Modified inlet manifold

[Clevo120Y 815]

Hey gentlemen, I've started some development work for a blokes speedway engine and thought I would share it along the way and the things I've discovered with the new flow bench.

I've only got a couple of weeks until the season starts so this first lot of development is reasonably basic just to get some improved results to go racing with and develop some more as time goes on. The bloke that the engine is for has asked me to do the inlet, head and carb for him, he wants to build the bottom end himself to save some time as the timeframe for development work is very short.

First of all the biggest restriction in the category is the use of the stock intake manifold, I started with an 84da manifold as they seem to have the most meat in the runners to work with, the stock manifold bolted to a stock head flows between 135 and 138 cfm, the best runners were number 1 and 6, the worst were 3 and 4.

The first thing that I noticed is the abrupt turn from the plenum into the runners, the air can't make the sharp turn so becomes very turbulent and noisy before it even starts to make it's way to the runners themselves, I found big gains in just reworking the plenum area for a smoother and more contoured entrance into the runners, flow jumped to 150cfm. This is a worthwhile effort for anyone that wants to gain a bit of power just by reworking the plenum of there stock manifold without having to do anything else, a cheap improvement that will just cost you some time and some new gaskets.

I've taken it a bit further and cut the manifold up to get access further down to rework the short turns of the runners themselves to improve the flow path further down the manifold.

The engine has to run a 350 holley, so an adaptor is used, the taller the adaptor the better I found the stability of the airflow into the runners, this also gives the plenum more volume which is what I wanted. All of the speedway guys I have spoken to told me that they swap a 500 holley baseplate onto the 350 holley, so I did this and run some comparisons to a stock 350. First of all a 500 base doesn't just bolt on, you have to clearance the venturis for the butterflys to clear, I blended the base plate and reworked the venturis, with just the carbs on the bench the stock 350 pulled 325cfm at 28in depression, my modified 350 pulled 360cfm which is a good gain for topend power. The thing that surprised me was that when I flow tested the carbs on the manifold and head the modified carb dropped airflow compared to the stock 350. After probing the velocities to find out why I discovered that the discharge point of the bigger butterflies was closer to the walls of the plenum and put airflow in a position that made it more difficult for the air to make the turn into the runners, the smaller stock 350 discharged the air more central to the plenum so made the change in direction into the runners less aggressive.

So after reworking the shape of the plenum again to make the walls of the plenum further away from the carb butterflies and change the contour of the curve into the runners I got to a stage the modified carb is no longer a restriction to flow.

After that I finished the rough shapes of the inner runners and there short turn areas which need to be made taller and a wider radius, to aid in airflow making it around the corner into the main runner which leads to the head port, then I finished up the texture on the walls in 80 grit and welded it back together and try to make it look like it hadn't been played with hahahaha

The finished product now flows between 162 and 165 cfm across all the runners so that's around a 20% gain in usable flow, as a comparison a stock 2brl redline manifold flowed 170cfm on the same head so my modified 1 is not too bad for my first prototype, the next 1 will have a bit more time put into it and needs a larger plenum so I will share that when I start it.

The head is next, it is just being reconditioned at the moment then I can start on those ports, with the restriction of the manifold the aim for the head is all lower lift flow so I will show the development of that as I go as well, again this will be on a very tight time frame so just the basics will be done but will show very good results.

Here's some pics

 

manifold I started with

 

After I cut it up

 

Pics of the rough burr work showing the shape of the plenum and runners, I forgot to take pics of the finished texture before I welded it back together, I always forget to take pics hahahaha

 

Welded back together and cleaned up

 

The 350 holley with blended 500 base

 

Some pics of the roughing out of a port getting ready for some port shape changes, more on this in the coming weeks

 

[n00bus m@x1mus 465]

Good Job!!! Thats a lot of R&D right there, hope hes paying you well... i know the kind of hours spent on die grinding and smoothing things like that out let alone stopping and checking every turn with the flowbench in the process of it all.

