[Warp Speed]

Building a 598 using a Donovan block (10.2 deck/6.300 sleeve length). 4.5 stroke with a 6.535 rod. The problem is the piston hangs out of the bottom of the bore a bunch (pin center line only .400 inside the bore). I have heard of guy's using 4.75 stroke with a 6.535 rod but even with a longer cylinder I can see this being a problem.
Is there any rule of thumb on this? I know this block ran before with a 4.375 stroke/6.535 rod and can go that route if needed but that's only a better case by .0625!?!?!
Can go to a longer rod if needed but.......
I live in a short stroke/long rod world, and compared to what I am used to working on it looks scary to say the least!

 

[Chris Uratchko]

You need to keep the peak of the skirt profile from exiting the cylinder. When I run into this condition I plan ahead with the piston design based off the cylinder length, and have the skirt profile peak moved up as high as possible.... not a best case scenario in design, but better than the skirt peak coming out of the bore and having the piston rock dramatically at BDC...


I would put a longer rod in there and get the piston more towards around 1.2-ish CH move the peak of the skirt up as high as they will manufacter it...

 

[G-Code]

Jay big blocks are just a pain aren't they All those years ago when I built the 565 I already had the Crower 6.535 rods. I had given some thought to a 4.375 stroke and this issue came up along with a few others so I went with the 4.25" stroke.

Can you get a custom rod easy enough ?

G-Code :-D

aka Sleeper CP

 

[Warp Speed]

You need to keep the peak of the skirt profile from exiting the cylinder. When I run into this condition I plan ahead with the piston design based off the cylinder length, and have the skirt profile peak moved up as high as possible.... not a best case scenario in design, but better than the skirt peak coming out of the bore and having the piston rock dramatically at BDC...


I would put a longer rod in there and get the piston more towards around 1.2-ish CH move the peak of the skirt up as high as they will manufacter it...

Thanks Chris!

I was thinking along the same lines as far as piston design and with the Ross pistons I have for it right now they hang out just at the edge of the peak. Looks like a 6.700 rod and some new pistons oughta do the trick.
Little differant from what I'm used to working on, but that's what makes it so much fun!
Something with differant challenges!!!

 

[Warp Speed]

Jay big blocks are just a pain aren't they All those years ago when I built the 565 I already had the Crower 6.535 rods. I had given some thought to a 4.375 stroke and this issue came up along with a few others so I went with the 4.25" stroke.

Can you get a custom rod easy enough ?

G-Code :-D

aka Sleeper CP

Ya, it's kind of a pain because it's not what I'm used to, but then again that is what makes it interesting for sure!! Really having fun with this project, just wish I had more time to mess with it!

Rods and pistons not a problem, just money right?

 

[ROB]

I'm sure you've got this covered but I'll add to Chris' comments & say that any bore notching and lower edge contours need to be barbered up well if much of the skirt pokes through at the bottom of the bores.

If the block's anywhere near 10.180" you may want to consider a 6.800" rod and possibly use a shelf-item 1.120" tall piston to keep costs down. If Ross has these readily available skirt profiling as Chris mentioned may be already built into them.

 

[Warp Speed]

I'm sure you've got this covered but I'll add to Chris' comments & say that any bore notching and lower edge contours need to be barbered up well if much of the skirt pokes through at the bottom of the bores.

If the block's anywhere near 10.180" you may want to consider a 6.800" rod and possibly use a shelf-item 1.120" tall piston to keep costs down. If Ross has these readily available skirt profiling as Chris mentioned may be already built into them.

That is the direction I ended up going Rob. I was a little concerned about about spraying a 1.120CH (nitrous rookie) but Diamond said "spray away" so.....!!

 

[ROB]

That is the direction I ended up going Rob. I was a little concerned about about spraying a 1.120CH (nitrous rookie) but Diamond said "spray away" so.....!!

I've got a low-buck guy who essentially has the identical setup in his IHRA T/S car (current points leader in Div. 3).

In this case the pistons are JE but at the end of the day it's the same deal.

He doesn't try to kill it with N02 every run but sometimes they run 150 shots, other times 200, and so on.

With the regular off the shelf catalog big-dome piston there were zero failures after about 750 passes, either with or without nitrous. For these pistons 250 shot was max but the car responded like it gained over 320 HP.

Now they run a purpose-built N02 piston and once in a while blow a 500 shot into it. These pistons are 1.220" with the 6.700" rod combination because I wanted to increase land thickness between 1st & 2nd groove and still have a reasonable skirt profile on it.

What are you putting this thing into?

 

[Warp Speed]

What are you putting this thing into?

The Family Barge! :-D

 

[638montecarlo]

just go with a 6.7 rod and a 4.75 stroke

 

[Warp Speed]

just go with a 6.7 rod and a 4.75 stroke

The problem I had was the short cylinders (6.300) and the 4.5 stroke/6.535 rod. The pistons were coming out of the bottom of the bore too far to be stable at BDC. The increase in rod length would/is going to help but the added stroke (going to the 4.75 from 4.5 as you suggest) would only improve my deal .040.
I believe the 6.8 rod I am going to should make things manageable.

 

[ROB]

The Family Barge! :-D

Very cool. Offering any rides in that thing? )

 

[Guest]

Very cool. Offering any rides in that thing? )

I think "on" that thing would be more accurate......:-D