351w Swap With 70mm Turbo


Mar 13, 2006
I'm swapping a 351 w roller motor into my 93 lx. I'm going to run the on3 kit with there 70mm for now. I'm wanting to swap to e85 at the same time. I know I need roughly an 80lb injector but I'm unsure as to fuel pump size. And also what mass air to go with? What's everyone running? Or are guys going to speed density instead? I'm shooting for 600 rwhp which I may or may not get to. thanks for any help
  • Like
Reactions: 1 user
  • Sponsors (?)

Hey man, good luck with everything. That sounds like a nice concept, but maybe there'll be a little more planning involved before you jump in. First, a 351W is a great foundation for trying to push those kind of power levels. So, I'd say you're on target, there. The 70mm turbo will support 600rwhp without issue, but I question the amount of back pressure you're going to have with a turbine that small. If I'm not mistaken, the 70mm offered by On3 is the same as the old MasterPower T70s. It's a good, cheap, reliable turbo, and it will probably run ok, but it's meant for significantly smaller motors.

On injector sizing, my rule of thumb is to run a injectors that are 1/10th the power output of the engine. It's not very scientific, but it will suffice. So, you'd be looking for somewhere around a 60lbs/hr injector. That said, the important thing is that your injectors should be large enough to keep injector duty cycle to less than 85% at WOT, and small enough that the injector drivers can be controlled well at idle and low load. If the injector is too large, you could have significant driveability problems down low. The thing is, last I checked, and I welcome anyone to correct me, the stock ECU is set up to run high-impedance injectors, and I'm not sure if there's anything bigger than the standard 42 lbs/hr injectors for high impedance. 42s might theoretically push 600rwhp, but that's a hell of a stretch, especially on a forced induction car. I don't know how accurate this calculator is, but it seems to call for a, surprise!, 60.9 lbs/hr injector with a BSFC of .60 and a target 85% duty cycle. I used 690 flywheel horsepower to approximate 600 rwhp. It might take more or less, given your transmission and drive train of choice.

I believe there are ways to adapt the stock system to run low-impedance injectors, but I'll leave that subject to the EEC pros. The stock EEC may have real trouble giving you good driveability at that power level with big injectors.

On MAF vs. Speed Density, I went Speed Density. It can be done with a MAF setup, though. Just make sure you're not pegging out the sensor at high flow. Basically, my advice would be to go with the setup your tuner is most comfortable with.

Good luck,

I run the exact combo you are looking to build. I'm using FIC 900cc injectors and an HPX maf. You don't need an extravagant engine management system, the EEC can handle it just fine.

As for your pump dilemma, there is no standard drop in pump that will support the power you are looking for. You'll either want an external, or look into the On3 fuel tank with multiple fuel pumps. I run a walbro 416 in my car, and I'm currently making 565whp.