[Clevo120Y 815]

Thanks Clint, this job is my one and only freebie, more sponsorship really, it works well for both of us, he owns the local wreckers and I now have access to as many parts for research purposes as I like for nothing, plus if the car performs well he will put a big sticker on his car for me and spread the word that I may have some idea LOL.

Your right about the hours, there is a solid 2 weeks of work in that and it's just about taking it slowly, remove a bit of material, put it on the flow bench and map the airflow, change the shape with some playdoh to get an idea of the radius needed to stop the air from shearing off the corners then put the shape into the alloy, test it again, some shapes helps some runners but not others so a happy medium for an even flow across the 6 runners is needed, I can get the 2 centre runners to flow over 170cfm but the other runners don't keep up, so a change in shape reduced the centre runners and picked up more flow in the others to get an even 164cfm average over 6 runners. Great fun but the alloy splinters in the socks get old real quick hahahahaha

[Thom 6,651]

Just a thought (you may have thought of this already so disregard if so) wouldn't the outer runners need to maintain a higher flow than the centre runners to keep the fuel distribution even between all 6 cylinders? Still, looks like your giving it a redhot go

[Clevo120Y 815]

Agreed, that's why I changed the shape to reduce the centre runners and boost the outer runners,1 and 6 flow the most at 165cfm and the centres flow 162cfm now, a priority of mine was to keep the airspeed up to the outer cylinders as well so they taper down nicely to increase airspeed with no reduction in cfm flow.

[ando76 4,354]

If you had to charge your time what would that manifold be worth? 

[ando76 4,354]

Just looking at the butterflies and noticed that the screws protrude a long way.  Most people cut them off flush and then loctite the feckers in and centre pop the edge of the thread.  small gains but they all add up.  Have you tried a twin hole spacer over an open spacer to see the flow difference.  You can also taper the two hole ones, similar to what they do with the aftermarket four barrel ones for good airspeed gains and better fuel metering. 

[Clevo120Y 815]

I would be happy with $1000, that is charging my labour really cheap plus some consumables, now that I have done 1 I could repeat the process for maybe $700. Your manifold that you developed with Mark may work better than mine and probably better value in the long run, I'm having fun mate and this is only the first stage of development, all your above suggestions are certainly on the list and when I get some more time I will be trying them all and record the results. 

[Ando81 2,949]

Great looking work there mate, seems like you are making big gains there! I bet it won't be long and your inbox will be full with guys chasing you to do performance work for their crossflows

 

 

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[Clevo120Y 815]

Thanks for that mate, I think I will have to get a few more runs on the board before the inbox starts lighting up but I hope it happens.

[Clevo120Y 815]

Had more of a play today, I removed the choke horn and smoothed it all out, put the carb back on the bench and it made zero difference to total flow of the modified carb. Saying that, it made no difference on the bench but I believe the difference would be noticed when an air cleaner assembly is installed, the top of most aircleaners are very close to the top of the choke horn and would be a restriction, that restriction would be gone with the choke horn removed. Next on my list was to skinny down the boosters, I probably made the walls of the boosters half of what they were so I could probably remove some more material if I wanted, doing this made a 13cfm gain bringing the carb up to 373cfm at 28in. I then shortened the throttle plate screws to be flush with the shaft, this amazed me as it was worth another 6cfm on the next test for a total of 379cfm.

 

 

I also did a bit of port work today playing with some shapes with pretty good results for minimal material removal, cracked the 200cfm mark with 202cfm at 550thou of lift, the cfm number isn't super impressive but what I'm happy with is I have moved the choke point of the port up 100thou in the lift range, the port is nice and quiet all the way up to 550thou then falls over, so this tells me that the shape is on the right track, so during the week I will work on it some more and get velocity readings in the port to tell me were the air is and were it wants to be. All of this is with a stock sized intake valve.

 

[slydog 7,873]

Awesome work bro...

[Thom 6,651]

Awesome work man, so with your bench can you determine what valve oversize starts to cause a loss in flow due to shrouding by the bore?

