L20 SUs ? / Webbers ?

[diggerrROCK]

Hola ..so i have been a member for ..long enough.. I enjoy this site very much- there s a wealth of information and experience.

I just want to start my own conversations from my own question. I dont want anybody banging on me for asking MY question nor-automatically be classified under any inferior participant list.

i also DO NOT want to be told to use the f$@#!^n search bar..........that seems to happen alot- and many times i understand why.

I just want anyone who will honestly discuss the matter. and wants to HELP me understand from their experience to correspond with me. thanks.

 

so - i am resurrecting my dat 72 sedan. after 15 years of storage-AFTER a moderate front end collision.

its powered by an L20b. it has dual "SU" carbs. oh! and the head is A87(relevant?)

 

i was told by a respectable individual that WEBBERS are hands down- the superior choice for performance. i dont doubt him but would now-

like to learn WHY? and by HOW MUCH?

Whats the best i can get out of SUs, and is it even worth it?

anybody running SUs with great results?

anybody have experience with both?

what are important factors that combine with either for success? (ie manifold, exhaust, headwork)

 

In summary- can any O.G engine guys drop some science for me? Id appreciate the time greatly.

[metalmonkey47]

It's really sad that people have been so anal that you (new member) felt the need go.bring it up.

 

 

 

I hope you.get the answer you're looking for. It's a valid question.

[Ratwagon1600]

http://community.ratsun.net/topic/20338-su-vs-weber-vs-mikuni/

 

http://community.ratsun.net/topic/9198-sss-sus-vs-weber-38dgev/

 

http://community.ratsun.net/topic/29136-dual-su-carbs/

 

I've run Su's, Dellortos and webers in my 25+ yrs of Datsun ownership.

 

There's a bucketload of reasons why each have their advantages and disadvantages.

 

They have been addressed in numerous threads previously including some of the attached links which I searched for on your behalf.

 

P.s. welcome to a great site, hope you stick around.

 

P.p.s. my personal preference is either Webers or Delortos. Massive degree of tuneability for these carbs and the induction noise can't be beaten IMLTHO.

[Son_of_a_Datsun_Guy]

I haven't run either sets of carbs yet, but I know what it's like to be in the hunt for carbs. I'm going to run SUs on my 2.1 L motor. If I went with Webers I'd get about 10-15 more horsepower. 

 

My reason for going with SUs is that they are more street driving friendly (from what I've been told, my dad has run both SUs and mikunis on the same motor). In addition to this the SUs will get better mileage. 

 

Now that's not to say that the SUs can't deliver power, visit Z Therapy's site, or even send the owners an email. They have more knowledge about SUs than any body that I know of. They have different needles and such that can add a lot to your SU's performance. Another option I've heard of is trying to find a set of Z SUs. They are 46mm instead of the SSS's 38mm, which means more fuel. So more power. 

 

As far as price goes, a set of dual Mikunis is lots of $. I've searched around a few times looking for options for my motor and couldn't find anything rebuilt for less than $1,200. Even ones that need rebuilding aren't cheap, and then you need to either rebuild them ($ for a rebuild kit) or have someone rebuild them. 

 

A completely refurbished set of SUs from ZTherapy is around $700-$750, so it's definitely the cheaper option. 

[Eagle_Adam]

ive never run webber/solex's/mukuni's but i did just put 2 sets of SU's on 2 diff L motors with great results and WAY cheaper that any other side draft ive looked into.

 

with that said im still on the hunt for a set of  webber/solex's/mukuni's so i too can see for myself. Bang for the buck tho id start with SU's 

 

 

Welcome to ratsun 

[cruznude]

The Webers hands down!!! I had some 40dcoe's on my last 79kc L20b and with the mild engine work these rocked when it came to performance.  And they sound so FN good!!!

[zerow]

I love my SU's. Yes, much more streetable than a set of side draft Webers or Mikunis, and easier on the pocketbook, too.

I run 38mm's for the economy. The 46mm's off a Z car will give you quick power, and cost you in gas. It all depends on what you plan to do with the car.

