Rich,

I didn't want to get into all of that really because I have gone into the depths of velocity, accleration and force in relation to stroke before but THANK YOU. That was a great post.

To me it doesn't make sense to build a motor which will have higher engine speeds and compound on that with a long stroke motor.

Now I realize this is not as much of an issue with the lighter weights of a SBC vs. BBC and the higher mass components used in those motors. The problem is we are physically limited to the size of the parts in motors with tighter packaging problems.

On a side note:

Your Oliver rods are some of the BEST designed connecting rods on the market. There is a good story about the design by the late Carrol Smith comparing them to the contemporary H beam used by Eagle and Carrillo. I know it's one of those old things where guys think Carrillo is the best but I firmly belive that Oliver is one of the best connecting rods compaines out there along with Arrow Racing Components. They both have exellent contacts in the materials and racing industry.

Bret

 

4" stroke is alot and I dont know if it will be better or worse for what I am looking to do but i figured it is something different to try in my naturally aspirated quest.

 

Only 4.0" stroke ~4.0-bore motor I've seen in person was Chuck Riddeck's. When I was at his place last year, the engine was basically a dyno mule but it was putting better than 600hp to the crank with LT1 heads. As I understand it, he never intended to keep the engine in his car for more than a year or so anyways.

On that note and with regards to longevity, I just don't see it being a problem. Most guys who build something of this caliber aren't planning on getting 50k miles out of it. They rebuild every couple of years. So piston/cylinder loading, acceleration, lala, la (not to sound like an a$$) but... WHO CARES?

I definitely wouldn't but thats just me.

I'd just go to an aftermarket block at this point.... hello, Dart, WP and company.

-Mindgame

 

Mindgame: I am glad you are back posting again.

Rich Krause

 

Mindgame, I second that.....good to hear from you How is that motor running....love that thing.

 

I agree.

Long time...

 

Actually the longer the rods the less rpm you will have at any given piston speed and the easier the rod bolts will have it because rpm is far more important than piston speed in the loads that the rods see. Turning 4700 FPM with a 3.000 inch stroke will put the rod bolts through hell but with a 4.000 inch stroke they are taking it easy.

With a 6.000 inch rod and 4.000 inch stroke the rod bolts see 3800 Gs at TDC at 7100 RPM.

With a 6.000 inch rod and 3.000 inch stroke the rod bolts see 4760 Gs at TDC at 9450 RPM.

With a 6.500 inch rod and 3.000 inch stroke the rod bolts see 4690 Gs at TDC at 9450 RPM.

So you can see that even with a huge 2.17 rod ratio the smaller stroke engine is tearing the rods and pistons which also see this load up! The reduction in friction is also sometimes evident when doing testing on the larger engines even with short rods even though most people think they have more!

.....now turning the SAME rpm the smaller engine DO have less stress and friction but you're also now making way LESS hp too so they are no longer comparable. You can again do the larger engine and come out way ahead in reliability at this newer lower hp rating too if you run the larger engine slower to match the smaller engines piston speed and power and you'll come out ahead again usually.

You only have so much room however and the 4 inch stuff starts hangining out the bottom of many SBC blocks which I don't like depending on things. Overall bigger is always better if it fits!

 

Yep, 33% more rpm increased the piston gs (and rod load if masses remain the same) about 24% in your example.

8.3% longer rods decreased the gs about 1.4%
My conclusion is rod length has very little to do with rod bolt loading. As you said, it's RPM that counts.

Are you sure that rod length affects average piston speed?

Avg. PS = rpm x stroke / 6 if I remember correctly. Maybe you didn't mean average piston speed?

 

Thanks for the welcome gentlemen.

Jason,
How are ya?
The "motor" is running beautifully! I wish I could say that for the transmission. It's a goner thanks to my last trip down the 1320. So, I'm looking to either put the beef to another T56 or go with a stick-shift alternative. Following some leads posted in AT here a while back about strengthening the T56 so we'll see where that leads me.
On another note, these cars are a little different suspension-wise and I'm having a time getting the car to ET like it should. I think I need to send a bit more money to BMR, then maybe I can pull off some times *close* to what our buddy Joe Overton is running. The mph is there.... the rest aint yet.

-Mindgame

 

What about that 472 SBC they did on Horsepower TV? Couldnt you do a setup similar to that?

 

Didn't see the HPTV 427. But yeah, you could build an engine based on the Gen1 small-block and have anything from 350-500 cid. Then you have to make it work in an f-body. That'd require some fabrication skills but it's been done.

The gentlemen I mentioned in my first response, is/was running a 434 ci Gen1 in his car. 700+ hp na and to my eyes, ears and buttometer... very streetable, so not too shabby... or inexpensive for that matter.

-Mindgame

 

Mindgame, stay with the M6! I am amazed at how the cryo treatment of the mainshaft really has withstood alot of great 60ft times in some of the more stout M6 cars. That may be something you want to look into.

Did you get any better passes than that 10.4@137 with your setup since then? I can only hope that my car will trap 135+ NA....certianly *should*.

Thanks

 

Oldstrokerss,

Right, the average piston speed never changes with rod length just the peak.

 

MG, curious, what breaks the most often on the T-56? Is it the input shaft? Also, do you have a similar problem to what a lot of the mustang crowd has with the car not going into gear? I know a lot of guys convert to pro-shifted stuff. It also looks like a lot of the LS1 crowd is going that route as well. I wasn't sure how much street time your car got, and everyone's opinion of "streetable" varies, but for some reason, I could see you dealing with it.

 

I don't know much about the stang's T56, except that it was used on the Cobra R and the 2003 Cobra (w/blower ).

If there's a problem with getting into/out of gear it may be a shift-pattern problem, or the way those damn mustangs put the shifter half-way up the dash (just feels wrong when comparing it to my Pro 5 w/Lou's Short Stick).

The stangs probably upgrade their input shaft a fair bit as well... I belive they use a 10-spline shaft, while the Fbody/Viper unit uses 26 or 29 or sumthing much higher.

In most f-body failures it's actually the other end that goes... the output shaft. There's a few companies out there that will machine the Fbody housing to fit a Viper shaft (and more importantly, the thicker output shaft bushing). D&D performance does this for ~$700, while those with a bit more inititive can get the machining and parts for ~$500 (but I belive the D&D kit comes with extra pieces like a 16-tooth reluctor wheel).

To my knowledge the T56 is pretty damn solid up to ~600hp or so (when in a 3000 to 3400 lb Fbody).