The Stovebolt Site Forums The Shop Area Engine Shop DIY intake manifold

Hi folks I may take this project on,, anyone been down this road?

What is your goal, and how would fabricating a manifold accomplish it better than an OEM item, or one of the aftermarket manifolds that are available? Do you have the engineering background and the shop facilities necessary to evaluate your project once it's been completed? I would think a flow bench and an engine dyno would be necessary, at a bare minimum. Do you have the foundry facilities available to make castings, or do
you plan to use welded exhaust pipe, etc. ?

One of the projects I have in the pipeline (if I live long enough) is making a 3-carb setup for a 230 engine, using Keihin side draft carbs for a Harley-Davidson motorcycle. That will require fabricating three small adapters from aluminum plate and conduit to transition from the carb bases to the cylinder head.
Jerry

I like to do weird things sometimes just for the heck of it but you need to take a hard look at the end product after all your work and dollars spent. You will still have a low rpm engine with siamesed ports and four main bearings. If 6 in a row is what turns you on check out the wicked Aussie 250 Ford 6 and all that is offered with it for go fast. Paint it grey or blue and slap a Bow Tie sticker on the valve cover and you will be time and money ahead. If it must be Chevy then follow Jerry's "Dumb" 4.2 Atlas engine build. With this engine GM finally, after just 65 years, offered a six that a rodder can appreciate.

Evan, I believe his engine is a 292, which is a little easier to hotrod. It does need some tinkering with the intake ports to eliminate the bosses for the head bolts that bisect the ports.
Jerry

The lump port conversion to the 230 cylinder head (same as a 292) frees up the laminar flow enough to overcome a lot of restriction and turbulence. A roller cam, a rev kit, and some extensive valve work and pocket porting, followed by flow testing for equalizing pressure rise/drop for each port, followed by dyno testing for final mixture and ignition timing tuning is obviously going to be necessary. The small port adapters needed to mate the side draft carbs to the intake ports are extremely simple to make and flow test. They should be no more than 3 inches in length, probably less, with NO turns- - - -just a straight passageway from the throttle plates to the ports. A simple water manometer, a shop vac to provide airflow, and a few functioning brain cells can yield a lot of useful information about port flow rates. Then it's on to the dyno.

Making a 235 head and manifold flow better is about as likely as finding a chicken with lips!
Jerry

"Hi folks I may take this project on,, anyone been down this road?"

Bo,

Check with Joe Hand on this forum. He made a beautiful manifold for his '37 Chevy car. My street rod is a '32 Ford roadster, not a Chevy, but if you get into that fabrication you may find interesting the cold air ducting I made for the. air filter. To me making that kind of stuff is a big part of the fun of this hobby. I even dolled up the tig welded aluminum ducting with polished surfaces and engine turning. I'd be glad to send you a photo if you're interested.

You know what they say, nothing ventured nothing gained. I like to tinker so I have ventured and done two intake manifolds. One for a 261 and the other for a later 250. They both worked, to what degree remains to be seen, but they did not fall flat on their face, lol. I built a 2X2 intake for a pair of Holley 2300 carbs for a 261. No one made a commercial manifold for that set up so I made one. It worked pretty good. It was pretty basic, kept the overall volume of the interior chamber down to keep the velocity up, used a shop vac, a plexiglass top (for mock up) and an old fashioned smoke bomb I bought in South Carolina at a fireworks place to look at the smoke flow pattern inside the manifold and shaped the inside to go with the flow so to speak, then welded the aluminum plate on top. It worked fine. I would not do the smoke bomb thing again, lol. Whether it worked as good as it could have if I had access to professional equipment remains to be seen, but it was fun and frankly that is all that matters because life is short.

