EFIDynoTuning Forum

How big does the fuel supply line need to be for my returnless system to be more than adequate for the demand of this boost/ power level? I’m also wondering if there’s any recommendations regarding materials for the system?

8an is fine

Nope. I use 1/2" aluminized tubing and never any problems.

I went ahead and installed a -8 supply line with larger fuel rails. I backed off the fuel pump prime time to .5 seconds because the more efficient pump was pegging 90 psi at key on and contributing to hard starting with that excessive pressure on top of the injectors. Now I’m wondering if my stock 20 year old exhaust is done and/or the stock 20 year old valve springs… Would it be recommended to upgrade the exhaust system and/or valve springs at this point?

if you were getting 90 psi that means some idiot removed the pprv. Definitely need to drop the tank and add one back in or add an external fuel pressure regulator as a PPRV.

springs and exhaust valves should be upgraded on any engine that gets boost added

stock marauder exhaust is good for about 425rwhp except for the stock cats which all seem to clog up.

Well, I incorporated the PPRV so I’m guessing it just wasn’t effective enough as I’m seeing excessive fuel pressure during fuel pump prime time (which I believe is contributing to long crank/hard start conditions). I’m thinking this means I’m going to delete the factory PPRV and install an external pressure regulator close to the tank. I’m wondering if I should delete factory (likely comprised) cats first for tuning purposes, and then equip long tubes. Or should I go long tubes with “performance cats” and tune from there to start with? I’m also reassessing and wanting to get some improved cylinder head/valve train components (valves springs and seats) Are there any recommended vendors for this work for these “C type” heads? I know this is a lot of questioning and it shows my inexperience with building a “steet machine” but I’m grateful for access to this forum and it’s knowledgeable members. Please share your thoughts fellow members. I’m wanting to learn more and I value all of your feedback.

that means the pprv isn't functioning correctly, I would just replace it rather than swapping in a regulator

Yeah cats on all marauders are pretty much gone these days. Mine even failed and were clogged closed.

might as well toss long tubes in while your at it with some cats as its far easier and less work.

any local machine shop can cut new seats and punch new guides in her. Yeah anytime you boost an n/a engine you should upgrade the springs and exhaust valves.

Update: Currently have pulleys to run 18 lbs of peak boost now with the 2.65 tvs and the engine doesn’t “fall apart” with valve float that I thought might be happening at 20+ lbs. I clearly didn’t think enough about improving valve train components for that boost/power level. I will entertain the idea of springs and valves + guides if I run into additional issues as I was unaware. It seemed quite a few 03 cobra owners were getting away with more than it seemed in this sense…. I am wanting to hear or understand more wisdom on this topic please

I'm not sure what your asking ?

Edit: Decipha is correct, see his post below, boost does affect required spring pressure based on valve size

In theory, the extra pressure you have behind the intake valves should also be inside the combustion chamber on the front of the valves from the intake stroke.

Engine RPM, seat preload, and actual valve weight (and actually spring weight as well) and of course how much lift you are trying to achieve from cam selection are going to be the major factors contributing to valve float, not so much boost.

Also, belt slip might look like valve float at the top of the rpm, not sure if that's something you could be running into not knowing the full details of your setup.

If you are or think you're going to be running into valve float, look into beehive or conical springs. Probably a good idea to do this if and when you upgrade your valves anyway.

On the intake stroke the cylinders are under vacuum that's where your engine vacuum is created.

The stock intake valve is 1.46" diameter which gives you a surface area of (1.46/2*3.14==2.29 square inches)

18 lbs per sq in of boost == 18*2.29== 41 lbs of spring pressure lost due to boost. It may not be an issue if you have sufficient spring pressure already but if your on the edge then it could cause a valve to float.

Here's a couple articles if you want to check them out.
https://www.enginebuildermag.com/2017/0 ... -pressure/
https://www.dragzine.com/tech-stories/s ... -pressure/