Technical Making decent power with trips?

Hey all! I'm working on putting together a 3x2 setup for my 331 Chevy. First off, I would like to state that I am aware that a single 4bbl on a well designed intake has been dyno proven over and over to be superior to just about anything besides tunnel rams or FI for peak HP. With that said, my little Chev is built entirely with 1960s tech, and I'm trying to make 1960s power. Think of this more like an exercise in getting the most out a setup that time p***ed by. I'm not looking for maximum power, per se, but the max from this particular combo.

The intake I have is an Offenhauser 3558. I have heard that Offy tripower intakes aren't really the greatest design, but has anybody done any modifications with success? Porting, some epoxy work to the sharp turns, etc... thats the main thing I noticed with it is the abrupt 90° turns from the center carb. The transitions when all three are open don't actually seem that bad. Overall it's really not any worse looking (functionally) than the Z28 style Weiand intake I am currently running.

For carbs I am running 2Gs, matched pair for end carbs that I am modifying into true secondaries. My friend (jebbesen here on the HAMB) gave me a set of J2 style throttle levers that he made,, and is going to help me machine some new throttle plates out of br***, which I will probably lap in and maybe use a little epoxy for a perfect seal. Idle circuits are to be filled with epoxy, and power valves deleted, along with chokes and related hardware.

Some quick engine specs:
I'm running what I'd consider a pretty decent street cam for the era, an Elgin 1091P. Solid flat tappet with .504 lift, ~290adv. duration on 105lsa. Heads are 461 heads with no work done except for hardened seats and "Z28" springs. I haven't cced the chambers, but ***uming they are on the larger side I calculate around 9.75:1 or so.

One thing I'm unsure of is how I want to handle carb spacers. I was initially thinking a fully divided spacer on the primary, and open on the secondaries. My train of thought was to help low end a little when driving on just the center carb, but then when the end carbs kick in the open spacers would help out on the top end. What are some thoughts in this department?

Another area that I would love some input on is air filters. I will probably just run screens at the strip, but I don't really want to choke it out with those little 4" filters you usually see. They do look cool, especially with the louvered bonnets, but I'd like to figure out something that is breathable enough to perform when that little Civic at the light wants to throw down.

Any other advice or input on getting the most out of this project is welcomed and greatly appreciated! I'm really excited about this project and I'm really looking forward to seeing what it can do.

 

I'm working on basically the same setup you just described. What's it going in?

 

It'll be going in the '60 Biscayne that's my profile pic. I'm trying to make it into a mid-60s street/strip machine, with a lot of influence from the Modified Production cars of the day.

 

It's been my experience on the dyno that you can't fix a pig but you can improve a decent manifold. I've seen air flows so bad you would have swore it was an electrical problem, and that was on an open single plane manifold. I changed the intake manifold and the difference was 80 hp and 90 ft torque.
Improvements to the plenum and the one inch spacers sound good. If you start making major changes its like head porting you can make less power easier than making more.

 

Rough idle quality with heavy lope - (Note: Intake vacuum will not operate power brakes, etc.) Good mid to high RPM torque in 3800-5000 range. Good high RPM power, operating range 3200 - 6500 RPM. Average to poor fuel economy, definitely do not use for towing. Increased compression ratio required 10.5 to 1 to 12.0 to 1. Compe***ion engine modifications required. Use only heavy duty manual or automatic (with high stall converter) transmission. Recommended spring pressure 125 lbs. for valve on seat; 325 lbs. for valve open. Axle ratio at 4.20 to 1 is best. Compe***ion headers and valve job recommended. Recommended for oval track or bracket drag racing

 

Are you going with flat top pistons or dome? I have a 333 ( 327 .040) with L2166NF040 pistons,decked and 492 2.02 heads shaved to 61 cc chambers. I used to have an Offenhauser 3x2 on it,then an old Torker, and an old Weiand X?? , but it´s much happier with an Edelbrock Performer RPM intake. Better low end and still very zippy in the high rpms.

