# Big cam with dual carbs question



## VWaddict01 (Dec 12, 2011)

I have a 1.6 rabbit, and I recently aquired a 1.6 carburator head that has been ported/polished/shaved,3angle grind, has big valves and HD springs and a 298 delta cam(as told by PO) already put together and ready to drop in.

My question is, if I get dual 40 weber side draft carbs, will that cam still be too big for the street? I can deal with a super lumpy idle as long as my motor doesn't cut out all the time.


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## B4S (Apr 16, 2003)

Cut out?

No cam is too big for the street, but it might be too big to be pleasant to drive. Especially if it's only tuned for WOT. A proper tune, with the proper internals in the carbs will go a long way towards making it driveable, but with a cam that big, you're going to have a very soft bottom end for sure.


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## VWaddict01 (Dec 12, 2011)

B4S said:


> Cut out?
> 
> No cam is too big for the street, but it might be too big to be pleasant to drive. Especially if it's only tuned for WOT. A proper tune, with the proper internals in the carbs will go a long way towards making it driveable, but with a cam that big, you're going to have a very soft bottom end for sure.


Cut out, like not bieng able to keep an idle. Yeah that's what I was thinking, it'll be fun in the freeway, but around town it might be a hassle. I'll probably go down to a 288 then...


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## B4S (Apr 16, 2003)

Ah, ok. It would definitely require a higher idle to stay running I would assume. Might need to be ~1300-1500, but I have no experience with a cam that heavy.


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## antichristonwheels (Jun 14, 2001)

It gonna be an all or not much affair. Small displacement + really big cams means you will have a high idle and power is not gonna come on until about 5k. It will work but you will have to wring its neck to get it to respond well. A 4.25+ final drive would help. also you need as much compression as you dare. 12:1 and race gas.

To me this would not be a daily driver choice but for a toy car you may as well go ahead and see what you think. It's easy enough to change the cam later.


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## VWaddict01 (Dec 12, 2011)

Yeah, I figure I'd try it out, since it's already in there, like you said at least cams are easy to replace. Wouldn't of been my choice of cam though. A close ratio tranny is on list. I guess I was just hoping the dual sidedrafts would help compensate for the big cam.

Thanks for the info!!:thumbup:


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## B4S (Apr 16, 2003)

Well, they'll certainly make it a bit more liveable than a stock plenum-based intake on CIS would, lol. Unless you go for some tiny chokes, your bottom end will be soft as all get out. That'll kill the top end though .


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## candm (Apr 27, 2003)

probably the most important thing i have learned in my time with sidedrafts is to use the smallest chokes that will give you full power. you can go larger but as mentioned above, you will have a very weak signal down low and the only way to compensate for it will be to run much richer ( accelerator pump jets and or pump bleeds, idle jets , main jets and even a different set of emulsion tubes possibly). having the proper choke that is not too big will make low speed running alot more manageable with the proper jetting . i would probably stick with no bigger than a 32 set of choke tubes for your 40 webers if you try that 298 cam. with a 1.8 or 2.0 liter, you would need larger chokes but yours being a 1.6, a 32 probably will get you to full power and , with proper jetting, make driving on the street somewhat livable


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## VWaddict01 (Dec 12, 2011)

Wow, thanks. I didn't even think about using small chokes, I will go that route. A lot of things to consider and great information.:thumbup: A lot of shops in my area don't even deal with tuning carbs anymore(water-cooled), it's almost a lost art. It's great to have the knowledge on hand here on Vortex.

Cheers!


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## dr770 (Dec 31, 2011)

dont use dual weber use cv bike carbs, they have variable ventury , you will have very smooth idle.ı am on a similar project , this is my way. 36 mm mikuni carbs.is your head 8v or 16v ? can you put some photos of port polishing job? 
think about the old bikes 1000 cc and 140+ hp with an idle no more than 1K .they are also using wild cams. use bike carbs and have smooth idle+more responsive engine. and they are far easier to tune than webers.i can get some where 500 rpm idle with them no vibration, standart cam, now i am swithing to 272 web cam. use a FM,fd,fk code tranny, can use a 4.25 final drive from mk4 golf.


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## VWaddict01 (Dec 12, 2011)

dr770 said:


> dont use dual weber use cv bike carbs, they have variable ventury , you will have very smooth idle.ı am on a similar project , this is my way. 36 mm mikuni carbs.is your head 8v or 16v ? can you put some photos of port polishing job?
> think about the old bikes 1000 cc and 140+ hp with an idle no more than 1K .they are also using wild cams. use bike carbs and have smooth idle+more responsive engine. and they are far easier to tune than webers.i can get some where 500 rpm idle with them no vibration, standart cam, now i am swithing to 272 web cam. use a FM,fd,fk code tranny, can use a 4.25 final drive from mk4 golf.


it's a 8v head. Which manifold would you use for the mikuni's? Or is it custom? But still either way I would be stuck with the 298 cam that might be too big. But looking into bike carbs might be cheaper, just getting the right manifold might be a pain. Is 36mm the biggest they made back then?


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## jetta86GLI (Apr 2, 2012)

I tried to put a 306 cam on a 1.6, the car wont start it was to many compression and i changed to the 286, and you will need to use racing fuel or your going to have a lot of pre ignition, the 4.25 final drive, you can found it in the AVX transmission the only have it in the caddy 1.6 Diesel these transmission is very slow so you can change the internal gears from a quicker transmission, like 9A, 4K, 2H, 4Y for the bike carbs the bigger are from the Yamaha R1 they are 40mm, and Honda CBR blackbird the are 42mm


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## Urwrstntmare (Feb 22, 2011)

I'm runnin a 306 cam in a decked JH big valve head on an ABA bottom end, 3A dizzie and knock sensor. No prob at all! :thumbup:


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## Urwrstntmare (Feb 22, 2011)

Oh yeah runnin dual DCOE Weber 45's


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## antichristonwheels (Jun 14, 2001)

a 2 liter engine will tolerate bigger cams much better than a 1.6.


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## Urwrstntmare (Feb 22, 2011)

Yes it will, still have the back compression on start, and you have to run premium with octane booster at least.


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## jetta86GLI (Apr 2, 2012)

When I tried to put the 306 cam on my 1.6 engine I was using racing fuel (115 octanes), I checked the timing, the carburetor was running good I checked everything in the car, just wont start it was too much compression. 

Right now I have the project of the ABA engine with 16v cylinder head, I was thinking to put in a bigger intake cam but I found out the you can put an exhaust cam, instead of the stock intake cam, the exhaust cam is bigger so it will give great torque and hp, and I will be running some mikunis carbs, headers, cylinder head ported and polished, Saab distributor, MSD ignition box, etc


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## dr770 (Dec 31, 2011)

well i made the manifold myself , but i can not upload the pictures at the moment. i used a diesel manifold cut from the 5th cm from the head, with inside diameter 0f 30 mm(diesel manifold). then i used lathe and made 16cm conical tubes with one end 30 mm the other 36 mm inside diameter, all made of 5083 aluminyum. then welded together. But it is not that easy ı had to make 2 jigs when welding. if you give me your e mail adres i can send you the build pictures. all the job finished in 2 days , but the work was nice. İ have also made a resonance tuning 3rd harmonic at about 6300 rpm with a %8 boost. İ used a suzuki carry fuel pump with a custom hand made pressure regulator. at first crank the engine started with no broplem.İf you are dealing with 8v head my photos would help you so much i belive.36 mm is way enough for 1.6 lt, i dont think you need bigger ventury. most of 40 mm webers have 32 mm ventury. what is your inlet valve diameter? for the maximum drivable performance stay under valve size when chosing ventury.


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