Don Terrill’s Speed-Talk

for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

tchapps88 wrote: ↑Mon Mar 02, 2020 9:25 am for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

Is there a YouTube link to that or something? I'd love to watch that.

tchapps88 wrote: ↑Mon Mar 02, 2020 9:25 am for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

No ... not at all.
Some people have simply kept their mouth shut because all the "experts" out there know everything; without actually testing.

ClassAct wrote: ↑Mon Mar 02, 2020 9:37 am

tchapps88 wrote: ↑Mon Mar 02, 2020 9:25 am for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

Is there a YouTube link to that or something? I'd love to watch that.

not for this one, its on motor trend on demand

tchapps88 wrote: ↑Mon Mar 02, 2020 9:25 am for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

I have to ask if the intake and exhaust tracks as well as the cams matched to the individual rod ratios before I believe that a short rod ratio will make more power than a long rod ratio.

Only because of less piston/cylinder side-loading for the longer rod ratio is all.

pdq67

pdq67 wrote: ↑Mon Mar 02, 2020 10:15 am

tchapps88 wrote: ↑Mon Mar 02, 2020 9:25 am for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

I have to ask if the intake and exhaust tracks as well as the cams matched to the individual rod ratios before I believe that a short rod ratio will make more power than a long rod ratio.

Only because of less piston/cylinder side-loading for the longer rod ratio is all.

pdq67

All of the 900+ hp sprint cars went from 6" to 5.9" rods as the intake tracts grew larger.... Like 2.900 or 3" butterflies.....
But its probably as much about the piston and rings as it is about the r/s

pdq67 wrote: ↑Mon Mar 02, 2020 10:15 am

tchapps88 wrote: ↑Mon Mar 02, 2020 9:25 am for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

I have to ask if the intake and exhaust tracks as well as the cams matched to the individual rod ratios

Exactly. If the camshaft wasn't optimized for each rod length, The test is meaningless.

Those of us there back in the day remember the 302" SBF would never make any power "because the rods are too short for a 3.00" stroke" and today with good heads, those little suckers are running a 3.40" stroke with a worse rod/stroke ratio and making enough power to split the block.

A 302" has a 3.00" stroke with a 5.090"connecting rod. The 347" increases the stroke to 3.40" and a 5.40" rod. This drops the rod ratio from 1.696:1 for the 302" to 1.588:1 for the 347".

In my experience the only time a shorter rod makes more power is when the intake port is too big for the cubic inches and they keep the same heads and intake, headers. Joe-71

PackardV8 wrote: ↑Mon Mar 02, 2020 12:06 pm Those of us there back in the day remember the 302" SBF would never make any power "because the rods are too short for a 3.00" stroke" and today with good heads, those little suckers are running a 3.40" stroke with a worse rod/stroke ratio and making enough power to split the block.

A 302" has a 3.00" stroke with a 5.090"connecting rod. The 347" increases the stroke to 3.40" and a 5.40" rod. This drops the rod ratio from 1.696:1 for the 302" to 1.588:1 for the 347".

In 2003, I built a street driven SBF 331 using 289 rods that are 5.155". I used a KB322 383 Windsor piston. Rod Ratio works out to be slightly less than a 5.4 rod 347...1.586. I also used fully ported '70 351W heads with 1.94/1.6 valves and had some valve unshrouding done (160cc intake ports and 60cc exhaust ports). 9.8:1 compression. Single Plane intake, 750 HP, 282S Comp Cam, Dougs stepped Tri-Y headers. The engine makes 430 HP @ 6500 and is still making 400 HP @ 7000. More than just about anyone in the SBF community would have believed. Maybe i got lucky and choose components that all worked very well together.

tchapps88 wrote: ↑Mon Mar 02, 2020 10:08 am

ClassAct wrote: ↑Mon Mar 02, 2020 9:37 am

tchapps88 wrote: ↑Mon Mar 02, 2020 9:25 am for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

Is there a YouTube link to that or something? I'd love to watch that.

not for this one, its on motor trend on demand

Ok, thanks.

CamKing wrote: ↑Mon Mar 02, 2020 11:40 am

pdq67 wrote: ↑Mon Mar 02, 2020 10:15 am

tchapps88 wrote: ↑Mon Mar 02, 2020 9:25 am for the ones that watched it what was your take on it? Were you surprised the shorter rods made more power?

I have to ask if the intake and exhaust tracks as well as the cams matched to the individual rod ratios

Exactly. If the camshaft wasn't optimized for each rod length, The test is meaningless.

^^^^^^^^^^^^^^ I agree with this statement. One of the advantages of longer rods is the fact that there is more piston dwell at TDC, however the camshaft needs to be designed to take advantages of this feature, as well as other features of long rods. Camshaft design for a long rod engine will be different than the camshaft design necessary to take advantage of short rod features.

On the show, they had basically 'too much cam and head'... The short rods made more top end, and the long rods made more low end power. But it wasn't huge either way. When they did a steady state run (engine locked to one speed) the numbers were pretty much identical.
478 inch Big block Chevy (big bore, short stroke... 4.5" bore, and less than 4" stroke) with 365cc heads and a big roller.

Without each rod ratio engine completely optimized and tuned for that combination, I personally don't think it gives us anything except something to continue to discuss, which is fine. I do believe there is merit in using the best ratio for your particular application.
If memory serves me, I believe it was Pro Stock veteran Warren Johnson that said his rod ratio was whatever connected the piston to the crank, but he was also very cagey about what he was actually doing at times.

It's all combination, they both will work just like different things. In a wide open no holds barred build rod length would be way down the list for me. In a limited class rule type deal it can move substantially up the list in my opinion. Just swapping out rods and not optimizing the build is a waste of time and effort, maybe it works and maybe it doesn't.