[Clevo120Y 815]

Well I think so, I run the correct size bore for the engine in the bore adaptor to give realistic flow figures including any shrouding from the bore. To come to the conclusion that the bore alone is causing the shrouding would be quite difficult I would think, if you start upping the valve size too much it can lead to other problems like the short turn can become less effective as the valve face becomes more tucked in under the turn itself, putting a 4v inlet valve in a 2v clevo head has this problem, using a smaller valve can flow more efficiently, the trick is to find the biggest valve that doesn't lead to you going backwards as well as adding weight to the valve train. 

Here are some pics of the bore adaptor I made with inserts for the crossy to give the correct bore size.

 

[ando76 4,354]

202 cfm through a stock valve size is impressive.  I bet the low lift figures are well and truly up there.  If you have a set of internal calipers have a bit of a feel around in the inlet track.  There is a choke down in there which reduces cross sectional area. 

What valve seat cut do you have and have you back cut your valves?  Are the valves 'narrow necks'?

Have you thought about tapering the inlet valve guide boss protrusion?  I'll bet my lefty that there is another small gain in that little gem.

 

Good to see the 6cfm gain from shortening the throttle butterfly screws.  I always knew they were a restriction but to have it quantified gives me a warm inner glow.  Yes I need to get out more. 

 

Keep up the good work and photos.  I know at times it is a pain to take the photos and stuff as you are working but I, and probably a hell of a lot of others, appreciate the detail.

[Clevo120Y 815]

Thanks Tony, I thought the screws would give a couple of cfm but 6 is a good result, when you think about it that is like a 1.5% increase, and chasing the 1%ers is the difference isn't it.

The valve is just a standard crossflow unit as is from the factory, just a single 45 cut on the valve no back cut and no skinny stem. The valve seats do have a 3 angle cut, 45 seat, 30 topcut and a 55 bottom. the valve seats are not new so are a little worn so redoing the valve seats again would give an increase in the low lift again plus I will be using a 5 angle on the race head, using the angles above plus a 65 and 75 on the bottom cuts. The race head will also have 1.84in intake valves and standard size exhaust valves, the valves are a single piece single groove for added insurance, they will also have a back cut, so getting good figures with the stock gear at the moment will hold me in good stead when we upgrade to the bigger valves and more angles.

I haven't even touched the C1 chamber yet to unshroud the valve at all so some more flow should be there for the taking, I will do a full test on this port today and post up the results, I just did a quick test from 400 to 550 yesterday as It was getting late, the low lift should be up as well but I don't want to speculate until I prove it.

Yes the valve guide will get some shaping next on this test head, I have asked for the race head to have the guides removed for when I do the roughing out of the port so I can shape the bosses easier, then I will go to the machine shop and get them to push the guides in until they just pop out of the bosses instead of hanging out so far as they do now.

I was happy with the carb results, I was chatting to Zok from Zok race carbs and he said he gets 390cfm out of them so I'm not too far away from the pro's, not bad for my first real go at it, cheers for your input Tony, floating ideas around is brilliant, you can only try them and see if it works or not then you know what does what.

[ando76 4,354]

Zok - Zoran he is still around. I met him years ago when he did an engine and a carb for a friend of mine.

 

Your flow figures are truly impressive considering that you have not yet touched the inlet swirl, although they are no where near as restrictive as the c2 swirl. There should be more gains to be had in the chamber. The multi angle cut is no doubt helping you. I got good flow figures from Jason's current c1 head with just bowl and chamber work on a single seat cut. I've just had Cam do his multi seat cut on another c1 head with a 1.84 inlet. I'll port it when I get back and then take it to the same bench I flowed the other C1 head to see what gains I can make. It will also have narrow neck valves so it will be interesting.

 

Do you plan on doing a comparison with head flow figures with and without the manifold? I reckon your airspeed will be good with a well balanced, even flowing inlet manifold, so it will be interesting to see what drop - if any there is.

 

A racer up in Cairns just fitted one of the new manifolds and he rang me to find out where his engine had gone. They thought they had wiped lobes off the cam the engine was so calm and happy. Shows what an even flowing manifold can do, even on a grumpy flat tappet motor.