Yes, getting a 235/261 head to flow is a near impossible challenge, particularily on the exhaust side, but there are a few things you can do to improve the flow. Just keep in mind, no matter what you do, it will never flow well. For example, if you run your finger down the far side of the exhaust chamber, you will feel just a little tiny bump/depression. This little bump causes the exhaust flow to stall at about .300 lift. So one thing you can do is use a piloted cutter and take the bump out, not too much, just enough to straighten the wall out. I also like to hog out the exhaust valve bowl just a little and install 1 5/8 small block chevy exhaust valves, and a little bit of relieving to take advantage of the larger valve. Might not make a big difference, but makes a little. I also generally like to hog out the valve bowl for the intake side and install 50-52 chevy powerglide 1 15/16 intake valves. Do a little hand blending and a little polishing. I occasionally will machine the bump in the head at the intake port (helps keep the manifold retaining ring in place) to either remove it (if you are running a Clifford 2X2 like I am the manifold does not use the retaining rings) or take it out as much as possible, and match up the intake manifold. I don't have any quantitative analysis to show what improvements if any those modifications cause, but my motors run pretty well, so I think they are helpful, but what do I know, I am just a backyard hacker at heart!

I have also done the bolt in lump port conversion for the 230/250/292 motor. Its a good project. You need a few tools, but you can do it at home. I own a sissal lump port head (a photo of it is in Leo Santucci's book. It was originally his head with epoxy lumps for a turbo application). Using some dividers, I traced both heads and the results are reasonably close. The lumps keep the velocity up after the bolt boss is removed, changes the flow pattern and improves the short side radius. Pretty fun project that you can definitely do at home with a few basic tools.

Following to see what info you might obtain. My last post a month ago went so far off track with tales of past dirt racing and unnecessary banter so i abandoned ship. Hope you have better luck. Pm if you want BoToepfer I am on board with your efforts to play around and have some fun.

Wolfcub,Dragsix,Yar,HotrodLincoln,Coilover,, Thanks you all for you posts, Here is what I am after, I wish to build this for the cool factor not a drag racer , but a mild hot rod, I would love to see pictures of things you have built. I like the overall look of the PSE manifold, That 12 bolt shows on his web site, but I also like the home made look of fine TIG welding. I wish to bend the tube/ pipe is a slope and perhaps hang 2 two barrels on it, I do not have any tech background other that I can stick snot to a fish in welding speak !

Jerry Funny Thing you mention Harley carbs I thought that would come in top of th elist on the cool factor,, I saw some parts at a swap meet two weeks ago but the guy thought it was barrett Jackson time

The Keihin carbs are available brand new or in good used condition on Ebay all the time. They're also common to a bunch of riceburner bikes. I'm thinking about using three of the diaphragm-piston carbs designed for a bike with approximately the same displacement as one cylinder of an inline six, since the firing order of stovebolt engines has only one cylinder at a time being supplied by any particular port. That's why running dual carbs is such a boneheaded stupid idea. With one carb per port, the size of the carb can be tailored exactly to a specific engine displacement and RPM. Then the only gremlin to battle is keeping all three carbs synchronized. The upside is the ability to impress the mouth breathers at a car show who don't have the common sense to pour pee out of a boot with printed instructions on the heel!
Jerry

Hear is what I have learned from making intake manifolds. Back when I was drag racing Pontiac's, I had more time then money. I always wanted a tunnel ram so I whittled out some flanges and set about bending heavy sheet metal. I borrowed a friends mig welder and hooked it all together. It wasn't pretty but functioned almost as good as what I had been running. Turned out the engine didn't need the extra length runners anyway. The second manifold was a little lower but made much better. It too almost worked, but fell off at high rpm due to runner size and the plenum shape. Lesson learned, keep with what I had.

After I got my '37 on the road, I cam across three NOS Rochester model H carburetors from 1961 Corvairs. They are not very friendly carbs to work on, no moving parts, so no metering changes with throttle opening. To change metering, you change the jet which effects the whole throttle opening range. The manifold was easy enough to make with rectangle steel tubing and some flanges cut out from 3/8" plate steel. I used a drill press, hack saw and lots of files, sanding disk and grinding wheels. I had the benefit of an extra 250 head and block to work from. The engine ran well when jetted up, but as you can imagine, the fuel mileage suffered. Jetting lean brought the mileage up, but then it would lay over at higher speeds. Cold weather was a problem since I had no chokes or heated manifold. The next manifold built was the same design using the three Model H Rochester only with a header instead of the cast manifold. It was more of a tapered pipe with six little stubs and a single 2 1/2" pipe down and out. Since I changed nothing else, I saw no improvement in performance. The local drag strip was near by so I went and made six runs back to back. The following week I went back, same general weather conditions, and made six more runs back to back only this time with a stock manifold, Monojet, and factory exhaust. All twelve runs were with-in .005 seconds of each other and the MPH stayed with in .5 of each other. So basically it was a draw. I could say I built a manifold that run as good as a stock setup, or you could say it only ran as good as a stock setup, either way it made no difference having three small carburetors or one sized properly. Had I made the header with really long head pipes with 1 1/5" pipe diameter, I probably could have improved the lower rpm torque, but I didn't want to try and snake them down through and around the steering / frame area.



