Honda Intake Manifold

[madjak]

Hi everyone,

I know this topic has been discussed several times before but I'm looking seriously at trying to do this on my N/A engine as prep for a Rotrex install later down the line.

I plan to use an aftermarket Honda B18 intake but instead of cutting off the flange and welding on a mazda flange, I plan to build a transfer flange that will bolt directly to the head with countersunk bolts (remove the existing studs) and then have the honda stud pattern threaded into the flange. This means I should be able to bolt the Honda intake on and do any port matching in the transfer flange.

If I do it this way, it means I can chose to run the injectors in their standard locations in the head and plug the intake manifold, or alternatively run the Honda sized injectors in the intake and plug the head. The benefit to the Honda injectors is that I can use the Honda fuel rail or aftermarket on and get a bit more room around the head.

Also, the cut and welded flanges have been cracking and require a lot of bracing to survive any period of time.

So other than a better flowing intake manifold, larger ports & plenum, it also means I can run a larger Honda throttle body and not risk the failure of my stock one.

Can anyone see a major issue with the above plan?

[project.r.racing]

ports are only big as the smallest ones. the head ones will still be the same size. Doesn't matter what you bolt to it.

you can increase the inners of a b6 intake manifold it some light machining.

b6 engines have aftermarket fuel rails available.

b6 engines have aftermarket bigger throttle bodies available.

the biggest problem i see is trying to reinvent the wheel.

[oztrackdays]

it's not that cost effective but it does make it lively.

[madjak]

not really reinventing things... this has been done a fair bit in the US with gains larger than installing a square top manifold or porting an existing. The only different idea here is the conversion flange, which looking at the hole positioning won't work quite as I had thought anyway. I may have to move a few mount mounts on the intake flange. The mounting points are too similar, with the bottom holes on the Honda manifold less than a hole width lower, and the top holes offset to the side around a holes width.

To port the stock intake manifold is a lot of work or $. You have to cut it open and reweld or use extrusion honing and even then the benefits are minor. The other option is to buy a squaretop manifold and mod the flange to make it fit but results show the modded Honda manifolds perform better anyway.

The after market throttle bodies and fuel rails for the Honda set up are half the price due to volume. I think if I was looking at a square top manifold, plus larger Skunk2 throttle body, plus fuel rail you'd be in the $1500 + range. The Honda manifold + throttle body can be had second hand for around $300.

[madjak]

it's not that cost effective but it does make it lively.

You've done the Honda inlet manifold? In Monda, not only did you change the inlet manifold, but the head and block too

[NitroDann]

Post results of this manifold on n/a cars please.

Dann

[madjak]

Post results of this manifold on n/a cars please.

Dann

Yeah I'm planning on dynoing with the stock NA8 manifold for reference, Honda manifold then again with e85 tune. All with my current N/A setup. At least that way we'll know how much all these options help. Depends a little on costs and time if I do the stock NA8 one first as I've already done that just on a different dyno.

I need to decide if i want to run with the Mazda injector location in the head or Honda manifold injector location. I'm ordering some 1000cc injectors for the e85 upgrade and the Mazda ones are 14mm with the Honda ones 11mm.

Anyone know if it would make any difference? It's probably easier with the stock Mazda location and bung up the Honda one, but thought it would be good to get the fuel rail away from the heat in the head. I suppose if the Honda manifold doesn't do much at least with Mazda injectors I can revert back.

[NitroDann]

I'm asking you to back up your claim of US cars improvements and post sheets from the US that you used to influence this decision.

[madjak]

Dann, you've probably read the thread on MT. Around page 38 of the Honda intake thread.

There are mostly turbo'd cars but Emilio compared an Edlebrock manifold to a flat top and found approx 5 hp over the flat top throughout the range, more if he could fit the full runner length in there. The manifold I'm looking at using is the Skunk2 Ultra street which I think can have the flange modified slightly and bolt straight up. From my measurements I think it will fit in as stock so the runner length would be close to 10" which I think is almost ideal for my car as my target rev range is higher than Emilio's.

This is comparing to the flat top manifold, not the stock NA8 one which is shown to be a lot worse than the flat top.

[NitroDann]

If memory serves me it was a whammy engine.

[madjak]

Also, I'm not saying this will help a stock engine... My head is heavily ported with oversized inlet and exhaust valves plus very large cams and a 3" exhaust. I think my bottleneck is now in the intake side which is still entirely stock. I'd be surprised to see no improvement with a more free flowing manifold and larger throttle body especially in the 6000-8000 rpm range.

[madjak]

If memory serves me it was a whammy engine.

yes it was, he got around 170 whp if memory serves me right with the manifold. I'm around that power with a stock NA8 manifold with peak power around the 7800 rpm mark, though dynos are all different so who actually knows if that compares. Anyway my engine should be in the ballpark at least.

I'm surprised there is no encouragement on this forum for anything different. It seems everyone wants to build the same thing all the time. Screw that, it's boring! There will be more cost in the dyno time than the manifold itself!

[slug_dub]

As with IRTB's, aren't you going to have a bad time with fitment since we have stuff all over the intake side?

[NitroDann]

I incorrectly assumed that your engine was close to standard.

Carry on

[sailaholic]

I'm all for it. I just didn't have anything technical to add so I was keeping quite. You should now feel encouraged!


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