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Discussion Starter · #1 · (Edited)
Hello. I'm sure this question has been asked and answered several times but hopefully y'all can help me out. I have an 87 prelude that I use for dirt track racing. i have looked at doing just a distributor and ecm swap so that I can do some tuning but I was wonder if I can do a head swap as well?? If the head swap is possible, will it help the performance aspect. Please help me out with any info. Thanks
 

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Discussion Starter · #3 ·
Ok, I am sorry. It has the 2.0 engine. And that is my question. What head, if any, can I put on there that would help up my performance and at the same time house the newer style distributor so that I can run the newer exam so that I can tune them??
 

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Discussion Starter · #7 · (Edited)
Yeah I have read and studied some threads on just doing the distributor and wiring swap. I was wondering if there were any other cylinder heads that will bolt to that engine and work. We race modoc in South Carolina and swainsboro in Georgia
 

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Lord Magnum
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No, no heads will swap. The A18 dual carb Prelude head will, or any A20 head, but if you're just looking to go OBD1 then I believe that you just need to mod a distributor to fit, or get an adapter from Cygnus x-1, then wire in the new ecu. There's good info on 3geez if you search around there you should find all the answers you need.
 

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Do you need to run injection? If you can swap back to carbs you would get greater performance from putting on A18 head on A20 block and tuning carbs appropriately stock ignition is fine and independant of ECU
 

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Discussion Starter · #11 ·
You know I wondered about that. Does the a18 head have smaller combustion chambers than the a20? But I would like to stay with fuel injection and I probably know the answer before I ask but will the a20 fuel injection intake fit the a18 head?
 

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The intake manifold bolt pattern is different for the 2 heads. I looked at it the other way around - putting carbs on a 2.0 head. I think you could make an adapter plate if you had access to a machine shop, but doubt it's worth it. We raced 1/4 & 1/2 mile asphalt and there was another lude with twin carbs that was supposed to be a pretty fast car. Our 1st race against him he hit the wall hard and I never saw the car for the rest of the season. We did well with a colt cam and stock injection, but the trick was in the corners. For asphalt a bigger rear sway bar helped alot, just find a workable width one (can even be a front bar from any proper size car) and make up some mounts to make it fit. Nobody in tech knows anything about these cars anyways lol. Also the factory rear springs are too soft. I know nothing abut racing dirt, but there's some info. There's also 3 different gear ratios if you can find them, we used to pull strong up to 6000 and had 3 different transmissions for 3 different tracks. 40 minutes to pull the motor to switch the trans...
Maybe getting off topic here but here's a short clip of an old video from a 1/2 mile track: (we're the #20 black & orange)

https://www.youtube.com/watch?v=wxmEJsq2ttk

My son was about 13 in that race and the rest of the drivers were adults. Shows what a Lude can do...I think only 2-3 cars finished on the lead lap & he was lapping some cars every 5 laps or so.
 

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injection or carbs

the A18 head has completely different inlet port setup with the ports offset to the side of centre line of each port this was done in an effort to increase swirl into the mixture to produce a better combustion. Whether this actually did or not is another thing with direct port injection this was a bit of waste of time hence why they went to big fat oval ports direcly over the central line of each port/chamber. Seemed to be a common thing with carbed engines from Honda but some odd reason not done on D series heads, just preludes and accords.

The chambers on A18 are indeed smaller putting this onto a A20 block would increase CR ratio considerably giving you more torque and bhp but also the carbs are more tuneable than the stock injection system, you could also run different carbs if this is allowed in the rules which would way surpass any injection system you used with exception to Individual Throttle bodies used on racing injection systems.

My A18 is bored out to standard A20 specs current short block not even blue printed as I just did a partial rebuild with new big ends, and std size rings didn't bother gapping them as was in rush to get running for track event.

With a lot of time spent on headwork the only non standard Honda parts are inlet manifold for pair of Weber DCOE 45's and the 45's as well, re ground camshaft at 285 degrees and 10mm lift (lift is bit short ideally 11 to 12mm would be better for mine), custom 2-1 downpipe and system, cylinder head intake and exhaust valves custom made (33mm inlet 37mm exhaust), the rest of the engine is stock the rods stock, pistons stock, rings stock, block stock just decked, head skimmed, stronger bearings used, stock flywheel but machined down to 10lbs in weight and uprated clutch.

