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  View original topic: 36 VS. 40 DRLA Dells on a stockish 1600DP performance loss?
PHAT4 Sun May 08, 2005 7:07 am

I did quite a bit of reading after a search on DRLA.
I found a few people who wanted to know wich would be better and if a 40 could be used successfully.

The answers were always the same...
A 36 would probably be better to run and yes you can run a set of 40's with some tuning.

My question is what would you be giving up if you choose to run a set of 40's that have been dialed in over a set of 36's.

Are we just talking about a milage thing or would there be a loss of throttle responce, bottom end torque, and midrange power to go with it.

I'm not a carb idiot as I know Holley's pretty good from my small block Chevy racing days.I've tuned 650DP,750VS,750DP,830DP,850DP,750HP,and 950 HP's.
It's just that the Dellorto and Weber carbs allow you to arrive at a closer to perfect A/F ratio in the low-mid range area.

Bruce Sun May 08, 2005 12:47 pm

There will be a significant loss in bottom end torque with the 40s over a pair of 36s. Throttle response will also be off.

The best analogy I could think of is what would happen if you stuck an 850DP on a stock 283.

PHAT4 Sun May 08, 2005 5:36 pm

:shock: You can't be serious...

Have you ever tried to run an 850 on a stock motor under the 427 CI range....
Maybe you meant a 750DP on a stock 283-400.
It still won't work well but at least you can limp it around a bit.

I have seen an 850 on a stock 350.. all I can say is :lol: :roll: :lol:

Here is an example of what John at aircooled.net said about the above question
http://www.thesamba.com/vw/forum/viewtopic.php?t=88632&highlight=drla

I trust this guy when he gives advice, plenty of experiance.

Does anyone have experiance with this?
Care to give any input?

stevemariott Sun May 08, 2005 6:57 pm

I don't have any experience with an 850 on any V8, but Bruce has plenty of experience with both Dells and Webers and I consider him to be a pretty darned good source for info. Venturi size is another thing... 40s will operate better with 28 or 30mm vents on a stockish 1600 than the 34mm vents they ususally come with "stock" - with those I can see where you would be running into loss of bottom end and other issues.

PHAT4 Sun May 08, 2005 7:19 pm

After reading many of his replies I see that he is trusted by many.
I apologize about how I wrote my above answer.I reread it after a while and realized it came off like I was being a know it all ass.
That is not the case, not even close so I re wrote it.

I wish he would have gone into further detail about why you can't make the "Dialed in 40's" work as good as a set of 36's.That is what I was talking about.Not a stock carb.I know changes will have to be made.
After reading about some people saying they will work I wanted to know more.It would have cleared up things in my mind better.

Bruce Mon May 09, 2005 3:10 am

I will typically recommend a smaller carb than most around here. The reason is that a smaller carb will give you better bottom end torque and throttle response than a bigger carb. Since I drive my VW every day in traffic and on long highway trips, bottom end torque is much more usefull than top end hp. Most of the guys on this site don't drive their cars every day in traffic, so they don't care about bottom end torque, all they want is more hp.

On my current driver I have 40 DRLAs. It is a 2 liter engine that makes about 120hp. If I used some 45 DRLAs it would make more top end hp, but at a loss of bottom end driveability.

When you ask anyone how driveable a combination will be, you will get some saying it has great bottom end, while the next will say it sucks. There is no absolute definition of what is good driveability.

Your engine was originally built by VW with a single bbl 34mm in dia. A pair of 36 DRLAs will have 4 bbls that are each slightly bigger. By comparison that is a huge jump. If you look at the entire intake tract with 36 DRLAs, the carbs are not the limiting factor. It is the intake ports, valves, and cam timing. 40DRLAs won't make any more hp, they will just throw away bottom end torque and driveability.

In that link to that other discussion, the question was about a pair of 40 DRLAs with 28mm venturis on a stock 1600. Most 40 DRLAs have 34mm venturis, not 28mm. John and the others were saying 40s with 28mm vents would work, but even then 36s would be better.

IMO for a stock 1600, even 36 DRLAs are on the big side. But they are the smallest you can get, so go with them.

PHAT4 Mon May 09, 2005 4:27 am

Bruce wrote: I will typically recommend a smaller carb than most around here. The reason is that a smaller carb will give you better bottom end torque and throttle response than a bigger carb.

In that link to that other discussion, the question was about a pair of 40 DRLAs with 28mm venturis on a stock 1600. Most 40 DRLAs have 34mm venturis, not 28mm. John and the others were saying 40s with 28mm vents would work, but even then 36s would be better.

