[PSIG]

Lots of ways to come at this, but I'd look for other reasons first. Are your throttles opening fully? Is your camshaft useful above 3500? Probably not, as peak HP is typically 3400-3800 rpm then falls like a rock. Is it maintaining fuel pressure at WOT? Your engine only makes 10 to 15hp (on a good day) in each cylinder, stock. The volume of your cylinders is not the factor, but the flow, calculated as volumetric efficiency (VE).

Volumetric efficiency for VW boxers ranges from 49 to 62% VE in those models. Peak torque is around 2000-2200 rpm. I can't say if yours is performing poorly, or if you're asking for different performance than it is designed for. I know from driving older carbureted versions, that they move along fairly well at first, but fall on their face at higher rpm. Perhaps that's it, but keep looking, and post your fresh tune and a new log of some runs so we can look for clues.

[roger.rrgt]

I'd think 40mm throttles for 400cc cylinders.

I think of that too. Most of the double throttle bodies kits online are either 40 or 45 mm.

Lots of ways to come at this, but I'd look for other reasons first. Are your throttles opening fully? Is your camshaft useful above 3500? Probably not, as peak HP is typically 3400-3800 rpm then falls like a rock. Is it maintaining fuel pressure at WOT? Your engine only makes 10 to 15hp (on a good day) in each cylinder, stock. The volume of your cylinders is not the factor, but the flow, calculated as volumetric efficiency (VE).

Volumetric efficiency for VW boxers ranges from 49 to 62% VE in those models. Peak torque is around 2000-2200 rpm. I can't say if yours is performing poorly, or if you're asking for different performance than it is designed for. I know from driving older carbureted versions, that they move along fairly well at first, but fall on their face at higher rpm. Perhaps that's it, but keep looking, and post your fresh tune and a new log of some runs so we can look for clues.

okay, they can open fine. Probably not much. Im 99% sure it does. Im asking for some advices on this becausa when carbureted, it didnt felt like being dragged. Of course it never had much power to beggin with, but when giving pedal i had some instant response and rpms climbed way faster. Will post some logs in the very near future. The msq file on the last post dont work?

[LAV1000]

Make sure that O2 sensor (wide band) is calibrated and post some logs.
When running ITB's then there is not much gain in going bigger than the inlet port of a single cilinder.
for an NA setup an each cilinder its own itb.

[JHolland]

Have you double checked the cam timing?

[roger.rrgt]

Make sure that O2 sensor (wide band) is calibrated and post some logs.
When running ITB's then there is not much gain in going bigger than the inlet port of a single cilinder.
for an NA setup an each cilinder its own itb.

NB is on the mail, better than nothing. And my setup is not ITB but two throttle bodies feeding the 4 cylinders. My inlet port and valve are bigger than the throttle plate about 6mm in diameter.

Have you double checked the cam timing?

Cant be done without splitting the engine open, but for this i can say im sure it is timed correct. I rebuilt the engine myself 4 years ago and triple checked timing before closing the cases.

[PSIG]

Just for reference, any engine with rockers or pushrods can be checked for cam timing, using a dial indicator and a timing wheel. If you don't have those, your local engine shop will, and a pizza or beer will usually get the job done. We're not looking to spend all day here, but only a few minutes to verify something isn't off far enough to cause issues.

Degreeing_cam_timing.png (112.81 KiB) Viewed 1967 times

[roger.rrgt]

My project is not dead! yet. Time to mess around with things is tight those months. Now to the important part.

After installing some air filters, those cheap conical filters, i saw a significant drop on the map value above 2k RPM, and it was running as good as a moped. After that i went back to the logs paying attention to the correlation of tps and map and at some points i could see the map value falling while the tps was constant and I did what most brainer thing someone could do and bought this lovely thing below.

IMG-20221020-WA0000.jpg (260.56 KiB) Viewed 1334 times

Brand new and dirty cheap!
This one has 46mm plates and is more than enough for the engine to breath. The intakes will be modified and if the tubes used there become the next restriction, the inner diameter of the tubes is slight smaller than the header holes, entirely new intakes will be made. Having access to a lathe and milling machines is like a dream.

Just for reference, any engine with rockers or pushrods can be checked for cam timing, using a dial indicator and a timing wheel. If you don't have those, your local engine shop will, and a pizza or beer will usually get the job done. We're not looking to spend all day here, but only a few minutes to verify something isn't off far enough to cause issues.

After playing a while with this no problem was found, at least with timing as one of the head studs busted from the block

[PSIG]

After installing some air filters, those cheap conical filters, i saw a significant drop on the map value above 2k RPM, and it was running as good as a moped.

OK, so is the issue the TBs or the air filters? Use the data to confirm you're not chasing squirrels, extending the project. My first reaction is that the old TBs and manifolds should feed 55hp OK, no?

[EDIT] I think it's something else. I didn't search the thread, but weren't you using 28mm, one per-cylinder? I ran the calculator for the horsepower one 28mm ITB could support on one cylinder. Yeah, it's good:

28mm ITB HP 1 cyl.jpg (20.35 KiB) Viewed 1294 times

And here's the flow data, showing 28mm is not working very hard to make the power of one cylinder. Even two or three cylinders per 28mm throttle body is no issue. Hope that helps:

28mm flow data 14hp.jpg (52.49 KiB) Viewed 1294 times

[CD..]

I have only driven one aircooled vw engine, and thats in a formula V, they are 1300cc engines with a single 30mm std carb, and make about 70hp. They arent the smoothest at low revs but sings pretty well at high revs, the trick is the head porting and cams. twin 28mm throttles (if I understand it correctly) that you ran shouldnt be that bad.

[roger.rrgt]

OK, so is the issue the TBs or the air filters? Use the data to confirm you're not chasing squirrels, extending the project. My first reaction is that the old TBs and manifolds should feed 55hp OK, no?

The air filter only did it worse, way more. I think its a combination of throttle plate and intake tube restriction.

I have only driven one aircooled vw engine, and thats in a formula V, they are 1300cc engines with a single 30mm std carb, and make about 70hp. They arent the smoothest at low revs but sings pretty well at high revs, the trick is the head porting and cams. twin 28mm throttles (if I understand it correctly) that you ran shouldnt be that bad.

The solex pic 30 right? Mine is 1600cc with oem cam, very smooth and responsive at low rpm and has peak power at 4500 and torque around 3500, but i cant say any exact numbers, only that its less 70hp.