articfriends

My head porter had them made. The original bore was 2.400 and they are bored to 2.550. We saw a definate hp increase normally aspirated, blown I think we gained even more, we were going to make a blown pull with the stock throttle body on after we were done to see what the actul gain there was but never did it. I bought several throttle bodies off E-bay and had them bored to sell on a exchange basis but haven't advertised that much. As far as the manifold porting, originally when I made 950 hp the time before this I milled the top of the runners down myself then cut the plenum dividers then hand blended the top. I then port matched the intake to the heads. This time when I made 1115hp I was going to have my head porter full port the manifold, he was all for it until he actually started doing it then called me up and said it wasn't going to happen. I then took it to my snowmobile porter who went crazy on it, when I got it back it didn't look real professional, I made long mandrels and went in with a box of tootsie roll sand rolls and did some clean up work on it myself. It I had it to do all over again I would send it out to be extrude honed, Smitty

snapmorgan

I am running a similar N/A 540 making about 575hp with the stock mag intake. I was planning on ditching the intake and installing a FAST or Holley setup or possibly having injector bosses installed in a carb type manifold and running a throttle body. But after reading the thread on the modification of his intake, I might try that myself. I am only looking for 50-75hp, and i think it is hidden in the intake manifold somewhere. I really like the MEFI system and it would be considerably cheaper to modify what i have.

articfriends

I am doing another project right now, a mefi controlled efi pontiac 455, By the time I bought a good throttle body (2000 cfm Scorpion), the manifold, rails, plumbing, injectors, etc I have a small fortune in it. It is going to the dyno very soon, we expect 600-625 hp from it. You could modify what you have in a similar fashion to what I did and get some gains but remember when My 540 was dynoed I wasn't turning any accessories, the more generous 60 degree sae factor was used although we did use cmi boat headers so for comparison sake you have to account for that for my 657hp. One thing in your favor though was my compression was around 8.2-1 (motor was built for running boost) and there was some left on the table there.I could run 87 octane if I wanted when running Normally aspirated, Smitty

Young Performance

Here is a MPI manifold I just finished. Normally, I wouldn't port them as I would just send them out to be extrude honed. The customer started this one already and made a mess out of it. So, I couldn't swap it out for one that was already extrude honed.
I put it in the mill first to shorten the runners. Then took after it with a HUGE single cut carbide bit. After I took out about 5 pounds, I blended it in with cardrige rolls.
Eddie

Young Performance

A few more.

swan2

Eddie,

I was just wondering how much one of those intakes would be if I sent mine to you for exchange. Its a 502 mpi with m1 procharger and you repinned my wiring harness and sold me the mefi3 and help me set up the fuel system also. And most of all would it make that much difference to notice thank you its great to deal with someone like you.

Young Performance

I think the swap out is around 750 or so. Yes, you will definitely see a difference. However, you will need to do some tuning with the addition of the intake.
Eddie

snapmorgan

who does the extrude honing swap? Has anyone ever used Kevin Thompson's manifolds for a conversion? He will add fuel rails and injector bosses to almost any manifold and and has billet throttle bodies in many sizes. I assume I could have an air gap or something similar done and use my Merc controls and injectors and have Eddie tune it up for me again. How much better (or worse) would this work as opposed to modifying the stock intake.

Eddie, that $750 you quoted, was that for a manifold that is extrude honed, milled and ported? The one in the pics sure looks good.
Thanks, Joe

Young Performance

The one I did is not extrude honed. Normally I would send it out and swap it for one that has been extrude honed. However, you have to have an untouched, virgin manifold. This one was already milled on by the customer. He thought he could do it himself and made a mess of it. Since is was milled already, I couldn't use it for a core. I could still get it honed, but I would have to wait until the next run. They will do about 10 or so at a time. The problem is that they only do them every several months. Especially now that there isn't nearly as much demand for it as there was 8-10 years ago.
I opened up the throat a bunch bigger than the extrude honed version. But, they are able to open the entire runner up, where I can't get in there all the way. I think I would rather have one extrude honed. What I did on this one was a TON of work. I bet I have about 25 hours in it to get it where it is. Ideally, I would love to have one extrude honed and then go at myself and really open up the throat.
You just get to a point where it isn't financially feasible. I replace a bunch of them with an EFI setup from Holley. It works great and will free up some power. It also really has no limits like the MPI manifold does. Even with all the honing and porting, the MPI manifold has it's limits.
I usually only do them for Procharger setups. It's makes sense to do since you already have a Procharger setup to work with that intake. On the NA engines, I usually go with the Holley intake. I do have a few people that want to keep the look of the MPI intake, so we do whatever we have to do. You can make a real sleeper that looks stock.
Eddie

SB

Eddie - if you don't mind,
those center dividers are really to sharp. The top and and the sides (i see a sharp transition on the side about an inch or two down) should be more rounded. This will help with keeping the air straighter and let more air go in.

I agree on the Holley type intake being better overall...for power and for ease.

Hope this helps.