4-barrel intake: THE FACTS

[Drax240z]

Ford, Gm, Chrysler ALL had inline 6cylinder engines that came from the factory this way. I doubt they would have done this and continued to do this for decades if it was an inherently flawed system.

 

You can't seriously think that just because lots of people are doing it, that it is good... right? The only reason this was done was because it was the cheapest way to get it running.

[johnc]

The only reason this was done was because it was the cheapest way to get it running.

 

Not true. Cheapest is not the sole criteria for OEM engine deisgn with the Domestics. Same as engineering tour-de-force is not the sole criteria for OEM engine design with the German manufacturers.

 

Look at the Pontiac OHC Sprint 6 clylinder as an example: SOHC 3.8L, 10.5 to 1 CR, Quadrajet 4 barrel, 215 hp at 5,200 rpm and 255 ft. lbs. at 3,800 rpm.

[datsunlover]

I guess it comes down to the proof that the Z 4bbl intake is BETTER than the OEM twin carbs/stock FI. All other things being equal, I would think that the oem set up was 'the best all around' when it was designed, (The 70-72 anyway..) and the SU's are quite simple/easy to adjust IMO. The FI is also a good system when it's in good order. (yah, right.. lots of those left around! )

Hmm... A question to anyone who has done this 4bbl conversion here; Did you switch to the 390 carb from a perfect original setup? Or was this a swap done to fix failing FI or SU's? (obviously a new 4bbl/intake would be a vast improvement over junk carbs/stock FI) BUT: If you switched from a properly tuned OEM system, did you find a huge diffrence in power, or is it just a little easier to start, slight increase in 'get up n go' , and slightly worse fuel mileage?

[JMortensen]

It's going to be a completely different feel and I think it would be hard to give a "seat of the pants" judgement, datsunlover. Those secondaries open up and your bound to think "WOW, this thing hauls butt!"

 

When I was trying to get my 240 to pass smog I drove it to the smog place with the timing severely retarded. Thing had no power at all, but when the mechanical advance kicked in it would spin the tires. In 3rd gear. If I didn't know any better I would think it had a lot of power (it was breaking the tires loose in 3rd), but really it was just that it was suddenly getting back some of the power that it had lost from the drastic timing change that I had made.

 

Dyno proof is proof of power. EGT on each cylinder would be proof of the lean #1 and #6. Listening to a guy who admits that he has no idea about SU's but does know that his were totally worn out talk about the improvement that the brand new 4 bbl made is just that, like you pointed out.

 

First there is absolutely no way that the SU's give anywhere near the performance that my 4-barrel intake with the Holly 390 carb gives.... that's just a fact and I dont care who rebuilt the SU's or how they were tuned....SECOND THE SO CALLED ISSUE OF MIXTURE DISTRIBUTION DOES NOT EXIST.

 

This is the only part of this whole thing that I don't buy. I think this is a good product for people who can't tune SU's or want to get rid of flat tops that don't run well anymore. I have NO DOUBT that plainswolf found a big increase in performance by bolting this thing on.

 

I'm feeling like I'm coming off like the guy who has something against Dave, but I have REPEATEDLY defended his oil pan, and I have bought from him 4 or 5 times now. Just wanted to point that out.

[Drax240z]

John I was thinking specifically about the 1bbl carb on the inline 6 when I was making my above post... that was almost certainly done because it was cheap. You are absolutely right that there were 6 cylinders out there with carbs that weren't done just to be inexpensive.

[datsunlover]

Well, I will agree with drax there. Like I said about my buddys Jeep, a single carb like that is just not ideal for an inline 6, but it works and it is cheep. This guy compleatly rebuild his engine last year. upgradded cam (its a jeep, so he wanted more low end grunt for trail riding, climing ect) had some head work done, ect ect but he was on a budget so he just rebuild the stock carb and thrwe it on. IIRC, there is a 4bbl conversion for the 4.2 Jeep as well, but it is pricey. Anyway, it runs ok, but it refuses to run 'just right' because of the single little carb in the middle of this big engine.

[ninja240z]

Dave is on target. I have used them all. SU's, 4bbl and 2bbl. All have there unique qualities. But you just can't use POS carbs and expect them to perform. Start out with fresh parts and you will get good results. I love my downdraft setups. I have a JDM downdraft manifold for a factory 2bbl,also a clifford research and Arizona Z brand manifolds. In the past Chevy and Ford and Chryler has used a 1 bbl downdraft carb in the past with good results on their straight six engines. A good seal and a low CFM carb is the ticket be it a side draft or down draft setup. Too much CFM for a 2400cc to 2800cc will actually lower horsepower according to bench dyno's.

[brokebolt]

I think the point missed here concerning manifold issues only, is that the two version of 4bbl that I have run and seen for the Z car is that, the first is a plenum (Clifford research) the second is a dual plane, log style (Bob Sharps original design) and later a true dual plane, log style (AZCars). They are not the same and do not perform in the same way. In a plenum style the air is only restricted at the runners. The plenum style, the runners are all the exact same length and diameter! Go here and look at the construction of this manifold, http://www.eng.fsu.edu/~jthagard/ (Nice work!) it is a plenum style due to the box that will be installed over the intake horns. This is how all plenums should be designed. But I've yet to see another for a Z car like this. The other dual plane style has a smoother flow pattern and here the runners too are the same length and diameter, the last runner (cyl one and six) the log turns and ends at the runner, or becomes the runner if you so would like to look at it. This is a good design because the runners snake off the log and flow very smoothely into the runners. The SU manifold for the Z car is designed like this and performs very well.

