Effective CR

Burro

Full member
Points
48
From
Gold Coast Australia
Car
Daihatsu Feroza II
Hi all,
I'm rebuilding my Daihatsu 1.6L HD-E for supercharging to go into my Feroza 4x4.

Having a bit of a disagreement with a mechanic mate and looking for some other (preferably qualified/knowledgeable) feedback please.

Please bare in mind that this is for a 4x4 which is also my daily, not a racing car so I'm aiming for drivablity in real world conditions. I've gone with blower instead of turbo as I want instant boost and linear throttle response (and if I can take down some young blokes from the lights that'd be a bonus ;b/). Mechanic mate keeps trying to push me to go turbo but tbh I really don't think it's what I'm looking for.

He's also giving me grief over my plans to lower my CR.
I've done the CR math (with pistons recommended by a couple of guys who are getting close to 300hp out of the same engine - which is waaay more than what I have planned) and have some figures that should be in the ball park.

Factory CR = 9.5:1
Static CR (with Nissan GA16DE pistons) = 7.17:1
+Boost - 11.38 PSI = EFFECTIVE CR = 12.72

Does this sound workable or am I missing something?

Practical feedback would be really appreciated, cheers. |B
 

TCJBOLDIE

Torque King
Points
662
From
Brisbane
Car
JB Starion
I had a turbo car built forged bottom end that had 8.7 - 1 CR and 20 psi so the effective CR was something like 16-1 and it was fine with that for many years as it had been tuned/mapped on a dyno for 98 RON.

Don't know how good the stock components are in your car so do your research as much as possible.
 

Burro

Full member
Points
48
From
Gold Coast Australia
Car
Daihatsu Feroza II
Thanks for the reply |B. I've got forged H beam rods to go in and will clean up the crank and get it shot peened, I'd imagine this will be sufficient as I'm not running particularly big boost. I also only run 98 Ron too.
The only remaining concern I have is the static CR of 7.17:1. I know that's pretty low but do you think that's likely to have a negative impact over all?
 

TCJBOLDIE

Torque King
Points
662
From
Brisbane
Car
JB Starion
Low Static CR is IMO old school thinking and it affects the off boost response and allows for a higher boost pressure to be used safely PROVIDED that it is mapped correctly BY SOMEONE WHO IS EXPERIENCED AND KNOWS WHAT THEY ARE DOING.

I always told my tuner that I didn't want the last possible HP reading and that I wanted to not have to worry about the ambient temperatures when competing so IIRC he put a bit extra fuel into it @ WOT so there was no risk of it running lean or detonation.
 
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Burro

Full member
Points
48
From
Gold Coast Australia
Car
Daihatsu Feroza II
Cheers buddy, that's where it's all got a bit confusing for me. I've been reading that it's best to lower the static and up the boost to aim for effective CR around 12 but then I've got guys telling me to leave the static at the factory 9.5 and retard the timing in the tune (I'm running an Autronic ecu) so I don't know if I'm Arthur or Martha. The low comp pistons I've got are floating pin but if I go with the factory pistons (9.5:1) I lose that unless I get some made (more $$). Ahh, too many decisions.
 

TCJBOLDIE

Torque King
Points
662
From
Brisbane
Car
JB Starion
Here is the link to the chart for those who don't understand what we are discussing.

A turbo or supercharger forces way more air into a cylinder than a non turbo NA can possibly suck in so more air in being compressed into the same combustion chamber volume = a much higher ECR

https://www.rpmoutlet.com/boost-compression-ratio-chart.htm

So my old car with 8.7 pistons and 20 psi had an approximate ECR of 19 -1

https://dsportmag.com/the-tech/boost-vs-compression-benefits/

Have a close read of the last paragraph under "boost pressure"

PS A high Static CR is best up to 20psi but a lower SCR will produce more power at higher boost levels.
 
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Burro

Full member
Points
48
From
Gold Coast Australia
Car
Daihatsu Feroza II
"PS A high Static CR is best up to 20psi but a lower SCR will produce more power at higher boost levels."

Mate, thank you. I owe you a beer. Anytime you're on the Gold Coast with nothing to do, hit me up |B.
I guess that's the defining point I've missed, "under 20psi".
So, just so I'm 100% completely clear, in the modern world the CR calculations I've previously done to aim for an ECR of 12:1 are null and, with my '96 full alloy 1.6 16V EFI with aftermarket ecu and forged rods, I can safely run factory CR of 9.5:1 on around 11psi with the right tune.
(Please tell me I've got it right, I'm gettin' old and the grey matter isn't quite what it once was) 
 

TCJBOLDIE

Torque King
Points
662
From
Brisbane
Car
JB Starion
Had my last beer 60 years ago but thanks anyway :)

To my way of thinking you seem way to concerned about the effective CR and for a DD car what you suggest is on the money.|B

Am heading to Mt Tambourine for a family lunch today.
 

Burro

Full member
Points
48
From
Gold Coast Australia
Car
Daihatsu Feroza II
Excellent . Thanks for your advice and taking the time to help, it's really appreciated. This is my 3rd rebuild in as many years (snapped crank and then blown out rings) so, yeah, I'm nervous and really want to be sure everything is done properly this time. So far our little hobby build (father/son project) has been more of an expensive pain in the butt :rolleyes: and, a personal word of advice to anyone considering a similar build, ......don't ;).
Mate, enjoy your day and have a great New Year, thanks again for your help.
 
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