View Full Version : DCOE Intake Manifold Questions

10-30-2006, 09:54 PM
Okay, so I've been searching around the site alot, but I'm still not 100% sure on what to do about this:

I e-mailed Aaron at WierRacing and he said that he would be willing to make me a DCOE intake manifold for my A20. At $300, I figure that I can't go wrong buying it right now, even though I don't have the dual carbs yet or even the engine built.

He is asking me a few questions as to what specs I would like it made to.

First off, he was asking me the angle I'd like the runners at. I read that you want them tilted forward 5 degrees. I can't find anywhere the angle that the engine is tilted forward, though I KNOW I've read it here on the site. I get the feeling that it's tilted around 25 degrees forward, so I would want the flange welded at 20 degrees, as Aaron said he had done one before.

I also am not 100% sure about the runner length. I know that if they're a bit longer that I'll get more bottom end torque, but I don't think I have the clearance for anything longer than 2 inches.

I measured out the clearance to the brake booster and there's only about 11 inches. So I figure, the carbs are 5.5 inches long, with 3 inch filters / velocity stacks and maybe an inch (to be safe) for the flanges, that only really leaves me about 2 1/2 inches on the runners if I squeeze it. So I thought I'd have them done 2 inches long to be safe.

Also, he asked about running 40's or 45's. I figured I would just go ahead and go with 40's. From what I've read, I can't really utilize 45's on this engine, because I at least want SOME streetability.

So here's what I plan on telling him for mine upon some good approval from you guys:

20 degree tilt on the intake manifold flange
2 inch runners
40mm ports

Sound ok? Thanks for the help!

10-31-2006, 08:39 AM
I'll have to double check most of this, but the engine is tilted about 15 degrees forward so you want to have the flanges welded at 10.

The max runner length is something like 2 inches. What you have to worry about is the brake booster. The inlet for the #1 cylender is going to line up right with the bolt that holds the master cylender to the brake booster. IIRC my runners are 2.5" and I have 1" stacks. I can't run air filters because of the brake booster.

Theres nothing wrong with the 45s. The only reason to run 40's is because they are more readily available (read alot cheaper on ebay). 40s are too small for the engine. Really if you are going full race the 45s are a bit small. You're problaby going to want a choke size some where between 35 and 40 depending on your cam selection (the higher you expect peak power the larger a choke you need). The stock cam makes peak power at 6200 rpm iirc which would warrent a 36mm choke. 36mm is the largest choke you can put in a 40 dcoe, and is the normal size for a 45 dcoe (36 * 1.25 = 45). if you buy a set of 45s theres a good chance they'll come with 36mm chokes, all the ones I've seen seem to come that way. The chokes are expensive, expect to pay $100 for a set plus a full rejet, which is why my carbs still have the 36s in them even though I need 42s (which require atleast dco 48 carb but really need a 50, both of which cost a small fortune and won't fit my manifold). Streetability in my car is not a major problem. With 45 dcoes and a 272 cam. The biggest problem is the car looses traction quickly if you give it too much gas :D.

All and all though the costs of carbs are going up and the cost of efi is falling. I know I've preached carbs on here for years. But no longer do you have to spend a grand to get a decent standalone efi system and another grand for a used laptop to be able to program it.

If you don't cut corners and don't manage to score any deals the carb cost is going to end up something like this:
45 DCOE carbs: $500+
40mm Chokes: $100
Misc Jets to get it to baseline for the 40mm chokes: $100
More, jets to get a final tune : $100-200 (shipping kills on these too unless you are lucky enough to find a local supplier)
Air horns (the ones that come with the 45 dcoe are too long): $100

+ misc other stuff that can nickel and dime you to death

As you can see you'll easily spend over a grand on this, and I didin't even figure in the cost of the manifold. Though things can get alot cheaper if you can score some used carbs. Thats where the 40 dcoe carbs come in. You can alot of times find a rebuildable set on ebay for around $100, which takes a signifigant chunk out of the cost. You can also run the 40s on a 45mm manifold no problem (or any dcoe manifold larger then 40mm for that matter) with the intent on upgrading later.

