Dellorto 40 DHLA

[fugetaboti]

Hi there, I'm pretty new to this site and I have a question. I have a 73 240z with L28 and N42 head. I'm thinking of buying a tripple set of 40 DHLA carbs and I want someone's opinion on them. Also the ones for sale are not jetted for a Z. Does anyone know what jets to use, and also how far I can mod the engine before they become too small? I wanted Mikuni 44phh, but they seem to be hard to find and the Dellorto's are available to me right now pretty cheap. Would I be better off with the S.U's instead. I plan to add flat top pistons, and a higher compression head as well as headers and 2.5" pipes all the way back. Any advice would be much appreciated.

[cremmenga]

Do what I'm doing if you want that much hp, drop in a V8.

[my_mad_z]

I've got a set of tripple Dellorto's on my L28, 40mm. I haven't had a chance to tune it properly as the Z is still being restored.

The size of the carbs depends on how far you want to go with engine modification. "How to rebuild Weber/Dellorto" book specifies that 40mm tripple Dellorto's are the right size for a mild L28 engine..... however many prefer to use 45mm carbs. If the mods you have mentioned are all you are going to do, you may be better off sticking with the SU's......if you're going to change cam, port the head, increase comp, headers, electronic ignition, etc, then go the tripples. As for size, it depends how far you want to go!

Fuel supply from the 40mm seems to be ample for my L28; I've got the F54 block with the flatop pistons and a shaved N42 head, approx 10.5:1 comp ratio, a set of headers, mild porting, 240z cam, and electronic ignition.

I'm not sure how readily available jets are in the US, but I recently priced jets here in Australia and they were approx. $15AUea! That's not cheap considering there are 12 jets in total and it's a matter of trial and error before you get the jetting right! I ended up soldering the holes on the existing jets and redrilling the holes to suit my application.... drill bits this small don't come cheap either! I think I used 0.4mm on one of the jets. Once again, jet sizes depend on engine modification.

There are a number of jets that need to be selected to suit the application; off the top of my head there is the idle jets, accelerator pump jets, and main jets. If these are not correctly selected, the engine will not accelerate smoothly. You also need to select appropriate emulsion tubes and there is another component that sits at the end of the emulsion tube but I can't remember the name.

I'm not at home at the moment, when I do go passed home, I will check the jetting combination that I have selected and will post the details for you. It's only a rough guidance as I still haven't tested/tuned.... it's only been a theoretical selection. I'll also post the recommended carb size.

The setup is only temporary as I am going to turbo charge my L28 in the near future.

[fugetaboti]

Thanks, that would be awesome if you could give me a roundabout jetting config. I have electronic ignition and plan head work, higher compression and all that good stuff. I'm just hoping that when all is said and done, the 40's wont be too small. I'm sure they will work great for now with virtually no mods. Can you feel the difference with tripples as opposed to su's? I'm sure it's a dumb question, but I've heard guys say that su's run better and sometimes make more power. I just cant see how two carbs would outperform three. Plus I think tripples look great too!

[my_mad_z]

Don't fall into the trap thinking that 3 carbs are better than 2 on a stock/mild motor! There is no point in having extra fuel if your motor can't deal with it....it will result in a rich mixture that can actually reduce power output and also cause premature engine wear.....execess fuel washes the oil film off the bores resulting in galzed the bores.

The only difference I have noticed at the moment is induction noise; I still haven't been able to take it for a test run, does good burnouts in the garage though :tapemouth ..... to get the full potential out of the tripples, I would need to get an aggresive cam in there and do some more head work but I'm going for a turbo setup soon so it will stay as it is!

I find the SU's very easy to tune...... I'm still learning with the Dellorto's; and as you said, they do look great! But no point having something that looks great and doesn't work. You can get a lot out of the SU's! There's a Z that's running 11.9sec 1/4 mile times using SU's!

I'll get that info on my jet sizing to you as soon as I can.

[Nigel1943]

[quote=!

Fuel supply from the 40mm seems to be ample for my L28; I've got the F54 block with the flatop pistons and a shaved N42 head, approx 10.5:1 comp ratio, a set of headers, mild porting, 240z cam, and electronic ignition.

.

Just as a matter of interest you say you have 10.5:1 comp on a shaved N42 head. It's my understanding that you get 10.4:1 with a standard N42 on a flat top L28. How much have you had shaved off and have you installed camshaft pillar shims to take up any slack in the timing ?

[my_mad_z]

I did say approximately 10.5:1..... I was told the head would be shaved to give me approximately 10.5:1 comp ratio and it would not require shims to compensate for slack in the timing chain. After the head was shaved, I assembled the engine and I checked to make sure that the timing chain didn't have slack; all of the guide notches lined up!

I have had to use cam tower shims on an L26, the E88 head was warped like a banana and required serious shaving..... had to use shims after this was done. The L26 I had was one of those freak motors; would love to rev and had plenty of go..... however it was short lived when I got excited during a drag and over revved it; heard a big bang and then a cloud of smoke came out of the exhaust! It kept running for 2 weeks and then I decided to tear it down and examine what had happened...... I did a comp test and all cylinders were within limit.

When I pulled each piston out, every compression ring was shattered into pieces! I counted 26 pieces on one of the pistons!!!! I was baffled as to how the engine was still running and showing good comp readings. It was not feasible to rebuild so I decided to go for an L28 and have never looked back.

[Nigel1943]

. After the head was shaved, I assembled the engine and I checked to make sure that the timing chain didn't have slack; all of the guide notches lined up!

Yeh, which suggests the head is more or less standard.

The reason I mention this is because I have a similar set-up and am trying to achieve not less than 10.5:1 for a mild competition engine and as yet the head is unshaved as far as I can see. Also whilst some people suggest you need cam-tower shims I'm not convinced unless the head is heavily shaved, after all the tensioner is designed to take up slack and just moves a little further out of it's hole. I previously built an L4 engine with the same tensioner set-up, taking 60thou off the head and never had a problem.

Oh BTW, I'm running triple 48 Dellortos having previously run two of them on my L4. Set up properly with a good cam I feel they are superior to Webers. Mine would pull cleanly from 1800revs to 7000 with no problems.

[my_mad_z]

I finally got the jetting sizes that I am running in my Z.

These are the theoretical sizes:

Main Jets: 142

Emulsion Tube: 7772.6

Accelerator Pump Jets: 40

Idle Jets: 50

Idle Jet Holders: 7850.1

I calculated these sizes based on the information specified in "How to build and power tune Weber and Dellorto DCOE and DHLA Carburetors" by Des Hammill..... very useful book!

The selection is based on 466cc per cylinder, mild head work, headers....

Sorry for the delay, hope this information helps!

Marc.

[fugetaboti]

Do you know about the other component sizes like chokes and venturis?

[my_mad_z]

I'll get that info for you tonight if I can. I've got it written down somewhere, just have to find it!