 

If you want to test exhuast gas temperatures on each cylinder (EGT) use a lazer temp gun, Fluke makes one for about 100 bucks. This will test surface temps only but is a good easy to use tool. Point at the metal base of each plug, not the cylinder head. Make sure the plug holes are clean and the plugs are in NEW condition, and use some plug thread goo for good, equal thremal transfer. This is as easy as you can get for EGT testing. I don't beleive that cylinder distribution exists on these two manifolds. Or even the SU manifold eventhough the 2nd and 5th runner lengths are shorter.

 

A better test would be to buy six "coulor tuners" and you can see the color difference in each hole and compare for cylinder distribution. Use six temp probes in the hole for the smog pump injectors and test for EGT there. I'm just too cheap to purchsae this quantity of equipment. But if anyone has one for loan or items for sale at a cheap price, contact me.

 

I have seen other manufactures that take a runner off each cyl. and run it to the carb. That type of manifold would not yeild distribuiton issues with A/F ratios but the different length runners do affect the engine in negative ways. After the butterfly the A/F ratio is not changed unless negative things happen like puddling, which is a sign of other problems. As long as the runner diameter and length does not change from cylinder to cylinder it will not affect the engine dynamics.

 

I've run them all and I like the trippple's best BUT the 4bbl has some good design manifolds that perform well. Mostly becuase the people that designed them and there demand for performance.

 

I'd like to see that custom intake linked above have a plenum with a 4bbl on it or even a few sidedraft SU's. It would be so easy to change the plenum box and play around with intake combinations with that custom manifold. Gets a guy thinking...Hhhmmmmmm.

Mike

[Guest Bee's Z]

I had Z cars, 240s and 280s, when they were new. Don't post much, but I read a lot. Bought an early 260 for my 24 yo son about 18 months ago because it was almost the most fun I ever had and I hadn't forgotten what they feel like. Still working on the 260, so I bought him a 71 240 in better shape. The 240 needed some work too. The SUs were worn out. I read all these posts plus those on 2 more sites. I saw the arguments for and against the SUs vs the 4-barrel. I priced all the options and went with the 4-barrel. I bought an Arizona Z Car 4 barrel manifold, the coated headers, and a new Holley 4160 from Summit. The manifold and carburetor cost about what one SU does from Z Therapy. Put them on and touched it off. Drove it and the performance is excellent. I understand the purists reaction to this modification, but the fact is I fixed my problem economically and the car performs like it's supposed to. For those with similar problems, I think that this is the way to go. If you can read, you can do this. I intend to do it on an L28 and put it in the 260.

 

Thanks Dave, your products are outstanding. They are everything that you say they are. I appreciate it.

[Guest Bee's Z]

duplicate

[bubbleguinea]

lets put it this way:

 

SDS blows both carbs out of the water hehehe...

 

i agree with some of the first comments...the air is a stright shot into the head with SU's...i would think they would have better performance than a 4bbl anyday...IF they are tuned right by someone who knows what they are doing.

[2003z]

I'm seriously contemplating going the 4 barrel route just for ease of tuning and simplicity. It looks like overall, performance won't be that different. I'm a road racer not a drag racer.

[veritech-z]

Did this dyno shootout ever actually occur? This is a pretty old thread that kind of started big and sort of wimpered out...that would have been something to see, that's for sure.

[Silver Mine Motors]

i personally have a four barrle manifold from arizona z car, and i would like to say that it works perfect! cold starts are a breez, it runs great and tunning is easyer then tuning my weedwacker. it has better performance, and i would tell you about the gas millege but my gauge is broken. dave is personally a great person, who always answers my questons whenever i call, even when he's busy swimming in his pool. all i have on my l26 engine is the manifold, 390cfm carb, msds header, and msd6al. over all i am very satisfied! thanks dave i will be making more orders soon.

[2003z]

i personally have a four barrle manifold from arizona z car, and i would like to say that it works perfect! cold starts are a breez, it runs great and tunning is easyer then tuning my weedwacker. it has better performance, and i would tell you about the gas millege but my gauge is broken. dave is personally a great person, who always answers my questons whenever i call, even when he's busy swimming in his pool. all i have on my l26 engine is the manifold, 390cfm carb, msds header, and msd6al. over all i am very satisfied! thanks dave i will be making more orders soon.

I will be putting the same on my rebuild. I thought I read where he said to only hook up the vacuum for the brake booster and none of the other lines to the manifold. Do you have the pcv and valve cover vent lines hooked up?

[Silver Mine Motors]

no i just put an air fillter on the valve cover, and pluged up everything on the carb.the distributor advanance is hooked up to the manifold.

[OlderThanMe]

I am concerned about you BRAAP... Too much rootbeer tonight?

[BRAAP]

Skfloiciosln.. nsjdukehjhnbme 4bbl, l-6 wtf andkksopd lmao njudbneyhqu weohjehjs a wtf jsuthebniusi hgjcnvuew lmao lakjndneioidkjed. Handiwoqplnd, jusldunb nehjdud ndu. Wnnarace?

[tannji]

Braap was drunk, but not so drunk as to foget to edit that horrible typo. Need some higher octane rootbeer, I'm thinking.

[Corzette]

Yes, there was a turboed 4 barrel that was bought recently by one of the guys here, I think it was Bob Hanvey(?) Extremely fast, widebody kit, really really incredible car. Was set up for road racing. I think Bob was going to put an RB26DETT in it IIRC.

 

I've seen others too, but that one...

 

Here's some pics: http://www.geocities.com/row4navy/rb26swap/72Datsun.html

As to this:

 

 

I guess that's the reason those same vehicles came with that AWESOME log style exhaust manifold, right? Because they wouldn't put it on there for decades if it wasn't flawed... [/url]

 

 

WOW! who makes those wheels? I need a set!