help with my high compression 16v!!!!!

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help with my high compression 16v!!!!!

Postby jakes_hachiroku » Fri May 05, 2017 5:30 am

ok guys ill try to keep this short while putting as much info as I can down! I have a 16v with smallport head, cylinders bored 1mm over, and wiseco high compression pistons. last year this motor ran pretty well up until the end of the fall when I started losing compression in the back cylinders. at the time I had a big port head. SO... over the winter I decided to tear it all down. replace the rings with the proper wiseco numbers. new bearings. and I wend with a BRAND NEW REMANED small port head. and ever since ive been chasing this problem. I will put new head gasket. new oem Toyota head bolts ( I also tried ARP STUDS) ive tried oem head gasket, trd .8 head gasket, and cometic 1mm gasket. this is what happens. torque everything down. check the compression, and it reads 250psi in all cylinders. fire it up, and the compression goes down to 125psi in cylinders 3 and 4 and around 195 in the front. too much compression??? any help?

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oldeskewltoy
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Re: help with my high compression 16v!!!!!

Postby oldeskewltoy » Fri May 05, 2017 6:59 am

Just to be clear... what is happening now is the same as what happened with the largeport head?

When you tore it all down over the winter, did you do anything to the block? Is the block a 7 rib, or 3 rib?


First guess... an issue with the block - crack maybe??? I'd look for a replacement 7 rib block and then rebuild it?
OST Cyl head porting, - viewtopic.php?f=22&t=300

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Re: help with my high compression 16v!!!!!

Postby jakes_hachiroku » Fri May 05, 2017 7:02 am

it is a 3 rib block. I do have a spare 3 rib that i had bored to the same 82 mm pistons. but this same issue happened with the spare block and my large port head towards the end of last year. so i swapped everything over to this current three rib block, and put this small port head on it. :(

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Re: help with my high compression 16v!!!!!

Postby totta crolla » Fri May 05, 2017 9:09 am

Can you explain exactly how you are performing the compression test.

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Re: help with my high compression 16v!!!!!

Postby jakes_hachiroku » Fri May 05, 2017 10:03 am

totta crolla wrote:Can you explain exactly how you are performing the compression test.


when I put the head back on on sunday right after I torqued everything down I did a compression test with the usual tester in the spark plug hole carbs back on timing belt on everything hooked back up. all four cylinders read 250psi. I haven't touched the car because of work until yesterday. didn't bother to do another compression test because it had only been a few days and it hasn't run since. so I turned the key and just like before I took the head off again, there was white steam coming from valve cover breather and oil pressure was really high. soooooooo I check compression again and the back two where at 125psi and fronts were 250

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Re: help with my high compression 16v!!!!!

Postby totta crolla » Fri May 05, 2017 1:04 pm

jakes_hachiroku wrote:
totta crolla wrote:Can you explain exactly how you are performing the compression test.


when I put the head back on on sunday right after I torqued everything down I did a compression test with the usual tester in the spark plug hole carbs back on timing belt on everything hooked back up. all four cylinders read 250psi. I haven't touched the car because of work until yesterday. didn't bother to do another compression test because it had only been a few days and it hasn't run since. so I turned the key and just like before I took the head off again, there was white steam coming from valve cover breather and oil pressure was really high. soooooooo I check compression again and the back two where at 125psi and fronts were 250


When you did the test was the engine cold or hot ? Throttle open or closed ?
Valve clearances correct ?
Any fuel, water or oil in the combustion chamber ?

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Re: help with my high compression 16v!!!!!

Postby jakes_hachiroku » Fri May 05, 2017 1:45 pm

as far as I can tell. nothing is getting into the oil I know gasses are getting into the oil pan because smoke comes from dipstick tube and from valve cover breather. I thid the test with my carbs off and engine cold because I just put it back together. then I put the carbs on and ran it for 3 minutes maybe. checked the compression and it was low again

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Re: help with my high compression 16v!!!!!

Postby jondee86 » Fri May 05, 2017 5:05 pm

jakes_hachiroku wrote:... too much compression???

Very likely too much cranking pressure. Maybe the smallport head has less
chamber volume than the bigport head, and that has raised your cranking
pressure higher than it was with the bigport head ? Too much cranking
pressure and pump gas is a recipe for detonation... and it only takes a
a few decent detonation events to blow a head gasket.

Just a theory :) Maybe worth trying your bigport head again ? Or changing
the cam timing to close the inlet valve a bit later ?