If you start looking into the cost of converting to efi, esp if you start looking at things like megasquirt or hondata the costs are going to be similar. With our cars you can do fuel only efi with out having to worry about spark if you don't want to since we've got the fully mechanical ignition, makes things alot easier. If you used an a20 manifold and injectors it could problaby be pulled of for the cost of a 40 dcoe convresion and you could probably do itbs for what it would cost to build a 45 dcoe setup.

They're pretty much on an equal playing field now. You'll be able to get similar power gains from either system. They both have their advantages and disadvantages, but standalone efi's main disadvantage, price, is pretty much out of the picture now.

In just my opinion, if I were to do my car again, I'd build it using megasquirt for efi. I'd use a b16 plenum style manifold instead of the carbs and keep the rest the same. I would have started with fuel only using the stock ignition and once I got the fuel side worked out I would have added spark control with megasquirt/extra firmware and mods to the ecm. The car would have been faster at first because I wouldn't have been limited to the 40dcoe carbs that I could afford at the time and it wouldn't be sitting for as long as it has because I wouldn't need $200 in parts just to retune the carbs. But thats just my opinion. Your's may be difernet.


10-31-2006, 09:19 AM
Man thanks for all the good info. For the build, my friends keep telling me to go EFI. But that's mostly because they say they don't understand carbs. I don't really understand them either yet, but I don't understand EFI either. I am fairly savvy with computers, so I could probably figure out EFI a lot quicker.

I figured that's about what they'd cost me. I know they're more expensive to set up and get going. I suppose I could get the car going quicker the other way, plus it would be more set up for turbo down the road.

Sooo... I guess you're right, and EFI would definitely be the way to go. But I think I'm going to stick with the plan to run the DCOEs. I just love how they look, and my single Weber sounds great, so I can't imagine how dual 45's would sound. Plus I really like the old-school style setup with dual carbs.

I will take your advice and go with the 45's though. I've already got myself a cam from Colt with the 292/272 intake duration. So I guess I'll be looking for power a little higher up in the RPMs. But maybe it will be a little more power. :)

Thanks again for the help. I will get the 2 inch runners instead of 2.5 inch because I would like to run air filters, and I think that extra half inch will probably get me the clearance I need. (Hopefully). Also I will go with the 45mm runners, and the 10 degree flange. That should do it hopefully...

10-31-2006, 10:02 AM
Space is tight on the #1 runner. You might want to look into screens for your air horns. They take up a lot less space then the filters, though they don't filter out as much. They do keep leaves and stones and other things that would destroy the engine out. I'd keep the runners as short as possible, length can always be added with air horns. I've seen manifolds made from a cnc'd chunk of aluminum, runner length was probably down to 1" at most. At that point you'd have no trouble fitting some 2" or 3" horns (I believe the stock 45" horns are either 2.5 or 3", and at $25 a pop using the stock air horns is a big savings). If I have some time later this week I'll take the cover off the car and get some measurements. Talk to your guy and ask him how short he could possibly make the runners, thats how long you want them. Your cam is bigger then mine so you may want to look into bigger carbs. The big problem is cost. Carbs.net sells the 40 and 45 DCOE for $699 a pair. You might be able to do better on ebay for a price but to compare the 48 DCOE and 50-55 DCO sp are $549 EACH! ouch and those never show up on ebay. To get the most of you motor you might want a set of 50s. You'd have to talk to whom ever ground your cam to get and idea of where peak power is expected to fall, but with a strait 272 grind I'm at about 7000rpm, I should have 41mm chokes for max power. With that cam you want at least the 45 with 38mm chokes. Though looking at carbs.net's catalog I see they offer a 40mm venturi for the 45dcoe. That might be the ticket.


10-31-2006, 10:06 AM
You might want to check this out, some really cheap prices. $45 for a set of 4 venturis, I'm tempted to pick up a set at that price. Jets look reasonable too, but remember to buy a set to save shipping. http://stores.ebay.com/carbpartsdirect

10-31-2006, 10:37 AM
Shortest possible eh? Well maybe I can ask him how short he can go. I guess I would want to be able to fit a wrench in there at least. :) Maybe an inch would be good. I would REALLY like to run air filters if possible. I can probably mod them easily enough.

10-31-2006, 11:00 AM
Woah yeah $45 for 4 venturi's does seem like a good deal. Bookmarkin' that store for sure.