The Oldsmobile Connection

abbike18 · Joined: 17 Oct 2004 Posts: 30

does anyone know anything about or have any experience with upgrading rocker arms on a 1991 3.8l v6? i have not found any specifically for this engine, but i was thinking i could use the right size for a chevy v8. It seems to be a worthwhile upgrade to change the ratio for more lift and more power : ) thanks

88 Coupe · Posted: Sun May 15, 2005 8:58 pm Post subject: Re: Rocker arms for 1991 3.8

Hi abbike18, hello all,

Quote: does anyone know anything about or have any experience with upgrading rocker arms on a 1991 3.8l v6? ........
Only enough to know that the marginal gain would not be worth the time you've spent thinking about it.

Regards, Norm

abbike18 · Joined: 17 Oct 2004 Posts: 30

even if i upgrade the ratios so that there is a greater lift?

88 Coupe · Posted: Sun May 15, 2005 11:47 pm Post subject:

Please reread my post. Which part was not clear?

Hans · Joined: 28 Aug 2003 Posts: 156 Location: Pocatello, Idaho

you are looking at 8-10% probably the best improvment you can do on a n/a 3800.

http://www.seriesoneperformance.com has them on a group buy, quite a good deal.

Joes 94 cutty · Posted: Wed May 18, 2005 10:55 pm Post subject:

Ignore Norm. :lol: :lol:
-Joe

88 Coupe · Posted: Thu May 19, 2005 9:33 pm Post subject:

Hi abbike18, ALL

Sorry, I was short: it was uncalled for.

Quote: even if i upgrade the ratios so that there is a greater lift?
This subject has been covered several times on this board.

Over the years, various combinations of ratio combinations in performance engines have resulted in small gains or losses depending on the combo.

Changing the rocker ratio to get a higher valve lift in your computer car will net a zero to negative power gain.

If there is someone on this board with actual experience on the same combo as yours, I'm sure they will correct me, as that is what this message board is all about.

Regards, Norm

DrJay · Joined: 19 May 2005 Posts: 6

I'm a little curious as to why you believe higher lift and slightly longer duration will not equate to gains in a 3800.

I don't have a before and after dyno for the ones I sell simply because I don't have a stock 3.8 to test them on. While I use them on my engine, using my before and after numbers would be a little unfair and the results would be useless as compared to a near stock engine. On the other hand the SII rockers have been around for ages with dyno proof of gains.

You mentioned having a "computer car" as being an issue but that still doesn't make sense. Higher lift will pull more air, the MAF sensor will detect it and add the correct amount of fuel.

You also mentioned having a "combo" of ratios that decreased performance. I can only assume you mean between the cam lobe lift and rocker ratio. While the intake and exhaust timing can seriously affect power, I have yet to see simply more lift equate to less performance. Although I could imagine a stock engine with .608" lift not performing at it's peak, if you stay within reason higher lift coupled with lower friction through a roller tip is always a good bet.

Hans · Joined: 28 Aug 2003 Posts: 156 Location: Pocatello, Idaho

drjay....

did not know you had a 93 88 as well..

really looking forward to the NGK plugs. :P

88 Coupe · Posted: Fri May 20, 2005 12:54 am Post subject:

Hi DrJay,

Quote: I don't have a before and after dyno for the ones I sell simply because I don't have a stock 3.8 to test them on.
Dyno numbers would be a welcome addition to this discussion.

If the factory did not optimize the cam timing for his engine combination, I might agree.

I've seen both gains and losses when when such band aids have been used to cover a poor cam choice.

Roller tips are worth considering if one is replacing a worn out rocker set.

Regards, Norm

88 Coupe · Posted: Fri May 20, 2005 1:23 am Post subject:

Hi DrJay, All,

Quote: .......... SII rockers have been around for ages with dyno proof of gains.........
I think you need to add "in selected applications".

Quote: ........... Higher lift will pull more air, the MAF sensor will detect it and add the correct amount of fuel ..........
And that will make 10% more horsepower in his application?

Quote: .......... I can only assume you mean between the cam lobe lift and rocker ratio........
Please explain.

Regards, Norm

abbike18 · Joined: 17 Oct 2004 Posts: 30

My 1991 SI 3.8 has pedestal mounted rockers. there are aftermarket pedestal mounted rockers out there, but not a great selection. Is there any way I can convert my pedestal system to stud mounted? Is that what these are for: Rocker Arm Studs

Thanks for everyone's help so far

88 Coupe · Posted: Sat May 21, 2005 4:48 pm Post subject:

Hi abbike18, All,

Quote: Is there any way I can convert my pedestal system to stud mounted?
There is always a way. I suggest you first decide if the expected return is worth the time and expense.

Quote: Is that what these are for: Rocker Arm Studs
Yes.
Among professionals These are prefered.

Mine are visually identical, but are a generic brand.

I have them on my 454 Chev, one small block Chev, and one 468 Olds.

Either Crane or ARP can tell you about part numbers for your application.

Regards, Norm

DrJay · Joined: 19 May 2005 Posts: 6

88 Coupe wrote: Hi DrJay,

Quote: I don't have a before and after dyno for the ones I sell simply because I don't have a stock 3.8 to test them on.
Dyno numbers would be a welcome addition to this discussion.

http://www.intense-racing.com/8ball.html Hope this will do for now.

If the factory did not optimize the cam timing for his engine combination, I might agree.

The factory puts out cams that compromises power for fuel efficiency, emissions and reliability. That's why you can upgrade the cam to begin with.

I've seen both gains and losses when when such band aids have been used to cover a poor cam choice.
"Dyno numbers would be a welcome addition to this discussion." Besides, many people enjoy the ease of installation and gains received from rockers. Of course a camshaft is a better solution, but not everyone is willing to dig that deep in their engine so for them this is a good alternative.

Roller tips are worth considering if one is replacing a worn out rocker set.
I look at reducing friction as a benefit reguardless of replacement necessity. Obviously GM agreed with that because in 1993 they switched to roller fulcrum rockers and thinner low friction rings.

---
And that will make 10% more horsepower in his application?
The manufacturer claims an 8-10% increase in performance. A good way to estimate power gains is by looking at the increase in airflow. Generally speaking 1% more airflow will produce 1% more power. Many variables involved in that statement, but for our little bench dyno discussion I'm sure you'll agree it's usable. With our intake lobe lift of .250 a stock 1.6 rocker will take it to .400" at the valve. With the 1.72's we're looking at .430". That's an increase of 7.5%. Add that to the reduced friction and lightweight aluminum design and I'm sure you can easily see where they got the 8-10% figure from. Stack other modifications on top of it and gains are likely to increase.

Of course 7.5% more lift doesn't always equal exactly 7.5% more flow, but again for our bench dyno it should suffice to explaining the estimate.

Please explain.
.... Over the years, various combinations of ratio combinations in performance engines ...

Your statement was a little confusing about "various combinations of ratio combinations" so I figured you were talking about a "combination" of a rocker ratio and a certain lobe lift. Such as X cam with Y rockers didn't work, but Y rockers with Z cam did.

Hope this helps to explain a few things.

Hans - Don't worry, they're out the door ASAP! :D

abbike18 · Joined: 17 Oct 2004 Posts: 30

what is the stock rocker ratio on series 1 3.8 liter engines?

thanks