- When it comes to selecting a connecting rod for your next build,
one of the hot topics out there that's always been controversial is whether
an H bean or an I beam design is superior.
Admittedly we've actually spent a lot of effort trying to get to the bottom
of this too and there's just so many conflicting stories, that we decided to
get right to the heart of the topic and we're here with Richard from CP Carrillo.
Carrillo are well known for producing some of the industry's best conrods,
and we're here to find out what the exact answer to that question is.
So Richard let's get to the bottom of it.
H beam or I beam, is one superior or does it just not matter?
- It doesn't really matter anymore, you can design either to be as equally
strong for the application you're designing it for.
It all has to do with the cross sections and how you design the connecting rod.
- So it's really about the material in the rod and where abouts that material
is located in the beam that makes the rod strong or weak?
- Correct, that is correct.
- OK so one of the common myths that I hear about this, or let's assume that
it's a myth now that we're talking about these, is that when your'e designing
an H beam rod, due to the layout of the material, it by design must be
heavier than an I beam conrod, is there any truth in that?
- That's not always the case, you can design the H beam rod to be just as
light as an I beam rod, it's how you design it.
- Now the other common myth that we hear in the industry is that between
the two designs, if we have to pick a winner, and while admittedly a lot of
the information suggests that the two rods are very close anyway,
that it comes down to the H beam rod is a little bit stronger for engines
that are producing high cylinder pressure versus the I beam rod is potentially
a little bit superior for very high RPM engines where the rod weight
is more critical.
Again, is there any truth in those two topics?
- There's benefits to both but you really can design either one for either
application if you design it correctly.
- Alright so in Carrillo's career or history so far, you've really embraced the H beam
rod, I think that's probably what Carrillo are best known for.
But more recently we have seen you bring out designs that are I beam design.
So can you tell us why you've moved into the I beam design as well?
- We did some I beam stuff originally for lower horsepower applications
and then recently we started doing some near net forged I beam rods for a little
more power that, just less cost doing that way when you're doing near net.
Other than that that's really the only reason.
- Just for those that aren't aware, that near net that you're talking about,
can you explain that in a little bit more detail, what's that actually mean?
- That means we actually forged the rod very close to the final products.
We do machine about 90% of it and we leave the pocket of the eye section
left as forged.
- So that just reduces your machining time, your machining costs and hence the cost
of the finished rod?
- That's correct.
Our bullet line which is our budget line of rods that we do.
- Now you've also got another rod that you showed me off camera earlier
which is kind of a combination of the best of both worlds I guess.
You've got an H beam design but you've also taken some I beam design aspects
into that as well, can you tell us why you've done that and where the
advantages are?
- We did that, it's an H beam with some pockets underneath the pin and above
the bearing and that helps disperse the loads from the 6 o'clock and the 12 o'clock
positions around the parts so that it's not getting the hot spots that you're
normally seeing.
- So more consistent bearing wear over time?
- Yes correct.
- Alright so now that we've dealt with the H beam I beam and really what it sounds
to me like is a lot of it out there in the greater industry is really just marketing
ploy as much as anything.
But I also wanna talk about another really hot topic which is how someone
would select a rod for their particular application.
And I know that a lot of the rods that Carrillo are now producing have a
horsepower rating on them but when it comes to selecting a rod it's really not
the horsepower that's so critical so can you talk to us about what you really
need to know?
- Inertia load and compressive loads are important and that can be calculated
using the bore stroke, RPM, piston assembly weight and then combining
that with the connecting rod length and weight, we can determine if a rod
is gonna be suitable for a given application.
That's also the same information you use for designing a connecting rod.
We do use the horsepower number but that's to determine how much
cylinder pressure there is.
- So really what you're more interested in from a compressive aspect is the
cylinder pressure.
Now of course the cylinder pressure is linked to the horsepower but it's
not a direct correlation there.
So am I right in saying basically you're giving a horsepower number because it's
something that's really simple for people out on the street when
they're selecting parts to decide hey look 800 horsepower, I know I'm gonna
be under that, so I'm gonna be safe?
- Yeah that's correct.
- But if someone was on the other hand, designing something that's outside of
your realm of your off the shelf rods, so let's just say for example someone
was building a Mitsubishi 4G63 and they wanted to make let's say 1600
horsepower and rev it to 11000 RPM, probably beyond what your shelf
stocked part will do, so are they best to come to you and give you the
design of their engine so you can actually make something suited?
- Yeah that's exactly right, that's the best way for us to design
something that will live in what you're trying to do.
- Now we've talked about the compressive loading and that obviously comes down
to the horsepower but the other side of the conrod strength which is really
important is the tensile forces in the rod, particularly at high RPM,
this becomes a problem.
So can you tell us how that affects the design elements of the rod
and what's critical to holding that rod together at high RPM?
- At high RPM you have to select the correct bolt so it can handle the
inertia loads that are seen.
Along with that is the design of the rod as well to maximise the inertia
load capabilities of the rod itself.
But if you don't have the right bolt, it's gonna fail under
higher RPM conditions.
- Look it's been great to get some actual insight into the design of a rod.
Richard, appreciate you giving us that feedback.
If people wanna find out more about Carrillo or maybe have Carrillo design
a rod for their application, how are they best to reach out?
- You can go to our website at cp-carrillo.com or call us at
9495679000.
- OK great thanks a lot Richard.
- You're welcome.
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