[wayno]

I have been running SUs for about 15 years now, I would stick with them for the time being.

You have an A87 head, look on the front of the head just to the right of the oval inspection cover(towards the dist.), is there any number in the casting?

SUs are basically set them up and forget about them, they don't need to be tinkered with all the time, I have never had any of the other brands on my engines, so I cannot give you any feedback on them, if I did, it would be the blind leading the blind.

[KlassicMotion]

It looks like everybody assumed you were talking about DCOE side draft webers.  There is also the down draft weber.  I've run SU's on all my British cars.  It's not a difficult job to set them up, but it can be time consuming, and you will need a couple specialty tools to do it.  Maybe these Hitachi SU's are different, but contrary to wayno's experience with SU's, every British car I've had, has needed the SU's tuned and tweeked.  There are a couple of reasons why the linkage can easily get out of sync. 

 

I also have a 510 with an L20B.  I have a freshly rebuilt set of 38mm Hitachi SU's sitting in a box.  While they were being rebuilt (by a proffesional, who took 8 months to do it), I bought a Weber 38mm DGES Down draft.  It was a few hundred $$ cheaper than the single 40mm Weber DCOE side draft, and I thought I just needed it temporarily.  I also like that it was 38mm same as the SU's.  My L20B is a 1980; I used the stock L20 intake, but port matched it to the carb spacers and carb.  So far I have no complaints for performance.  The one thing I have found to be true, that I read after buying the unit, is that unlike the Weber 32/36 DGEV, it does not have and idle shut of valve.  So on occasion, it will run-on/deisel when shutting it off.  Right now I live with it, because I don't have the time to figure out a way to add a shut off.  I just slowly let the clutch out as I turn the key off.  Anyways, It runs so good, performes like the SU's, and the only adjustments needed on it are two air mixture screws on the sides.  Easy Peasy.  I've had 32/36 carbs on 1.3 liter engines, and they always seem to be lacking in power/ lacking in fun.

 

I think you will find eveyone likes the carb they are running, and dislikes the others for some reason.

 

Most racers, you willl find have the side drafts, unless regulated by rules to run the Weber 32/36, like I.T. racers.  They say the side drafts make more power.  Theory supports why they make more power: The air traveling through the carb into the engine has a straight shot (like the SU's), unlike the down draft carbs.  The side drafts you see most guys run are 40mm or larger.  Dont' make the mistake of over carbureting for the street.  Too much carb and you will only be good at wide open throttle.  I haven't tried a 40mm, but I personally wouldn't go larger than a single 40 for the street.  The larger you go the more fuel you will burn.  The factory couldn't have been too far off with the 38mm SU's for performance and economy.

 

Side drafts definitely have a unigue sound.  Some people shy away from the Mikunis because of cost and parts availability.

 

I think you will find some negativity towards down draft Webers, even though they are the cheapest option, and very reliable.

 

My advice:  If you have SU's, run them.  If you don't think you like them after a few hundred miles, then look towards something else... Probably a single Weber 40!?  I don't believe you need dual side drafts unless your full on throttle all the time.

 

When I want to swap carbs, I always buy NEW.  Spend a little more money up front, and save time, effort, and probably money in the long run.  Every used carb I've gotten has needed a rebuild.  Sometimes they run after a rebuild, sometimes they turn out to be junk.  Buy NEW, get new, get all the hardware and mounting accessories with it.

 

As with any engine, the more mixture you shove down the intake, the more you need to get out of the exhaust.  Every L series exhaust manifold I've seen, has been of a decent design.  Maybe it doesn't flow quite as well as a header, but not bad.  Exhaust pipe on the othe hand;  The stock L20 came with 2" pipe from the manifold back.  If you don't have that, you may want to consider changing that.

 

Also, The more mixture you shove down, the more need for the head to flow, the cam to compensate and if you can increase bore, or stroke to increase volume, the better your results.  So if you have a stock engine, don't over carburet.