 

Forgot the the cam, its also Performer RPM, 234°in/244° ex @ .050 , 112° LSA, lift is 0.488 in/ .0510 ex
long tube headers an 2,5" exhaust system

 

As far as air filter restriction goes, a single large filter is much more efficient (less restrictive) than a bunch of small ones. This is a bit of a simplification but essentially each cylinder is drawing in air only one forth of the time (the intake stroke). This means that for a given restriction a filter large enough for one cylinder will serve four equally well. A typical combined filter as seen on factory triple setups has a lot more area, and therefore less restriction, than two of the little chrome pots we see on hot rods. I've measured the actual area of the louvers and slot that admit air into one of the bowl filters on the quads of my '33 (when I got it) and found it to be less than the carb throat area. That's like having the choke pulled halfway out all the time.
regards,
Phil

 

I have run a number of multi two barrel carb setups. Anywhere from three to six. The common trait that the most successful ones share is not running a big cam. You need good air velocity through the carbs to meter correctly. In some cases carb spacers can help with that. And none of them are "set it and forget it" kind of thing until you get it sorted out. A Uni Sync, or two, will be your friend. Sounds like you know what you are getting into, so have fun with it.

 

Sounds almost exactly like my next build. I have another 327 block that is already .040 over. If it checks out ok I'd like to .060, find another forged truck crank, and throw some L2166NFs in it. I've got another set of 461s that are rusty enough they'll need milled anyways, so I'll probably do a little work with the die grinder and get them cut down to 60ish cc. I'll probably run a 4bbl on that one, unless I go crazy and get an X1 or something haha

But yes, the engine I'm working on now has TRW flat tops, L2165F. I didn't want too much compression because where I was living you couldn't get very good gas. Where I live now there's an oil company just a few blocks away that has 110 at the pump. 11.5 to one is not a problem now!! Except for my wallet...

 

You're talking my language!! Eventually I hope to get to that point. I am on the hunt for a 4.10 ge****t for a drop-out Chevy rear end. I only have 3.70s in there now.

 

It thought “trips” were on LSD... guess I’m not old to learn something new..

Offys sent the mixture from the carbs all to the front the under the floor you see to feed the intake runners that’s why they are the POS when compared to other manufacturers. I had one once and almost took a hole saw to the 6 carb holes to get to the lower level. You can find some guy on line who screws with the Buick nailhead ones that are made the same and makes them perform.

 

I get where you're coming from for the period correct look and build. But here's a couple articles it might be worth reading. They're for y blocks, but there's a lot of dyno pulls with different manifolds. You need to move a lot more air. Better heads more cam, more cid, etc.

the second article really compares the porting problems on the offy manifold. There's enough pictures you can probably guess if it's similar to the Chevy version. It's not encouraging. Down about page 9 there's a comment about the air cleaners that shows the numbers made in the point above.

Reading is free so you're only out a little time. But I suspect looking for a better manifold is going to be a better use of your time and money than dealing with what you've got.

https://www.eatonbalancing.com/2013/12/18/y-block-ford-3x2-intake-testing/

https://www.eatonbalancing.com/wp-content/uploads/2020/10/YBlock-146-Craine-3X2-Test.pdf

 

Thanks for those links! That's a really good read, and some good thorough testing. Just looking from the outside (and it's hard to tell exactly what's going on with runner routing with the stacked ports of a Yblock) the Offy 3558 they make for the SBC looks most similar to the Weiand or Eddie 553 in the article. That Offy he tested really looks exceptionally terrible! It sounds from the description that it's sort if an open plenum with longish dividers. The model I have is definitely dual plane, but it does suffer from some of the other qualities mentioned. The casting date on mine is 2005, so I don't know if the design has been changed at all from the 60s/70s.

I'll tell you what that article really makes me want to do... I know there's a guy across the river from me with an engine dyno. Maybe I'll have to go try to woo him with some cheap beer when I get this setup built and see how it compares to like a Performer or any of the aluminum "Z28" style intakes that have been made forever.

I'm with you tho that maybe I should be on the hunt for other intakes anyways. It seems like all the 3x2s made for sbc are 5.5" carb spacing, so I feel comfortable moving forward with carburetors and linkage. It would be no big deal to change intakes if all dimensions are the same.

 

I am also doing a similar build. I have a late model Vortec 350 roller cam block with Vortec heads and an Edelbrock tri power intake. My personal (lofty) goal is 400hp. For your setup, I have read - don't remember where - that the Offy is a better intake over the Edelbrock for the SBC. If they made one for Vortec heads, I would have used theirs. I have an old HRM article that shows the Edelbrock 3x2 is at least comparible to an Air Gap with a 650. If I remember I will post a pic or two of that.

