kenikh]

I think 130 - 140 HP is a little low. When a 2.4 liter Euro 911T makes 130HP (BA's book) on Zenith carbs with a CR just a half point higher (7.5:1), I'd have to question your methods of calculating that number.

By extrapolating the numbers from the 2.4L into the 3.5L, I get 184.8 HP after discounting the .5 points of CR (based on the CR graph on page 34 of "The Design and Tuning of Competition Engines").

Hope this helps and makes you feel better!

[Gordo2]

Originally posted by johncmng
I was thinking about going to 7.0:1 CR and Turbocharging it till I have $$$$.

I think you meant to write:

I was thinking about going to 7.0:1 CR and Turbocharging it till I am out of $$$$

Gordo

[beepbeep]

Originally posted by kenikh
I think 130 - 140 HP is a little low. When a 2.4 liter Euro 911T makes 130HP (BA's book) on Zenith carbs with a CR just a half point higher (7.5:1), I'd have to question your methods of calculating that number.

By extrapolating the numbers from the 2.4L into the 3.5L, I get 184.8 HP after discounting the .5 points of CR (based on the CR graph on page 34 of "The Design and Tuning of Competition Engines").

Hope this helps and makes you feel better!

930 has ~120hp w/o turbocharger. It's 3.3L.

[Zendalar]

Hmh, so what is restricting the power on those bigger displacement engines?

[kenikh]

I just thought more about this and I missed one big point: the big ports. You can't get enough intake velocity to make power. After more thought, 130HP isn't unreasonable.

[beepbeep]

Turbo engines have cams, intakes and ignition all optimized for boost. You cannot have six straight-shot Zeniths on turbocharged engine. It will be a maze of intercooler piping, turbo intake and (hopefully not) CIS barn-door.

Arguably, building a 7:1 C/R motor to perform well in N/A form awaiting turbocharging will cost you more than fixing everything right from the first place.

All this sounds nice when doing armchair wrenching but look at the reality.

Imagine that you build a 3.5 with 7.0:1 C/R and keep it N/A. You'll have to fit heaps of N/A stuff just to make it performe as worn CIS 2.7 with broken head studs. Then as soon as you want to install the turbocharger all thpose parts will have to go. N/A headers helping you to achieve all those ground-scorching 150hp must be removed and replaced with turbo headers (turbo doesn't care about equal lengths). Likely, all air-induction stuff will go throught the window as you'll need to re-route plumbing for moving air trought the turbo. Intercooler will take majority of empty spac under the hood, ignition and fueling will have to be re-mapped from scratch etc.

With other words, you'll probably loose twice as much money on "building a 3.5 to be turbocharged later".

Regards,

[johncmng]

Thanks BeepBeep and everyone else.
You guys probably saved me a bundle and stress.