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Carb head combustion chamber question.

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GPGoverMPG
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Carb head combustion chamber question.

Post #1 by GPGoverMPG » Sun Oct 28, 2018 10:05 am

So I do plan on running the 1131H 390 pistons (about $150 for set of 8) at zero deck. The valve pockets are +8cc which leaves me needing about 6 to 8 cc to get the compression where it needs to be. I mounted the head on the block and scribed the cylinder on the head. Do you think it's a good idea to try and get the volume in the combustion chamber rather than having the pistons cut. Leaving the quench area alone and opening up the valve and plug area seems like a lot of material. After polishing and getting the valves set it the head It looks like I could get more than my 81 82cc mark and finish volume with milling the head. I contacted SI Valves and Lee was super helpful so I'll be using their 194/160 valves. Thanks for the help. I included a photo of my mocked up intake.
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Re: Carb head combustion chamber question.

Post #2 by GPGoverMPG » Sat Nov 10, 2018 8:43 am

So here is an image of where I'm at. I cc'ed the combustion chamber and got 83cc with the stock valves. I have not received my new valves yet. I'm unsure what's going to happen with the new valves. 194/160 ford length from SI Valves. I hope I get enough volume to lower the compression were I need it. Any recommendations on improvements are welcomed. After the heads get screw in studs and the new valves installed I'll disassemble finalize and polish the chambers. I'm using a 150cc syringe, Lexan, and Marvel mystery oil to cc the chambers. Any ideas on getting the bubbles out from under the Lexan? Thanks
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Re: Carb head combustion chamber question.

Post #3 by pmuller9 » Sat Nov 10, 2018 10:34 pm

GPGoverMPG wrote: I'm using a 150cc syringe, Lexan, and Marvel mystery oil to cc the chambers. Any ideas on getting the bubbles out from under the Lexan? Thanks


Looks good so far!

Seal the Lexan to the head with a coat of grease.
Position the hole in the Lexan so it is on the edge of the combustion chamber and tilt the head up towards the hole.
All the bubbles should run up the Lexan and out the hole.
See post #177
viewtopic.php?p=606041#p606041

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Re: Carb head combustion chamber question.

Post #4 by GPGoverMPG » Sun Nov 11, 2018 9:10 am

After checking the link I think the Lexan I'm using may be to thin. I have not got my block bored .050 yet is using the head gaskets fire ring as a guide just to much? I think I will need to get the valves unshrouded more to work best with the larger valves. Anyone have pictures of a good '82ish carb head combustion chamber with the larger valves installed? I kind of interested in the quench side of the chamber. Most of what I found was EFI or early 240. Thanks again
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Re: Carb head combustion chamber question.

Post #5 by THE FRENCHTOWN FLYER » Sun Nov 11, 2018 1:06 pm

Don't use the gasket fire ring. It is too big - something like 4 3/16". Instead scribe the chambers to the block being used. Its easy enough to add .025 if you are going .050 over bore. Don't cut into the squish area. And try to find a piston that mirrors the combustion chamber or at least has all the dish centered over the chamber.

The nominal ccs for your head is 76, but in production they tended to run larger, so 83 for one that has been cleaned up does not surprise me. Mill and deck as necessary for the desired CR. I prefer decking the block over milling the head but both may be required.

I like a piece of stiff plexiglass about 1/4" thick with two dowel holes for ease of placement.
Last edited by THE FRENCHTOWN FLYER on Sun Nov 11, 2018 7:50 pm, edited 1 time in total.
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Re: Carb head combustion chamber question.

Post #6 by pmuller9 » Sun Nov 11, 2018 1:20 pm

Here is a picture of an 1986 chamber (Same size as yours) with 2.02 intake and 1.60 exhaust valves.
https://www.dropbox.com/s/9dpif5xrxob8g ... 0.JPG?dl=0

A head gasket fire ring is too large to use as a scribe line. As an example, the Felpro 1024 gasket is 4.180"
I also don't trust the alignment. The block will give you the exact bore location.

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Re: Carb head combustion chamber question.

Post #7 by F-250 Restorer » Sun Nov 11, 2018 2:17 pm

Did I miss something? Isn't the stock chamber 76cc? with a carbed head? I'm just curious how it got to 83cc. You scribed and opened up the chamber a bit...is that what happened? Are you going to mill the head to lower the cc of the chamber and thereby raise the compression ratio?

