Mesuring Compression after having your head & block shaved?

[quietskaterguy]

Hey guys,

I have a small port head that ive had a pile of work done to... The intake ports were gasket matched, port divider knife edged, throats blended. Chambers enlarged to HG, valves deshrouded, surface smoothed, head shaved about .017" total. Exhaust throats blended, knife edged the port divider, and enlarged to fit the TRD gasket. Valves cut and lapped in and new Toyota valve seals. Also has HKS valve springs.

Now, im building the block to which this will sit on and I have a 7 Rib block but it wasnt a high comp and so im looking at pistons to bump up the compression a bit.

SO! if my head was shaved .017" and ill be running a .8mm trd head gasket, and my block will be surfaced a hair for the metal head gasket... what will my compression be with stock bluetop pistons?. If I buy something like 11:1 aftermarket ones my compression will be through the roof (i assume) so I need to figure this out before I take my block to the shop to have the work done on it.

Maybe im better off just running the stock bottom end at this point? I assume ill be close to a Red top high comp ratio with this set up as is? or am I way out to lunch?

Any help at all will be great guys.

As always thanks in advance!

[quietskaterguy]

Also Id like to ask, if i end up running 264 In/Ex cams with this set up, what would be too high of compression to run with a Blue top crank and blue top rods?
Not too sure what ill end up with in the end but im hoping around 130hp at the wheels. and once its all tuned ill have a better idea on where it will redline but im guessing 7800-8200rpms

[totta crolla]

https://www.youtube.com/watch?v=V7V40ZWNgCo

As for compression ratio your limiting factor will likely be engine knock as a result of your fuel octane.
OST will doubtless be along to give you an idea of cc vs compression ratio.

[Rogue-AE95]

If anything, with accurate measurements (which you have minus the block) Yoshimitsuspeed can give you piston advice. He's designed some before, he could tailor-make some for your build for not much more than off-the-shelf pistons (and his would be better suited to your needs).

Are you running stock or aftermarket engine management?

[quietskaterguy]

Ill have too look into him forsure. I assume he is here on the board? Do you have any contact info for him?

ill be running a MS1 with Upgrade for an ecu. basic but should be all ill need. I purchased it mostly to run the 16v with the 20v itb's I have.

[oldeskewltoy]

Hey guys,

Chambers enlarged to HG, valves deshrouded, surface smoothed, head shaved about .017" total.

Now, im building the block to which this will sit on and I have a 7 Rib block but it wasnt a high comp and so im looking at pistons to bump up the compression a bit.

SO! if my head was shaved .017" and ill be running a .8mm trd head gasket, and my block will be surfaced a hair for the metal head gasket... what will my compression be with stock bluetop pistons?. If I buy something like 11:1 aftermarket ones my compression will be through the roof (i assume) so I need to figure this out before I take my block to the shop to have the work done on it.

There is just too much information that isn't included....

Here is what I need to calculate an ACCURATE compression ratio for you....

Bore = ?
Stroke = 77mm, or 3.031" is standard stroke - what is yours?
gasket thickness = .8mm
deck = ? Amount the pistons edge sticks above or below the blocks edge
Piston top volume = ?
Chamber volume = ? You told us a bunch of stuff, but not enough. You say the chambers have been opened up to the gasket.... that could be anywhere between 38 and 40cc, then you said the head was cut .017" (about .44mm), this will drop volume by about 1.5cc to 3cc. So guessing the chamber volume is between 38.5 and 35cc. That a huge span, didn't the person doing the head work check your chamber volumes??? It should have been done.


PS - I'd love to see some photos of your port work....

[yoshimitsuspeed]

Ill have too look into him forsure. I assume he is here on the board? Do you have any contact info for him?

ill be running a MS1 with Upgrade for an ecu. basic but should be all ill need. I purchased it mostly to run the 16v with the 20v itb's I have.

That would be me.

As far as calculating your compression ratio OST laid out the basics.
This guide goes into more detail. In your case you will definitely need to CC the chambers.
http://www.matrixgarage.com/content/4ag ... ormation-0

For what you are putting into this motor your expectations are really low. Granted if you don't do it right you might be lucky to make 130 WHP but if you do it right you should make a good bit more than that.

The dyno here is a customers build using my pistons, and Tomei poncams. Other than that it was a quality rebuild with some light cleanup of ports and chambers.
Stock ECU and pretty much stock everything else. He did use an AFPR to tweak AFRs a little.
This is a transverse motor so longitudinal would read a little lower.
http://www.matrixgarage.com/products/16 ... nd-pistons

[quietskaterguy]

Bore = will be 81.5mm
Stroke = 77mm(original stroke)
gasket thickness = .8mm
deck = I havent stuck a piston into the block yet as im in the process of trying to find what piston I need. Backwards im sure. Its my first time going inside an engine and building it.
Piston top volume = ? having no piston im unsire i can find that out.
Chamber volume = ? Ill have to figure out how to cc it myself. Looked on youtube. Seems simple enough.


Yoshi, I found your site last night and tore though it. I would absolutly love to do your piston/cam combo but the exchange right now between USD and CD is absolutly killing me. Take payment plans by chance?

OST, ill try and snag some pictures of everything for ya. In 11 years on this site ive never posted a pic, im sure it will be easy enough.

[yoshimitsuspeed]

Testing a piston in the bore will be a final check for deck clearance but for these calculations now you will want to know your actual deck height.

You can get pretty accurate measurements of your actual deck height by measuring the distance from the deck to the face that the cam cap sits on, on the block using a long pair of calipers. This will get us close enough to throw numbers around.
If the block hasn't been shaved this isn't as vital but actual height can vary between blocks so it's best to know what yours is.

I don't do payment plans.
I am working with Arias to improve their whole 4AGE piston line and will also have a couple shelf pistons of my own including the one in that kit. This will bring the cost of the kit down a little bit.

Bore = will be 81.5mm
Stroke = 77mm(original stroke)
gasket thickness = .8mm
deck = I havent stuck a piston into the block yet as im in the process of trying to find what piston I need. Backwards im sure. Its my first time going inside an engine and building it.
Piston top volume = ? having no piston im unsire i can find that out.
Chamber volume = ? Ill have to figure out how to cc it myself. Looked on youtube. Seems simple enough.


Yoshi, I found your site last night and tore though it. I would absolutly love to do your piston/cam combo but the exchange right now between USD and CD is absolutly killing me. Take payment plans by chance?

OST, ill try and snag some pictures of everything for ya. In 11 years on this site ive never posted a pic, im sure it will be easy enough.

[Illegal_Garage]

With most after market NA pistons for the 4AG you can cut up to .050" off the dome
this will help you lower the CR to where you want it
you really should talk to a local builder

I know 5 machine shops off the top of my head local to me in San Jose
I often drop in on them and ask their advice on these matters

Max

[mr2mk1hero]

Here's a post I wrote on compression ratio measuring for the 4AGE.
its based on what OST and yoshi said and has the numbers you need to put into the calculator.
Maybe it helps
http://www.driving4answers.com/compress ... calculate/