Chrysler Hemi 1/4 scale

[driller1432]

Question if I may.

The only engine that comes to my mind when I read "Chrysler Hemi" is the 426 CI hemi from the late 60s. That would make this a 106.5 CI engine, which is still pretty big for a model.

Is that right?

You are correct it is the 426 elephant engine.

 

[davidyat]

The bore and stroke dimensions do come out to 425.58 CI. But wouldn't the volume of the cylinder heads add to the 425.58 volume making it a bigger engine? I thought that's why NASCAR engine builders have to CC the heads with a liquid to make sure the total volume doesn't go over specs. Or are the pistons dome shaped to compensate for this?
Grasshopper

 

[L98fiero]

But wouldn't the volume of the cylinder heads add to the 425.58 volume making it a bigger engine?

It's the swept volume that is counted for displacement figures, the head volume doesn't change.

 

[davidyat]

I've never heard of "swept volume". What is it?
Grasshopper

 

[L98fiero]

I've never heard of "swept volume". What is it?
Grasshopper

Swept volume can be defined as the volume swept by the engine piston during one stroke. Swept volume is also the product of piston area and stroke. https://help.summitracing.com/app/answers/detail/a_id/5005/~/what-is-swept-volume?

 

[davidyat]

Thank you, I learned something today.
Grasshopper

 

[CFLBob]

I think I got this graphic here on HMEM but I don't remember anymore. It might be helpful for some folks.

The displacement equation is for one cylinder, so you'd multiply that result times the number of cylinders in the engine.

 

[bruski]

Bore X Bore X Stroke X .8754 X Cylinders

 

[CFLBob]

I think you swapped a digit. It's .7854.

 

[Willyb]

Good job. Enjoying the build.
Willy

 

[Noitoen]

The bore and stroke dimensions do come out to 425.58 CI. But wouldn't the volume of the cylinder heads add to the 425.58 volume making it a bigger engine? I thought that's why NASCAR engine builders have to CC the heads with a liquid to make sure the total volume doesn't go over specs. Or are the pistons dome shaped to compensate for this?
Grasshopper

I think that is used to calculate compression ratio by measuring the chamber's volume.

 

[driller1432]

Thanks for all the replies. Last couple days spent hogging out lifter valley and drilling lifter bores. The holes for the fifth head bolt were drilled first then the lifter bores were drilled
Because of the size of the lifter bores the boss for the head stud is very thin walled and one even broke thru. But the undercut on the bottom side of the boss has a lot of meat left so there should be no problem holding the stud as the boss is about .250 in length. I thought about building the boss up with tig welding but it would probably make it worse! The reason for the stud going down is so there isn’t a bolt going thru intake port. There is still a little more work in valley milling clearance for exhaust push rods which are at angles same as intake pushrods. So now a lot of work with rotary tool rounding inside corners and smoothing every thing out. Next back to crankcase and getting main bearing webs to final width and milling away caps. Set heads on block for a quick look . I haven’t posted pictures of rockers and shafts yet but I have them all made.

 

[ddmckee54]

Noitoen nailed it, they CC the heads to determine the compression ratio. Nascar has compression ration limits and they want to be sure nobody's cheating by using an engine with a higher ratio.

Don

 

[Badhippie]

So you are going to have studs in the lifter valley as on the original engine design. They were bolts in the original engine but everyone switched them out for studs. Very nice work glad to see a fellow mopar nut in the crowd
Thanks
Tom

 

[driller1432]

So you are going to have studs in the lifter valley as on the original engine design. They were bolts in the original engine but everyone switched them out for studs. Very nice work glad to see a fellow mopar nut in the crowd
Thanks
Tom

Hey Badhippie yes going to use studs for the fifth head bolt .

 

[Bentwings]

The bore and stroke dimensions do come out to 425.58 CI. But wouldn't the volume of the cylinder heads add to the 425.58 volume making it a bigger engine? I thought that's why NASCAR engine builders have to CC the heads with a liquid to make sure the total volume doesn't go over specs. Or are the pistons dome shaped to compensate for this?
Grasshopper

I don’t think chamber volum and comp ration will scale properly it would be best to adjust the piston and chamber to give a functional ratio according to the fuel being used if pump gas is suggest around 9.5 pistons and rings this size are not the easiest things to make as it is. Plain cast iron works for rings as you can simply crack them in your fingers the use a small fin file to fit them . The standard .004 in per inch bore diazepam still works ok. Even our model airplane engine one used this rule you wind up about .002 fitted gap. This size bore is pretty sensitive to gap so keep it snug. Since this would be liquid cooled... I think. It would have a better control of cyl temp than air cooled motors.
I thought of dyke rings on the engine I’m just starting but that’s a huge complication I don’t need. Tigh tolerance is one thing but with multiple operations on lots of parts is quite another. I would also consider a ring installation tool and make plenty of extra rings. Ductile iron is hard to control in this scale full size is easy but tiny is another story.
My 2 strokes had cylinder and pistons matched. Assembled the pistons had a slight stick at Tscheda as the engine warmed up clearances opened up. When this went away when cold it was time for a new liner and piston. Cr was pretty high bu lots of nitro was the rule in this days. I had a number of spectacular engine distractions. No fires but lots of pieces flying around. For small engines they made pretty Big Bang when they let go..

 

[driller1432]

Wow been 3 years since posting on the hemi build you probably thought I gave up on it. But work has continued I don’t take too many pics but i will post some that i have to get caught up. Only work on it during winter months. Combustion chambers were machined with crude tool made from drill bit with washer welded to it which worked very well leaving a nice finish.Then ports were machined next, valve seats will be press fit into head made from drill rod . With pressed in brass valve guides. All diamensions were scaled down from actual 426 hemi heads. Also found some original Chrysler drawings with no dimensions on internet.
I don’t use cad or cnc only drawings I did were the head bolt layout and pushrod holes etc. Only messed up two heads one by trying to make square exhaust ports and the other doing valve ports.
More to come try to update every couple of day's.

 

[kuhncw]

Interesting tool. Thanks for posting.

Chuck

 

[GreenTwin]

I am glad to see this build continue.
Great photos of the build.

And yes, that crankshaft is a work of art, and no doubt highly functional too.

Thanks for posting; what a great build thread.

The hemi is one of those iconic engines in my opinion.

.

 

[driller1432]

Wow been 3 years since posting on the hemi build you probably thought I gave up on it. But work has continued I don’t take too many pics but i will post some that i have to get caught up. Only work on it during winter months. Combustion chambers were machined with crude tool made from drill bit with washer welded to it which worked very well leaving a nice finish.Then ports were machined next, valve seats will be press fit into head made from drill rod . With pressed in brass valve guides. All diamensions were scaled down from actual 426 hemi heads. Also found some original Chrysler drawings with no dimensions on internet.
I don’t use cad or cnc only drawings I did were the head bolt layout and pushrod holes etc. Only messed up two heads one by trying to make square exhaust ports and the other doing valve ports.
More to come try to update every couple of day's
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