P & P Intake Manifold?

[maxsideburn]

Since I'm probably going to be replacing my entire intake manifold soon anyway, should I go ahead and get it ported and polished? Would there be any actual benefit?

[bobafett]

of course. :) but also getting it port matched to the head will help out... and you will probably get more of a gain from headwork than intake manifold work. but together you will yeild even better results.

note: headwork ain't cheap though. unless you do it yourself

[SteveDX89]

note: headwork ain't cheap though. unless you do it yourself

And don't do that unless you know what the hell you're doing. It's easy to take too much off and ruin the thing. I guess you could just bolt a big fat turbo on if that happens.

[speedpenguin]

note: headwork ain't cheap though. unless you do it yourself
Speaking of doing it yourself... I have my dad's old port kit in my basement, so I'm considering porting when I rebuild my block. I'm willing to do a lot of homework, but my question right now is: Is there anything I might really screw up and cause bad things to happen to my engine?

[bobafett]

i dont think you will cause damage unless you make each port / cylinder radically different so that one is more lean than another.

but its not like over porting will cause u to blow your motor, it will run run like crap, not idle, and not have a good powerband.

[speedpenguin]

Maybe I'll try it on my original head and then on the swap head once I think I can get it right.

[AccordEpicenter]

keep in mind its much much easier to hurt flow than it is to improve it on a honda head. I actually have an 86-87 a20 intake manifold that i cut the plenum off of and ground the runners quite a bit and jb welded the plenum back on, i believe it should be a noticeable gain. I was gonna use it for my turbo accord but i got a better intake mani... any of you guys use it? Most of the power gains in honda intake manifolds arent found at the flange, its deep in the runners near the plenum etc.

[speedpenguin]

What would be best then? Just widen it a lil and portmatch it to a new manifold? and what would be a good manifold for low-end? I was thinking B18B. I remember reading a thread about it, but I was confused over whether the B18B would cause a drop or gain in low-end. I know the other B18 manifolds and the B16 manifolds would drop it.

[Vanilla Sky]

being that guys over on honda tech practically give away b-series intake manifolds, i'd pick one of those up and port it instead. they go locally for around $50 complete with throttlebody. the reason is that a b16 intake manifold flows much much much better than our stock ones.

there is plenty of room for improvement on out intake manifolds, but starting off with a better part and modding is a better situation.

[speedpenguin]

That's what I'm asking. If I portmatch the head to a different manifold, which would be the best for low-end?
Of course, I suppose I can port any of them to be good for low-end, but I'd rather spare myself the trouble if possible.

[bobafett]

if you want low end stick with 88-89 efi manifold with the butterflys. :) hehe

[gfrg88]

with a b16 IM you arent going to see a big drop in low end, the guys that keep saying its going to lose some low end havent even tried out that intake manifold, atleast i didnt and the top end is awsome :rockon:

[89AccordResto]

Go to your local library and get a book on porting. It'll have tons of info that can't possibly be covered here. :)

[speedpenguin]

Go to your local library and get a book on porting. It'll have tons of info that can't possibly be covered here. :)
My library doesn't have shit. I'm going to be looking for some reputable info online, I guess.
What's butterflys?

[sinisterfuzzy]

i'm also interested in this, my dad said i could just port out my IM a little bit to get some more power. I'd be more open to doing that then replacing it since they're probly aren't any good bolt on IMs.

[Vanilla Sky]

with the carbed car, i'd find myself some DCOEs.

[rjudgey]

