Twin injector setup: is it needed?

[NickRP]

Hi Guy,

a friend of mine is re-building Suzuki Swift GTi engine for circuit and hill-climb racing. Last racing season was successful (he won 2nd place in his class), but the time has come to do some improvements.

To give a few details on the engine (I will make it very brief, because it is not so important for the topic to list all the details):
-high CR forged pistons (target CR 12:1)
-gasflowed cylinder head, reshaped valve head back sides
-316 degrees, high lift intake and exhaust cams
-4 into 1 custom exhaust header
-individual throttle body intake
-ligher, aerodynamically shaped crank
-light flywheel

Target power is in 150bhp range (at flywheel) at some 8500-9000RPM (extrapolation based on the last year power vs. RPM figures).

In the inlet manifold there is one provision per runner for injector pointed toward valve head and there is one provision for injector at the throttle body.

Last year we used only 4 injectors pointed at the back of the inlet valve heads. Injectors' dynamic range was big enough to cope with supplying proper amount of fuel under both low and high load conditions. But we could also drive 2 injectors per cylinder, with transition from one to another being triggered by RPM thresholds. But my question is: is there any gain to be expected from such a setup, to compensate from extra hassle for building and mapping such a setup and of course for extra weight of additional injectors, rail, fuel pressure regulator etc (it is not much, but still).

Many thanks,
Nikola

[Guy Croft]

Hi Nik
having two is a waste of time and injecting outboard of the throttle plate is better.
By the way I have stock of GC spec variable rate single coil competition springs for that motor that I produced last year, good for up to 10.mm actual lift/11,000 rpm I guess I may be the only one who has them for that motor, if you're interested e mail me.

You should meet your power target easily, I'd like to know the cam type (billet/regrind) & lift and get some feedback on that.

GC

[NickRP]

Thanks Guy, that's excellent piece of information!

As for the valvetrain, he purchased most of the parts from some company in Australia, that of course included cams, and springs to match the cams. The cams were made from billets - I will get the specs and post them here.

The engine (as it used to be last year) idled (although a bit rough) at 800 RPM, and AFR reading was in 16 range at idle (i.e. that was the reading I got when I adjusted fueling to get the most stable sounding idle, obviously misleading due to unburned mixture coming directly to exhaust). The engine was comming "on cam" at about 5500RPM. Advancing the intake cam is what we are going to try in an effort to broaden the torque range (last year cams were at 0‚° throughout the season), at least for hill-climb events.

Due to budget limitations he will have to use stock rods for now. Do you have some rough recommendations on how often they should be changed? Last year his rev limiter was set to 9500RPM, this year it'll be probably higher, so we are both worried about potential rod hazard.

Many thanks,
Nikola

[Guy Croft]

Sorry Nik,

I have no idea how strong the OE rods are on the Suzuki Swift.

I've done a lot of flow work on that head and I am convinced it should be a 180+ bhp engine, but I don't know anyone who has got near that (certifiable dyno result, not 'hearsay').

I think the stroke is only 75mm or so, so it should be capable of way over 9500 on race rods.

GC