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Re: Carb head combustion chamber question.

Post #8 by pmuller9 » Sun Nov 11, 2018 3:44 pm

You missed a lot.
The OP wants to use a 390 FE piston that only has 8cc valve pockets.
He is trying to lower the compression ratio down to 9.4 by increasing the volume in the combustion chamber.
76 cc chamber is only a specification and can vary quite a bit plus some material was removed by opening the chamber.
This is why the chamber volume should be checked before deciding on a piston or piston height in the cylinder

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Re: Carb head combustion chamber question.

Post #9 by GPGoverMPG » Mon Nov 12, 2018 8:29 am

Yea, that's pretty much it. I knew the fire ring was to big just trying to spit ball a way to find the .025 in radius I need. I've seen where cylinders were notched almost to the top ring for valve clearance. I think the extra bore will allow better unshrouding of the intake valve. I'll put the head back on the block and check where I'm at again then use a .025 feeler gage to make new guide marks. Sure hope this thing sounds cool spun up. I'm going to install one of my MSD 6ALs today. It's a work on my own stuff holiday. Thanks again
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Re: Carb head combustion chamber question.

Post #10 by THE FRENCHTOWN FLYER » Mon Nov 12, 2018 9:58 am

Just to bring everybody up to speed - myself included - here is what I understand you are wanting:
4.05 bore = 308 ci
Desired CR = 9.4:1
Total unswept volume desired = 100.3 cc

Total unswept volume will include combustion chamber size, valve dish and seat height, piston reliefs, spark plug, top ring land placement, head gasket thickness / diameter. If you need to find more volume I'd open up the chamber around the intake valve and radius the edge of the chamber around the exhaust valve.
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Re: Carb head combustion chamber question.

Post #11 by GPGoverMPG » Tue Nov 13, 2018 7:20 am

I only need about 3cc more. It's tough getting them all the same. Repeatability in my cc'ing process is what I'm focusing on now. I need to get away from the syringe and use a gravity system for consistency.
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Re: Carb head combustion chamber question.

Post #12 by THE FRENCHTOWN FLYER » Tue Nov 13, 2018 8:49 am

Pull the intake side of the combustion chamber down into the quench area to make it more like a kidney bean shape a la the 240 chamber.
Here again, I make a template of the first one out of 1/4" plexiglass with dowel holes for alignment so that chamber shape can be accurately transferred to the remaining chambers.
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Re: Carb head combustion chamber question.

Post #13 by pmuller9 » Tue Nov 13, 2018 9:52 am

My calculations show that you are at 9.425 compression ratio right now. Stop!
You will have to wait to see what the volume is with the new valves installed.
If both valves have a dished head like the ones shown in the link in post #6 you might? add more volume to the chamber.

Head = 83cc
Piston = 8cc
Head gasket 4.180 diameter, .039" compressed thickness = 8.77cc
Zero deck.
4.050" cylinder bore.
Last edited by pmuller9 on Tue Nov 13, 2018 12:16 pm, edited 1 time in total.

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Re: Carb head combustion chamber question.

Post #14 by BigBlue94 » Tue Nov 13, 2018 11:45 am

Just to nitpick a bit, his displacement with the 4.050 bore will be 303.84", not 308".

Averaging the stroke to 4" instead of the actual 3.98 makes a difference, especially when calculating compression ratios.
1985 Bronco. 309ci I6, NP435, 4.56 gears, Detroit locker and tru-trac, 4" lift, and 37" swamper tires. The 309 is 9.75:1 CR with a Schneider 140H cam, 4bbl, roller rockers, larger valves, and headers.

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Re: Carb head combustion chamber question.

Post #15 by pmuller9 » Tue Nov 13, 2018 11:56 am

Cylinder swept volume is 51.272
Engine displacement is 307.634

It is important that GPGoverMPG reads post #13 and doesn't do any further chamber volume work except to get them all about the same.

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Re: Carb head combustion chamber question.

Post #16 by GPGoverMPG » Tue Nov 13, 2018 4:14 pm

Thanks for the info. I'm going to try for 84cc with good repeatability planning on a .010 surface cut on the head. When I get the head back from the machine shop I'll cc it again adjust the volume and polish. I'm not going to try for a mirror finish just pretty smooth. Wish I could find the graduated cylinder they are using in the Permanent 300 CFM solutions thread.
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Re: Carb head combustion chamber question.