For carbs, I ported the venturi enough to clean up the casting mold lines and minor imperfections. I was able to compile enough venturi clusters with the air bleeds orientated in such a way that I could drill and tap for screw in air bleeds. For jets, I threaded the Rochester main bodies to accept Holley jets (much cheaper and easier to find). I also removed the air cleaner stud mounts that get in the way of airflow.





For the intake, I port matched it to the heads and cleaned up the core shift in the throttle bores. I also hand sanded a fillet where the throttle bores intersect the plenum to make the air flow (hopefully) better rather than a machined 90* p***ageway.













I'm still scheming air cleaners. I had no idea those 4" ones can essentially flow 330hp and that's all she wrote. I am also going to try 1" open spacers under each carb. I'm quite a ways off from testing, but hopefully my setup will be running soon. I built my carbs similarly to how you describe above. Best of luck!

 

HRM January 2002. Basically they tested a stout small block with a handful of tunnel rams, a cross ram, a C26 dual quad, then an Edelbrock tri power and an Offy 6x2.



For the tri power and 6x2, they changed up the baseline to a smaller cam (212/212 @ 0.050”, 0.435”/0.460”), an air gap, and a 650. Best I can figure as they didn’t come out and say it, this combo made 406hp and 428 lb*ft.

The tri power was lean and they weren’t able to change jets (no porting or mods either), and the 6x2 was untouched as far as tuning, too. Nevertheless, an interesting article. The tri power could hang with the air gap within about 10 numbers, so I think with some work, could be on par with the “gold standard” for a street setup.








Sent from my iPhone using H.A.M.B.

 

If you like the look of the three air cleaners, just replace the skimpy louvered ones with open ones. OTB Gear offers some nice ones with finned tops that will match your valve covers. I’m not saying they flow as much air as a single one, but at least you get to see there are three carbs under there - otherwise what’s the point?

 

I ran three deuces on my Model A with a 283, made plenty of power and was fun to drive.

 

Killer work, man!! I was thinking about gutting the airport as well, glad to see it can work out good. I love the idea of Holley jets, too, and the changeable bleeds. I think that right there is a big part of why multi carbs never dyno as good as single 4bbls; people don't take the time to really fine tune them. You can see tests where a carb out of the box vs tuned is worth a good chunk of hp, but that doesn't seem to really be applied to other configurations. At least not on common motors like the sbc.

Seriously, though, work is very encouraging!!! Please keep me posted on your progress with it as you get it running, I'm very interested.

 

Thanks. I think once the setup is up and running, the next low hanging fruit would be to trim the throttle shafts inside the bores to be more like a Holley shaft (instead of a slot cut into the shaft that the throttle plates live in, the throttle shaft is milled flat for the throttle plates to screw to).

After that, I think some sorcery with the boosters/Venturi clusters is worth a look. I don’t have sophisticated methods to test all this so I think progress will be slow. But it is fun to think about.


Sent from my iPhone using H.A.M.B.

 

I see a couple glaring issues with the build. Both being the Elgin 1091P camshaft you chose. First it's a split lift cam, so the .504" lift on exhaust is great, but it's a .538" lift on the intake, and with 461 heads, and even better springs, you may see spring bind if the valve spring seats weren't relieved. That's way too much lift for the 461 stock heads valve springs total height.
Second is the crazy close 105 LSA that will sound great, but not make any power below about 3500 rpm's! That cam is listed as a 3800-6500 cam, and not something I'd ever install in a mostly street driven engine. I'd want to be around 109 LSA or more for a mostly street driven engine. If the engine isn't in the car yet, I'd seriously reconsider a different cam with around ,500"-.510" lift max, and a LSA around 109.

 

I run the 58 Caddy tri power intake and carbs , small center and big end carbs. I installed bigger jets. I can be running 90 mph and kick open both end carbs and it's like instant acceleration setting you back in seat . A friend driving behind me said when I opened it up black smoke from exhaust and car took off like he was sitting still . I run the Crane hi rpm drag cam that makes power between 3600 and 6500 rpm Also ported and polished heads with lightened and polished big valves , and 12 to 1 compression

 

Those look real sharp! I do agree with seeing the carbs almost being a necessity.

