470 stroker shopping list

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wingrider

wingrider

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Hey All,

Just a breif history, I am slowly building a stroker engine for a boat that I am building. I had settled on the thought of making it a 470.

I finally got word that my 78 400 block is sound, and can be bored out without any worries. Now that I know that, I am putting together my shopping list. Right now I am just focusing on the pistons, rods, and crank.

So, what I have so far is a crank from Molnar:
3910NC6F 383/400 Chrysler - Rod Pins = 2.200", stroke =3.910, minimum rod length= 6.450 bob weight = 2300.

Molnar rods from Chevy BB:
CH6535VTB8-A Center to center = 6.535, grams = 736, bolt = 7/16", BE bore 2.325, Pin size = 0.990, BE width = 0.992, PE width = 1.065.

Then the piston might not be right. I had selected a Wiseco Piston, PT108H55.
Bore 4.375"
Comp Height 1.25
Comp Ratio @ 78cc 10.3:1
Comp Ratio @ 88CC 9.4:1
Dome Volume -10cc
Gram Weight 451
Rod 6.800"
Stroke 3.750"

Am I on the right track for these parts, or do I need to look at something different?

Thank you for any help!
 
i don't think you have the correct compression height.

a 1.32" CH works with a 3.91 crank and a 6.7" rod...
you seem to have a shorter piston AND and shorter rod...
 
Id go 500 4.125 stroke probably biggest you could go and still has decent rod ratios.
And rod ratio dont concern you much go 4.25 stroke.
 
cookietruck said:
i don't think you have the correct compression height.

a 1.32" CH works with a 3.91 crank and a 6.7" rod...
you seem to have a shorter piston AND and shorter rod...
Click to expand...

That was kind of my thought on it...not quite sure why I saved that piston in my notes...
 
For the price why don't you go with a scat 500 ci kit, 4.150 forged, H beam rods and Icon pistons.
I just ordered the same set for a friend, rings, bearings, internally balanced $2820 shipped
 
wingrider said:
Hey All,

Just a breif history, I am slowly building a stroker engine for a boat that I am building. I had settled on the thought of making it a 470.

I finally got word that my 78 400 block is sound, and can be bored out without any worries. Now that I know that, I am putting together my shopping list. Right now I am just focusing on the pistons, rods, and crank.

So, what I have so far is a crank from Molnar:
3910NC6F 383/400 Chrysler - Rod Pins = 2.200", stroke =3.910, minimum rod length= 6.450 bob weight = 2300.

Molnar rods from Chevy BB:
CH6535VTB8-A Center to center = 6.535, grams = 736, bolt = 7/16", BE bore 2.325, Pin size = 0.990, BE width = 0.992, PE width = 1.065.

Then the piston might not be right. I had selected a Wiseco Piston, PT108H55.
Bore 4.375"
Comp Height 1.25
Comp Ratio @ 78cc 10.3:1
Comp Ratio @ 88CC 9.4:1
Dome Volume -10cc
Gram Weight 451
Rod 6.800"
Stroke 3.750"

Am I on the right track for these parts, or do I need to look at something different?

Thank you for any help!
Click to expand...

Well the good news is that you are asking questions since the bad news is that if you bought those parts they wouldn't work. You would have about 6:1 compression with the pistons sitting 1/4 inch down in the hole.

The math isn't difficult, basically grade school level stuff. You need to know the deck height of your block then compare that to the total of the rod length, piston height and 1/2 of the stroke. Ideally you want the top of the piston to be close to the top of the deck. Maybe 0.005 down in the hole. If it was me I'd use a 6.700 rod and a 1.320 tall piston but there are several ways to skin the cat.

You will also need to know which cylinder heads that you are going to use before you pick the piston since you'll want to get the compression ratio correct. Once again the math isn't difficult but you have to actually figure it out. I use a little Excel spreadsheet but you can do it on paper or use an on-line calculator if you want.

When picking a piston you also need to make sure you have the correct pin diameter and you should confirm with your machine shop that you are getting the correct rings. And of course you'll need to order the correct bore size and then make sure that your head gasket matches your bore size. Engine building isn't difficult, but you have to pay attention to the details or else you will end up with just a box of parts and a big credit card bill rather than an engine.
 
Yep! Which was one of the reasons I put this together. This way I am just typing letters, and not CC numbers.

I guess the reason I chose the original parts was the info from 440 source. I will certainly take your advice though Andy!
 
"I had settled on the thought of making it a 470."

Sounds good to me.
 
If you look closely at the piston description you'll see that it is designed to use with a 6.800 long rod. That should tell you that you either selected the wrong piston or the wrong rod. I'm not sure the Molnar makes a 6.800 long rod, that isn't a very common length. 1.250 is a little short for a boat motor piston. That is more of a drag race piston. For a high perf boat engine I'd use the 6.700 rod. For a pleasure cruiser I might go with the shorter 6.535 if you can find a piston with the correct CR that matches. I think for a boat engine you would want to make sure you have the correct CR first and then worry about getting a good ring stack, and then worry about the rod length as the last priority. Engine builders are usually a lot more conservative with boat engines since they get used hard and also because you don't want your customer kicking out a rod in the middle of the lake.
 
