1991 RS 305

Hey, mines a 1985 IROC TPI 305. To those considering this mod, heres my "reall world" impression of 1.6 Comp Magnum roller tip rockers on a non-peanut cammed TPI. I just installed these a few weeks ago, after all the basic / free / first mods shown below that most do to these. Truthfully, doing the 1.6's after the other mods did nearly as much alone as all the other mods combined, no joke! The 85 TPI's had the decent, "L69" cam, .403/.415 lift, 202/206 duration. The 1.6's make it .430/.443 lift, with a possible "bump" in effective duration, though on paper, the duration would look the same. This made a very noticeable change on the butt-dyno, the car pulls considerably harder from 2500-5000, with no loss below that. I'm always skeptical of most huge claims from mods, but this mod is worth it, at least for me it was. I researched this quite a bit beforehand, and it seemed to make sense. For the money and time invested, a 10-15 hp gain is within reality, and well worth it!

The only downside, if there is one, is slightly more valvetrain noise at idle, similiar to the sound of the injectors. This is no doubt due to the added moving parts from the roller tips. To me, the rocker ratio change is a nice way to get the positive effects of a higher lift, stock duration cam, while staying within the parameters of the stock chip.

rudyt5000

yeah i been wonderin how those would perform.....i believe i have a roller cam on my 87 ..from what i understand....did you put them on yourself.....im learnin how to do stuff on my car...and i would like to do da same with the 1.6 roller tip rockers. thanks for postin this up ...really helpful

robsgta

All small blocks chevy's respond well to higher lift. My 383 dyno'd gain was 23 horsepower after going from stock rods to hardened push rods & crane dual 1.6's. most 350's gain around 20 horses at 5000 rpm. No matter how much your lift changes your duration always stays the same.
Yeah 1991rs305 they do get pretty noisy

1991 RS 305

Yes, my buddy & I did it, not difficult at all. Just do some research on setting lifters when doing the swap, and use ALL the assembly lube provided. I had mine apart 1 yr ago to do valve seals, and wish I would of done the rocker ratio swap then. Mine, being an 85, called for the "non-self-aligning" type. Just be sure of what you currently have before buying new. My friend has a 89 Formula L98., his are "self-aligning". We put Comp Magnum 1.6 "self-aligning" in his last may, his car woke up the same way. We had already put a Corvette servo in his 700R4 also, so he had a nice, crisp "chirp" on the 1-2 shift before the rocker change. Afterwards, the things lights em up on the 1-2 shift. Same for mine. We did his first when doing his valve seals. After seeing the results on his L98, I decided to go for it on my LB9. I'd do it again in a heartbeat. The GM stamped rockers are famous for not being a true "accurate" 1.5 ratio, usually 1.42-1.45, according to David Vizard. Therefore, you not only gain lift, its possibly more than going from 1.5 to 1.6. In addition, the exhaust note of both cars , while not being "lopey", like a cammy lope, seems "slightly" throatier / guttier especially at idle. BTW, heres the formula to determine what your lift changes to going from stock 1.5 ratio to 1.6 using my cam lift as example:

intake .403 / 1.5 = .268 * 1.6 = .430

exhaust .415 / 1.5 = .276 * 1.6 = .443

90-irocdx3

iTrader: (4)

well i have heard people using 1.7 rockers on a small block but i have no idea how it changes maybe even another 30,but i dont know if it is good for the street.sorry to go off topic a little.

rudyt5000

yeah the mustang 5.0 stock i think is 1.6 already...so they use 1.7 on their cars....i would think that is too big for our cars..havin clearance issues or something and 1 question to who may answer.....im on a budget so what would be a good 1.6 roller rocker....i know there are stamped steel, aluminum and etc.. and if possible can they be bought used ? i wanna be overhauled or pimp my ride

305q_ta86

iTrader: (1)

Wow, I had been considering doing that for a while, and I think I will on my LG4 now.

Do you need new pushrods or anything? Anything that doesnt come with the rockers?

1991 RS 305

Mine has 60.000 act mi, all adult driven, some "spirited", but never abused. The pushrods, springs are fine with the added lift. If you now have a stock lift cam, the rocker change won't be enough to go beyond what the stock springs can handle, unless they're weak from high miles, abuse, etc. You should visually check that its all in good condition now, with no galling on the old rocker arms anywhere, tips of pushrods / valve stems, etc. If so, I'd replace anything needed. I've been using Mobil 1 since I got the car from original owner at 45.000 mi and there were no signs of anything when I did mine. In fact, everything was very clean. Pushrod guidehole clearence is sometimes an issue, but was not on both my LB9 and my buddys L98, we watched for it.

robsgta

Well truth be known GM really went super cheapo on parts when they assembled our motors the valve train & valve springs are really weak.
If your going to do the roller rockers you might as well buy some decent hardened push rods as well under a load the stock ones have been shown to deflect and cause a small loss in power comparable to a good rigid set.
But keep in mind that push rods get worn down on the ends, when they do get worn from bothe ends that takes away from your total lift .

Just thought that I would throw this at some of you guys a few years back when I did have a pretty much stock 350 with all of the free mods known to man done at the time I had a real bad valve seal leak and my car smoked bad at start up. I bought a set of edelebrock 2.02 heads lightly ported the bowls bolted them on and went 13.30' at 104 mph.

bluroc

91RS305, are your heads 416's? Mine has the L69 HO and I have been considering this for a while, but I had heard some having trouble with pushrod clearance on a stock motor. Did you just replace the rockers and use your stock pushrods?

1991 RS 305

"bluroc", 416 heads, stock pushrods, same cam as you. Your HO 305 should have 416's also. Just pull a valve cover, its stamped on the head between springs.

vwdave

I have a LT4 Standard cam with some bolt-ons on a 350 TPI. Car really woke up. Went from a 446 lift to a 480 lift. 2500 rpms on up showed a really nice improvement. (My Torque Converter stall speed is at 2500 or so, so it might help even lower, who knows.)

A little pricey ($330.) But so far, well worth it.

(This was done with Pro-magnum 1.6's, self aligning.)