Different Strokes...

[Sandy]

This is a bit of a spin off of this thread

http://www.gt40s.com/forum/showthread.php?t=19154

and the titanium thread

http://www.gt40s.com/forum/showthread.php?t=19175


Anyone do any odd combinations of SHORT stroke (3" or less) on the 8.2" deck sbf?

I was looking at the spare parts bin and have some stuff kicking around, but was thinking of a combination like

302 (3") Crank, 5.4" rods and Compession height of in the range of 1.3". Just would need to have custom pistons. Pistons are only the expensive part.

289 (2.87") Crank 5.4" rods, Compression height in the range of 1.56", same here for custom pistons.

I'm not sure my math is right, but seems like a 5.4" rod with a 302 would be a nice combination.

Any one have other good short stroke combinations of interest with common parts?

Sandy

 

[Jac Mac]

302 crank-5.62 rod( Holden 308cu in-availablexscat{2.125/.927})-1.090" pin height piston from 3.4" stroker kit.---Total 8.210"---Rod Ratio-1.87 to 1

289 crank( grind throw's to 2.86"stroke/2.100"dia- 5.700" SBC rod-1.090" piston as above--- Total 8.210"---Rod Ratio- 1.99 to 1

There are others using the 5.56" 400SBC rod as well.

Jac Mac

 

[Doug S.]

I like the sound of the last one, Jac. Any chance the SBC con rod is available somewhere in Ti? The combo ought to be quite tight!!!

OMG--I can just hear it now at full wail!

Doug

 

[Jac Mac]

Jet Engineering, Lansing ,Michigan. had them available in 5.7" length some time ago. Interesting side note's; the side face's of BE were moly coated, weight is 400 grams.
This info is probably out of date now though.

Jac Mac

 

[Doug S.]

The moly coating on the big end must have been their fix for the scuffing, eh?

Doug

 

[Sandy]

Almost any Ti rods that I have seen are moly'ed on the big ends (v8's). Oliver had Ti rods, as well as a few other high end folks. I think in reading more that I'll stick with billet steel as my rod choice thinking what I have now and how they run (Rpm wise), the Keith Craft engine ran up to 8200, and that is with a 3.25" stroke. Chop that down to 3" or 2.87" and I think a bit more RPM will be able to be squeezed without too much trouble. I'm expecting valve train life to be more of a problem then bottom end.

I have a set of 5.4" rods that are nice, easy to get forged 289 crank and custom pistons. Doesn't look too bad (1.88 ratio).

The other that looks good too is the 5.7" SBC rod and a little work on the 289 crank and off the shelf stroker pistons not a bad way either.

The question I would like to tap from Mr. Mac might be this...

How does pin height affect things, skirt loading, scuffing etc? I don't like the stroker pistons have the oil rings into the pin area, but on all my 331's never had an oil issue (used Ross pistons) as I think the 5.4" rod/2.87" combo would move the pin down out of the oil ring area.

One interesting thing is that the pistons with the short pin height (stroker) seem to be generally ligher then the ones with longer pin height. Likely due to internal structure of the piston, but not sure.

Interesting stuff!

Sandy

 

[Jac Mac]

Different Strokes- pin height etc

Doug & Sandy,

The short pin height piston's have shorter skirts for a couple of reasons.
1. As most are originally made for longer stroke applications they need to clear crank counterweights @ BDC which are often bigger in dia.
2. As the pin is closer to the crown of the piston , the piston does not tend to rock as much @ TDC/BDC as a piston with a higher pin height would.

In the applications discussed above the rod swings thru approx 30deg arc while a typical stroker rod swings thru 36 deg, so in the short stroke setup the tendency to rock at TDC is a lot less.

Sandy, I have run pistons with a 0.900" pin height(Ross) where the oil ring sat in an alloy button outside the spirolox pin retainers and the bottom of the oil ring groove was virtually on the pin c/l. 2nd comp ring was approx 0.010" above pin bore. Engine in question had 4.00" stroke and was run in Trans Am type application. While this engine eventually suffered a huge blow-up due to a broken crankshaft, no problems were experienced in the piston/ring area & leakdowns etc were similar to more conventional combo,s.

With the higher rpm that may be able to be safely used with this setup the top ring may need to be an 0.043" wide type or the top groove drilled for gas ports to prevent ring flutter. Valve train components will need to be as light/strong as possible.

With Nascar stuff able to run in the 9000rpm area for long periods the tech is definitely out there.

Doug, the Aussie Alloy Clevo head has one version that is made for a 245 cu in class with smaller ports/valves that would be ideal on these combo,s.

Cheers
Jac Mac

 

[Doug S.]

Doug, the Aussie Alloy Clevo head has one version that is made for a 245 cu in class with smaller ports/valves that would be ideal on these combo,s.

Cheers
Jac Mac

Jac, are you referring to the Chi heads? My combo is looking like it will end up at 307 or 348 CID, depending on whether I use the 289 crank or the 302 crank. Plans are to use the Dart large bore (4.125") alloy block, and you know I love the Cleveland heads. Do you think that the heads you mentioned above will support 50 more CID at 7K RPM or greater, or do you suggest heads with slightly larger ports and valves for the 307? I'd think that with an extra 100 CID the 348 might need larger heads, but.....

Thanks again for sharing all your expertise!

Doug

 

[Sandy]

Jac -

Just to recap so I get it on the pin height, it is actually better to move the pin up in the piston for mechanical reasons?

Sandy

 

[Jac Mac]

Doug,

No, the small port/valve version would be suited to a small cube [290 ci or less] motor only as the valve center's were also brought closer together to eliminate shrouding adjacent to the cyl wall. In your case with 300 + cu in there would be no advantage particularly if you use the 4.125 bore. Any shrouding problems will disappear!

Jac Mac

 

[Jac Mac]

Jac -

Just to recap so I get it on the pin height, it is actually better to move the pin up in the piston for mechanical reasons?

Sandy

Within limits ,Yes. If you hold the piston/pin assy with the pin c/l horizontal, the piston crown will turn to point down. Now if the pin height is reduced as in the above combos we approach a situation where the piston may be able to be in balance in this exercise. This reduces the tendency to rock @ TDC which keeps the rings square to the cylinder wall for sealing.

Pin lubrication now becomes critical along with heat flow as the pin bore gets closer to the top, so the design of the piston gets complicated by the need to allow heat to flow out thru the rings/skirt without reaching the point where the pin bore is distorted. The Heat barrier coatings on the crown retain/reflect the heat into the chamber to prevent this.

For weight reasons, when you increase your rod from 5.400" to 5.700" and shorten your piston from 1.390 to 1.090 you will add less weight to the rod than you remove from the piston, as you are removing an area of the pin boss which measures approx 1.5"x1.5"x 0.300".

In naturally aspirated applications the longer rod seems to help, however in turbo or blown applications there is a trade off as the piston being 'parked' at TDC prevents the cylinder being filled. Buick found this with the INDY V6 and introduced a 'shorter block/rod' combo to make more power.

Jac Mac

 

[Sandy]

Jac (I never know should it be Jac Mac???)

BTW you read my mind by hitting my next questions of optimizing the Rod length weight vs the pin height.

I think I'll start looking for a nice set of chev 5.7" rods and a do a 289 ford crank with the 2.1" journals, and save with some off the shelf pisions. I think this is by far the most cost effective to longest rod SBF for the next motor.

Last (well not likely), but is the common pratice in this case (for off the shelf rods) to narrow the big ends of the chevy rods vs. do more expensive crank work? I'm guessing the narrower ford bearing is likely better for higher rpm work as well?

[Edited] Yep, another question, I beam vs. H beam rods. Never been able to get a solid answer on that from anyone or the web...

I can't say how much this has helped in understanding some of mysteries of the long rod. Much crap on the web that is highly suspect other then that it is a good thing to use a long rod! I would love to know the rest of the secret stuff that's inside your head!

Thanks again!!

Sandy

 

[Jac Mac]

Sandy, Either way, short for Jack McIntyre.

Perhaps I should take up the mind reading vocation!

In this case where you want to reduce the stroke by 0.020",just narrow the chev rod to the ford rod width . Check out the 4.3 V6 chev brg's( I believe they are narrower than the V8) or some of the race brg's for large radii journals. If you are happy to run less deck clearance or machine 0.010" off the piston crown you could have the chev resized @ the BE to accept SBF brg's (0.014" larger tunnel dia).

I-beam v H-beam-- I would not like to sit on the jury for that one! I think it comes down to whether they are forged or machined from billet. Its probably easier to machine the 'H' and forge the 'I'. When you look at some of the 'exotic' types like 'mechart' etc with investment casting process's you wonder whats next.

The Stuff in my Head ?? I have trouble with the 'search engine' myself!!

Jac Mac

 

[Sandy]

Mr. Mac -

I sold out, I was cruzin' Ebay and found a nice new set of Oliver billet 5.4" rods for SBF. So I'll guess I'll be trying the long rod 302 as the next motor. So will have a compression height of 1.3" or so and rod ratio of 1.8 for the slighlty longer rod. At least the crank will be easy to get.

Make that crank your sawing up a 3.0" stroke for me.

Sandy

 

[Jac Mac]

Mr. Mac -

I sold out, I was cruzin' Ebay and found a nice new set of Oliver billet 5.4" rods for SBF. So I'll guess I'll be trying the long rod 302 as the next motor. So will have a compression height of 1.3" or so and rod ratio of 1.8 for the slighlty longer rod. At least the crank will be easy to get.

Make that crank your sawing up a 3.0" stroke for me.

Sandy[/QUO .

What sound does a chicken make? Its not that much different from a blunt hacksaw blade. Guess I will just have to build it for myself, gonna need something to keep Mr Noble honest, unless you want to stick yours in a container & bring it down under for 4 weeks of Motor Racing Holiday, I will put you up for the southern part of the adventure, Russ could handle the ChCh end-he is good like that- Dont let them Aussies near it though, they seem to claim everything as their own if it touches their red dust- thats why we affectionately call them magpies.

Jac Mac

 

[Sandy]

What sound does a chicken make? Its not that much different from a blunt hacksaw blade. Guess I will just have to build it for myself, gonna need something to keep Mr Noble honest, unless you want to stick yours in a container & bring it down under for 4 weeks of Motor Racing Holiday, I will put you up for the southern part of the adventure, Russ could handle the ChCh end-he is good like that- Dont let them Aussies near it though, they seem to claim everything as their own if it touches their red dust- thats why we affectionately call them magpies.
Jac Mac

Those Aussies are tricky But arn't we all! Yes, I sold out for the cheep (but good) parts as I really like Oliver Billet Rods. I'm a I-Beam'er I guess. 302 with 4.125" I'll call that the American compromise! Just need heads, block and crank and $$

Sandy