Theres a magazine called practical performance car they did a excellent 5 issue spread on headwork fi you can order it worth getting, if not any fo the reputable engine building books on flowing heads for 4 pots is worth getting and reading.
Here is what i would do (bearing in mind i have 200bhp N/A tuned engines)
1. Don't increase size of ports.
2. Most of the increase in flow is achieved by making the air/fuel go round the valve stem and seat faster the port has very little if next to no effect
3. None of the ports need polishing not even the chamber they all get covered in Coke and soot no matter how highly polished they are, they should just be smooth to the touch but their are some exceptions.
Part 1. Fuel injected direct port injection inlet manifold and all the inlet port before the injector should be super smooth as no fuel mixing occurs before injector air flow needs to be the best it can, this also means flowing and machining parts of the Throttle body, plenum, and runners the inlet manifold that CKE has is a pretty good choice nicely made with excellent trumpet shaped runners.
Part 2. If Injectors are further up the inlet manifold or are placed on the trumpets on some ITB's and with using Performance carbs, the finish of the inlet manifold from carb into port or injector into port should be of a slightly more rougher feel, although machined edges and cast defects should be removed and blended into the walls and throat of ports. You can start of with a rough fininsh at the end nearest the injector carb with it gradually becoming a bit smoother towards the valve seat or you can just have a relatively rough finish all round upto to you makes little difference. But all parts and walls should be super smooth before the carb or injector still.
A rough finish would look similar to running 500-800 Grit paper on a sheet of Ally
A smooth finish would be like running 1000-1500 Grit paper on a sheet of Ally
4. Inlet and manifolds should be matched perfectly if possible only way to do this is to flow it with the inlet manifold attached this can normally only be done if your using Weber DCOE's or ITB's, if it cannot be matched if your using plenum the inlet port outer edge should be rounded of like a trumpet or bellmouth so that it covers the whole of the diameter of the inlet port manifold, exhaust headers should have the header ports larger than the diameter of the exhaust head ports. The idea is to remove any flat 90 degree edges that may hinder airflow, removing them is essential even if it's is just .5mm or 1mm out should be completely blended in or rounded off so it has minimal impact.
On carbs and ITB's make sure that they are matched to the inlet manifold again the inlet manifold that meets the carbed end can be trumpet shaped or bell mouthed or blended in perfectly depends howmuch metal you can remove and whether your going for torque or BHP narrow ports more air velocity more torque bigger ports lower torque more revs and top end BHP.
5. Working on the valve throat and seat area has the most gains as the machined edges are normally the worst and most heads have only one seat or a poorly cut 3 angle seat.
Remove the machined edges by blending them into the throat walls, no more is needed than to just make it smooth curve don't go making it bigger think this will help you want to keep the size of the throat and the area around this as small as possible.
Next concentrate on the area around the valve guide here on A20 nothing to worry about as the guide doesn't stick out the port roof although the roof has nothing in front of the guide which doesn't help, you can have it welded or leave it as it is welding will only gain you maybe 5-10bhp and you'd have to be running some serious mods to see the gains something you would do if you were building an all out race motor.
Next have 3-5 angle seats cut and have the valves matched to the seats with back cuts done too, you can leave it as it is or take it couple of steps further by smoothing of the edges caused by the seat cuttings on both head and valve, then theres also the finish of teh valve super smooth polished or swirl effect which can be done on lathe with a rough fininsh grinding stone tired both seem about the same, i think with a direct port Injection system go with rough finish on a carbed or ITB setup go with super smooth finish.
Exhaust Port is different though, the guide ramp and guide protrude badly into the port throat best mods to do is to completely remove the guide and the ramp that stocks out into the port or the race head way would be to turn the ramp and the guide into an aerodynamic fin that helps split the exhuast gas more smoothly around the valve stem the latter of the two takes a lot of time, skill and some precision dremel bits that cost a fair amount again this would only be done on a race head or someone after that last 5bhp that can be squeezed out.
6. Combustion Chambers should be very smooth finish and the valves should be given as much room to breathe as possible, so i tend to match the chamber to the bores to open them out a bit helps with ignition timing and preventing detonation. Then i makes sure that all the valve seats that have been cut are flush with the chamber roof any kind of edge will hinder airflow going in and out of valve. This can be done by using an old valve and useing some tiny dremel bits to go around the vlave using it as a guide to blend in the edges to the roof.
7. When all the work is completed and you've finished the chambers have the head skimmed adn then thoroughly cleaned by workshop to remove all the metal shavings in the head adn to increase CR ratio and remove any damage incurred by you working on the chamber yes the dremel will occasionally get the better of your grip but that's why you do this bit last!!
8. If your still after more then it's time to do some custom work. The best way to really improve your A20 is to put bigger valves in.
You can do this by re-using old exhaust valves and having them machined own to 33mm and reeming out the old inlet guides to same size as exhaust vlave guides and then having 4 custom exhaust valves madeup, or you can have for the ultimate 12 new race stainless steel or titanium valves made up which will have narrower stems which will give you more flow again. Although stainless is tougher and heavier titanium is only for race use or mad people with tons of cash to burn.
9. Valvetrain can handle the rpms but the springs are the weak link in the A20, swap the platforms and retainers for all A18 or ET prelude ones okay upto 285 degree cams with 10mm lift or the better alternative is to use Exhaust valve springs and retainers all round from Prelude if your using exhaust valves all round after a big valve conversion. If you are using custom valves with narrower stems then ET1 2G accord heads have double valve springs and platforms for stock size valves, which can be modded to be stronger by shimming the springs or by using stronger springs from aftermarket source.
10. If your building that race head for the ultimate then you would need to build up a flowbench and make sure that all the ports are balanced so that they all flow the same numbers, also usefull for the more intelligent of us who like dabbling with figures who can then work out all kinds of equations to get the CR ratio right and work out the supposed Bhp adn torque that is should generate.
Hope this is usefull and gives some people an idea of what they need to do to Flow a head on a A20. A18/ET/ET1 are a little different but mostly the same principles. If your still not sure i'm allways available on e-mail as most of you know there's at least 10 people i'm currently helping advise on engines and they all appreciate the info and feedback they get. There is a really good secret to headwork and that is you ahve to be a perfectionist!! Can mean 10-20bhp difference from one engine built to another!! People who tend to be really good at Headwork tend to be more on the Arty side of things good with making things with their hands, modellers, painters, DIY people, woodworkers, if your none of the above stay well clear cause a Bull in a China shop is gonna end up in a whole heap of trouble!!

[speedpenguin]

Awesome info! :thumbup: