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Discussion Starter · #1 ·
ok so after some talk on PP a few months back about the different heads and started thinking that I'm not getting near the flow with an A18 head that i could with a A20. after finding some nice pictures from AMERICAN HEADS" website and with a little photoshop magic i did some comparison of the two.










as you can see there is way bigger openings on the 20 and there is a MUCH more direct route for the air. i kinda feel like the 18 is not much more than a 8 valve engine. more proof of this is anybody who has pulled their head apart and noticed that the valve on the far side of the port is always WAY more gummed up than the closer one. good indication that it just doesn't get the airflow.

far valve on left (on my PACEO head and 45 weber DCOEs after 3000 miles)



far valve on right (on my stock head and 40 SK DCOEs after ~30000 miles)



master jedi rich i think is fully aware of this as he is using a 20 head on his big valve conversion with custom weber manifold...

but there are all kinds of questions this arises in my head. like would it be worth it to switch my heads? of course there is a compression difference between the two heads too i think. Hmmmm what about the FI and carb difference? I could do an ITB with MegaSquirt conversion like cygnus? but i would have to give up my pretty pretty webers :( I could do a custom manifold like rich too... Hmmmm.

anybody else have and input or things I'm not thinking about on these two heads? I started this thread as a discussion just to get some discussion going on the heads.

cheers Smeado
 

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well the a18 head def looks as tho the far valve would get less flow. thus the a20 head was born, for stock its probly not a huge gain but for bigger power custom intakes and the like it looks like the 2.0 is the better bet. with the right pishtons and engine work it should be the better of the two
 

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heads must roll!

Hmmm well as you all know i've pretty much tried every concievable combination of heads and blocks. And as much as i love the A18 i think with it's odd inlet port design it is the weaker of the lot between A18, ET1, and A20, now what could be interesting is that with the right amount of headwork, and also a custom cam profile to suit the A18 could be a real dark horse when it comes to torque, with long intake runners, and a cam custom configured like Colt cams staggered lobes but with the lobes matched to the ports, e.g. the valve with the longest distance to travel across the port should get more lift and duration the one with the shortest distance should get the smallest lift and duration, this would give you one hell of a wicked swirl entering the chamber!! Combined with a high CR ratio could give interesting results!! Now i'm running an ET/A18 in my red car and so far performance from this stock low mileage engine has been great what small tweeks i have done has lead to quite considerable bhp and more amazingly torque increases so it does suggest it is a torque monster rather than a high revving bhp killer!! So depending on whether you want better gas mileage, better pull from low revs a different engine will suit the application. As i'm going all out for power i chose the A20 head as yes it does have the port spacing and size to suit a 250bhp+ engine but lacks the valves as standard, but i also still feel after trying an ET1 2G accord head (for those who don't know the diff between ET/A18 and ET1) this head has much smaller ports like the A18 but with them centrally placed infront of the valves, this has the smaller chambers of the 1.8 block so when mated with a 2.0 pistons gives you really high CR ratio when used with A20A3/4 pistons around 10.5:1 roughly depending on what you do to the chambers i typically match them up a little and flow the chambers so my previous engine was more like 9.5:1 but this was due to using lower CR pistons from A20A1 as well so 10:1 with headwork is achievable, i believe the increase in flow from machining the chambers is worth the extra gain in Bhp versus the loss in CR ratio, worse case scenario you could shave the head 1mm to bring this back up!!, Combined with big valves i still think from running an A20 big valve head this could still have the best combination for money for easy power and high revs. I like the A20 though and when i'm able to get a high compression block going i easily feel that the power increases i've lost over the ET1 from the drop in CR ratio will easily be made up, i'm also bottlenecking the engine from having the worlds shittiest custom exhaust on there, as this is soon to come off and get replaced by something that is truly spectacular watch this space for some dyno results which should see a spectacular jump in torque, bhp and higher revs!! (Well hopefully or I'm going B20A or Turbo lol!!) But yeah all teh R&D i've done should see the current low compression A20 (8.5:1) achieve 190-200bhp with hopefully around 145-150lbft torque maybe more we'll see!! Then it's time to up the compression, get more serious on the valves and seat designs I'm using and see what we can really get!! Hoping for something along the lines of 235-250bhp and i would be really happy but again going to need some custom stuff done to achieve this one of which will be forged pistons to my own spec to get to 11.5:1 CR ratio, then some custom valves with slimmer waists, then on top of that custom cam grind which will need about 290 degrees duration increase in lift to 11.5mm on inlets and 295 degrees duration and 12.5mm lift on exhaust and that should make it really sing expected power range should be between 5k and 9k rpm might try a more conservative cam before but we'll see using a 285 degree at the moment but only 10mm lift all round which is really strangling the engine with the big valves i'm using so maybe something like a 275 or 280 with 11.5mm lift all round would work well too and still be streetable.

So as they say watch this space!! At the moment i'm just glad the exhaust is fixed and so far hanging on I have a feeling that the header was pulled out and has damaged the threads on the head studs so may have to take it off and have helicoiled the header had moved about 1mm away from the head when it collided with the folded pillar didnt notice at the time only when i finally got it back fixed and back on started it up and was still blowing really loud and found the problem with the header. As the new one is much lighter and will be properly fitted might get away with loctite thread lock in them we'll see!!.
 

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this thread looks like its got the makings of a sticky, cant wait to watch all the info and progress that is posted here
 

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Discussion Starter · #5 ·
is there any chance anybody can get actual measurements of the ports (circumference for the A18 and length, height, and height at injector bump for the a20)? i was kinda hoping to do some flow calculations. but i don't have access to any of these heads right now.

thanks

Smeado
 

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Once again! Rich, your knowledge and progress with your R&D is astounding! Keep up the great work! :) It gives guys with little to no money (like me, lol) a chance to see what various mods do power-wise before spending the little amounts of money available to mod our own. I think I can say for everyone here, THANKS!! :D
 

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For my ITB manifold design I've been using an intake gasket for the port geometry. So the A20 is easy.

The injector bump I would just ignore since it just blends back into the port wall and doesn't really contribute to actual flow in any way. The rest of the port area can be approximately modeled by 2 half circles with a rectangle in the middle. Like this:




Dimensions are in inches. The cross sectional area works out to 1.87 in^2.

The A18 ports I would estimate to be 1.28" diameter, given that both photos appear to be the same scale. I measured off the screen and did the math.

For port length (port face to valve) I've been assuming about 3" for my ITB calculations. Actual length would depend on whether you measure the inside or outside radius of the bend; outside will be longer than inside of course.

Over on 3geez there is a really old post where someone (username "Sean"?) talks about flow numbers for the A20, but I don't remember specifics. For some reason 220CFM comes to mind. Beyond that, IDK.



But yeah, the A18 intake port design is somewhat of a mystery. Anyone have any pictures of a factory ET-1 setup? I'm really wondering what the carbs and intake look like with the evenly spaced ports.
I've also been contemplating on trying to find an ET-1 head up in CA since they had them on some older Accords. My thinking is that the ET-1 might have a little better torque because of smaller intake ports. And since they're evenly spaced and centered to the cylinders there shouldn't be any flow distribution issues. But the unknown here is whether it would really matter. At say 160HP would the smaller ET-1 intake ports really be small enough to limit flow? Would low end torque really be significantly better with the smaller ports? I don't know. The round ports would make building manifolds easier for sure.

As for A18 vs A20, I think the A20 head wins for anything much beyond stock.


C|
 

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Here's an EZ which is a 1.6 liter version of the ET-1



And here's an ET-1.



I have no idea if those heads are the same or not, but they look the same externally, other than the valve cover... I wanted to buy both while I was up there, but I didn't have time to pull both heads. Next time...
 

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Hmm, interesting. I was thinking they would have dual carbs like the Preludes, but they wouldn't because they're Accords. Did Rich's ET-1 head come off an Accord then? Or did the EDM ET-1 have dual carbs? Mostly I'm just trying to figure out why the A18 intake ports are spaced like they are. My theory is that it has something to do with the spacing of the dual carbs. If there is a version of the ET-1 that also had dual carbs my theory would be wrong.

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hmmmm heads

Hmmm getting me all juicy EZ's never seen one in U.K. they do exist though 2G accord hatch quite often had 1.6l EZ sod the head you want the whole engine!! Would love to see the rod and crank from that!! Wonder if the block is the same height or did honda keep the rods the same but just decreased the block height for the shorter stroke? Would be interesting to try a 1.6 with 2.0 pistons in effect making a high revving 1.8 but as i said before revs is not really an issue for an ET1 or A20 in 2.0l sizes. But would be fun to experiment maybe it would rev up quicker or maybe gain an extra 500rpm's who knows.
For sure the ET1 head is a good one and if you have an early block that can take one it's certainly a good upgrade with bike carbs or webers on. And if you can do what i did put 2.0 pistons on you can get good CR ratio as well.
 

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For sure the ET1 head is a good one and if you have an early block that can take one it's certainly a good upgrade with bike carbs or webers on. And if you can do what i did put 2.0 pistons on you can get good CR ratio as well.
Oh that's right, the ET1 wouldn't have that oil passage sticking out the back of the block like the A20s and A18s. So you would need an older 1.8L block for it then. Ok, well even if I was able to get hold of an ET1 head it wouldn't really fit my block anyway. So no point worrying about it. It's only A20 heads for me then.

