5 replies to this topic

[R32Egor]

What valve sizes are usually in a stage 3 head for the SPI? I have the 12A engine with large valves anyway so what's the difference to a stage 3 head?

[R32Egor]

The main thing I was asking is basically how much bigger do the valves need to be to make a difference EG *stage 3*

[brivinci]

What are you actually looking to achieve with the car? I have never been a fan of vendors labeling thing "stage" as who created these guardrails. 

This has beed discussed nearly every time a question like this pops up but if you plan on keeping the original ECU and throttle body, the SPi is limited to about 85hp before you run out of fueling from the ECU. So, throwing a full-race head on one, with a standard ECU, is not really going to get the most out it. There are plenty of suppliers that create heads specifically for the injection cars. Have a look at Mini Spares, Mini Sport, and highly recommended builders like Keith Calver. 

[R32Egor]

I have the 63 hp high compression engine 12A2E.
So to get to the max I am thinking
Maniflow exhaust manifold - done
K&n replacement filter - done
Rc40 exhaust system - done

Duplex chain
St3 head - the problem I see is I have supposedly large valves already and do not know if getting an off the shelf st3 head is worth it
Throttle body - improved from Japan along with vacuum controlled fuel pressure valve
1:5.1 rockers
Then as this will probably max out the ECU going to concentrate on lightening and balancing

[brivinci]

Sorry is you current head stock? If so, a properly modified head is the key to HP in these injection cars. All the other bits and bobs really only aid in drivability but rare add much in the way of power. 

As above, look for companies that understand the injection motors and make heads that suit it. I have my doubts on the larger throttle body. If anyone has actual numbers that backup any gains, I would love to see them. 

With all that you already have, a sorted head will really bring the car to life. If the motor is out, now is the time to do a cam. Swiftune is always a popular one. The reason the JCG and others include a 1.5 set of rockers is that they typically aren't pulling the motor and doing a cam. If you were to, a 1.3 rocker set would be a nice addition but not going to gain you anything except at the VERY top end. 

Lightening would be great. I fitted an MED lighted flywheel and its a lovely bit of kit. You could also look to changing the final drive. Swapping for a 3.44 diff will give you a very noticeable shove...but you will lose top speed motoring comfort with a bit more revs.

[R32Egor]

Thanks for information

I know its a bit late but ...

 

Looks like the next purchase will be a modified head then.