Post #17 by pmuller9 » Tue Nov 13, 2018 4:29 pm

It's called a Burret.
It's found in Cylinder Head cc kits.

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Re: Carb head combustion chamber question.

Post #18 by BigBlue94 » Wed Nov 14, 2018 10:52 am

pmuller9 wrote:Cylinder swept volume is 51.272
Engine displacement is 307.634

It is important that GPGoverMPG reads post #13 and doesn't do any further chamber volume work except to get them all about the same.


Where did you get that figure? I didn't add the area around the pison down to the rings, but does that really equate to that many more cubes?

Burrets are common in chemistry classes. Most are glass and probably pricey, but I bet there's a plastic one available for cheaper. I used a cheap plastic pipette from work, but wasnt trying to be super accurate.
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Re: Carb head combustion chamber question.

Post #19 by pmuller9 » Wed Nov 14, 2018 12:01 pm

BigBlue94 wrote:Where did you get that figure? I didn't add the area around the pison down to the rings, but does that really equate to that many more cubes?

Please check my math.

Area of the bore:
(4.050)/2 squared = 4.100625
4.100625 x 3.1416 = 12.882523

Volume of the cylinder:
12.882523 x 3.98 = 51.272441

Engine displacement:
51.272441 x 6 = 307.63464

My compression ratio calculator comes up with the exact same numbers.

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Re: Carb head combustion chamber question.

Post #20 by Max_Effort » Wed Nov 14, 2018 3:19 pm

Cubic inch displacement is the swept area.

The simple way I calculate is:
Bore x bore x .785 x stroke x number of cylinders.

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Re: Carb head combustion chamber question.

Post #21 by GPGoverMPG » Thu Nov 15, 2018 8:25 am

Took the cc'ing kit idea and found just what I need on amazon under $25. Sometimes you get locked on a plan and can't see the forest for the trees.
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Re: Carb head combustion chamber question.

Post #22 by BigBlue94 » Fri Nov 16, 2018 11:14 am

Hmmm I use a simple formula

Pi × bore × stroke × #of cylinders.

My pi times 4.050 is 7.23450247

..... and now I see the error of my ways lol I'm doing circumference, not area :bang:

That puts my 4.060 300 at 309.15"!
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Re: Carb head combustion chamber question.

Post #23 by GPGoverMPG » Sun Nov 18, 2018 10:52 am

Improved cc'ing has resulted in a value of 81cc for my combustion chambers. I'm going to leave them alone until the new valves and screw in studs get installed. I will have the machine shop perform the least amount of cut possible to clean up the deck. The compression calculator I use at Wallace racing (I also have a '72 Ventura with a 455SD with 6x small chamber heads) says my compression is 9.56:1. With 93 octane how much compression can I live with on the street. Still thinking the Crane 500211 cam but I'm not committed to it. My plans have changed so much and this is not an every day driver . I also don't mind the near constant tinkering something radical requires on the street. Additionally is there a calculator for required octane?
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Re: Carb head combustion chamber question.

Post #24 by BigBlue94 » Sun Nov 18, 2018 11:33 am

You'll need to figure the dynamic compression for that cam, to determine what octane you can use. Pmuller helped me with the formulas.

I'm building a 9.75:1 engine, with a 7.49 dynamic CR to stay on pump gas. It has to do with when the valve opens and closes in relation to the location of the piston in the bore.

I believe I used Wallace for their calculations too
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Re: Carb head combustion chamber question.

Post #25 by THE FRENCHTOWN FLYER » Sun Nov 18, 2018 12:30 pm

I recommend installing the biggest hydraulic cam you can find.

You will be marginally acceptable at 93 octane with 9.5 CR . You might have to back off the spark a tad from optimal.

I run a 10.5:1 engine on the street and have to mix 93 with 112 race gas ($8 a gallon - yikes!) in the ratio of 4:1.
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Re: Carb head combustion chamber question.

Post #26 by pmuller9 » Sun Nov 18, 2018 2:29 pm

GPGoverMPG wrote: Additionally is there a calculator for required octane?


Octane requirement for the Ford 300 six based on the many 300 engine builds on this site indicates a Dynamic Compression Ratio range from 7.0 to 7.5 with gas octane from 87 to 93 respectively.

