WTB: L-series offenhauser intake manifold

[Dimerforlife13]

Let me know if you have one, I have a lot of stuff to trade, more so than money, but I could make that happen too. Let me know.

 

-Brett

[banzai510(hainz)]

those are overrated just bore out the stock one to the Felpro 1.5 inch intake gasket if your head isnt 1.5 inch already.

 

or open the top of the manifold wher the weber sits on.

[wildmaninid]

I had oneon my 70' 521 i should have taken it off before i sold the pickup....... I will say i agree wholeheartedly with Hainz, no real difference between that one and a stock one, other than it said offenhauser on it................

 

Bill

[Jesse C.]

I once ran an Offenhauser dual plane manifold and it did not work any better than the stock one. It actually felt like it made a bit of torque more than the stocker, but, it would not rev all that great. This was on a stock L-18 with a 32/36 Weber.

 

Just move up to SU carbs or run the stock unit.

[Dimerforlife13]

Thanks for the input guys, I was actually going to use it on my LZ22 I'm building. My buddy who is doing my port work looked at the L16 manifold and threw it in the trash. He told me with the work he's doing on the head he wouldn't let me run it. I bought a 38/38 to run on it, maybe I should just step up to some SU's, or maybe just some harley CV carbs. Maybe the weber is not the best idea. There are no larger port smogless manifolds right? Its going in a truck so I'm looking to have a set of side drafts on it or anything. Maybe I should have him port my L20 manifold...

[mike]

...too bad you threw the L16 one away, I gasket matched and enlarged the runners on mine and also hogged out the carb area and put it on my LZ22... Looks super clean and runs as good as the desmogged L20 one I had on there before except I can also run a crank case tube now, it made a noticeable difference on interior fumes in the wagon. I probably had about 5 hours of work into it to get it all smoothed out though... If youre paying by the hour its not worth it.

[Z-train]

Thanks for the input guys, I was actually going to use it on my LZ22 I'm building. My buddy who is doing my port work looked at the L16 manifold and threw it in the trash. He told me with the work he's doing on the head he wouldn't let me run it. I bought a 38/38 to run on it, maybe I should just step up to some SU's, or maybe just some harley CV carbs. Maybe the weber is not the best idea. There are no larger port smogless manifolds right? Its going in a truck so I'm looking to have a set of side drafts on it or anything. Maybe I should have him port my L20 manifold...

Why are you hell bent on a"larger" manifold?

[Dimerforlife13]

Why are you hell bent on a"larger" manifold?

 

Just going off of what my machinist was saying. The ports on the intake manifolds just seem very small, especially after they are collected to one. Probably just going to end up porting the L20 manifold a little bit. I'm not really looking for a top end screamer, and I was just curious about the offy manifold. Knew it was out there, but didn't know what it was all about. You built a LZ23 for your wifes truck right? How has it been? I remember it making some good number right off of idle, nice little torquey motor? Do you have the cam specs on that?

[Suspect]

I'm building a LZ23, has KA24E Performance 89mm pistons, large toobe long header, A87 Open Chambered head, Comp Cam 79-135-4, Cannon Intake, Weber 38/38......

 

Its ready to completely assemble but just haven't got to it yet. There is a Cannon intake exactly like mine on ebay atm. The auction is about to end but there is no bids and will probably be relisted.

 

http://cgi.ebay.com/ebaymotors/Cannon-manifold-Weber-carb-Datsun-L20-engine-NICE-_W0QQcmdZViewItemQQhashZitem1c160a40f5QQitemZ120628855029QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

 

 

 

There was also this one.... didn't impress me a whole lot but its shiny.

http://cgi.ebay.com/ebaymotors/Datsun-521-510-620-Truck-Weber-Carb-Manifold-Filter-Set-/400160605451?pt=Motors_Car_Truck_Parts_Accessories&hash=item5d2b6e450b

[dryheat]

If you really really want the Offenhauser ... here it is. This guy has been advertising it forever on the Phoenix Craigslist with no takers.

 

Offy Manifold

[datzenmike]

http://cgi.ebay.com/...=item5d2b6e450b

 

This one won't fit on a stock L20B before '78..... but it is shiny.

