Opinion on best CR for PD blower motor

[MadMaxHSV]

As I will be having the option to setup my engine to a desired compression ratio, what should it be.
There will be a PD blower involved which don't mind higher numbers, but should I drop it a little from stock for durability.

Obviously most LS2 people on here are running around at the stock 11:1, but would it be advantageous to drop it slightly.
I've canvassed the opinions of our friends across the pond who reckon anything from 9:1 to 11:1, and as a interesting reference the LS9 runs 9.1:1

Be interested to see what CR Wormus and S800VXR's new motors are running?

[jamiep]

Depends what power output you are going for a suppose, if 600bhp id stay with stock compression, the higher the compression the nicer the car is to drive i feel.

[stigmundfreud]

the benefit of dropping CR means you can use uprated parts. Whats wrong with making the charger work a little harder if the CR is dropped making the engine under less stress of course you could then push further. I'd be surprised if Roger didnt follow that route

[MadMaxHSV]

stigmundfreud said:

the benefit of dropping CR means you can use uprated parts. Whats wrong with making the charger work a little harder if the CR is dropped making the engine under less stress of course you could then push further. I'd be surprised if Roger didnt follow that route

You can use uprated parts and keep the stock CR.

I agree on the less stress (also read detonation risk) attributes of running a lower CR. Probably why the ZR1 is at 9:1 to maintain a good warranty. But Jamie has a valid point on a lower CR effecting off-boost driveability.
As always its going to be balance, trick is finding a good happy medium.

[jamiep]

stigmundfreud said:

the benefit of dropping CR means you can use uprated parts.

You can get "uprated" pistons in many compression ratios including stock.

[stigmundfreud]

yes I know you could just replace stock parts for uprated same CR but if doing it may as well drop CR if going forced. I doubt at the capacity of engine that dropping the cr slightly would do much to off boost drivability, not like in the old Fiat UNO turbos nothing nothing nothing ohmyfkinggod change gear

[MadMaxHSV]

kinda my thinking, figured between 10 and 10.5 might allow a bit more safe boost without killing economy or driveability, but was curious to see if my thinking was sound and which end of the scale to go for.

Also its easier to increase CR than it is to drop it should the need arise in the future....

[stigmundfreud]

I'm only thinking of what I'd do if going that route, be interesting to see Roger (monkfish) or Marks views

[after_shock]

As a daft question how would you actually alter the CR?

[monkfish1]

stigmundfreud said:

I'm only thinking of what I'd do if going that route, be interesting to see Roger (monkfish) or Marks views

Supercharge your car. Thought it was staying standard

You know im not going to express a view on this on here dont you?

[anonymous-user]

Mine runs standard CR on 14lbs boost. It has run 18lbs with around 770 whp so I should leave as it is.

[stigmundfreud]

monkfish1 said:

stigmundfreud said:

I'm only thinking of what I'd do if going that route, be interesting to see Roger (monkfish) or Marks views

Supercharge your car. Thought it was staying standard

You know im not going to express a view on this on here dont you?

it is staying standard whilst funds dictate but I like the look of your cam kit!

[monkfish1]

stigmundfreud said:

monkfish1 said:

stigmundfreud said:

I'm only thinking of what I'd do if going that route, be interesting to see Roger (monkfish) or Marks views

Supercharge your car. Thought it was staying standard

You know im not going to express a view on this on here dont you?

it is staying standard whilst funds dictate but I like the look of your cam kit!

Best get yourself a test drive in the Maloo

[stigmundfreud]

if I step one foot in it, it will cost me money thats reserved for the baby! After using your old demo car the missus was giving me the "lets get this exhaust" speach.

[Boosted LS1]

I can't see a 5.7 or bigger feeling a bit flat if the compressions been lowered a couple of points especially if there's a s/c involved, plus you will greatly lessen the risk of detonation imo. Detonation's never far away on these engines with stock c/r and boost.

[ringram]

Isnt the whole point of the PD the off idle boost?
So you wont have any issue there. Id be looking at the OEM level or maybe a little higher at 9.5:1 ish.

[stevieturbo]

Given how much they heat the air, crap intercooling etc. I'd err on the low side for a PD blower.

Why take chances. Any performance reduction from a slightly lower CR will be minimal. The safety margins added from it however, will be huge.

[anonymous-user]

stevieturbo said:

Given how much they heat the air, crap intercooling etc. I'd err on the low side for a PD blower.

Why take chances. Any performance reduction from a slightly lower CR will be minimal. The safety margins added from it however, will be huge.

At risk of sounding like a stuck record: TVS blowers don't really have the same problems as the older designs. All my mapping was done in the middle of August and intake temps were fine.

[stigmundfreud]

so you didnt drop your compression? How much have you set aside for the rebuild?

[MadMaxHSV]

Sound words of wisdom. I definately want to run less than stock, but didn't want to effect driveability 'off-boost' (i know this is minimal with the PD anyway).
The blower i'm strapping on will be more than capable of supplying the boost so another good reason for going lower and upping boost as required.