IMO for a stock 1600, even 36 DRLAs are on the big side. But they are the smallest you can get, so go with them.

Now that I understand.
Your saying that even if I was to change to a 28mm Venturi in a set of 40's that it still wouldn't make up for the loss of velocity, and that a properly set up set of 36's will be better.

I had hoped that since the venturi is interchangeable on the Dellorto and Webber carbs that the velocity could be maintained, and I figured that the 4spd would also help.

I am a firm believer in bigger isn't better myself.
I have prooved the point with runs on friends cars and my own stuff.
Example:My little Holley 650DP against the 750VS. on mild SB350's.
With a V8 and an automatic trans you simply can't make up for the loss of 60ft that even a 750VS. creates in a mild application.
The lack of velocity going through the Venturi creates a delay in the start up of the main metering system.Because of this the throttle responce is slower and there is a loss of bottom end torque.The 750 may end up with a higher MPH(meaning more HP) but the 60ft-660 is slower and it usually can't be made back up.
People can read and quote all the magazine articles they want, and they tend to on the V8 boards.It's a totally different world once your engine has to accelerate with the full load of the vehicle weighing it down.The engine has to react quickly and keep on pulling.
The use of the 650DP usually creates slightly quicker ET's with slightly slower MPH, and it's usually also more consistant.

Loopole Mon May 09, 2005 8:48 am

i am running 36s/30vents/120main/55idles on bone stock 1600, yes they are a little on the big side, however they run better than any other combo, good ignition and you will have excelent throttle response, go buy a set you wont be disapointed.

Danwvw Mon Aug 14, 2017 11:29 am

Interesting thread! I was thinking of trying a set of 40 drla's on a Stockish Type 1 dual port, as you can get smaller venturi's, I would think the Venturi's and correct jetting would be all that matters, well, cam may help.
The problem with running 28mm venturi's in the drla 36 Dellorto's is that the venturi's CB-Performance sells are made to fit the 40 drla and I have tired them in the 36 and they don't perform as well as the 30mm venturi's did. Video

Erik G Mon Aug 14, 2017 11:37 am

the dellorto venturies CB sells are junk, get real ones and try again

I like a lot of CB stuff, but all of their dell parts are sub-par in my opinion. The venturies dont even have the right shape

FreeBug Mon Aug 14, 2017 12:24 pm

How much CFM can a stock 1600 suck in? I'll bet less than the max CFM the 36's can deliver.

On a totally stock engine, I don't see what you would gain with 40's, probably lose-lose.

esde Mon Aug 14, 2017 3:04 pm

Danwvw wrote: Interesting thread! I was thinking of trying a set of 40 drla's on a Stockish Type 1 dual port, as you can get smaller venturi's, I would think the Venturi's and correct jetting would be all that matters, well, cam may help.
The problem with running 28mm venturi's in the drla 36 Dellorto's is that the venturi's CB-Performance sells are made to fit the 40 drla and I have tired them in the 36 and they don't perform as well as the 30mm venturi's did. Video

Running the small 28 vents in a 40 DRLA works ok, after you get the jetting tweaked for transition and main jets. When you put the little vents in the 40, there is a pretty substantial step where it meets the carb body, under the air horn. Whatever it does to air pressure makes the main jetting not what you'd expect. I think I had to run larger air jets to eliminate a flat spot right at transition. But I did get 40's to work on a 1600, though the 36's were much better.

txoval Mon Aug 14, 2017 6:33 pm

A lot of similar tuning discussion here:

https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0

My thread about adding dual 36IDF's to my 1200cc Okrasa engine

I ended up with custom vents to assist with drivability

modok Mon Aug 14, 2017 10:26 pm

over ten year old thread? well, better late than never. how "small" can you make 40 DRLA, that depends on the model, yes there are more than one model!
IMo you can run as small as 30mm with the big transfer ports, or as small as 28 with the small transfer ports. Which one do you have? look up the model OR take off the cover and measure the to transfer port holes. The big ones are like .160+ while the small is only around .120

CB's venturis are currently NG, but they used to be pretty good. I have some 27 vents I bought LONG ago, just rough cast but they were the right general shape at least. :roll:
Buy vents from Italy, prices are quite reasonable at the moment.

Erik G Tue Aug 15, 2017 6:34 pm

Amen

Here is what a good 30mm vent looks like.



The new ones are shit and super frustrating for newbies like me. I eventually bought all nice stuff but it was a 912 motor and I paid for the lessons



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