SpeedTalk Store - Opinion Columns

1.7 Rocker Arms SBC

General engine tech -- Drag Racing to Circle Track

Moderator: Team

1.7 Rocker Arms SBC

Postby 1989TransAm » Thu Jun 05, 2008 11:38 pm

Just wondering with the advances in light weight valve trains such as what is on the new AFR Eliminator heads would a 1.7 ratio rocker arm be feasible for a mostly street driven car with a 355 SBC and occasional track use? Also advances in light weight rocker arms, springs and the new roller camshaft designs might play a role in the scheme of things.

I was just basing the thought with the LSX motors in mind. The only big difference I can think of would be the diameter of the camshaft versus that on a SBC. I would think GM would want the valve train to last a minimum of a 100,000 miles for the LSX motors. So why wouldn't a 1.7 ratio rocker arm be feasable with today's components?

Reason I'm asking is to tap into the excellant head flow of AFR's new 195 Competition head in the Eliminator series. I'm talking of lift around .600".
1989TransAm
Guru
Guru
 
Posts: 3473
Joined: Thu Feb 15, 2007 8:43 pm
Location: Cypress, California

Postby revolutionary » Fri Jun 06, 2008 8:07 am

The common limitation on rocker arm ratio is the length of the arm itself - meaning the distance from the stud to the tip of the valve and from the stud to the pushrod. Moving the ratio up to a 1.7 is great but it really starts getting the pushrod cup close to the stud/fulcrum. One of the reasons LSx engines and many others like Fords run more ratio is becasue the rocker arm is so much longer. The only way to do get more ratio on a sbc is to either relocate the rocker studs towards the intake manifold side or use a shaft rocker with the arm relocated similarly and then use a longer arm like one designed for an 18* engine. BTW I had T&D make me a set of rockers designed like that for some AFR heads and they are muy nice.
Daryl

Revolutionary Performance and Machine
revolutionary
Guru
Guru
 
Posts: 1397
Joined: Wed Feb 20, 2008 10:43 pm
Location: Colleyville, TX

Postby ralph85 » Fri Jun 06, 2008 10:27 am

I've got 1.7s on my Track 1s. Haven't had any issues for about 3 seasons of racing and some street driving. However, the perf improvement over the 1.6s was minimal and if i drove it on the street more often, i'd probably go back to the 1.6s.
Ralph
ralph85
Member
Member
 
Posts: 150
Joined: Wed Sep 26, 2007 4:05 pm

1.7 rockers

Postby bigjoe1 » Fri Jun 06, 2008 10:29 am

The only way I would go higher than 1.6 is with a shaft setup. The gains would be very small, probably in the order of 6 or 8 HP. It is very hard to justify the cost.

JOE SHERMAN RACING ENGINES
bigjoe1
Show Guest
Show Guest
 
Posts: 5276
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703

Postby 1989TransAm » Fri Jun 06, 2008 11:24 am

Thanks guys. Valid points made by all.
1989TransAm
Guru
Guru
 
Posts: 3473
Joined: Thu Feb 15, 2007 8:43 pm
Location: Cypress, California

Postby jmarkaudio » Fri Jun 06, 2008 3:34 pm

A little more work involved, a cam change would be cheaper than shafts and could make better gains.
Mark Whitener
http://racingfuelsystems.myfunforum.org
____

Good work isn't cheap and cheap work can't be good.
User avatar
jmarkaudio
Guru
Guru
 
Posts: 3614
Joined: Wed Sep 26, 2007 10:26 am
Location: Florida

Postby Jason G » Sat Jun 07, 2008 8:23 am

If you are only talking about getting .600" lift using 1.7 rockers..........I would just change the cam as Mark mentioned.

Where do you want peak power to occur and where do you want to shift?

What size intake valve?

Jason G.
Jason G
Pro
Pro
 
Posts: 227
Joined: Mon Feb 21, 2005 8:56 pm
Location: TX

Postby 1989TransAm » Sat Jun 07, 2008 5:05 pm

Hi Jason

From an earlier long thread on rocker arms it was suggested that it would be better to use a higher ratio rocker arm than a higher lift on the cam lobe. I agree if one had a 1.7 rocker arm in mind from the start than grinding the cam that way would be beneficial.

In my case I was just toying with the idea and wondering in todays world if that would be a feasible way to go in a mostly street car with some strip time. Again in my case I expected peak power to be in the 5800 to 5900 rpm range with shifting in the 6200rpm range.

Well after getting the car on the dyno and after some tuning the car was making peak power at 6350rpm and still climbing. It was shut down at the 6350 mark and I could not pursue it further as there were other cars waiting to get on the dyno and I already went past my allotted time.

So maybe shifting in the 6700-6800 rpm range. Intake valve is 2.08" on the AFR 195 competition heads I will be putting on the car. They come with a light weight valve setup for higher rpm operation. Current valve lift is .576". Was thinking about picking up a few more ponies with getting the lift up to .600" or so and also the increase with effective duration.

Joe has stated it just is not worth the extra money spent for the 8 rockers arms for the few horsepower that one might get. My thought was based on how well the new AFR 195 Competion series heads flow that it might be worthwhile having the intake valve spend a little more time at the higher lift. :wink:
1989TransAm
Guru
Guru
 
Posts: 3473
Joined: Thu Feb 15, 2007 8:43 pm
Location: Cypress, California

Postby BAD67355 » Sun Jun 08, 2008 6:54 am

on average what are the gains usually in hp going from a 1.5 to a 1.6 rocker?
BAD67355
New Member
New Member
 
Posts: 25
Joined: Wed Jan 30, 2008 9:29 pm
Location: Newark DE

rockarms

Postby bigjoe1 » Sun Jun 08, 2008 9:28 am

I have done this at least 100 times, it does have something to do with how much HP you have to start with, but is is common to see a gain of 10 maybe up to 15 or 17 Hp on a 450 to 500 HP engine. Some engines respond more than others, and the cam grind will vome into play too.

JOE SHERMAN RACING ENGINES
bigjoe1
Show Guest
Show Guest
 
Posts: 5276
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703

Postby Alan Roehrich » Sun Jun 08, 2008 10:16 am

Back before the crate engines took over, we were running 1.7:1 intake rockers on the two barrel small block Chevy circle track engines we built, up to about 7000 RPM or so. Angus Racing made them for me, they were 7/16" stud rockers, and with so careful fitting, they worked fine on those engines in that application. Peak lift was about 0.600 or so.
User avatar
Alan Roehrich
Guru
Guru
 
Posts: 2676
Joined: Tue Jul 04, 2006 4:58 pm
Location: Murfreesboro TN


Return to Engine Tech

Who is online

Users browsing this forum: 9500plus, DanE2, Google [Bot], Robban 54 and 11 guests