Why bigger injectors?

[cognum]

Probably a stupid set of question about supercharging but why do the 2018+ direct & port injection engines with stage 2 whipple need bigger port injection injectors?

Would have thought the direct injection handles everything on boost?

If you have a diverted valve for low throttle then it should only need the same as a standard mustang at low engine speed and idle?

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[EFI]

Because eventually you will run out of injector, even with the dual setup. The OEM capacities are intended for stock power levels N/A with a little bit of headroom for safety, so regardless of the type of fueling you still need more if you're going to add a bunch of power.

The PI still does the majority of fueling, the DI is just there for support as needed.

 

[WildHorse]

$$$. The DI can take up the slack no problem IMO.

 

[engineermike]

The stock gdi pump can fuel 400-450 hp by itself but the stock port injectors are positively tiny. I think they’ll only support about 200 hp by themselves. That said, I think most people and companies overkill the port injectors. Whipple does for sure.

 

[cognum]

The stock gdi pump can fuel 400-450 hp by itself but the stock port injectors are positively tiny. I think they’ll only support about 200 hp by themselves. That said, I think most people and companies overkill the port injectors. Whipple does for sure.

I'm guessing there's no easy way to upgrade the GDI pump? Makes me wonder how the little VWs and others do it. They all used to be DI no PI a decade ago.

 

[engineermike]

I'm guessing there's no easy way to upgrade the GDI pump? Makes me wonder how the little VWs and others do it. They all used to be DI no PI a decade ago.

xdi sells an upgraded gdi pump, which I happen to have. On stock injectors you can get about 10% more gdi flow and run a higher pressure. But you still can’t get by on stock port injectors.

 

[WildHorse]

But you still can’t get by on stock port injectors.

You just need larger port injectors cause there only like 24# LU47's + stock DI will handle most needs IMO.

 

[Deleted member 72210]

$$$. The DI can take up the slack no problem IMO.

Try that on a 1000whp application

 

[engineermike]

Whipple initially supplied 38’s with their kit, later upgrading to 55’s. Roush supplies 55’s with their phase 2 kit. I found the limits of the 38’s, but they carried me farther than most because my upgraded gdi system carried more weight.

You also have to keep in mind the fuel system has to supply enough fuel for cot (.68 lambda) at all possible ambient conditions resulting in even very negative DA’s. There is a massive difference in fuel flow at .82 lambda at 90 deg f vs .68 lambda at 30 deg f, all with the same blower and pulley.

 

[WildHorse]

Try that on a 1000whp application

 

[cognum]

Whipple initially supplied 38’s with their kit, later upgrading to 55’s. Roush supplies 55’s with their phase 2 kit. I found the limits of the 38’s, but they carried me farther than most because my upgraded gdi system carried more weight.

You also have to keep in mind the fuel system has to supply enough fuel for cot (.68 lambda) at all possible ambient conditions resulting in even very negative DA’s. There is a massive difference in fuel flow at .82 lambda at 90 deg f vs .68 lambda at 30 deg f, all with the same blower and pulley.

That's interesting.

Probably a pointless follow up question since its easier to upgrade port injectors, but in theory if you were going for 800hp and not 1000hp+ could you upgrade the gdi pump instead of the port injectors?

 

[engineermike]

@cognum yes you could but you’d need more than just the pump.

The stock gdi system is capable of about 330 lb/hr if the tuner knows what he’s doing. Most don’t and as a result it flows well under 300.

Upgrading the pump alone can get you 360-370 lb/hr.

Upgrading pump and injectors can get you 400 lb/hr.

Add the exhaust cam with a bigger pump lobe can theoretically get you to about 480 lb/min.

IMO this is actually the better way to do it on pump gas because it gets you a lot of knock suppression. However, the gdi side upgrades are rather pricey, in the $4-5k range, and finding someone who really knows how to tune it properly can be nearly impossible for an ordinary Joe.

 

[cognum]

@cognum yes you could but you’d need more than just the pump.

The stock gdi system is capable of about 330 lb/hr if the tuner knows what he’s doing. Most don’t and as a result it flows well under 300.

Upgrading the pump alone can get you 360-370 lb/hr.

Upgrading pump and injectors can get you 400 lb/hr.

Add the exhaust cam with a bigger pump lobe can theoretically get you to about 480 lb/min.

IMO this is actually the better way to do it on pump gas because it gets you a lot of knock suppression. However, the gdi side upgrades are rather pricey, in the $4-5k range, and finding someone who really knows how to tune it properly can be nearly impossible for an ordinary Joe.

I like the idea of gdi taking over allowing knock suppression and better fueling at idle and cruising from small port injectors if I had a supercharger.

Probably have to go to one of the few gdi specialists rather than the local tuner then I guess.

I've learnt a lot from this thread and theoretical questions. Thanks Mike for the patience and explanations.

 

[engineermike]

Probably have to go to one of the few gdi specialists rather than the local tuner then I guess.

If you find one I’d like to know who it is. I had to learn it and do it myself. Even xdi was very little help. They knew how to make the pump work properly but no idea how to tune to maximize its performance or optimize the gdi parameters.

 

[beefcake]

most tuners hate the gdi, and we have found the cars typcially make more power as you lower the di mix, we just went through this on our 22f150 truck

as we decreased the di mix , power would climb, you wouldn't think that would be the case but the dyno doesn't lie

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