Lt1 Injectors or Pump?
 

The common thread in all the builds I've seen so far (well the majority of them) is to upgrade to both the lt4 pump and injectors.

However I also know off previous cars I've built, that when a platform is still relatively new (even the earliest of c7's especially considering the popularity of port vs direct), things haven't usually been fully investigated. And as time goes on, limits (in terms of strength, durability etc) become more concrete/understood. This can be a pretty big factor in cost to build.

Has any shop/any individuals explored which one is actually the limit? I've seen at least a post or two suggesting that the lt1 injectors really aren't the issue, but the pump is. It would make sense that the pump is solely the limit, as an increased fuel lobe will take the fuel system noticeably further. (Low pressure issues assuming to be fixed).

Any comments, thoughts?

Well I'm at 670 rwhp with the Lingenfelter Big Bore Pump and stock Lt1 injectors. Never ran out of fuel, however I do run a Aem Meth/water injection for addition fuel. I'm getting ready to install the Lt4 injectors so I can run a little more boost without worrying too much. I'll be maxed out after that I'd say at about 730 rwhp.

Wow that's great! That's really good to know. Instead of buying injectors and a pump, going straight for a lingenfelter pump is a much better long term solution for the same price.

I'm curious how do you route your meth nozzels? Are you pre/post blower? I guess not direct port. Nobody on here seems to be concerned with meth distribution; not many people talk about direct port.

I think for these engines especially you'd be mad not to run water meth. Really should do wonders for carbon build up and give you more fuel affordably.

I have a Lingenfelter pump for sale. 2000miles max. $950 shipped.

I'd take you up, but currently on the market for my next car (leaning really strongly to a new ss). I don't buy parts before I own the car :laugh:

Also Love what you're doing with the MS3Pro. That's really awesome. I thought about doing just that, but I think I want to keep this car real point and shoot simple. Did the race car thing, and this time I want a true street car/daily

Parish I might have someone interested in the pump. I'll get hold of him and let him know you have it.

The limits of the LT1 engine are all very closely intertwined around 550 whp. GM developed this engine to make 450 hp and when you exceed that you run into multiple problems.

1. Fuel - you oversimplify with the LT4 pump and injectors. The car has both a low pressure side fuel system (electric in-tank pump) and a high pressure (mechanical) pump system. The biggest power boost can be gained by upgrading the low side pump. Not a lot of discussion about this because it is easy. Any of the pump upgrades from gen5 port injected cars can be used to supplement the low side.

High side upgrades are the main limiting factor in these engines. It is really hard to get the amount of fuel required to make big power through a tiny direct injector in a fraction of a second. High side upgrades currently can be done with a cam (increased lobe size gives more pump from mechanical pump), pump upgrade, or injector upgrade. Because the car uses direct injection these options are very limited. To this day very few aftermarket parts exist that are better than the stock GM parts and those that do exist are very expensive. Lingenfelter sells a 1000hp pump and injector set for $6000 and that is as far as I know the only direct injection system than can dyno 1000hp period. No other systems can touch this power level stand alone. The GM stock LT4 pump and injectors will give you around 800 hp max and it is really best to run them as a set. The injectors are designed to run a certain fuel pressure. The LT1 pump and injectors were developed along side each other and so were the LT4 parts. You can run the LT4 injectors on the LT1 pump but they are not as efficient and same with the LT4 pump with LT1 injectors.

Perhaps the easiest way to overcome this direct injection fuel restriction is to add a port injection system on top of the direct system. This is exactly what GM did to get the power they wanted from the new ZR1 corvette engine. Many builders have done this to make big power builds but so far the factory computer does not support this and the aftermarket is a cluster of not well tested products. There is no doubt in my mind this is the direction we are heading to beat the limits of direct injection but the tech is still relatively new.

2. Compression - The stock LT1 is 11.5 to 1 compression. Boost has a multiplication effect on the compression ratio of an engine and when you add a forced induction system you are very limited in the boost you can give the engine before the fuel is so compressed you get detonation. If you run alcohol this not an issue but most of the fuel sold in the USA is less than 10% alcohol. In reality that means unless you are making specialty purchases of fuel like E85 or race gas the LT1 engine is only going to safely make about 650 whp on a tune where you could drive the car across the country and buy gas at the pump.

3. Piston and ring design - the LT1 was not designed to run boost and many, many people that have boosted the LT1 engine over 600whp have experienced an engine failure related to pistons, rings or even rods. To be honest the previous GM LS pistons and rings were better able to handle boost than these new LT1 engines. The stock LT1 engine really needs a piston and ring upgrade if you plan to take the engine over 600 whp and run it hard.

In my opinion the LT1 is about a 600 whp max engine without major upgrades. The LT4 is about a 1000whp engine without major upgrades because GM adjusted the compression ratio and piston and ring problems. So, not just the LT1 injectors or mechanical pump but a cluster of limitations.

Are you using the meth injection for more fuel system headroom or just for increased octane?

Great. Thanks

In our experience the High pressure pump is the first Limiter and and a very hard limit that is unaffected by low side pressure unless low side pressure drops to around 30 psi then its range is limited even further.

I have run both 400 Kpa and 500Kpa low side pressure and the hard limit of fuel delivery was unaffected.

The reason is because the high side pump is a positive displacement piston pump and fuel is not compressible.

The LT-1 pump runs at 2175 psi and the LT-4 pump runs at 2901 psi, this will extend the range of the injectors but you will find the limit.

The big bore pump takes it to the next level.

You find that limit of the injectors by logging the High pressure pump and injector opening time.

When you exceed 6 milliseconds start looking for larger injectors.

Hope this helps.

You got your pump sold didn't you?

Yep. Sold and shipped. Thanks! :)

Your welcome and hopefully you can help me out with something some day. You should be going pretty dam fast this year. Hopefully you can make it to the Camaro Fest this year. Its a really good time and a shit load of fast cars.

sounds like fun but I don't plan on doing any safety stuff yet so that is probably not going to work for me. maybe next year. I just know the safety stuff is going to make the car less safe on the street.