 

Keep up the good work.

[Clevo120Y 815]

Yeah I will do comparison tests with manifold on and off, the flow figures quoted above for my manifold is with it bolted to a stock head that flows 184cfm so even on stock head the modified manifold is still a restriction but is even , still a lot better than the 135cfm it was pulling before when on the head, I'm hoping that if the port can pull more cfm that it will draw on the manifold harder and the manifold will be a percentage restriction instead of just capping flow at 165cfm if that makes sense. So my thinking is if the port can pull 220cfm and the manifold is a 10% reduction as it is now (184cfm down to 165cfm is a 10% reduction in flow) then I can still get 198cfm through the manifold if it works out that way. 

I didn't get time to work on the head today but I did some other testing today on some things I had in my head, the effect of aircleaners to flow. I tested a stock 350 holley again and my modified 350 holley, to start with I checked my notes and my first post I said a stock 350 pulled 325cfm but it was 321cfm so my mistake there too many numbers hahahaha, anyway I started with a K&N 9in x 2in filter assembly, the filter has done a few kms but in no way full of shit so I thought this was a realistic test filter. With this setup the stock 350 pulled 311cfm, a 3.1% reduction, the modified 350 pulled 365cfm which is a 3.7% loss. What I believe this shows is the low filter on the stock 350 is restrictive so close to the choke horn, it has about 1in clearance so the change in direction is more dramatic, I have come to this conclusion because the same filter pulls 365cfm on the modified carb which is less than what the carb can pull but I think that's about the limit of the smaller filter with some dirt in it.

 

 

So I put another filter on top of that one and both carbs pulled to there full cfm values, what I think this proves is even with a small carb it needs plenty of filter surface area and some height above the carb for the airflow to settle and have room to change direction. I will probably make a suitably sized carb hat for the race car that is plumbed to an airbox in the cabin with a large panel filter, then duct some cold air from above the dash to feed the airbox.

Don't choke your carb with small filters guys.

 

[ando76 4,354]

14" x 3" minimum and a k&n stub stack and extreme top filter for the win.

[Clevo120Y 815]

^^^^I agree, I would like to test the extreme top, being able to pull air from directly above the carb would be a benefit I think.

[ando76 4,354]

my extreme top has the same dirt pattern above the carb after every meeting. tells me that it is getting the majority of the air from there. I run a modified K&N stub stack on my carb as well.

[Clevo120Y 815]

Started on a new manifold, this one will have a lot more work in it, I am doing this primarily to get more plenum volume and hopefully pick up some cfm as well. I cut it up similar to the first one but a bit further up towards the carb mount, this left more material before the short turn into the centre runners to work with, I also cut along the bottom to get access to the bottom of the manifold, I have removed the floor of the plenum and the runners to use the space that the water in the manifold normally uses, this is the main part of gaining more plenum volume that I'm chasing. I will be making the inside of the manifold out of sheet ally to get the shape I want and the part I cut off will simply be cap that I will weld back on so the manifold looks stock again. Were I have cut the end runners off I have removed the floor to give access to the water area again, I will be tapering the floor from the runners to the plenum so It's not a big blunt step up, anyway here are some pics of what I'm doing so far and I will keep this updated during the week as I work on it, the plan will become clearer with pics as I go. 

 

cut up top view and bottom view, I have removed the floor in the main body already in this shot

 

 

here is the main body that I have started removing the unwanted material from

 

 

First pic is of the runner section with the floor section removed, second is the other runner section with the floor still in place, these are the sections that will have the blunt stepup blended with ally sheet to make for a smoother flow, the bottom pic will also have the extra water section to the side plated up so it is the same shape as the first pic.

 

[slydog 7,873]

Awesome start bro...shows how much thought and work goe's into these things.

[gerg 10,871]

Wow the stocks manifolds really are rubbish!

[Clevo120Y 815]

Yes a lot more thought in this one and a lot more fabrication to come, Yes Gerg the stock manifold really is rubbish hahahaha, the 1 thing that is a bonus with them is they have a decent amount of material to work with.