LB9GTA

iTrader: (1)

I have a '91 GTA with a 305tpi and roller rockers(among other mods).

I have noticed that my 1/4 mile times have not improved(even got worse) since I have added the roller rockers.

I have a comp cam - grind #xr258
gross valve lift - int.480 - exh..487
dur @ .006 258 264
dur @ .05 206 212
lobe lift .3200 .3250
lope sep .110

I have also added 981-16 stiffer valve springs.

Is there a chance that I have maxed out the air coming into my motor with the 1.6 roller rockers?

Am I trying to put more air into the motor but it can't use it?

Do I need better heads in order to utilize these roller rockers?

I am considering switching back to the stock arms and will post times and differences.

LB9GTA

iTrader: (1)

anybody?

BC GTA

I have the exact same cam in my new GM 305 engine. First, I would like to say how satisfied I am with this cam for all around performance for my daily driver. I could have gone for a cam with more lift and duration and a rough idle. However, this was a good choice for my use. Second, I asked my mechanic who installed the engine and cam about up grading to 1.6 ratio roller rockers. He advised it would be too much for my application. It may have something to do with the tight lobe separation angle. Plus it would produce a rough idle which I did not want.

bnoon

If your heads are unported, you're stalling out the ports at the .48 lift with the 1.5 ratio rockers. At .512 lift with the 1.6 rockers, you're well beyond air stall lift values of the stock ports. Once you reach stall, adding more lift doesn't help. Port and polish the intake and exhaust and then put the 1.6'ers back in and you'll notice the difference you were looking for.

You're going to want to search for 081 or 416 port and polishing topics. Basically, the 081 and 416 heads are the same ports, just the 416 is the earlier perimiter valve cover version of the same head.

LB9GTA

iTrader: (1)

So are you saying that I should go back to the 1.5 factory rockers??

They will be better than the 1.6's?

Will I notice the difference??

1989GTATransAm

iTrader: (3)

On the intake the lift with the 1.6 rockers is .512 inch. On the exhaust side the lift is .520 inch. This is way to much for stock heads. I don't know if your heads have been modified for this much lift or not.

LB9GTA

iTrader: (1)

my heads are stock.

So, the exhaust is too big or the intake?

What if I just changed the intake rockers back to the stock 1.5 arms?

billyhoss

iTrader: (1)

i think what there tring to say is that there both too big for ur stock heads, with the 1.6 rockers on the stock heads it can not flow more air in then if u had the stock ones back on.basicly ur maxed out on air flow with the 1.5`s, thats why u never seen a gain, u said u have stock heads with the 1.6 rockers? did u get any work done to them for the added lift of that cam? with the 1.6 i would think that u would run into problems with spring bind on the stock heads,hate to see u break some thing cause ur valves are bottoming out. iam also in sask so not far from u

LB9GTA

iTrader: (1)

Hey BillyHoss, where are you in SK?

I have put stiffer valve springs in.

Will I gain anything by putting the stock arms back on?

billyhoss

iTrader: (1)

i live in prince albert, north of saskatoon, u may gain, u may not, depends on how much they are out flowing with them 1.6`s on, iam goign to guess u will not see a difference, like someone already said if u take the heads off and port and polish them up u should see a gain with the 1.6`s then

BT283

iTrader: (3)

hey what is up guys. I have a nice set of already ported, polished, bowl hogged, 305 heads. They have a Manley race flo valves, that are swirl polished, stainless steel, and have undercut stems. they have screw in studs and oh yea they run great. they have apprx. 1k miles, since they were built 250 dollars let me know