Cheers... jondee86
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Re: help with my high compression 16v!!!!!

Postby jakes_hachiroku » Fri May 05, 2017 6:27 pm

jondee86 wrote:
jakes_hachiroku wrote:... too much compression???

Very likely too much cranking pressure. Maybe the smallport head has less
chamber volume than the bigport head, and that has raised your cranking
pressure higher than it was with the bigport head ? Too much cranking
pressure and pump gas is a recipe for detonation... and it only takes a
a few decent detonation events to blow a head gasket.

Just a theory :) Maybe worth trying your bigport head again ? Or changing
the cam timing to close the inlet valve a bit later ?

Cheers... jondee86


this is very true. i do have a new set of T3 adjustable cam gears that i can throw on tomorrow morning and see what i cant do! the only thing is i have no experience adjusting the camshaft timing so would that mean i adjust them clockwise or counter clockwise to close valves later??

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Re: help with my high compression 16v!!!!!

Postby jondee86 » Fri May 05, 2017 8:31 pm

Because this stuff is interesting, I dug this out of a random webpage (author was
talking about single cam engines, but if you advance/retard both cams on a twin cam
the results are the same). Retarding the intake cam only will have some of these effects..

Cam retard
Retarding the camshaft (the intake & exhaust valves both open & close later) has these general effects:
» cranking pressure is reduced
» tendency to knock at low speed is reduced
» low speed power is reduced
» idle speed is probably reduced
» idle smoothness is increased
» peak torque may be reduced, but at higher RPM
» peak power may be increased
» intake valve to piston clearance increased
» engine vacuum may change


Image

So retarding the intake cam requires the cam to move anti-clockwise with respect to
the cam pulley. You need to figure out how to work that. I usually set everything to TDC
and the vernier pulley to zero. Then if you are good, you can loosen the belt and slip the
stock pulley off and the vernier pulley on without disturbing anything :)

Cheers... jondee86
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Re: help with my high compression 16v!!!!!

Postby totta crolla » Sat May 06, 2017 1:52 am

jakes_hachiroku wrote:smoke comes from dipstick tube and from valve cover breather

If this is obvious smoke and only after a short time of running it would suggest a piston and/or piston ring problem.
Changing valve clearances has the same effect as changing the cam timing and a reason why it is essential to have all cylinders at the same clearances.

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Re: help with my high compression 16v!!!!!

Postby jakes_hachiroku » Sat May 06, 2017 7:22 am

totta crolla wrote:
jakes_hachiroku wrote:smoke comes from dipstick tube and from valve cover breather

If this is obvious smoke and only after a short time of running it would suggest a piston and/or piston ring problem.
Changing valve clearances has the same effect as changing the cam timing and a reason why it is essential to have all cylinders at the same clearances.

its not so much smoke as it is steam. it smells sweet like coolant.

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Re: help with my high compression 16v!!!!!

Postby jakes_hachiroku » Sat May 06, 2017 7:24 am

jondee86 wrote:Because this stuff is interesting, I dug this out of a random webpage (author was
talking about single cam engines, but if you advance/retard both cams on a twin cam
the results are the same). Retarding the intake cam only will have some of these effects..

Cam retard
Retarding the camshaft (the intake & exhaust valves both open & close later) has these general effects:
» cranking pressure is reduced
» tendency to knock at low speed is reduced
» low speed power is reduced
» idle speed is probably reduced
» idle smoothness is increased
» peak torque may be reduced, but at higher RPM
» peak power may be increased
» intake valve to piston clearance increased
» engine vacuum may change


Image

So retarding the intake cam requires the cam to move anti-clockwise with respect to
the cam pulley. You need to figure out how to work that. I usually set everything to TDC
and the vernier pulley to zero. Then if you are good, you can loosen the belt and slip the
stock pulley off and the vernier pulley on without disturbing anything :)

Cheers... jondee86


thanks for the helpfull advace my friend. im going to re torque my head and slip my adjustable cam pullys on and see what happens. i guess just a little adjustment makes a big difference so i will maybe go over two notches and start from there

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Re: help with my high compression 16v!!!!!

Postby oldeskewltoy » Sat May 06, 2017 12:02 pm

jakes_hachiroku wrote: its not so much smoke as it is steam. it smells sweet like coolant.


something is amiss.... new head gasket should = no coolant smells.... unless block is bad, head is bad, or gasket is bad......
OST Cyl head porting, - viewtopic.php?f=22&t=300

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Re: help with my high compression 16v!!!!!

