BIgger exhaust ports??

[89accorder]

Is it possible to port match the exhaust ports to fit a larger diameter header tubing?? if so how much?? is there any water passages i might run into?? a custom header will have to be made but i have till july till i get my liscense back. I really think that this is a limiting factor of the a20.

[bobafett]

the size of the exhaust valve probably limits more than anything. you could certainly port it out slightly bigger, but going alot larger will just kill your lowend power completely. i would just port match the exhaust ports to an a20a exhaust flange (can buy from BMC or a few other places im sure ~ $37) and then you could build the header using that flange... that way you could take your time building it and make sure the port matching is really good.

btw im curious how you like your 282 cam, i have one in my new motor, and im wondering if you still pull enough vaccum to use the brakes and such...

[bobafett]

well the problem is there isnt a whole lot of room to increase the size in the first place. rjdugey seems to have done it, but when i look at it, it looks awefully close already. :(

but i agree that a good polish and PM will help you out and be worth your time.

[89accorder]

i just pulled my motor and head. so i havent got a chance to use the cam yet. i am going to do a rebuild and use the 282. do you think ill be able to keep my brakes?? i have a stock cam as well in a spare motor. im thinkin im gonna P&P it myself after sending it to be cleaned. Think i should make a custom 4-1 header to go along with the cam??

By the way, hoe does it sound with that cam?? like half a v-8??

[bobafett]

as for the vaccum issue and brakes, i dont know... i know it was fine with a 272, but a 282 probably has different amounts of lift, which is what i BELIEVE causes the decrease in vaccum.

if you are going to bother building a fancy custom exhaust flange thats all port matched to your head, a nice ELR 4-1 would be a great idea.... :)

and the car only sound like half of a v8 when i set my valve lash in the wrong order. :( when i got them set properly it just sounds a little more agressive but not radically different... people say the car 'sounds' fast, and sounds really good, but its still slow, so im not happy.

[A20A1]

The extended Duration / Overlap lowers vacuum

[bobafett]

in that case the 282 should not be radically different than the 272, do you know the duration of a stock cam for reference?

[A20A1]

Is it possible to port match the exhaust ports to fit a larger diameter header tubing?? if so how much??


You might be able to, our ports are oval though so unless your flange has an oval to circle transition you might want to consider adding a bit of material to the outside before porting if you want to mate it to a round exhaust tube. Keeping in mind you want to leave room for the spark plug removal tool.

Port matching can be good, but with a smaller diameter port to a proportionaly larger diameter header tube you'll end up with an EXHAUST STEP which can help draw out exhaust gasses... though this will only be benificial at certain rpms.

[Accordtheory]

polishing a surface which will soon be covered in carbon crap..oh yeah..polishing is for people who don't know about carbon or boundary layer separation..in other words, a waste of time..
Changing the contour can be good though, but you just as easily fuck up a head as improve it. I would much rather buy a stock head than a "p&p" head..

your shit is an lx? So it's carbureted..? That's the limiting factor.. upgrade to obd-1, the aebs IM, and tune the thing. Then double whatever you just made with around 12 psi..lol

[rjudgey]

Bigger the valves the better but as a rule exhaust valves only need changing if your compression ratio is low or being un altered if you raise the CR ratio it makes it easier for the exhaust gas to escape, but if you've increased inlet valve size and done inlet mods like ITB's or Webers, combined with headwork then bigger exhaust valve and a well modified exhaust port will definately help but only if you have a custom header or at least aftermarket one with a 2.25" system, if you use the stock cast manifold which is good upto 190-200bhp that will then start to become the bottleneck.
Valves i use in mine are 33mm inlet valves and 37mm exhaust valves, it's not the size of the valve or the valve throat thats important it's about making the smoothest entry in and out the chambers through the valves, so 5 angle valve seats with a huge 60 degree cut will work best or if you can really find a specialist a 5 angle with radiused cut's is the ultimate as it is exactly like a trumpet without any sharp angles or edges caused by seat cutting.
It would be impossible to fit anything bigger also the thinner the valve stem the better as well.

[Oldblueaccord]

rjudgey is right as always

prolly need a 44 mm exh. valve minimium to make it 66% of the intakes. Depending on the flow of course there some numbers out there intake vs exhaust you can look up.

EDIT : for an example a typicial Chevy 350 head performance wise you want a 2.02" (51.3mm) intake and a 1.60"(40.64mm) exhaust valve that about 79%



wp

[Accordtheory]

what is that ratio on a typical 4 valve per chamber head?

yeah, we all know the chevy small block is the epitome of high performance..as opposed to a honda making like 120hp/litre..lol

but f it, I'll build a chevy soon..

[Oldblueaccord]

what is that ratio on a typical 4 valve per chamber head?
yeah, we all know the chevy small block is the epitome of high performance..as opposed to a honda making like 120hp/litre..lol
but f it, I'll build a chevy soon..
heh well a nascar motor does pretty well with JUST 2 valves LOL :eek5: I saw some numbers this year that were all over 800hp. Thats on a 355 cu motor.
Not sure ill look up a type r head valve size Id be interested.
I posted some flow numbers on a type r head sometime ago. One thing we still dont have is a flow rating on our head we need that for a baseline to compare to other heads.
wp

Type r intakes 1.299" 33 mm
exhaust 1.103" 28mm so 2 each i get 84%
valve stems are listed as .214"
this is off rockauto 1999 Type R
heres a 1 min google search for flow numbers
http://www.cylinderheadtech.com/flownumbers.pdf
mind you these are at 25' hg instead of the usually 28"
I'd say where down near the VW 8 v range just guessing.
wp

[rjudgey]

corvetter LS series engines don't do so bad either and they rev to 7k not bad for a antique 2 valve engine!! It's not allways about the number of valves and two valves create awesome torque.

The exhaust to inlet valve size ratio is variable as it depends on teh CR ratio your running the lower the bigger the exhaust valve the higher the smaller hence why a Integra Type R only has 28mm valves as it's got a super high CR ratio doesn't need to be any bigger than a B20A exhaust valve which runs 9.4:1 CR ratio.

If you want to see some maths i've got some excelent articles on it but you'll need an aspirin after reading it as it will give you a headache!! (did with me)

With my B20A head i'm working on i'm looking at 35mm inlet valves and 30mm exhaust valves which will fit as the seats are massive and the valves are nicely spaced apart from each other unlike A20 also the port and the valves are at a steeper angle which makes for higher velocity and to top it off quite a bit can be taken off the head surface to bump up the CR ratio. Vut been playing with the port shapes around the guides, their isn't enough metal to just simply remove them completely or you'll end up saying hello to inside of the rocker area, but their is enough to dramatically reshape the boss and the ramp so that you get a much nicer flow past the valve stem.

With the A20 head the exhaust port i have actually removed the guide boss and the ramp that builds up to it completely and unlike CKE has mentioned it is actually in a perfect shape of the port as well, but what i'm planning on doing next is to not remove all of the ramp but to dramatically reshape it so that it has an aerodynamic fin that leads upto the valve stem thickening as it gets nearer the valve but to barely no more than the stem diameter, this will then help the exhuast gas flow smoother past the valve stem instead of just hitting it. I don't think it will make a huge difference compared to previously just removing the whole lot but when your seeking that last 3-5bhp every little thing helps, the amount of extra time required to do this properly is a whole load of grief for just a few bhp!!

The same thing can be done to the inlet guides as well on ET1, ET, A18 heads but A20A heads kinda suck their as Honda just left a great big hole might be worth considering welding up the area in front of the A20A inlet valve and reshaping to help the mixture enter more smoothly into the chamber.

[Oldblueaccord]

Have you gotten any flow numbers stock or otherwise?


wp

[Justin86]

it's not the size of the valve or the valve throat thats important it's about making the smoothest entry in and out the chambers through the valves
also the thinner the valve stem the better as well.
this is what head design is all about. The size of the ports and valves is in inrelation to the size of the cylinders and also there is a role between valve area and port area. So just throwing in bigger valves and bigger ports isn't gonna allways be the best idea. I belive our weakest part of our heads is on the intake side not exhaust, but do the research yourself and talk to the engine builders that have been doing this stuff all their lives. Get our hands on the most info you can then see where your at. :wave:
oh don't plan on learning much over night.

