Compression Ratio advise please on forge build

A

abbott

Member +
My engine is not far away from completion people who have been following my build can see bottom end is build up and head work is near finished and would like some advise on what sort of C/R would you advise me to run?

thoughts were to use a Athena 1.4 head gasket but its in question at the moment.

as want it to be reliable but still spool up and be responsive

looking to run 1.5-1.6 bar full boost

car is intended for fast road and doing a fair few track days and looking to enter Toyota sprint series

basic spec list


Engine

4E-FTE Block

Wossner 74.5mm pistons

PEC rods

ACL main bearing

ACL big end bearings

ACL thrust bearings

ARP head bolts

ARP main stud and nut kit

Toyota oil pump

Toyota water pump

Toyota full gasket set

Toyota dizzy cap & rotor

NGK iridium spark plug

Magnacore 8mm HT Leads

Light weight crank pully

Light weight power steering pully


Head and inlet

Attain Throttle Pulley

Standard Inlet manifold ported to match head

Ported and polished head

3 angle valve job

PEC 1mm oversize big valve conversion

Toyota Yaris 1nzfe solid buckets

standard springs

standard cams



Fuel system

HKS highflow fuel rail

Sard fuel pressure regulator

Sard 550cc injectors



Turbo setup

Greddy TD05 16G turbo

Tial MVS 38mm vband wastegate

Race-Tech custom manifold


engine management

Power FC



any advise would be great
 
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sx_turbo

sx_turbo

Lifer
8:1 for extreme high boost

8.5:1 for anything else, you can quite happily and easily run 26psi (most likely even more to be honest) on this cr ratio with a mls gasket and arp head bolts.

this would be a really nice with quick turbo spool and easy off boost driving, whilst still keeping things at a safe level on boost.

the restriction on the 4e and 5e engines is the size of the con rod bearings, if they were much larger you could easily be running cr of 9:1 or even 9.5:1 on boosted applications because the combustion load would be more evenly spread over a larger area.

the key to the reliability would be in the balancing and the tuning.

imo i would ditch the lightweight crank pulley, even on a well balanced engine this is not a good idea unless for race use only.

i would personally recomend using the stock harmonic balancer pulley and getting the bottom end lightened and balanced with it, this will give you an extremely smooth engine, and providing its done right, will be extremely reliable.

(also just use the 1.2mm athena gasket will be plenty and will make it easier to keep the cr ratio close to stock)

on my old engine, a light skim of the head and block with a 1.2mm gasket and wossner pistons the cr was 7.88:1 wasnt great off boost if im honest but was liveable.
 
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A

abbott

Member +
spuddy said:
Just keep the ratio stock
Click to expand...

thanks chap

sx_turbo said:
8:1 for extreme high boost

8.5:1 for anything else, you can quite happily and easily run 26psi (most likely even more to be honest) on this cr ratio with a mls gasket and arp head bolts.

this would be a really nice with quick turbo spool and easy off boost driving, whilst still keeping things at a safe level on boost.

the restriction on the 4e and 5e engines is the size of the con rod bearings, if they were much larger you could easily be running cr of 9:1 or even 9.5:1 on boosted applications because the combustion load would be more evenly spread over a larger area.

the key to the reliability would be in the balancing and the tuning.

imo i would ditch the lightweight crank pulley, even on a well balanced engine this is not a good idea unless for race use only.

i would personally recomend using the stock harmonic balancer pulley and getting the bottom end lightened and balanced with it, this will give you an extremely smooth engine, and providing its done right, will be extremely reliable.

(also just use the 1.2mm athena gasket will be plenty and will make it easier to keep the cr ratio close to stock)

on my old engine, a light skim of the head and block with a 1.2mm gasket and wossner pistons the cr was 7.88:1 wasnt great off boost if im honest but was liveable.
Click to expand...

rick thanks for your info I will take all this in to account and give feedback to my engine builder. regards to the pulley the bottom end has all been balanced already with it.

I have added on original post what max boost pressures I am hoping to run missed that out
 
G

GP82

Member +
There is also the effective compression ratio you should take into account. This is the compression your engine will be performing on your target boost pressure. The theory is every 2 psi of boost = +1 to your C/R. So for example if the C/R of the engine is 8.2:1 and you run 16 psi, your effective C/R will be 16.2:1. There is a limit to the max effective C/R you can have on normal fuels before you are prone to detonation, it does vary depending on the octane of the fuel used. In my opinion i would always leave some room for showoff and also to stay away from detonation.
 