Postby jondee86 » Sat May 06, 2017 2:36 pm

jakes_hachiroku wrote: i guess just a little adjustment makes a big difference so i will maybe
go over two notches and start from there

Yes, you will need to go in steps of maybe 2-1/2 ticks (= 5 degrees at the crank) and
run a compression test after each step to track the change. You need to get all four
to around 180psi before you try running the engine. I can't predict how it will perform
at that level of retard, but it should reduce the chance of det.

From what I have been reading, it seems that camshaft duration and cranking pressure
are linked... its a kind of balancing act. Using a long duration cam with high comp will
close the inlet valve later for better cylinder filling at high rpm. Short duration cams like
the factory cams, are designed to work with lower compression and can safely close the
inlet valve earlier.

A calculator such as this... http://www.wallaceracing.com/dynamic-cr.php
... will give you an estimate of cranking pressure if you enter up the basic details of
your engine. You will be able to see what difference 5 crank degrees retard makes to
your cranking pressure, and that might save you a bit of compression testing time ;)

Cheers... jondee86

PS: Just by chucking some guessimated figures in the calculator, it looks like you will
need to take something like 25deg out at the crank (12.5 at the cam). Maybe try 10deg
at the cam first up and see what you compression tester says. Go from there.
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Re: help with my high compression 16v!!!!!

Postby totta crolla » Sun May 07, 2017 2:13 am

jakes_hachiroku wrote: the back two where at 125psi and fronts were 250


Maybe I'm missing something here but the problem appears to be a difference in cylinder pressures rather than them being too high.
I don't see how re-timing the cams can change the pressure difference between cylinders.
A leakdown test would help identify the problem though.

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Re: help with my high compression 16v!!!!!

Postby jondee86 » Sun May 07, 2017 2:57 pm

The suggestion to retard the intake cam is to try and determine if too much cranking
pressure on this engine is causing detonation. If the engine does have detonation, then
this would be a likely cause of damage to the head gasket and loss of seal.

There are other possibilities, but the OP has not offered any evidence to support such
things as cracked bore or damaged pistons. Neither do we know camshaft specifications
or how the cams are timed. However, a cranking pressure of 250psi is considered to be
too high by most comentators, so a good place to start :)

Cheers... jondee86
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Re: help with my high compression 16v!!!!!

Postby totta crolla » Sun May 07, 2017 10:39 pm

Makes sense but I also think it would be useful to know if it had actually blown the head gasket each time.

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Re: help with my high compression 16v!!!!!

Postby jakes_hachiroku » Mon May 08, 2017 4:48 am

ok guys! I have dug up my old low comp pistons and rods from when I bought the chassis and last night I tore the motor down and swapped these in in place of my wiseco high comps! luckily ive torn the motor down enough times this isn't a long task. so when I get home at 5 today im guna finish putting it back together and in the car and run a comp test and see what we get. if all is right with the world after switching pistons we will know that the wiseco pistons were just too much for a stock small port head

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Re: help with my high compression 16v!!!!!

Postby jakes_hachiroku » Tue May 23, 2017 12:33 pm

SORRY FOR THE LATE RESPONSE! all is well with my 16v! so I swapped my low comps in and the motor runs great with no blow by and no excessive crank pressure! just fired it up yesterday and ran some compression tests and all looks great. I will be driving the car today around 5 30 to make sure of this. will be sliding again in no time! SOOOOOO. correct me if im wrong. my high compression pistons would have probably worked if I had some head work done with some bigger cams. but the factory smallport head and 250+ psi per cylinder just couldn't hang? haha thanks for all the input guys! ill be back when I **** something else up

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Re: help with my high compression 16v!!!!!

Postby jondee86 » Tue May 23, 2017 3:35 pm

To understand the factors that affect your combination of parts, you need some
measurement that predicts the likely result when you run the engine. The tool for
making that prediction is a Dynamic Compression Calculator such as the Wallace
Racing calculator that I linked above :)

This article... http://kennedysdynotune.com/dynamic-compression-ratio/ gives
a reasonable explanation of Dynamic Compression versus Static Compression and
after reading that and playing with the calculator you will come to understand why
high cranking pressure is an indicator that your DCR is in a dangerous place !!

It's not the head or the pistons; it is the combination of these with early closing of
the intake valves that pushes your DCR up into detonation territory. Put in a cam
with more duration (or change the lobe centerlines on an existing shorter cam) so
that the intake valves close later, and your DCR comes down. It's a balancing act.

Cheers... jondee86
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