LT1 High Pressure Pump max

[Ben Charles]

C7 LT1 uses a different High pressure pump compared to the Z06 LT4. I have not had the chance to mess with the High pressure pump settings in tune. What I have learn that over 600rwhp is possible on the factory fuel system (93 octane) without Meth as a secondary fuel source playing with the SOI and EOI tables targeting a mid 12 AFR.

The LT1's pump FACTORY flows 2176 PSI, but in the tune has a HP PUMP MAX of 3118 PSI

The LT4's pump FACTORY flow 2901 PSI, but in the tune has a HP PUMP MAX of 3989 PSI

HP PUMP MAX limit is 4641 PSI by default


My question is has anyone just increased the pressure capacity of the LT1 pump to LT4 pump levels in the tune and tried this for increase fuel capacity?

[doc350]

That's an interesting thought. How is the pump regulated? I can't recall any sort of return line coming off the pump.

[DSteck]

There's a relief valve on it.

You need to drive the pump harder with an aftermarket cam if you want higher pressure. You can get 20MPa out of it.

[Ben Charles]

I know for fact another tuner pushed 17.5 MPA (2550PSI) through it with an aftermarket camshaft.

An LS7 Lash cap by itself is good for around a 20% increase in fuel from what I have seen (cost $13 from GM) but the pump has to be pulled which isn't too bad. Need to change the gasket too which its cheap too.

Dave thanks for chiming in with that info.

EDIT: IT just thought of this. The factory Z06 cam has a slightly larger lobe on the camshaft to drive the HP pump compared to the LT1, I assume they did this for the above reasons (again the Ls7 Lash cap would come in handy here)

[veee8]

Are you saying using an LS7 intake valve lash cap on the LT1 or LT4 pump? Any benefit of just switching to the LT4 pump on a boosted 6.2 silverado with stock cam?

[Ben Charles]

You can run the ls7 lash cap on either pump. You can run the lt4 pump, it's around $900 and you have to buy 1 new line hardline as well.

[Ben Charles]

I don't have any proof, but I bet an ls7 lash cap on the lt1 pump (be the same difference as the slightly larger lt4 cam lobe) and and psi change in the tune would be the same as a stock lt4 pump

[gmtech16450yz]

Hey guys, if you want to learn about the Bosch DI fuel pumps, do a search over in the 4cyl section of this forum. Us LNF guys have been working with DI for almost 10 years. We've learned a lot about things like "Injection Window Misfires", torque based ECM's and what the HPFP's can do. For instance, there is no "Relief Valve" ON the pump that "regulates" the pressure. The pressure is determined electrically. That's why you can't just make a cam with an additional fuel pump lobe and have it work without modifying the ECM. The ECM has to know EXACTLY where the pump piston is in it's travel. (Which makes me wonder about the valve lash mod???) There is an INTERNAL pressure relief valve in the DI pumps, but those only bypass at super high pressures, they have nothing to do with the pressure regulation.

The HPFP's in most turbo 4's are 200bar. They normally run roughly 2000psi, but I have run them to almost 3000psi with no issues for years on many different cars. The highest output Bosch pumps will now put out 500bar, or 7500psi. At one time I knew what the specs on the C7 pumps are, but don't remember right now. My point is I don't see any reason why the pumps in any of the C7's can't be safely run significantly higher than stock.

Like I said, there's a LOT of info on DI over in the LNF threads.

[Ben Charles]

Good info gmtech, I run e85 currently NA, but plan to run a modest 5 to 6 psi on e85. Going to try to get more pressure out of the lt1 pump, then may do the lash cap then lt4 pump if I need to.
From what I know the lt4 cam is only 0.3mm larger than the lobe on the lt1 cam

[Higgs Boson]

stock LT1 fuel lobe, LT4 pump, lash cap, just sheared off the pump mounting bolts.....

[thewrx]

stock LT1 fuel lobe, LT4 pump, lash cap, just sheared off the pump mounting bolts.....

guessing that was not on purpose?

[Higgs Boson]

guessing that was not on purpose?

you should be on a tv game show with guesses like that.

I am running LT4 hpfp with no lash cap now with no issues. I would never recommend a lash cap after that.

[thewrx]

yeah going with a hpfp on my DI truck, not at the 500 road block with the PD setup yet but truck was tuned with corn, so will need extra volume.

[Higgs Boson]

I am running LT4 pump, rails, and injectors. Seems to work good, but I won't know for sure how close to 85% I can get until I get a second lift pump in there as it is giving up first.

[69camaro5speedefi]

stock LT1 fuel lobe, LT4 pump, lash cap, just sheared off the pump mounting bolts.....

I am thinking this happen to me after a pull.
Fuel rail pressure dropped,set a low rail pressure code and dies.
Made a pull engine was running fine got to about 3 mpr and shuts off after
looking at the log rail pressure bounces up and down at same engine speed and about the same load then drops engine shuts off.
Pressure will not come up to command cranking psi to start just to lift pump pressure

Has anyone seen regulator stick or other problems to keep pressure down?

[Higgs Boson]

Pull your intake manifold, takes only a few minutes. At least shine a light underneath it and see if you can see oil or anything funky.

[69camaro5speedefi]

I took the blower off it was a pain, if it was .030 bigger it would not fit wow its tight.

Not sure what's wrong nothing looks broken

Maybe the pumps bad from a big lobe cam and lash cap?

[Higgs Boson]

is it an LT4 pump? HPFP's do fail in general but a lash cap obviously can make it happen faster. from what I understand, the rod moves less in the LT4 pump so a lash cap just slams it against the limit over and over.

[69camaro5speedefi]

I turned the motor over to check cam travel with calipers (ruff idea) it does not come up to the pump height

With the outer spring off the pump looks a little funny.
I need a new one to check height

[69camaro5speedefi]

Yes it is a lt4 pump