GT500 lower intake on GT Supercar heads?

Anyone running this combo? I know the differences, so I'm sure there's not that many out there if you're already starting with GT500 heads, but I'm looking to see installed/after pics of the lower intake since the 2 front inboard bolt holes don't line up on the GT500 and GT. I've heard they can be slotted to make it interchangeable (the OEM gaskets actually come slotted to work with either head) but the GT500 intake manifold is 2-3" thick at those specific misaligned holes, not 1/2" thick where the rest of the bolt holes are, so slotting it doesn't seem realistic. Almost seems like a better option would be drill & tap a separate hole which gets tricky since the 2 holes would likely overlap.

Thanks for any info or pics if anyone has any.

For reference I've got a 2000 HD F-150 that I'm putting a fully built 4v into. GT supercar block, darton wet sleeved 5.8L, CNC ported GT supercar heads, Cobra Jet lower intake manifold, GT500 style 4.7 KB, etc. Longblock is assembled and on the stand so I'm at the point of ironing out the small details now before dropping it in.

You could weld the bolt holes up on the heads and then transfer punch your new set onto the heads... Seeing as your long block is assembled probably not the best solution. Ive seen people use a long aluminum grub screw and locktight it in place sticking out 1/4 or so. Then cutoff the hex key part so it is smooth with the top of the head, then proceed to drill a new hole ovelapping the old screw hole that is now filled in with the grub screw... Again not the correct way.... But a way... If you know someone with a mill they should be able to do it they would just need to machine it upside down and upside right... Its doable. I would try a local machine shop. If its only off by 3 or 4mm it should be fairly simple. I would try this first. Or if you really want to get fancy you could remove the waternecks all together and run -16an out of the top of the cylinder heads... MMR makes the fittings to be able to do this but you will have to machine the front water necks off....or ill trade you some gt500 heads for your fancy ones.... Good luck

I just ground down a seat on intake then redrilled front holes and slotted rears, can take Pictures in a couple days

thanks for the input guys. Much more helpful than the "just slot the holes" answer I got from the seller feeding whatever to make a sale lol

Welding the holes isn't an option at this point, and would have been easier while they were apart getting checked after getting them and seeing they weren't as described in the first place, but I was still under the impression it was a quick slot to realign at that time. Would have been easy to have them welded and re-drilled/tapped while they were getting CNC ported.

I like the idea of the aluminum grub screw locktited in, then drilled/tapped the adjacent spot. A quick look it appears it would only intersect the original hole by maybe 30%.

Jazz when you get a chance I'd appreciate pics of your method. I'm pretty sure I'm envisioning what you're talking about but a pic would help. I will be getting my lower intake ported, powdercoated, etc, so machine work on that isn't a problem.

Certainly not cutting the water necks off, my top end setup is all GT500 (4.7 KB) so keeping the OEM manifold in tact keeps that setup the cleanest. And my longblock is already assembled and heads already CNC ported so I'm not changing out now haha. More than 1 way to skin a cat, I appreciate the ideas fellas.

You can see how i milled down beside the neck to a decent height and that gave me room to drill a new hole and fill the old one with jb weld

And the other one

And if you choose the jb weld route put a bolt in your new hole wrapped with tin foil, when u pull it out some of the tinfoil stays

perfect thanks for the pics. That's what I was picturing you did. Glad to see the lower intake can be machined pretty cleanly. I can have that done pretty easily at my local fab shop since the lower intake is still brand new and untouched. Not quite as simple as just ovaling out a hole like I was originally told, but simple enough with an endmill at a fab shop. And I won't have to risk potentially screwing anything up with the heads that are already assembled and on with trying to fill the hole & re drill/tap.

I know you said you filled the old hole with JB weld, I may try and just leave it slotted so then my lower intake would work on GT500 or GT heads, probably help the resale if I ever change setups (post on FB about a CNC billet lower intake w/ upgraded IC and rear IC ports that looks pretty appealing but not out yet, that'd be about the only thing I'd end up changing to down the road).

Appreciate the help guys.

Do you have a Billet crank in that beast ?

I wish lol. Had to draw the line somewhere. It's a CJ crank, ATI balancer, Kinetic "crank saver" ARP crank stud. GT supercar block with darton wet sleeves, 5.8L big bore, CNC ported GT supercar heads, manley pistons, manley I-beam rods, built/assembled by JLP.

With a 4.7 ? Oh boy !!! I know all about the Kinetic ARP deal ... Oh boy !!!! Bad ass unit though. She dying for a turbo . Lol . Best of luck . Bad ass piece !

Who cnc'd the heads ?

Turbo is a whole different can of worms, I've got enough on my plate going from 2v to 4v. It's been a long process doing the swap and I've got a ways to go, but fortunately at the end I can literally bolt on the 4.7 and be done, and not have to find some shop I'd trust to fab up a turbo setup from scratch.

Not to mention, that more quickly opens the next can of worms of the trans. I've got a built 4R100 right now, but not looking to do a TH400, trans brake, etc. anytime soon. Blower will get me into the 8's. I've already been 9.88 with a 2.6 KB on my iron block 2v and 1.34 sixties in my big ol' limo truck lol

JLP did the CNC port on the heads. I've got pics on my other computer I can post tomorrow.

Killer 60 foot ! Would love to see some pics !