G

GP82

Member +
Vincent-ep91 said:
what do those compression ratios mean, and what is the stock ratio?
Thanks!
Click to expand...

It's basically how much the mixture of air and fuel in your engine is compressed before ignition. I believe stock is 8.2:1, but also heard that the zenki EP82 were of higher C/R 8.5:1.
 
A

AdamB

Member +
It would depend on how wild the head has been ported, if the combustion chamber is seeing like 50cc (38cc stock I believe) then even running a 0.6mm gasket won't bring you upto 8.2:1.

Agree with what Rick has said, anywhere between 8.2 and 8.5 will work well :)
 
V

Vincent-ep91

Member +
GP82 said:
It's basically how much the mixture of air and fuel in your engine is compressed before ignition. I believe stock is 8.2:1, but also heard that the zenki EP82 were of higher C/R 8.5:1.
Click to expand...

Compressed (speaking in volume [m^3] or mass [kg] ?) So the mixture is compressed 8.2 times the original amount then is is?
 
sx_turbo

sx_turbo

Lifer
the combustion chamber on the 4e head doesnt require any work, all it requires is just a small amount of smoothing to remove the sharp edges, all the gains on 4e heads is in the exhaust and the valve throats.

dbilas do +1mm valves for 4e engines along with stronger valve springs to suit.
 
G

GP82

Member +
Vincent-ep91 said:
Compressed (speaking in volume [m^3] or mass [kg] ?) So the mixture is compressed 8.2 times the original amount then is is?
Click to expand...

The mass air flow that enters the cylinders gets compressed. The volume within the cylinder is the amount of space the mass airflow can occupy. How well it does this is volumetric efficiency. So the volume that is present between the piston top, headgasket and combustion chambre when the piston on the cylinder is at top dead centre multiply that by the amount of times it can occupy when the piston is at bottom dead centre.
 
sx_turbo

sx_turbo

Lifer
Chris@CCM said:
I would go for a lower then stock cr if ur using pump fuel
Click to expand...

there is absolutely no need to be that safe, if using high octane fuel on a permanent basis there is no problems at all.

old shitty turbo charged a series engines dont run lower than 8:1 cr, and they have some serious design flaws that only serve to increase chances of detonation.

evo engines dont tend to run less than 9:1 cr,

and stock starlet engines with a multilayer steel gasket in place can run 24psi safely all day long.

there is no need to over compensate the safety margins, all that will happen is the engine will be lazy and sluggish off boost and generally be crap to drive on road.

maybe we should take a look over the pond to jamaica and even japan, and see what they do with the stock internals,

anyway at the end of the day its whatever your engine builder tells you is best as he is (at least should be) warranting the engine
 
E

elison

Member +
Dont need to go with 1.4mm buddy. 1.2 will be good to be around the stock comp ratio. I recently finished my forged build with wossner pistons also but with a 1mm mls headgasket and head was in perfect cond but was refaced for a perfect seal and piece of mind. Car is a daily driver with 1 bar and i have to say it does pretty good. It all depends if you go with the flat tops or the -6cc or -10cc from wossner. And make sure you are being honest to yourself. If you want it to run big boost and big numbers you have to build the engine for that. If you want a dd you have to build it for that. At the end it all depends on what you as the owner/drivers want.

Best luck with your build
 
Tim@TBDevelopments

Tim@TBDevelopments

Lifer
8.5:1 is perfect.

There isn't anything wrong with higher compression but it does put more strain on the block, and headgasket/studs. As long as the parts used can take it there fine.

what does surprise me is that people are raving about the PEC parts. In the 3sgte world there considered a joke and i've had nothing but issues with them. Got some nice pictures of a few bent like bananas lol

Tim
 
sx_turbo

sx_turbo

Lifer
Tim@TBDevelopments said:
8.5:1 is perfect.

There isn't anything wrong with higher compression but it does put more strain on the block, and headgasket/studs. As long as the parts used can take it there fine.

what does surprise me is that people are raving about the PEC parts. In the 3sgte world there considered a joke and i've had nothing but issues with them. Got some nice pictures of a few bent like bananas lol

Tim
Click to expand...

the pec rods dont have great qaulity control i will agree with you, i've had nothing but issues trying to sell them and now refuse to sell them,

there isnt really much else available for the 4e though,
 
Tim@TBDevelopments

Tim@TBDevelopments

Lifer
the scat rods for the 4e I've been using for a quite a while without any issues.

Had lots of issues with PEC stuff.
DSCN4333_zps54c7740d.jpg
 
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