 

You have an A87 head.  Is it a Peanut head (closed chambered)?  That would change your compression ratio.  Compression does a lot for an engine.

 

If your engine is close to stock, I'd be surprised if bolting on a Weber will get you much more than 5-10hp gain.  Maybe you can squeeze that much or more out with a big carb, but what will you be sacrificing on the the low end as far as economy and drivability?

 

-Kyle

[john510]

For a daily driver stick with su's.I had them on my l20b and loved the way it ran.The motor has an a87 peanut head that is ported and a better cam than stock.It ran great from idle on up to 5000 rpms,thats where it ran out of breath.Now i have 44 mikunis,its not quite as crisp at low rpm but makes great power all the way past 6000 rpms.This is not a daily driver but i guess it could be.Another thing you will definitely notice will be horrible gas mileage with the mikunis if you dont keep your foot out of it.

[KlassicMotion]

I just met Jason Gray.  He was riding bye on his bicycle and saw me working on the 510.  We had a good conversation about 510s.  I asked him his opinion.  He too loves the SU's for the street.  But he also said he has a set of Dual 40mm Weber DCOE's with 30mm chokes on them.  He said that combo on a built L16 was snappy off the line and great on the track, but only good to about 5500 rpms. He was comparing the feel of those, to his turbo setup.  He said the turbo setup had the traditional turbo lag, so it lagged off the line, but fun after that (you should have seen the smile on his face when he was telling me about it).  He too thought the 32/36 DGEV was blah.  He hadn't tried my 38 DGES....  I should hit him up and make him drive my car to get his opinion on it's performance in comparison to what he knows.....

 

Anyways, there is another opinion for you.

 

Again, if money is any issue, just run the SU's.  It sounds like they do well on the street. 

 

I might just have to put my set of SU's on and see what the difference is.  And if I get a little crazy, maybe I will have to buy a single side draft intake and try a 40mm....44 or 45, or maybe a 48, and then see if I can borrow Jason's dual 40's and see how they all compare.  If I get that crazy I will have to find a chassis Dyno and do a write up on it.   Again though, my engine and I believe yours, are stock engines.  Without a little more cam, we won't get the full potential out of running bigger carbs.

[izzo]

^^ Seriously?

 

You were working on your shit and Jason Grey just was strolling by on his bike? that shit is more intense then the shit about the carbs..

[KlassicMotion]

^^ Seriously?

 

You were working on your shit and Jason Grey just was strolling by on his bike? that shit is more intense then the shit about the carbs..

 

Good, I was trying to be modest and hide my excitement.  It was like meeting one of your favorite authors, only he knocked on my door!  Great guy too.

[EricJB]

The only SU's I have are on the 411sss. If I could find a manifold, it would have dual DCOE's. It runs good as is. but for tuning versatility, parts availability, performance (and sound), you cant beat Webers.

 

And once you run big ones, you cant go back.

[KlassicMotion]

 

And once you run big ones, you cant go back.

 

Big ones are over rated.  Small and perky are fun too....

 

Sorry, couldn't resist.

[tr8er]

I just met Jason Gray.  He was riding bye on his bicycle and saw me working on the 510.  We had a good conversation about 510s.  I asked him his opinion.  

Good choice, wait, wtf.  nice.

[diggerrROCK]

HAHAHAH!! hey thanks so much. ive got alot of great info from you fellas. and a few laughs. im going to stay with the SUs because they WERE working fine- and the object of getting her running and rolling is most important(AT THIS POINT) .the horseplay will come into effect a lil down the road. but ya. 

thank you guys so much and ive been researching on my own as well(dont worry)

[KlassicMotion]

Good Deal.  Let us know what you think of the SU's on the L20 when you get it up and going.

[68datsunroadster]

Hi all. I ran both solex 44 and the stock su's on my u20. It has port work done and a B cam and some heavy valve spring and light wieght retaners. The su's pull real smoth from bottom to 7000 rpm. The solex carbs pull hard up to 8200 then it goes flat. They are to different animals. Imo run what you have.