View Full Version : engine question?

08-13-2010, 09:23 PM
i have a spare 3sfe engine that i am going to rebuild. now what i need to know is the 3sfe a interference or non interference engine? if it is non interference how much can i take off the head before it becomes interference. i want to know just in case the head is warped and needing to be decked. also how much can you bore the cylinders. and what would the compression ratio be for .xx milled from the head vs XX bored from the cylinders? thank you for the help. :mj:

08-14-2010, 01:16 AM
It is non interference. But don't increase compression too much. 3sfe rods aren't real strong. You would be better swapping to a 3sge or a 3sgte.

08-14-2010, 01:43 AM
nah not really into the whole swap thing just wanting to know how far it can go. as far as the rods go they can be changed to stronger ones :).

08-14-2010, 05:37 AM
To get a warped head straight, it usually doesn't take a very big cut off of the head to make it flat. Probably insignificant in terms of compression ratio effect.

I can see grinding the head flat if is warped - to prevent headgasket failure.

Why do you want to slightly increase cylinder bore size?

08-14-2010, 11:52 AM
The 3sfe really isn't an engine to mod. It's built for fuel economy. It's been done before yes, but most times the $$$ you spend on modding that engine you can drop in a 3sge and gain more power and have an excellent base to mod.

---------- Post added at 03:52 AM ---------- Previous post was at 03:50 AM ----------

Here's a good read for you.


08-14-2010, 02:27 PM
because when you change the pistons it is good to bore a little to smooth the walls if the engine was abused. the one i am rebuilding has 298k on the clock. so i just want to be sure what the limits are on this engine before it is to much. again this is not a matter of modding the engine for power it is about bringing it back to life. i just want to know if i do so will there be a change. like if i bore .010 over which is normal for a rebuild, what would the compression and engine size be then?

08-14-2010, 11:34 PM
ok after looking at 4thgenceli's thread on his car going under the knife i now understand what to look for when tearing apart my engine. hopefully my block will look as good as his. the head does not scare me in the least.

08-15-2010, 05:31 PM
Not sure if you will find stock pistons in a 0.010" overbore. Seems that 0.020" is more common as the first step up with the ones I have looked at from Mahle and others.

On a 3sfe boring out 0.010" will give you a bump of .5 CR from the stock 9:1 to 9.05:1. A 0.020" overbore will give you .1 and make it 9.1:1.

Unlike cylinder blocks you cannot just shave the bottom off a warped head to make it straight again. The cams would bind. It needs to be heated up and pulled back straight again. After that a few thousandths can be taken off to make it perfectly flat. I had this done to an old 22r head a long time ago. They heat the head up to 300-400 degrees, put shims under it in the right places, clamp it down to a steel plate and let it cool.

If you want to shave the head to raise compression then 1mm off will bump you up to 9.5:1 for stock bore and 9.6:1 for a 0.020" over. 2mm will get you to about 10.1:1 stock bore and 10.2:1 with 0.020" over. 3mm will get you about 10.8:1 with stock bore and about 10.9:1 with 0.020" over. For every millimeter you shave off, your cam timing will advance by about a degree so be aware of that. If you want to put it back where it should be or be able to adjust it get a 2jz adjustable cam gear and have it machined to fit.

To answer your original question, you probably have more the 1mm you can shave off before the engine becomes interference. It depends on a lot of things though like how well the head and pistons were cast and of course any other mods you do. What I do when I put an engine together is install the cams in the head and turn each pair of valves to full lift. I then set the head on the block without the head gasket and slowly hand turn the engine until that cylinder's piston gets to the top. If I feel the piston hit or the head lift then I know they are closer then 1mm or maybe even interference. For a non-interference engine I then figure out where it is hitting and shave a little off the piston with a dremel. To find out exactly where it is hitting you need to put something on the valves or piston that will transfer to the other when they touch.

08-15-2010, 05:31 PM
Double post darn it.

08-15-2010, 06:31 PM
thank you that is what i needed to know. so having the head decked most likely will not change compression at all that i would notice. that is very good to hear.