[rjudgey]

Yep it's nothing you can do yourself overnight, i've learned over best part of Five years and still am learning, recently found some excellent magazine articles by a professor of engineering mechanics and his theories and ideas just completely blew me away they all made sense and they make 70% of people claiming they know how to P&P heads look like stupid amateurs!!
Also flowbenching with biggest figures being the best is not allways what it's about, i have a simple flow bench setup which gives me a reading so that i can match all the ports to makes sure their all about the same so i flow balance the whole head, haven't go the time and maths in my head to go any further than that which is a shame as that will be the limiting factor to why i want ever get more than 230-250bhp but i'm happy experimenting with different ideas i have with the laws of aerodynamics which seem to have a good result, different types of finish on the port and the valves, different valve shapes and seat shapes etc. A lot of missed power is not from achieving the best flow figures its from creating the best possible mixture from the air and the fuel combining inside the inlet port and manifold, quite often a head which has bigger flow numbers will not mix the air and fuel as well as another head which has lower flow numbers but this will be the engine that puts down the most power and have a better torque curve.

Anyway my current build i'm working on will have flat top forged pistons 83mm diameter with CR ratio of around 10.5-11:1, probably some uprated rods but may stick with stock as i've not broken one yet uprate the bolts, 33mm inlets valves, 37mm exhaust valves, A20 head with 5 inch long inlet manifold runners to Weber 45's, custom 4-2-1 long primary exhaust similar to Bike engine types, 2.25" straight pipe exhaust system with single rear silencer, custom cam profile running a 285-290 inlet duration with 11-12mm lift and 290-295 exhaust duration with 12-13mm lift combined with a OMEX mappable crank fired ignition setup should run pretty sweet hoping to score 230-250bhp with this lot and make a whole load of noise you guy's should hear what a A20 sounds like with 33mm inlet valves and webers the noise is just awesome stereo's are useless as you just can't hear anything.

[rjudgey]

We will see thats what i'm aiming for if King motorsport can get 340bhp then realistically should be able to get 230-250bhp without having to go to the extremes of custom titianium cranks and rods etc.!! I'm basing everything on that 33mm inlet valves in other 4 pots have been tuned to 230-250bhp successfully the key is to the inlet valve size the bigger the better most hi performance 2.0 litre 4 pots have 33mm plus valves e.g. Cosworth have 35 and 36mm inlets and 30-32mm exhausts which is why those engines can hit 270-300 bhp without too many porbs N/A with the A20 i know it will be a real struggle to go beyond 230-250bhp because of the valve sizes and the fact ti's only 12 valve anymore than that i'll have to switch to FI but you just gotta love the noise of a full on N/A setup it is sweet as!! Although my vids and soundclips give you some idea it's nothing compared to being in the the car or even worse outside the car with me flying past at full throttle!!!

Quite a funny story before i blew my car up just before autumn took it out for a run to charge battery and get it warm i have an excellent Freeway that runs about 100 miles from London to Dover which is a big port on the channel it's 3 lanes either side and has some excellent hills on the way pretty steep excellent for testing re-builds on quickest going up hill was 130mph, but one day was hacking along as you do i know the road really well and where the Police hide etc.etc. so i'm shooting up my favourite hill gaining speed upto 130mph plus then 1 minute later i get a phone call from someone at work who has never seen my car or heard it but knows about it and said something along the lines of F$$K me was that you just gone pass me like a scalded cat on fire you just scared the S$$T out my girlfirend in the car, excellent!!
Made me laugh just the fact that it only could have been me and he knew it i think i can easily lay claim to the loudest A20 thats road legal and man should have heard it when the center pipe snapped of the downpipe sounded liek a god damn Merlin engine in a Spitfire or Mustang was excellent shame you can't legally drive around like that mind you the vibrations and noise would have drove you insane after a while though!! Anyway the louder the engine the more power your putting down as your creating a larger explosion by having more fuel and air going into the engine. So if anyone wants a really good power gains you have to change your valves for bigger ones!!!! Dead easy just get loads of exhaust valves, and springs and turn those on a lathe with a diamond cut bit and grinder too to reshape and your good to go!!

[rjudgey]

Can't wait to get new engine up and running not used A20 head before should be interesting to see if it will pull the same rpms and torque as the ET1 which i think is still the engine and head to use for good all round bhp and torque A20 will be better at high rpms say 8-9K with a trade off of loss in torque at the low end. We'll see.