Piston/Top guided in street applications

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
englertracing
Guru
Guru
Posts: 1123
Joined: Thu Sep 29, 2011 8:55 am

Piston/Top guided in street applications

Post by englertracing » Tue Dec 04, 2018 5:49 pm

Hello,

I am curious how a piston guided setup holds up on the street.
I hear differing opinions on the setup, some say that they are fine and some OEMs are going in that direction.
I don't love the idea, as the piston can rock quite a bit in the bore, I feel that this could allow a significant amount of yaw on the connecting rod, and create a sort of chamfer on the rod bearing.

Has anyone put any mileage on one of these setups, like 30 or 50k?

Thanks,
Aaron Englert

User avatar
needforspeed66gt
Guru
Guru
Posts: 2030
Joined: Sat May 06, 2006 6:18 pm
Location: North Bay, California

Re: Piston/Top guided in street applications

Post by needforspeed66gt » Tue Dec 04, 2018 6:47 pm

I did a few for offroad AMC and Jeep engines, it's been over a decade and I know they're still out there running.
Nate
Engine Machinist

englertracing
Guru
Guru
Posts: 1123
Joined: Thu Sep 29, 2011 8:55 am

Re: Piston/Top guided in street applications

Post by englertracing » Wed Dec 05, 2018 5:07 pm

do you remember how much side clearance you had?

naukkis79
Member
Member
Posts: 168
Joined: Tue Jul 29, 2014 5:14 am

Re: Piston/Top guided in street applications

Post by naukkis79 » Wed Dec 05, 2018 6:16 pm

Whole piston guiding rod thing is stupid, engine will survive even when rod is not guided but it's weaker and rod oscillation actually increases friction and decreases piston sealing - you are losing power with piston guided rods.

Some OEM used that in 80's, you recognize those engines easily(volvo, mercedes) as rod flapping makes easily herd sound at low revs. Rods usually survive with NA but Volvo used those rods with turbo-engines as well and there it's very easy to bend rod, problem easily fixed by changing proper crank guided rods....

pamotorman
Guru
Guru
Posts: 2740
Joined: Thu Mar 06, 2014 11:55 pm

Re: Piston/Top guided in street applications

Post by pamotorman » Wed Dec 05, 2018 6:30 pm

englertracing wrote:
Wed Dec 05, 2018 5:07 pm
do you remember how much side clearance you had?
i freshen a jr johnson built BBC NASCAR engine with piston guided rods and it had .060 side clearance on the crank. it had phosphor bronze thrust washers in the wrist pins between the rod and piston .

PackardV8
Guru
Guru
Posts: 5542
Joined: Sun Jul 30, 2006 2:03 pm

Re: Piston/Top guided in street applications

Post by PackardV8 » Wed Dec 05, 2018 6:44 pm

Be interesting to know which recent OEM designs are piston guided rods and why.

I'm accustomed to the obsolete stuff where there's enough space in a crankcase to swing a cat by its tail. Every recent engine design I've been inside, I've been awed by the tight packaging. There's literally not room on any of the cranks I've seen recently for any extra side clearance. Take a look inside a Subaru
Image
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering

hoffman900
Guru
Guru
Posts: 1775
Joined: Sat Feb 23, 2013 5:42 pm

Re: Piston/Top guided in street applications

Post by hoffman900 » Wed Dec 05, 2018 7:52 pm

naukkis79 wrote:
Wed Dec 05, 2018 6:16 pm
Whole piston guiding rod thing is stupid, engine will survive even when rod is not guided but it's weaker and rod oscillation actually increases friction and decreases piston sealing - you are losing power with piston guided rods.

Some OEM used that in 80's, you recognize those engines easily(volvo, mercedes) as rod flapping makes easily herd sound at low revs. Rods usually survive with NA but Volvo used those rods with turbo-engines as well and there it's very easy to bend rod, problem easily fixed by changing proper crank guided rods....
NASCAR uses them
-Bob

naukkis79
Member
Member
Posts: 168
Joined: Tue Jul 29, 2014 5:14 am

Re: Piston/Top guided in street applications

Post by naukkis79 » Wed Dec 05, 2018 8:26 pm

hoffman900 wrote:
Wed Dec 05, 2018 7:52 pm
NASCAR uses them
F1-engines used too until they discovered that bending pistons against wall with rod is increasing friction versus traditional big end trust bearing.

There might be reasons to use piston guiding with crossplane cranks, those might flex so much at high revs that not supporting rods against crank might keep them straighter and bending piston less. But for low rpm use crank guiding rods are always the better option.

pamotorman
Guru
Guru
Posts: 2740
Joined: Thu Mar 06, 2014 11:55 pm

Re: Piston/Top guided in street applications

Post by pamotorman » Wed Dec 05, 2018 8:29 pm

PackardV8 wrote:
Wed Dec 05, 2018 6:44 pm
Be interesting to know which recent OEM designs are piston guided rods and why.

I'm accustomed to the obsolete stuff where there's enough space in a crankcase to swing a cat by its tail. Every recent engine design I've been inside, I've been awed by the tight packaging. There's literally not room on any of the cranks I've seen recently for any extra side clearance. Take a look inside a Subaru
Image
the side clearance on the BBC I worked on was done by narrowing the big end of the rods. I believe some of the porsche engines used piston guided rods.

pamotorman
Guru
Guru
Posts: 2740
Joined: Thu Mar 06, 2014 11:55 pm

Re: Piston/Top guided in street applications

Post by pamotorman » Wed Dec 05, 2018 9:40 pm

just noticed that crank has the journals cross drilled.

n2xlr8n
Expert
Expert
Posts: 557
Joined: Tue Jun 28, 2005 9:01 pm
Location: Bama

Re: Piston/Top guided in street applications

Post by n2xlr8n » Thu Dec 06, 2018 9:26 am

pamotorman wrote:
Wed Dec 05, 2018 9:40 pm
just noticed that crank has the journals cross drilled.
Yes- the US-versions do.

The much higher rpm EJ207 varieties do not.
He who is in me is greater than he who is in the world.

User avatar
needforspeed66gt
Guru
Guru
Posts: 2030
Joined: Sat May 06, 2006 6:18 pm
Location: North Bay, California

Re: Piston/Top guided in street applications

Post by needforspeed66gt » Thu Dec 06, 2018 5:18 pm

englertracing wrote:
Wed Dec 05, 2018 5:07 pm
do you remember how much side clearance you had?
I made little shims so that the side clearance at the pin end was .005"-.007"
Nate
Engine Machinist

Newold1
Guru
Guru
Posts: 1628
Joined: Fri Apr 08, 2016 9:50 am

Re: Piston/Top guided in street applications

Post by Newold1 » Thu Dec 06, 2018 8:18 pm

Piston guided rod assemblies would not make economic sense on the street for the little power increase and sealing they MIGHT provide.

The teams and engine programs that use this system are using very expensive special built parts and assemblies to achieve the clearances and fit they want for very high levels of racing and track performance.

Kind of like buying a $150K Peterbuilt tractor to pull your 5000lb. weekend warrior car trailer. :roll:
The Older I Get, The Dumber I Get :wink:

Post Reply