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man that ez looks like it has sooo much potential
 

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rich im just saying man cause i know we had the conversation about destroking the a20 and you said in the end it probally wouldnt be worth it but just think about it man, it would be a fun thing just to do for the hell of it, something unique, and you never know it might turn out to be something insanely great
 

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Discussion Starter · #15 · (Edited)
well I didn't know where else to put this and I doubt its important enough to start a new thread with, but here goes.

anyway I was at the Junk Yard yesterday to find a A20 (A3 to be exact) head for a big valve conversion. anyway I found a nice one and pulled it out and brought it home and realized that the intake valves on it were different (Smaller) than the ones on the other A20A3 I had pulled off an accord a few weeks ago (which are just like the ones off my A18). also while I was at the junk yard I nabbed a valve spring, retainer and spring seat from an F22 engine just to see what it was like in comparison. I was stunned how similar the smaller valves of the A20A3 and the F22 were.




Next paragraph doesn't really have to do with the previous one...
Since recently I have had no luck finding any head shop that will cut me new valves for my big valve conversion I have been looking into finding something that might fit and work with different valve seats. so far I have had no luck F22 intake valves were close but not quite there (part of the reason I yanked the ones I found at the JY). part of the problem is that Honda went from a ~6.5MM intake and ~7MM exhaust valve to a 5.5MM one for most other applications. anyway one of the head shops around here recommended that i try Ferrea valves for a custom setup. I have looked into them and I will probably have to have custom valves made if i want to do this but I noticed that they make valves for the B18A1 and while the valves don't fit, they are 6.5MM in diameter and doing my best to measure on my head and the valves I have it really looks like the springs/spring seat/Retainer would fit the A20 head. the best that i could figure the springs are Ferrea S10046 (~$14), the retainers are titanium E11023 (~$8), and the seats are SL1017 (~$4). now thats kinda Pricey ~$208 for just intake springs but it is interesting.

of course what this this made me think about is being a cheapo and getting the F22 exahust valves and since they stand about 3.5MM taller I would get a little extra strength in my springs for pulling to 10,000 RPM :) I don't know the pring constants of any of the stock ones and I have to do some more research to find out but the idea is interesting.



PS anybody know somebody who will make custom valves?

Smeado
 

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Discussion Starter · #16 ·
PS. i did some paper napkin calculations and you gain .0968 HP (at 8000 RPMs) in just rotating mass alone with the smaller valves of the A20A3... Hmmm whatever, I'm going to bed

Smeado :)
 

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valves

Lol don't you listen to anything i say?

Go to SI valves, you can either buy their Exhaust valves and have them cut down in size locally or you can get them to make what you want to any size and spec, ideally i suppose the stock size stem size with 33mm head or bigger is best but to save cost the and to be able to use stronger springs i'd suggest just having the 7mm stems from the exhaust valves, have them waisted and use the exhaust valve springs and retainers that come from honda they are more than upto the job of keeping springs on, then just get Honda A18 exhaust valve springs which are very hard and tall. You could get springs custom made or find something thats suitable from another car. I'm running A18 exhaust valve springs and they are no problems upto 8krpm and will be good for upto 9k i reckon.
 

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Discussion Starter · #18 ·
Lol don't you listen to anything i say?

Go to SI valves, you can either buy their Exhaust valves and have them cut down in size locally
haha no I don't :)

actually that is my problem I can't find anybody locally who will cut them down, I have a shit ton of SI valves lying around now, I just need somebody who will cut them! is there a difference between the dual spring exhaust springs on the SI(A20) and DX (A18).

maybe the machine shops in Alabama aren't up to spec with the ones in GB.

I'll keep searching

Smeado
 

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When Rich says SI valves he means the company SI, not SI Prelude.

http://www.sivalves.com/


That's strange about the different A20A3 valve sizes. Can you take a picture of the two side by side? Your napkin layout shows the A18 vs A20A3 intakes.

Also I think only the A18 ever came with dual exhaust springs. I believe all the A20s had single springs all around. So the thing to do would be to use A18 exhaust springs/retainers/platforms for ALL the valves. Or just get all aftermarket springs with whatever specs you want.

Over on 3geez in the suspension section there is a post with the method for calculating spring rates given the physical dimensions. I think it's even stickied. If you have a decent caliper/micrometer you should be able to get a good estimate of the rate on any of those springs.


Oh, and you might try contacting Bisimoto, since they're now starting to make some parts for the A20s now. So far they just have cam regrinds but I think springs were in the works.

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Discussion Starter · #20 ·
cool, thanks for the info. I guess I was confused. SI seems like a really good alternative. I am also hoping for some word from bisimoto about what they are going to offer.

for spring calculations I think I will use a press and a scale to determine the K, since material can play a big part in spring stiffness.

anyway as far as heads go I have no idea what is normal on A20 heads but this is what i have found. on both the A20 heads I have pulled form the junkyard they both have had the dual springs on the exhaust valves. the first head was off an 87 Accord LX A20A3 and the second was off a 87 Prelude Si A20A3 as well. the first head had the springs that look identical to the springs i have floating around from my old ET-2 head. the second head the exhaust springs were the same (still dual springs) but the intakes were considerably smaller. See Below:


Cheers,

Smeado
 
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