Ok, it would seem like I would want a CR of about 10- 10.5-1. That should keep me running on pump gas. I am strongly considering using the Trick Flow 240 heads, which have a CC volume of 78cc’s. Not quite sure which springs I should go with, but that is down the line. looking at pistons, I have found Ross pistons that are 1.320 high, and have a .990 pin. Am I thinking correct that I would need to go with a Chevy piston in JE to get the smaller pin with a 1.320 height?
 
wingrider said:
Very true Andy...I plan to tune down the engine a bit from the high HP you have seen with Your builds to try and keep the boat in one piece.

I must say, up until today, I had never seen this link...True Tales – Low Deck Stroker | AR Engineering

It would seem if I used this as a shopping list, I would have a solid engine!
Click to expand...

That is a very old build. It was the hot thing at the time but those days are gone. Back when I wrote that article nobody made cheap stroker cranks. We had to offset grind factory cranks to get to 3.90 stroke. If you wanted more stroke you had to weld and grind. Manley had those killer rods but they discontinued them years ago. The RAS rocker arms were a steal back then but like the rods they are also long gone.
 
wingrider said:
Ok, it would seem like I would want a CR of about 10- 10.5-1. That should keep me running on pump gas. I am strongly considering using the Trick Flow 240 heads, which have a CC volume of 78cc’s. Not quite sure which springs I should go with, but that is down the line. looking at pistons, I have found Ross pistons that are 1.320 high, and have a .990 pin. Am I thinking correct that I would need to go with a Chevy piston in JE to get the smaller pin with a 1.320 height?
Click to expand...

JE makes a 1.32 piston with the 0.990 pin but it is only a -6 cc dish so the compression might be a touch high for you. I think Diamond has a -12 cc dish and then Icon has an even bigger dish. Here see if you can open this PDF. This is the type of spreadsheet I was talking about earlier. If you are going to be an engine builder you need to create things like this. Otherwise you're just chasing your tail.......
 

Attachments

  • 470_Stroker_Kit.pdf
    111.8 KB · Views: 511
Andy, I will whole heartedly admit that you and IQ52 and many others have forgotten more than I know when it comes to building engines. I was setting up something similar to your spreadsheet last evening, but ran out of options for this list. Hopefully I can continue it today.

Thank you for sharing that! It is extremely helpful!
 
the mahle piston in the 1.475CH in andy's pdf is something i would be looking at. i think those come with rings as well.
 
Yes, I had wondered if Andy Highlighted that one, or if that was just what line it was on when he copied it.

I have read a little bit about the rod ratio of short rods vs long rods. I know Andy had said the shorter ratio would be good for a pleasure cruiser. My boat originally was designed for a 350-400 hp engine. I figure she can take a little more!
 
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I just had that row highlighted when I created the PDF. The Mahle piston is probably the best piston available but it is only 8cc dish so your compression will be fairly high with the Trick Flow heads. If you switch to Edelbrock heads with the 84 cc chamber then the compression ratio drops down to 10:1 which should work. The other option is to buy the Trick Flow heads and then have someone open up the chambers a little bit so you get the compression ratio that you need.
 
wingrider said:
Yes, I had wondered if Andy Highlighted that one, or if that was just what line it was on when he copied it.

I have read a little bit about the rod ratio of short rods vs long rods. I know Andy had said the shorter ratio would be good for a pleasure cruiser. My boat originally was designed for a 350-400 hp engine. I figure she can take a little more!
Click to expand...
Maybe Andy can explain that rod ratio statement. I believe longer rods create less friction on the cyl walls, and produce a small , small gain in torque. I developed that from reading Bill Jenkins book on race engines. ??????
That`s why all the nascar hemi`s used to run a longer rod than street hemi`s. 7.1 versus 6.86 . A trick back in the day used to be to run 7.1 rods in ur drag race engine.
 
A pleasure boat isn't a drag race engine or a NASCAR engine. In this case I'd pick the best piston with the best ring pack and use the rod that fits.
 
You are absolutely correct...this isn’t a race boat. So, it would seem that the Mahle piston with a 1.475 CH would be a good option.

I should think it would then make more sense to go with the Edelbrock head with the larger chamber, and put a little money into cleaning them up vs opening up the chamber on a Trick Flow. Am I on the right track with that?
 
AndyF said:
A pleasure boat isn't a drag race engine or a NASCAR engine. In this case I'd pick the best piston with the best ring pack and use the rod that fits.
Click to expand...
Wouldn`t a longer rod that still has a stable piston be better for friction tho? I gotta admit I have never built or researched a 470, and don`t know what combinations there are for them, just asking.
 
wingrider said:
You are absolutely correct...this isn’t a race boat. So, it would seem that the Mahle piston with a 1.475 CH would be a good option.

I should think it would then make more sense to go with the Edelbrock head with the larger chamber, and put a little money into cleaning them up vs opening up the chamber on a Trick Flow. Am I on the right track with that?
Click to expand...

That is a possibility. If it was my engine I'd start by calling Mahle to see if they would make that piston with a bigger dish. If they would do that then I'd run the TF heads. If they tell you to pound sand then I'd consider other options.
 
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