 

For best throttle response and economy the runner should be small enough to keep the intake air speed as fast as possible. Even air is subject to inertia, in other words once up to speed it tends to keep moving. The stock L20B intake valve closes 52 degrees past BDC! That's 1/3 of the way up the cylinder on the compression stroke. High intake air speed will continue to crowd into a cylinder even though the piston is rising and trying to force it out. The lower the air speed the less air crammed into the cylinder and less power produced. Now as you can see what works at 2K is restrictive at 6K so a port size has to be a compromise. A larger motor can have a larger port diameter and still have the same air speed as a smaller motor.

 

Increasing the port diameter will allow better flow at very high RPMs but the low speed air speed will drop and so will throttle response. The Offy intake is a poor attempt to have a small runner diameter for the primary at low speed and a larger increase when the secondary opens. This works inside the manifold but as it enters the much larger head port, it slows dramatically and most of the gain in speed is lost. Ideally what we need is a variable port that is small at low speed and becomes larger as the motor revs up.

[bonvo]

http://cgi.ebay.com/ebaymotors/Datsun-521-510-620-Truck-Weber-Carb-Manifold-Filter-Set-/400160605451?pt=Motors_Car_Truck_Parts_Accessories&hash=item5d2b6e450b

 

im running this set up on my 76 l20b my intake has been port matched to 1.5 mine isnt that nice though

 

the stock l16 manifold works fine when its ported to be honist the fact that your machinist didnt consider that option kind of worries me

[Z-train]

This one won't fit on a stock L20B before '78..... but it is shiny.

 

For best throttle response and economy the runner should be small enough to keep the intake air speed as fast as possible. Even air is subject to inertia, in other words once up to speed it tends to keep moving. The stock L20B intake valve closes 52 degrees past BDC! That's 1/3 of the way up the cylinder on the compression stroke. High intake air speed will continue to crowd into a cylinder even though the piston is rising and trying to force it out. The lower the air speed the less air crammed into the cylinder and less power produced. Now as you can see what works at 2K is restrictive at 6K so a port size has to be a compromise. A larger motor can have a larger port diameter and still have the same air speed as a smaller motor.

 

Increasing the port diameter will allow better flow at very high RPMs but the low speed air speed will drop and so will throttle response. The Offy intake is a poor attempt to have a small runner diameter for the primary at low speed and a larger increase when the secondary opens. This works inside the manifold but as it enters the much larger head port, it slows dramatically and most of the gain in speed is lost. Ideally what we need is a variable port that is small at low speed and becomes larger as the motor revs up.

And people go "HUH"? when i tell them that the manifold on my LZ-23 is just a port matched L-18 intake.

[datzenmike]

Sure that will work nicely and be easy to live with day to day.

[I'm BLUE]

^ I agree with datzenmike :D

[Dimerforlife13]

Thanks for all the replies. To me it looked like the single intake runner after the 2 runner meet would be small. I still have my L16 manifold that I could have port matched. Do the L18 manifolds have bigger ports? I think I have one of those somewhere. I actually didn't know the offy manifold was a dual plane manifold, I was thinking something more like the cannon. I'll just go for the L series manifold, it will probably match my cam that I'm getting anyways. Its looks like it will have a range of 2k-6500, so I shouldn't be worrying about huge ports at all, being that I don't think air speed will be an issue at 6500 with smaller ports. I appreciate all the opinions. Sounds like most of this is just coming from inexperience on my part. Its going in a 620 anyways, thanks for the enlightening everyone.

[datzenmike]

..... Its looks like it will have a range of 2k-6500, so I shouldn't be worrying about huge ports at all, being that I don't think air speed will be an issue at 6500 with smaller ports.

 

Yes, air speed will be high but also the ports could be restrictive, like sucking through a straw. The motor will run fine at mid range but may not reach it's full potential at high RPMs. Use something that works best in the range you drive in most. Huge carb(s) with huge ported manifold and ported head with oversize valves may be dissapointing for city stop and go daily drivers.

[J.Chimpo]

not to thread jack but what about 4bbl offy intakes anything on them?