Just wondering what adding 1.6RR's to a stock L98 would do to help it?? My neighbor has a 92 RS that has had a TPI 350 put in place of the TBI 305. He is wanting just a little more power and has done some mods(plenum, runners, etc etc etc) I have an extra set of Crane 1.6RR's here at the house and was wondering what that might give him?? He cant afford to rebuild/mod the motor and being that it only has 40K miles on it, I cant blame him. Any suggestions about this? The stock GM springs are good to about .490 lift right??? Thanks in advance.....

 

They won't help much with the L98 cam, and stock heads, but they'll help a little I would think. Maybe 10hp & 10tq b/c of the plenum and runner work he has done.

 

I put Comp Pro Magnum 1.6's on my stock L98 and shaved the stock valve covers for them to clear. I bought them because I couldn't afford the head and cam swap yet, and I knew I would need the rr's for my new engine anyway, so I figured what the heck. May as well buy them first and pop $300.

I was hoping for around a tenth or 1 mph or 10 hp/tq, but I can't tell what they did. At the same time I installed the rockers, I removed the underdrive pullies and put a new chip in.

The result of all 3 changes was going from a best of 101 mph to a best of 98 mph. I think most of the loss is from less timing in the chip though.

In hind sight, I would have waited to buy them until the new engine is installed. I would dare call it a waste of money to put on a stock L98.

 

Did you guys have to elongate the pushrod slots when installing 1.6 rockers?

 

No. No mods required except taking a dremel tool to the stock valve cover support braces.

The Comps are wider than the stockers and there's only about 1/8 inch clearance between them. The factory valve covers' support braces won't fit between the rockers so you have to cut them out. Once you see the underside of the valve covers you'll understand. It's no big deal at all.

 

I put some on my L98 when it was stock, cant say it gave me more HP/TQ. But it did rev a little quicker. I put on some Mr. Gasket RR that didnt need any grinding.

 

The early iron head Vette L98s most often require the pushrod slots to be elongated when going to 1.6 rockers. I suspect this applies to the engines installed in F Body cars too.

The pushrod cup on the 1.6 rocker is moved closer to the fulcrum; that's how the additional ratio is achieved. This, too, causes the pushrod to ride against the pushrod slot in the heads.

Camshafts with higher than stock lift contribute to this interference problem too.

Ask me how I know. I'll send you a bunch of bent pushrods.

Jake

 

esams, Can the stock baffles stay intact when installing the pro mags?

 

Jake now you're making me wonder if my pushrods are rubbing and causing friction. I have a ticking that seems a little loud to be the injectors.

25THRSS, which part do you mean when you say baffles?

Maybe I should just take a pic when I pull them this weekend.

 

When I installed 1.6 Pro Magnums, I had to slightly squeeze the breather baffles for that little extra clearance, but other than that they cleared the stock valve covers.

The oil drippers have to be ground down though. DO NOT try to break them off. Often, they will break in such a way as to leave a nice hole in the valve cover. So take the time and grind them off instead.

I can't speak for other late model heads, but I know that the 86 iron Vette heads call for the push rod slots to be enlongated for clearance.

When I was rebuilding the engine, I told the machine shop I was going to run 1.6s and asked that the slots be elongated. They only did the intakes, which is something I should have caught before I bolted on the heads.

I didn't, and ended up with a bunch of bent exhaust pushrods. That meant I had to tear down the engine again to pull the heads to have them modified. A lot of extra work and expense for something I should have caught back at square one.

I usually catch things like that, but that one slipped by me.

Jake