Compression ratio's

[NZ4age]

Hey everyone,

Would anyone know what the compression ratio would be if using smallport 10.3:1 pistons, .5mm skim off head and .8mm TRD headgasket?

Currently have 2nd gen 4age, Bigport T-VIS with red and black lettering on cam covers. Has 7 rib block with 9.4:1 compression ratio .
Looking at doing a rebuild to freshen the engine up as has done just over 290,000 km (180,000 miles). I thought while doing this I'd swap the pistons with the higher compression smallport 16v pistons and bump the compression up a little more with the skim and headgasket. Also at the moment I have a spare head I'm working on to improve flow and matching the manifold ports to the head, Pretty much doing everything on this DIY porting page link http://www.86atlanta.proboards.com/inde ... &thread=22

Another question I have would be, with increasing the compression would it require an aftermarket ecu?





Any help would be much appreciated,

Cheers Grant

[yoshimitsuspeed]

http://www.csgnetwork.com/compcalc.html

Bore 81
Stroke 77
Headgasket bore 82mm for stock
Compressed HG thickness stock should be 1.2mm
Combustion chamber volume is about 36
Deck should be very close to 0

It would be best if you can get piston dome measured directly off the piston because the numbers I have seen just don't quite add up.
Since we don't know that we can leave it as our variable right now and solve for 10.3:1. -.4 cc gets us to 10.28:1.

Now you can just play with changing the HG thickness. .5 skim and .8mm hg would get you to about 11.4:1.

How much compression you can run on an ECU depends on too many variables to easily answer.
I do have a customer running 11:1 pistons with poncams and he is getting a little detonation in the mid RPMs. I don't think it's enough to be worried about but it is noticeable. One thing though is he isn't running his EGR. This may be contributing to the knock. I would say though that on stock cams at that compression level you will NEED to monitor for knock and you may have some trouble controlling it. If you have your EGR then that might be enough.
That said you would be smart to run some cams anyway. It will open up the top end a ton and due to the compression bump you should still gain a little in the low to mid RPM but up top it should feel much faster.

This is by far my most popular selling cam. http://matrixgarage.com/store/tomei-1

These are the pistons I designed for the aforementioned customer build. They should be 11:1. He wanted to keep it non interference with the poncams so the reliefs are a little deeper than normal. If you wanted to go with an interference motor the reliefs could be smaller and the top much smoother. These were custom Wiseco's and the price is pretty impressive and in my opinion well worth being able to tailor a piston specifically to your build. It will also be stronger and hold up better to the occasional detonation or tuning error.
If you went with an 18mm rod supertech has a pretty nice 11:1 piston. I am working with them on a design based very closely off the custom Wiseco's above. For these a piston and ring set will be pretty close to OEM pistons and rings.

[oldeskewltoy]

Hey everyone,

Would anyone know what the compression ratio would be if using smallport 10.3:1 pistons, .5mm skim off head and .8mm TRD headgasket?


Any help would be much appreciated,

Cheers Grant

.8mm gasket will add about 4/10 of a point, so from 10.3 to about 10.7. A half millimeter skim on the head will drop volume of chamber to about 34.75cc. That should bump compression a further 4/10s, so to about 11.1 to 1


Concerning porting.... having glanced @ the link you posted... a few of the pics are mine... but there are a few inaccuracies.... the biggest one is the exhaust side NEEDS rather extensive porting... it requires changing the taper the two exhaust streams merge at inside each port. Only polishing the exhaust port only really helps the port shed carbon build up, it doesn't improve flow to any significant amount

[NZ4age]

http://www.csgnetwork.com/compcalc.html

Bore 81
Stroke 77
Headgasket bore 82mm for stock
Compressed HG thickness stock should be 1.2mm
Combustion chamber volume is about 36
Deck should be very close to 0

It would be best if you can get piston dome measured directly off the piston because the numbers I have seen just don't quite add up.
Since we don't know that we can leave it as our variable right now and solve for 10.3:1. -.4 cc gets us to 10.28:1.