Jump ahead a year or two, I came across two Monojet's the same part number, same metering, linkage the whole bit. When building this two carb manifold, I used the same size rectangle tubing and some more flanges I cutout. I added a heating chamber under the manifold which bolted to a stock exhaust manifold. I now had heat out to the ends and under each carburetor. I took the time to round all the corners instead of just squaring them off. It looked really good, but doubling the carburetors where only one was needed did nothing for how it ran. I went for a decent drive and could actually see the fuel gauge moving. At full throttle, it did run pretty good but you had to get the truck rolling first. It didn't take to many trips before this went in the basement for storage.

Next, I talked with Jon Hargrove about the W-1 carters and decided to give them a try. I dug out the dual carb manifold, made adapters to change bolt patterns for the W-1's and added a different linkage pivot. I have been running these for three years now and am really pleased with how it performs. The W-1 is super adjustable with multi-step metering. I don't believe the intake has much to do with how the engine runs if the carburetor choice is right.
I measured the stock manifold inside and choose tubing very close to that size, I also made the runners the same length. I spaced each carb 1/2 way between 1,2,and 3, and 4,5, and 6 cylinders. Each carb can feed all six cylinders. The real advantage is the end cylinders have better access to the fuel mixture so all six cylinders run even. With one central carb, the center cylinders always ran richer then the ends, the spark plugs showed this. Fuel mileage is now higher then it's ever been, and performance is better. Our local drag strip closed so I can't prove it, but seat of the pants tells me it's running much stronger. With the addition of an Air/Fuel ratio wideband gauge, I now have it dialed right in on performance and fuel economy.

Send me a PM with your e-mail and I can get some photos out to you. If you go down this road of making something, stick close to the OEM measurements and be sure to add some type of heat. Aluminum would be easy to work with if you can weld it, but steel isn't all that bad. When welding the flanges to the runners, be sure to have it bolted to heavy plate steel or a head to absorb the heat and keep warpage to a minimum. Trying flatten out steel flanges is not a easy thing to do, I have been there!

Dad has a couple of Pro-version engine analyzer programs, so I played around with them trying to determine what would help. I would go to extremes just to see what changes I could make. Unless I was willing to raise the rpm, nothing was making much difference. The really long (35" x 1.5" diameter ) head pipes did improve the torque, but would have been a nightmare to build and install. Cams didn't make much difference as long as I kept the rpm parameters the same. Sticking to 4500 rpm redline really limits the amount of improvements that can be made. Using the dragstrip time sheets and knowing the weight of the truck, I calculated out the HP needed to run the mph (78.5), The engine was making about 140 at the flywheel and 110 at the tires, pretty much stock spec's for a 1970 250. Figuring off the et instead of mph, it made 150 and 120 at the tires.

We also have a SuperFlow 110 cylinder head flow bench. I used my second cylinder head and ported the exhaust and intake runners. I gained 18 to 20% more intake flow and around 15% more exhaust using stock intake valves, no lump ports or cutting of the head bolt boss, and bigger exhaust valves. I added epoxy to the intake floor to raise and change the short turn radius, but kept the head bolt boss. On paper it looked good, and the analyzers both said it should pickup hp and torque. It didn't, it actually ran the same at full throttle, but ran terrible at mid throttle. Around town you couldn't tell any difference. It took about a year of endless test drives and swapping of parts to figure out why it wouldn't run. With the head back on the flow bench, we determined the exhaust flow to intake flow ratio was way off. At mid throttle, the exhaust was working so good, that when the valve openings overlapped, the intake mixture was being sucked out the exhaust causing an extreme lean condition. This head is now in the parts that didn't work bin. I finally have learned that if no other changes are to made, don't bother looking for HP or torque. I ran all my stuff with the same 2' exhaust, gear ratio, tire size, and stayed at the same rpm limit. Thats why nothing ever really changed. And when I say this head wouldn't run mid-throttle, it would shake the engine trans so hard, it broke the shifter mounting points off the transmission! It was a violent shake, the only way out was go full throttle or let off.


