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HPFP upgrade vs LPFP + MPI

gti925

gti925

Passed Driver's Ed
Location
SF Bay Area
Is simply upgrading the HPFP still considered an acceptable way to support fueling requirements for bigger turbos? I'm thinking IS38 on E30 or EQT on 91 (or maybe E30)

HPFP:
+ Cost
+ Simplicity
+ Enough added fuel capacity for 450ish (?) whp
- Not future proof
- Your tuning software must know about it? (not sure if this is correct)

LPFP + MPI
+ Future proof. Ie, enough fuel for pretty much anything under the sun.
+ No more carbon cleanings
+ Coolness factor
- Expensive
- Major surgery vs HPFP

Please feel free to add to each one and/or make corrections.
 
aaronc7

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
I think you're on the right track. HPFP upgrade gives you a nice increase in fueling capacity, but doesn't have capacity or future upgradeability of a MPI.

Cobb will take full advantage of stock and upgraded HPFP by being able to adjust the injection window etc (I don't know all the details, but some other tuning platforms can't do this)

Ed told me that HPFP upgrade with IS38 and full E85 is possible but will be close to the limit... LPFP upgrade not a terrible idea at this stage just to overbuild the system a bit.

If you think you may go bigger turbo eventually with ethanol mix or E85 then I would skip HPFP upgrade completely and just get MPI.
 
P

PacDawg

Drag Race Newbie
Location
Gilroy, CA
If you are honestly just sticking with e-blend is38 or pump on EQT then just hpfp will be enough. But CA 91 is ass so I'd go for an e-blend on a eqt also and a lpfp/hpfp combo will be just enough fueling capacity. But might as well just go MPI to give more head room for fueling.
 
crxgator

crxgator

Autocross Champion
Location
Raleigh, NC
Car(s)
All the MQBs
I thought HPFP upgrade needs a true custom tune to get the most out of it?
 
R

roystr

Ready to race!
Location
California
PerceivedShift said:
About what is the cost of both options? (Parts only)
Click to expand...

The Autotech HPFP upgrade (internals only) is $350.
An upgraded HPFP pump (HPA) is $650. Ideal if you want to swap back to stock someday.

MPI costs anywhere from $1300 (Precision Raceworks MPI kit + LPFP) to $1500 (APR kit).
 
jimlloyd40

jimlloyd40

Autocross Champion
Location
Phoenix
Car(s)
2018 SE DSG
roystr said:
The Autotech HPFP upgrade (internals only) is $350.
An upgraded HPFP pump (HPA) is $650. Ideal if you want to swap back to stock someday.

MPI costs anywhere from $1300 (Precision Raceworks MPI kit + LPFP) to $1500 (APR kit).
Click to expand...

Plus installation and a new tune for the MPI.
 
G

greggles

Drag Race Newbie
Location
usa
Car(s)
GTI
I assume if you swap the HPFP do you also have to retune just to keep the car from running ultra rich immediately?
 
Hoon

Hoon

Autocross Champion
Location
Rhode Island
If you do an HPFP without tuning you will get high RPM fuel pressure spikes.

The ECU compensates by reducing the injector pulse width, so from the drivers seat you'll never know it, but you also don't want to be putting 250+bar to the injectors which I believe are rated for a max 230bar operating pressure.

I've also notice that fuel pressure instability seems to be correlated with knock.

If you are using Cobb, HPFP is a good budget fueling mod for some added headroom. Any other tuning solution it is a waste of time and money.

Ultimately, LPFP and MPI is the way to go if you want to move real fuel volume. Leave the HPFP stock, aftermarket HPFPs are a detriment on MPI setups. Again, this goes back to control and stability.
 
PerceivedShift

PerceivedShift

Autocross Champion
Location
Virginia
My next and final power goal for the GTI is between 400-450whp, glad to hear a HPFP upgrade is likely all I'll need besides the turbo upgrade.
 
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