The DCR is calculated using the intake valve's closing point referenced to the Advertised duration or when the lobe lift is .006" from closing.
It is important to note the cams installed intake lobe center position as that will affect the intake valves closing point.
After calculating the intake valves closing point ABDC use that number in your favorite DCR calculator.
Also note that a Fel-Pro 1024 head gasket has a 4.180" bore and a .039" compressed thickness.
https://uempistons.com/p-27-compression ... lator.html

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Re: Carb head combustion chamber question.

Post #27 by pmuller9 » Sun Nov 18, 2018 2:47 pm

GPGoverMPG wrote: Still thinking the Crane 500211 cam but I'm not committed to it. My plans have changed so much and this is not an every day driver . I also don't mind the near constant tinkering something radical requires on the street.


The initial plans was to go off road occasionally and play in the mud and/or do some rock crawling.
You also wanted a cam with a rough idle and low rpm which the Crane 500211 will provide.
The engine may not smooth out and make torque till 1300 rpm. Would this be OK for the rock crawling?

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Re: Carb head combustion chamber question.

Post #28 by Max_Effort » Sun Nov 18, 2018 7:51 pm

GPGoverMPG wrote:Improved cc'ing has resulted in a value of 81cc for my combustion chambers. I'm going to leave them alone until the new valves and screw in studs get installed. I will have the machine shop perform the least amount of cut possible to clean up the deck. The compression calculator I use at Wallace racing (I also have a '72 Ventura with a 455SD with 6x small chamber heads) says my compression is 9.56:1. With 93 octane how much compression can I live with on the street. Still thinking the Crane 500211 cam but I'm not committed to it. My plans have changed so much and this is not an every day driver . I also don't mind the near constant tinkering something radical requires on the street. Additionally is there a calculator for required octane?


If your going to shell out $230 for a Crane “shelf cam”. You’d be better off contacting Mike Jones and having a custom cam made for your application.

I’ve used Jones for my custom cams for about fifteen years now. I still like to come up with what I think would work, but I have Mike choose the design (and see how close I am).

For my upcoming project, a 300-6, I did some research, checked on this forum. I was pretty close to what Mike recommended.

Jones Cams will be right on the money, straight and finished well.
http://jonescams.com/street-performance/

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Re: Carb head combustion chamber question.

Post #29 by GPGoverMPG » Mon Nov 19, 2018 7:13 am

Yea, I think the 500211 fits the kind of stuff I'm going to do. The np435 in first and the xfer case in low range should idle over everything down here. I think the crazy intake I built is going to be the problem at low RPM. Was just thinking a more aggressive cam might let me get away with more compression.
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Re: Carb head combustion chamber question.

Post #30 by pmuller9 » Mon Nov 19, 2018 8:41 am

If you want a more aggressive cam with more midrange for running through mud and be able to use a higher compression ratio then I suggest
Jones Cam hydraulic, F300-I6, H72334, L/C 108 along with the J875H lifters.

Cam specs:
Seat Duration 288*
.050" Duration 232*
Valve lift with 1.6 rocker .534"
LSA 108

Mike Jones did my last Ford 300 cam.
Same lobes only on a 112 LSA for smoother idle and better gas mileage.
Idles at 900 rpm, breaks the tires loose at 1200 rpm in second gear (T18 tranny) and still gets 18 mpg @ 70 mph highway.

The 108 LSA will give you a rough idle and a very strong low to midrange torque with a long tube header.

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Re: Carb head combustion chamber question.

Post #31 by GPGoverMPG » Tue Nov 20, 2018 8:16 am

I'm going to check out Jones cams and play with a dynamic compression ratio calculator. I was planning on staying with the EFI manifolds for durability but can see a future where I Fab up a set of long tubes. With all the space I have I could make the first bend off the head a very large radius. Dang it, now I thinking about headers and I'm not done with the important stuff yet.
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Re: Carb head combustion chamber question.

Post #32 by THE FRENCHTOWN FLYER » Tue Nov 20, 2018 9:22 am

GPGoverMPG wrote:...With all the space I have I could make the first bend off the head a very large radius.

Just don't come straight off the exhaust port. It will run / flow better if some downward curvature is maintained in the exhaust tract.
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Re: Carb head combustion chamber question.