Joe

Joe, that's the most logical performance analysis I've seen on this forum in a long time, and it's based on your own experience, not some cut and paste information from some obscure source on a website somewhere, submitted as "personal" experience by some windbag keyboard jockey. Your research reinforces the impressions I've gotten from decades of round track racing- - - - -either build a street engine, or a race engine, but don't expect race performance from anything that can be driven on the street at a variety of speeds and traffic conditions. If an engine is designed to go fast and last a short time, use it for what it's designed to do, and be willing to put up with all the downsides of your work. Doing that on the street will make you very popular with your local traffic court judge- - - -as he puts the vacuum cleaner to your bank account!
Jerry

Take a pass on the Clyde Norwood reproduction intake manifold. I had an original manifold which I sold . It is really a race manifold and not a street manifold. The PES intake requires the use of Clyde's specific bolt in lumps. Works great for the intended use but no so much for a street car or a drag motor, not really. I ran that intake on an drag altered and it was a bear to run on gas. Just did not run well on gas for that kind of use. Really, it was designed for round track use where the manifold is at its best with the motor running at a certain sustained rpm. The only time it ran well at the drag strip was on alcohol. I never tried it on a street motor but I cant imagine that would be an easy project.

One of the more interesting intakes I have seen was a modified Clifford 3X2. At one time Clifford made a 3X2 cast aluminum ram intake. Really an independent runner manifold originally designed for three Rochester's but most ran them with three holley 2300 carbs (500 0r 350 cfm). In original form it was a strictly race manifold. The one that I saw many years ago was on a 50s pickup truck (and have a photo of it somewhere. I thought it was so cool that I ended up with one myself for a future project. Just did not get around to the project, lol) Jim Tinsmith made a rectangle box for the top, thus creating a plenum. Set it up for three Rochester 2 bbls with progressive linkage. Fit under the hood of the truck. Man did that manifold run well. So you have that option as well, use an existing manifold and modify it. Like I said before nothing ventured nothing gained and life is short so go build an intake if you want and see how it comes out. I did and it was a good learning experience.

I try stuff for the fun of the build, trying to figure a good way to make it with what I have. Even if it's a total flop, I still had the fun of making it. I will build or modify before purchasing new every time. If I can't get right, then I pull out the catalogs.

Good morning Bo.

Carbking (Jon) posted some information on this forum concerning multiple carburetion indicating that good results are available if done properly:

https://www.stovebolt.com/ubbthreads/ubbthreads.php/ubb/showflat/Number/839696/Searchpage/1/Main/123382/Words/%2Bcarbking+%2Bdual+%2Bcarbs/Search/true/re-dual-carb-setup.html#Post839696

Also Joe H points out the personal benefit of taking on a challenge like this. Even if the results are disappointing you have the fun of the experiment and maybe learning some new skills. Sometimes you get a success and sometimes not. I have a good buddy who although now retired worked a whole career high in Toyota management. People in the vehicle industry all know each other. So when Edelbrock wanted to develop manifolds or other pieces for Toyotas he would arrange to borrow vehicles or engines from my friend. Even after extensive R & D the Edelbrock pieces sometimes did not yield an improvement over the OEM parts and the Edelbrock engineers freely admitted that. So there are successes and failures in this.

To me the fun in this hobby is in doing these home projects. My 2 recent ones are adapting a tandem master cylinder into my restored '36 Chevy pickup and building a cold air intake duct and plenum to feed cool outside air to the air filter of my sbc powered '32 Ford roadster. Next will be seat belts in the '36.

Very coo lYar I am on the ground looking up to the lowest tier of knowing anything ! haha, and respect the knowledge shared herein