 

I think you have that backwards... tight LSA generally produces more low and midrange torque than a cam with a wider LSA. Thats why circle track guys use them, more torque out of turns 2 and 4. You can look up numerous published dyno tests that corroborate that.

The 1091P is darn near a square grind, just a little difference is duration 256/264 @ .050. Lift is .504" on both I and E. I see the listing you are referring to when you Google it, but it's incorrect. Both my Compe***ion Products catalog and my cam card straight from Elgin have the specs I outlined above. Edited to add that those specs were verified by myself when I degreed the cam.

https://www.compe***ionproducts.com...04-105-LS/productinfo/ELGE1091P/#.YBR7hVNMFPw

 

I think you should look up some of Little Man's builds, especially the little model A p/u, although he ran a 6 carb intake the meticulous work he performed on those carbs to eventually get a 9 second time slip is simply amazing !

 

^^^X2^^^


Sent from my iPhone using H.A.M.B.

 

Here is my 2 cents on this subject. In my opinion tri power set ups can be a real kick in the pants. I have driven - raced several different versions. 421 Pontiac, early 60s Model A with a stout 301 that really hauled *** and the 406 sbc I had with the holley Tri power set up . If you are going to use 3 rochester 2gcs on your set up make sure the outer carbs have the correct base plates with no idle circuits and that the throttle plates seal very well in the bore. Make block off plates to seal off the secondary carb openings on the intake and tune your engine at idle with the primary carb only. You may have to drill out the idle circuits depending on the cam and CID of your combination. After that install the outer carbs and set up your throttle limkage.

 

You're wrong. A narrow LSA creates more overlap that means the intake and exhaust valves are open at the same time, nullifying the low end power. I've been building SBC engines for 50 years, and those circle track guys go with tight LSA's to make high winding engines. Not sure where you got your info, but it's dead wrong.
Check here:
https://www.enginelabs.com/engine-t...lobe-separation-angle-and-power-relationship/

Even Elgin's own site calls that cam a 3800-6500 rpm range, so not sure what data you got that defies their own specs?

 

The article you just linked directly contradicts what you are saying, and supports what I said about tight LSA improving low end torque. Here are a few quotes from the article:

“The tighter the lobe separation angle, the peakier the power curve will be,” confirms Bolander. “It produces peak torque earlier—coming on quicker and stronger—but also it falls off quicker too. On a torque graph it tends to resemble a triangular shape.”

“On a naturally aspirated engine, the lobe separation angle has an effect on whether the engine reaches peak torque a little earlier or later in the rpm range. Typically, narrower lobe separation develops peak torque at lower rpm and widening the separation tends to build peak torque higher in the rpm range."

To put that another way, narrow LSA=high peak torque at low rpm, wide LSA=lower peak torque at higher rpm.

As for my cam specs, Elgin's own website doesn't even list specs for the 1091P. I can link to the Comp. Products page for you. According to them, and my cam card from Elgin, power range is 3,200-6,500, well within reason for my heads. Which is moot anyways, because I was disputing the grind specs that you called out, not the operating range.

https://www.compe***ionproducts.com...04-105-LS/productinfo/ELGE1091P/#.YBlW-apKg1I

Doing something for a long time does not inherently make a person good at what they do, it only makes them more confident. It is entirely within reason for someone to hold onto misconceptions for many years without acknowledging they are wrong.

 

You're miss reading it. Peak torque comes on earlier, but don't take that as "peak torque comes on at low rpm's". It's just earlier, not down low. It's earlier, but still not a low rpm torque range.
“The tighter the lobe separation angle, the peakier the power curve will be,”
This cam has a very narrow and peaky power band. It will come on strong at 3200, and fall of quickly at 6500. Doesn't sound like a nice cam for "trips".

How do you dispute the grind specs when every site that lists the Elgin 1091P lists the same specs of .538/.504, 290/295 duration, 105 LSA. And they all list it as a "circle track cam" with 3200-6500 rpm range?
Do you think 3200-6500 rpm range sounds like a cam that makes low end power?

Go ahead and use the cam, but I guarantee it will be too high an RPM cam, and too peaky for most street use. Better have some low gears, and manual trans, or a big torque converter. I'm done trying, as you're set on making the mistake.