Post #33 by GPGoverMPG » Wed Nov 21, 2018 8:02 am

I was thinking straight (in alignment with exhaust port not mounting surface) for an inch or two then two large radius bends. I have not run a calculator on tube size. With this head I didn't think equal length was very important for scavenging. Three into two with 2.5" collectors. If I keep them short enough I can keep them in the engine bay of my "72 F250 and tie into my existing system. I need to get the head out and get it done first. Should I go ahead and have 7/16" rocker studs installed? Does it open up choices for off the shelf rockers that fit?
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Re: Carb head combustion chamber question.

Post #34 by pmuller9 » Wed Nov 21, 2018 10:03 am

GPGoverMPG wrote: Should I go ahead and have 7/16" rocker studs installed? Does it open up choices for off the shelf rockers that fit?

Yes
You will want to use a full roller rocker.

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Re: Carb head combustion chamber question.

Post #35 by GPGoverMPG » Thu Nov 22, 2018 8:05 am

I did contact Jones Cam Designs and they recommended a F300/I6, H67300-69310-110, 212/220 @.050, .300/.310 lobe lift, .480/.496 valve lift (with the 1.6 roller rockers), 110 LSA. They do have lifters and I asked about springs but they needed additional Info. I asked for a single spring recommendation and they needed to know Max installed hight, Max outside diameter, and minimum inside diameter. I'll get that info together and send it off Friday. Should I run longer valves or stay with the 194/160 in Ford length? Medical issues have kept me from completing my order with SI Valve so I could still change it. Jones Cam was super fast responding to my request.
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Re: Carb head combustion chamber question.

Post #36 by pmuller9 » Thu Nov 22, 2018 8:46 am

The seat to seat duration on that cam is 268/276.

You would have to drop the compression ratio down to 9.1
The engine would idle very smoothly.

Did you explain that you wanted a rough idle
The static compression ratio will be around 9.5 and the dynamic compression ratio could not exceed 7.5

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Re: Carb head combustion chamber question.

Post #37 by GPGoverMPG » Thu Nov 22, 2018 9:33 am

Yes, told them 9.5 compression, 93 octane, 1.6 roller rockers, the big valve sizes, and the 2-2v carbs I'm going to run. I even said I didn't mind a solid cam, the additional tinkering doesn't bother me. I also told them it's an F250 4X4, 4 speed, 4.10 gears on 35-12.50 x 15s toy street driven but able to play in the mud spinning the tires to clean the sticky stuff out. I tried to give them as much info as possible. The duration and LSA seemed off when I read it. More duration and maybe 108 LSA. Lift was OK the flat tops and zero deck mean I going to need to check interference just working the head it seems the intake with a 1/2" lift may be getting close and it'll be worse with the 194 intake installed.
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Re: Carb head combustion chamber question.

Post #38 by THE FRENCHTOWN FLYER » Thu Nov 22, 2018 9:39 am

You should not have a problem with V / P clearance even with a flat top at zero deck. The valve seats are about .300" off the deck and at TDC the valve lift is nowhere near .3".

Just the same, I like to set my valve pressures so that the intakes will invariably float before the exhausts. Generally speaking if the spring pressures are equivalent then this will happen if the intake valve weighs more than the exhaust valve.
If the exhaust hangs open the piston is near TDC; if the intake hangs open the piston is down down down in the bore and there is a greater time (degrees) for that intake to get himself back on his rocker tip before bad things happen.
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Re: Carb head combustion chamber question.

Post #39 by pmuller9 » Thu Nov 22, 2018 10:15 am

Adding to what FTF said, .500" valve lift happens when the piston is 2.9" in the hole.
The intake and exhaust valves gets closest to the piston just as the exhaust valve is closing and the intake valve begins to open between around 10 degrees before and after TDC.
It never hurts to check and it would be good to know so do it anyway.

When you say rough idle are you expecting something like a Comp Thumpr cam that has a very abrupt transistion from rough to smooth then Bang! your in the power band like someone flipped a switch or something a little less?
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Re: Carb head combustion chamber question.

Post #40 by GPGoverMPG » Thu Nov 22, 2018 10:21 am

Your right, I forgot where the piston is at max lift. Should be around mid-bore where piston speed is highest and valve over lap happens at the top. The long intake runners I'm going to use and the free flowing exhaust should help clean spent gasses out of the combustion mix. Plus the over lap should help accelerate the intake charge a bit to get good cylinder fill. I put a straight edge across the head deck and opened the intake until it touched and measured that distance like it was going to tell me something. Head was firmly inserted into a dark area.
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Re: Carb head combustion chamber question.

