4age 20v build, too much compression?

[Hakon]

Hi there, my 4age recently stopped, and i have known this was coming for sometime, the piston rings had gone on it.

I am going to rebuild it, and the base parts of my build are as follows:

Cp pistons
Brian Crower h beam rods
(pistons and rods are designed for 12:1 compression)
Tomei poncam intake cam shaft (264, 9.0mm)
Toda Exhaust cam shaft (272, 9.2mm)

i have decided to go with pearl automotive for machining (as he is 2 minutes from my house)
however when discussing the build with him, he lead me to believe that my high comp will only cause my engine to go bang unless i use race fuel.

I plan on letting him source locally made valves, vale springs and retainers to keep costs down.

From what i have read the increased duration means more over lap meaning the compression will actually be lower then the static 12:1.

My question is, will this build work on 98 octane?
If not, do i need a "spacer" to lower the comp?
Has anyone has done a similar build, if so what did they achieve, or what should i expect the engine to produce power wise?
Any other advice people could give would be really helpful.

[Matt]

the compression ratio should be ok on 98. cars are running 13:1 and higher these days on it.

What ecu do you have?

[Sam-Q]

As above that compression rate is fine, it's something that's pretty common. So long as it's tuned right and the quoted CR doesn't end up being more in reality then it's no problem

Even with the small squish areas of the 20V engines it's always a bad idea to increase the quench height. It messes with the combustion chamber dynamics and can promote detonation.

No need to change the valves, from what I hear increasing the valve size on anything but the exhaust makes you loose power. That is unless you run the two outer intake valves bigger and the middle one smaller, that might work, no one seems to know for sure on that one.

I suggest Supertech springs.

[Jimmee1990]

Depends which CP part number you have, and which 20v cylinder head you have also. Silvertop has a much smaller combustion chamber in the head than blacktop. None of the aftermarket 20v pistons will work out at the quoted compression regardless so you will need to cc the crowns and your finished combustion chambers.

Definitely don't space the head or run a thicker gasket, even though it's decreasing the compression ratio it will lose all the squish area and will run closer to detonation. I would be setting the piston to head clearance with the head gasket, and setting your compression ratio with the pistons only.

Valves aren't worth touching at that power level, neither are the collets or retainers unless they're worn and just replace them all with standard parts. Springs I would recommend for those cams however if your standard springs are okay they will still be fine.

Sams right about the valve sizes also, bigger inlet valves (Especially the middle) shroud the others quite badly and will lose airspeed rather than gaining.