I have a very nice GT lower intake, would that help?
Been keeping it for a future project due to the dual injector, but could sell.
Man that seems like a killer project!
Didn't KB just release a 4.9?!
-J

Keeping the GT500 style lower intake. AFAIK the IC is bigger, but aside from that I'm not dealing with 16 injectors (cost or tuning lol), I'm still on a factory 02 HD PCM (for at least the next couple years), and my whole top end setup is GT500 (already have the blower).

I did see they mention a 4.9 which has me thinking lol. I really don't NEED it, but a lot of this build is about being excessive at this point haha. I'm actually selling my polished 4.7 KB to buy a black 4.7 KB so the time would be now to jump to a 4.9 since I haven't bought my black 4.7 yet lol but I think I'll stick with the 4.7. If anyone is interested in a polished 4.7 let me know. Haven't listed it yet but I will be soon. I basically want to break even for a black 4.7. I bought it off Ryan Ayrcock (sp?) with a whopping 200 miles on it. Ended up deciding I want to go black to keep the HD theme of monochromatic with just small polished/chrome accents rather than fully chrome/polished under the hood.


Few pics attached.....the GT heads CNC ported by JLP, my new 4v longblock on the stand, my old 2v setup in the truck, and a launch pic on a 1.34 sixty, lifting the tire in my limo lol

Great pics. I guess I was misunderstanding but it seemed like you were having an issue by using a GT500 lower in place of a GT Supercar lower.
I think it'll look sweet with a bad black KB, but a polished one isn't a bad alternative, I bet they're screamers!
-J

The issue was just the forward (and I believe rearmost) bolt holes. The rest all line up, but those are a little off. The gaskets are actually the same and just slotted from the factory to work on either one. A GT version would bolt right up but be a whole new can of worms for other reasons with the top end. I've got enough challenges as it is on this lol

If I can't get a good price for the polished I'll keep it, but I'd prefer black and I'll pass along a killer deal to someone, they'll basically get a practically new 4.7 in polished for the prices of a black one. I haven't checked all the pricing but on the 2.6 blowers for the L/HD trucks polishing was like a $600 option, so basically whatever that cost is on the 4.7 it'd be a freebie for someone.

Searching for other stuff, and stumbled across my old posts so I figure I'd update folks on what I ended up doing, incase any folks in the future are also looking to do the GT500/CJ lower intake on GT supercar heads.

I've heard slot the manifold, but there's no way to slot it far enough without breaking thru the sides on the front portions, plus you'd have to machine out a flat seat again since it's in the sloped coolant port towers. It actually wasn't bad at all to re-drill new holes in the heads, adjacent to the factory GT supercar holes. PATIENCE & PRECISION are key. The holes are literally the thickness of the threads apart.


First I bolted the intake down with all the bolts that lined up (just the 2 fwd & 2 aft ones don't). Then I got a drill bit the exact size of the manifold thru holes so I knew it was perfectly centered, and I lightly drilled a dimple in the head for dead center




Then starting with a very small drill bit, I drilled a pilot hole straight thru, then slowly stepped up drill bit sizes till I got to the exact drill bit size for an M6x1.0 tap. IIRC it calls for a 5mm drill bit. I bought a set of metric bits specifically for this. You could find a close enough SAE bit, but with tiny screws like these, close enough isn't good enough, I wanted exact per spec for the tap. You don't need crazy expensive metric bits, a $15 set on amazon is perfectly fine for drilling aluminum. IIRC I started with 1/8" SAE, stepped up a couple sizes, then swapped to metric bits and went 3.5, 4, 4.5, 5. You can step up sizes faster, but like I said, patience & precision are key here...

In this pic, I did thread an M6x1.0 bolt from the bottom up to fill the factoryy hole, but it's not necessary. The others I did not do that.




Tapped the hole with M6x1.0 tap, little WD-40, then cleaned with carb cleaner. Slight chamfer on the top with a deburring tool to slightly chamfer the edge like the OEM hole for easier bolt alignment.




Repeat that anxiety-inducing process 3 more times, praying you don't screw one up lol. Luckily enough I knocked out all 4 perfectly. (I also popped those rear freeze plugs out later for my coolant crossover).




Sit back & admire the Ford engineers that decided to shift the 4 outer bolt holes by 1 bolt diameter, just so people had to work a wee bit harder to interchange parts lol Separate the men from the boys haha




Bam.....dual bolt patterns! If I ever wanted to change things up down the road, I've got the flexibility now of either style lower intake, and if I ever parted/sold this combo down the road, it'll work for either crowd. Not that I plan on doing either, but it's a nice solution.




Everything bolted back together. And before people start getting concerned how close the 2 holes are to one another, sit back and think about it for a minute. There's something like 15 bolts holding the lower intake down, and they're only torqued to like 89 in-lb or something very light along those lines. There's also zero shear/torsion forces on these bolts, no side loading, no twisting, they're simply applying a downwards pressure. There's no concerns it would ever break thru the other adjacent hole, and honestly you could run entirely without them. Aftermarket coolant port fittings only use 1 of the 2 bolt holes. It's more of a peace of mind/OCD of using every manifold bolt for the most ideal/even clamping force.






All mocked together.....which is already all back apart lol. Mocked up to figure out what other ARP hardware & AN fittings I needed, now back apart till the replacement permanent goodies arrive.

@Harley#356 nice work. I agree with you on the forces exerted on that thin area.

However it wouldn't hurt if from the underside of the heads you threaded an allen head set screw that's as long as the threaded hole but tip sits just below the mounting surface. The screw will fill up the void space so if the thin wall area did start to flex it would act as a brace and help stop flex.