Post #41 by pmuller9 » Thu Nov 22, 2018 10:26 am

I remember you starting the port work.
Do you have any pictures of the completed port work to this point?

I realize the bowl work will change once the larger valves are installed.

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Re: Carb head combustion chamber question.

Post #42 by GPGoverMPG » Thu Nov 22, 2018 10:38 am

I spent most of my time cleaning up the bowl areas stayed away from short side radius and cleaned up the ports. Can still do more if you think it will help. Kind of chickened out didn't want to hurt more than help.
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Re: Carb head combustion chamber question.

Post #43 by pmuller9 » Thu Nov 22, 2018 10:51 am

That's good enough and safe as far as hitting water jacket.
The throat will open up with the larger valves and you will just simply do some blending.

In order to keep a 9.5 compression ratio the advertised duration of the intake lobe should be around 288*
It can be less by 4 few degrees if the cam is installed 2 degrees advanced instead of 4 especially if it has a 108 LSA.

We can push it and figure an absolute minimum of 280 degrees with a 108 LSA.

That would be a 224* .050" duration in a Jones cam but the exhaust duration would need to be 232* to have 12 degrees of overlap.
The cam will idle between 800and 900 rpm and will smooth out just above 1000 rpm.

There are a few here running 218 to 220 degree .050 duration cams and they are still mild.
Hot street really doesn't start till you get near 230 degrees intake duration.
Jone's recommendation 212 degrees is way too short for what you want to do.

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Re: Carb head combustion chamber question.

Post #44 by pmuller9 » Thu Nov 22, 2018 1:00 pm

So try again but this time supply these numbers.
All the engine measurements as last time plus the following.

Cam Type = Hydraulic Flat Tappet
Lifter Diameter = .875"

Max engine rpm as 5500 rpm
Max HP at 5000 rpm
Intake valve diameter 1.94"
Exhaust valve diameter 1.60"

Intake Port Flow:
@400 = 192
@500 = 204
@600 = 212
Max Flow = 213 @ 650

Exhaust port flow:
@400 = 145
@500 = 163
@600 = 178
Max Flow = 185 @ 650

Exhaust header Type = Hedman 1.5"

Intake Manifold = Custom ram tube

Carb Size = 600 cfm.

In the comment section say
Off road mud competition. Need strong midrange and upper rpm power with peak power at 5000 rpm

Then see what you get back for a cam recommendation.
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Re: Carb head combustion chamber question.

Post #45 by GPGoverMPG » Thu Nov 22, 2018 1:27 pm

Yes Sir, I'll send it off in the AM. I'll also get some more recent pictures of port and combustion chamber work. Thanks again
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Re: Carb head combustion chamber question.

Post #46 by GPGoverMPG » Sun Nov 25, 2018 8:54 am

Here are couple of more recent photos of where I'm at with my head work. Thanks for the help. Any recommendations for improvement will be considered and attempted if I can. I sent the updated request to Jones Cams we'll see how they respond.
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Re: Carb head combustion chamber question.

Post #47 by pmuller9 » Sun Nov 25, 2018 9:08 am

Don't remove all of the material from behind the valve guide. Leave a small bridge
Work a little more around the sides of the intake guide to make a wider path.

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Re: Carb head combustion chamber question.

Post #48 by GPGoverMPG » Sun Nov 25, 2018 10:27 am

I can do that for sure. I'm taking my time and trying to make sure they all match as closely as possible. I have seen some pictures here where the exhaust guide is removed to the roof of the exhaust port. Seems extreme, is it worth it?
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Re: Carb head combustion chamber question.

Post #49 by pmuller9 » Sun Nov 25, 2018 10:37 am

At the rpm range you will be operating at there is plenty of time for the exhaust to blow through the port with the work you have done.
The larger exhaust valve will complete the job.

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Re: Carb head combustion chamber question.

Post #50 by GPGoverMPG » Sun Nov 25, 2018 11:07 am

Thanks again, that kind of confirms what I was thinking. I'll do the additional work on the vacuum side and get after it with some sanding drums to smooth it out a bit. I think with the intake I built I'll have trouble with laminar air flow pulling the fuel out of the mixture. Run it fat to make up for it I don't think leaving the short intake port rough will help any.
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