With all that in place this engine puts down 200bhp @ 7600rpm and 160lbft at 5500rpm which in a car that is weighing in wet at 875kg's approx is pretty scary even with open diff and wet type road tyres 1/4 mile is just under 14 seconds at 100mph with decent dry track tyres and LSD it would do mid to low 13's easy. Thing is I've still got a lot more power to come with use of different aftermarket pistons with a flat top and 3 valve relief pockets instead of 4 I could increase CR ratio to 12.5:1, the valves aren't the best shape or specifications for head design so I've found some with much narrower stem, plus waisted and the head shape has higher flow around it due to a nice small seat and 60 degree back cut it's also flatter which works better for low to mid lift power. Combine this with a pair of Weber DCO/SP 48's with a 44mm choke and finally a custom exhaust manifold with 1.75" primaries and 2" secondaries and 2.5" collector would give me around 220-230bhp and 180-190lbft peak bhp at around 8000rpm but really I need a custom camshaft that's ground from blank Cat Cams in Holland can do this but will cost quite a bit around £1200 pounds but I would get a cam with around 295-300 degrees and 11.5mm intake lift and 12mm exhaust lift which could net 5-10bhp extra and higher peak rpm again.

But this is on hold till I sort out the bodywork which needs some minor welding work to stop it rusting further and make the shell more rigid. I don't mind spending the time and money on the engine as I can use it in my other car which has no rust.
 

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Discussion Starter · #14 ·
The intake manifold bolt pattern is different for the 2 heads. I looked at it the other way around - putting carbs on a 2.0 head. I think you could make an adapter plate if you had access to a machine shop, but doubt it's worth it. We raced 1/4 & 1/2 mile asphalt and there was another lude with twin carbs that was supposed to be a pretty fast car. Our 1st race against him he hit the wall hard and I never saw the car for the rest of the season. We did well with a colt cam and stock injection, but the trick was in the corners. For asphalt a bigger rear sway bar helped alot, just find a workable width one (can even be a front bar from any proper size car) and make up some mounts to make it fit. Nobody in tech knows anything about these cars anyways lol. Also the factory rear springs are too soft. I know nothing abut racing dirt, but there's some info. There's also 3 different gear ratios if you can find them, we used to pull strong up to 6000 and had 3 different transmissions for 3 different tracks. 40 minutes to pull the motor to switch the trans...
Maybe getting off topic here but here's a short clip of an old video from a 1/2 mile track: (we're the #20 black & orange)

https://www.youtube.com/watch?v=wxmEJsq2ttk

My son was about 13 in that race and the rest of the drivers were adults. Shows what a Lude can do...I think only 2-3 cars finished on the lead lap & he was lapping some cars every 5 laps or so.
Hey buddy, I just checked back in because I didn't get much response to the post. But you hit it with what I have thought to be a big deal which is the trans and gear ratio. I was told all that I could do is swap the internals from a 1986-1989 integra. Those trans are hard to find. What are the three different ratios that you were able to use and what do I need to do. Thanks so much
 

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It's been a few years and I gave my notes away when I sold the racecar, but I believe there are 2 different ratio trans for the Prelude - the ratios for a carb car are different than an SI. We had problems in 2nd hitting the limiter on a 1/4 mile flat asphalt track, or it was gutless in 3rd. I got a CG trans from an Integra and used 3rd gear and the final drive from it. I always welded the differentials solid and never had any problems. I never played with the ECU, I think it covers a pretty good range - I never had any codes. You can drill a bunch of holes in the bottom of the intake if you need to use the factory one, put a block off plate on the fast idle valve, pinch the return line if you're running a cam and need more fuel (and cant run a regulator). You can also play with the temperature sending unit so the ECU thinks it colder and dumps more fuel to the injectors. Of course only do this if your plugs look lean after some hot laps. There's also a head / piston combo that will give you .5 more compression, and thinner head gaskets. I wouldn't port the head, too easy to tech and if you don't know what you're doing you'll likely hurt it anyways. You're better off grinding out the exhaust manifold if you can't run a header.
 

