I am working on a fully modified upper and lower intake right now. I should have some Dyno results in the next month or so.

Are you modifying the original 500EFI manifold or are you remaking the upper and lower halves? Can you share details? I'm really interested. Thanks

I am modifying the originals. I am working a 525 right now, but it will be the same process for the 500. I would be selling them on a core exchange basis.

Do you know if the 500EFI and 525EFI manifolds have the same runner and plenum sizes? I know the TB's are different size.

Do you have dyno plans in near future? I am pulling my hp 500efis soon, switching to afr heads, tweaking the intakes then dynoing and tuning on the dyno at my shop, would love to test yours at nc or would be interested in having mine done or both

Yes, the 500 and 525 manifolds are the same except the 525's IAC valve on the upper, and the lower on the 500's have brass inserts for the water passages.

We have done quite a few where we removed the 500 efi intake and replaced it with the Holley single plane setup. We have also used the Edelbrock intake as well, but I prefer the Holley. We buy the intake without any electronics in a complete kit. This includes the intake, 2000cfm throttle body, fuel rails, injectors, TPS, IAC, ECT and MAP sensors. You just reuse your Mefi 3 ECM and harness. The harness will require some mods or we offer a replacement harness that is tailored to fit the intake perfectly. It's a really nice setup that works great. If you do reuse your harness, you will need to repin the IAC connector as the Holley comes with a Chrylers IAC instead of a GM. It's a simple mod but must be done for the IAC to work.

Several years ago, I built a 555 ci engine and tried to use the 500 efi intake. It was a pretty healthy piece with some pretty large heads, cam 10:1 compression, etc. The customer insisted on using that intake. Well, we got it on the dyno and it was a complete turd. It struggled to make past 600 hp and wouldn't pull beyond 4800 rpm. I knew it wasn't going to work, but I had to prove it to him. So, we pulled the intake on the dyno and put a Holley intake and 2000 cfm throttle body. The first pull netted 80 hp more. With some tuning, it made 700 hp. It was a completely different animal to say the least. This is an extreme example because it was to much CI, head and cam for that intake. My point is that the farther you get from a 500 efi, the worse the intake is.
Eddie

My advise to you is ditch the MEFI system. The 500 EFI manifold is not as bad as everyone seems to think. I built a modified 540 EFI and had the stock 500 efi intake assy. with the top mount Tyler Crockett throttle body kit. This engine was 693 Hp at 6000rpm on the dyno. I had the same engine refreshed after 20 hours run time and switched to a Holley EFI system with an Edelbrock intake. This motor is 714 HP. Identical motor except the intake and injection system. So the 500 EFI intake costs roughly 25 HP on a 700hp engine. Mefi system is nothing but a headache. Not being able to tune anything yourself is a joke. My mefi system was always rich or not running right in some shape or form. With the Holley system you just put in the o2 sensor and it basically tunes itself. . Sending a mefi ecm back and forth for tuning gets old. Since switching to the Holley System the boat runs night and day different. It is worth every penny and selling your old system with net you half the cost of a Holley system. Call Mark at MER performance and get some real numbers from him. He has done both my motors and just got done doing a set of motors with ported stock 525 intakes and larger throttle bodies with the Holley Injection installed on them. Jeff Wurl

But you are comparing tuning an engine in the boat to tuning an engine through the mail. There is no comparison between the 2 scenarios. The Mefi can be tuned by any individual with software such as Mefi burn. It's actually quite simple once it has a decent base map. It doesn't self tune in closed loop, but it isn't very hard. Just like any other ecm out there, it should be tuned in the boat. I won't do tunes through the mail. There is nothing good that can come from that. I will only tune them in the boat.

As for your 500 intake, you are comparing a highly modified 500 intake to the aftermarket Edelbrock. You removed the weakest link of the intake....the small, front mounted throttle body. That isn't really a fair comparison. Please don't take this the wrong way. I not trying to pick on you or start any chit. I just want to be sure that the OP has the correct info so that he can make an informed decision. I would bet that if you would have used a stock 500 efi intake that it would have been down substantially on power from where it was and there would have been way more that a 25 hp difference. You essentially turned it into a cross between a single plane intake and a tunnel ram. You took out the biggest restriction.

I'm not saying that the 500 intake is bad. I'm just saying that it has it's limitations. As for the tuning, it really doesn't matter which ecm you use, it's only as good as the tune that's in it. You could have the best ecm that money can buy, but if it has a crappy tune in it, then it will run like crap.
Eddie

I totally agree with everything Eddie is saying in the above post. Also If your having your Ecm tuned the only way to do it is in the boat. I learned the hard way. BUT, once you make the investment of buying the software to tune your ecm or travelling to having your Ecm tuned and paying for that service. + Buying a new intake or buying the parts needed to make a 500/525 intake flow. ( throttle body, porting, ect) You are way more than half way to the cost of a complete Holley EFI system. Plus you still have the resale value of selling off your old parts. ($800-$1000) This is just my opinion from previous experience . I can not say enough about how easy and nice the Holley efi system works. Jeff Wurl