Now you can just play with changing the HG thickness. .5 skim and .8mm hg would get you to about 11.4:1.

How much compression you can run on an ECU depends on too many variables to easily answer.
I do have a customer running 11:1 pistons with poncams and he is getting a little detonation in the mid RPMs. I don't think it's enough to be worried about but it is noticeable. One thing though is he isn't running his EGR. This may be contributing to the knock. I would say though that on stock cams at that compression level you will NEED to monitor for knock and you may have some trouble controlling it. If you have your EGR then that might be enough.
That said you would be smart to run some cams anyway. It will open up the top end a ton and due to the compression bump you should still gain a little in the low to mid RPM but up top it should feel much faster.

This is by far my most popular selling cam. http://matrixgarage.com/store/tomei-1

These are the pistons I designed for the aforementioned customer build. They should be 11:1. He wanted to keep it non interference with the poncams so the reliefs are a little deeper than normal. If you wanted to go with an interference motor the reliefs could be smaller and the top much smoother. These were custom Wiseco's and the price is pretty impressive and in my opinion well worth being able to tailor a piston specifically to your build. It will also be stronger and hold up better to the occasional detonation or tuning error.
If you went with an 18mm rod supertech has a pretty nice 11:1 piston. I am working with them on a design based very closely off the custom Wiseco's above. For these a piston and ring set will be pretty close to OEM pistons and rings.

Thanks for your reply, would you think just changing the headgasket thickness would be the better way to go without running into too much trouble? The tomei poncams you sell, are they compatible with the oem valve springs?

[NZ4age]

.8mm gasket will add about 4/10 of a point, so from 10.3 to about 10.7. A half millimeter skim on the head will drop volume of chamber to about 34.75cc. That should bump compression a further 4/10s, so to about 11.1 to 1


Concerning porting.... having glanced @ the link you posted... a few of the pics are mine... but there are a few inaccuracies.... the biggest one is the exhaust side NEEDS rather extensive porting... it requires changing the taper the two exhaust streams merge at inside each port. Only polishing the exhaust port only really helps the port shed carbon build up, it doesn't improve flow to any significant amount

Thanks for your reply, do you have any detailed info/photo's or webpage links regarding the exhaust side porting?

[yoshimitsuspeed]

Thanks for your reply, would you think just changing the headgasket thickness would be the better way to go without running into too much trouble? The tomei poncams you sell, are they compatible with the oem valve springs?

You have to build the motor as a whole so how much you can increase the compression really depends on the cams, porting, valves, engine management etc. If you went with bigger cams I think the head shave and HG should be fine. If you went with stock cams and wanted a safe reliable tune it might be better to just go with the HG and a minimal shave to get the head flat.
Those cams will work great with stock redline. If you planned to spin it faster you might need to consider upgrading.

[oldeskewltoy]

Thanks for your reply, do you have any detailed info/photo's or webpage links regarding the exhaust side porting?

stages of an exhaust port



notice the amount of material removal between the top panel and the middle panel.... the bottom panel is once the taper has been changed, blended and mostly finished

[NZ4age]

notice the amount of material removal between the top panel and the middle panel.... the bottom panel is once the taper has been changed, blended and mostly finished

Thanks, that helps alot. Quite a considerable difference between top and bottom photo. Just looked through your many other photos on your photobucket, many good interesting photos on there

[apsogosGTi]

Hello and good morning!have you relocate the battery?and where exactly?thanx

[NZ4age]

Hello and good morning!have you relocate the battery?and where exactly?thanx

Hey yes I have, relocated it to the right side of the boot/trunk in battery box secured to the boot floor with heavy duty well insulated cable from Auto electrician. Also ducting up from under the front bumper to the filter

[apsogosGTi]

awesome sauce mates!perfect a clean like mine!+ 20bhp from me!

[totta crolla]

awesome sauce mates!perfect a clean like mine!+ 20bhp from me!

+20bhp from what mods ?