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Discussion Starter · #16 ·
It's been a few years and I gave my notes away when I sold the racecar, but I believe there are 2 different ratio trans for the Prelude - the ratios for a carb car are different than an SI. We had problems in 2nd hitting the limiter on a 1/4 mile flat asphalt track, or it was gutless in 3rd. I got a CG trans from an Integra and used 3rd gear and the final drive from it. I always welded the differentials solid and never had any problems. I never played with the ECU, I think it covers a pretty good range - I never had any codes. You can drill a bunch of holes in the bottom of the intake if you need to use the factory one, put a block off plate on the fast idle valve, pinch the return line if you're running a cam and need more fuel (and cant run a regulator). You can also play with the temperature sending unit so the ECU thinks it colder and dumps more fuel to the injectors. Of course only do this if your plugs look lean after some hot laps. There's also a head / piston combo that will give you .5 more compression, and thinner head gaskets. I wouldn't port the head, too easy to tech and if you don't know what you're doing you'll likely hurt it anyways. You're better off grinding out the exhaust manifold if you can't run a header.
Alright man. I appreciate all of the info. I wanted to do the obd1 conversion to try to maximize tuning capabilities but hate to spend a bunch of money if it isn't going to help me much or even hurt me. Tech is not that bad at the few tracks we race unless you are going out there and just dominating but we have a few fast ones and and I'm just trying to nip at their heels. But if none of this works I'm prob gonna retire the car and go with something a little newer. But our local track is 1/4 mile and same thing, you almost have to go to third when you hit the turn so when you hit third it's just dead going through the turn and just loose so much ground. So trans mod should help out a lot. How do I adjust or modify the coolant temp sensor?? I know on the newer stuff if you unplug the temp sensor it goes default which I think it is -44 degrees and full rich. What does putting a block off plate on fast idle do?? And one more question. When you said drill holes in bottom of intake, are you referring to the manifold or the intake tube?? Sorry for all of the questions, just trying to get this thing to perform at a higher level. I appreciate everything. Thanks
 

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Sounds like you really need that CG gear box. When I switched the cam the idle got pretty rough, there's a valve on the backside of the throttle body that you really don't need. I made a solid gasket and put it between which really smoothed out the idle. We had to run the stock plastic air box, so I drilled a bunch of 1" holes in the bottom of the 'dirty' (fresh air intake) side of the air cleaner to get more air to it. If you know how to use an ohmeter you can check the resistance of the sending unit when the car is cold, mid temp, & race temp. You'll see the different values and can buy resistors to bypass or add to the temp sensor. If you don't know what I mean, maybe leave it for now. Leaving it off will likely make it run too rich. Also advance the timing as much as you can but keep an eye on the temp & sparkplug color.
 

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Discussion Starter · #18 · (Edited)
Yeah I definitely need the cg trans. I have been looking all over the place for one. On that swap, are you just lookin for the third gear ratio or is it the ratio of the whole set up?? Reason that I ask is because I was wondering if I could just locate the third gear and swap it? yeah I have a pretty decent idea about adding the resistor to the temp sensor but that will prob be later in the build so that I can play with it to get it right. I got an email from colt cams yesterday and they sent me a list of three setups one being just a bump up from stock, one being more of a race cam with noticeable idle change and then race only, loppy idle. Do you remember close to what you went with on your setup??? Once again sorry to bombard you with questions but you seem to be pretty familiar with that car and because of the age of it, it's a thing of the past so not a whole lot of people care much about them. Thanks again
 

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No problem on helping you out, it was our first real race car and have some good memories with it. We went with the middle cam from Colt, & I think I mathematically needed the 3rd gear and final drive. If you find all the gear ratios online you can figure out your tire rpm at 6000 and then plug in different numbers (ie your current 2nd & 3rd) and figure out where you want to be.
 
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