I am wondering what is the largest cam I can swap into iroc 350 tpi without having to worry about piston to valve clearance..... will be going in a supercharged iroc let me know thanks

 

L98s have dished pistons from the factory, so I doubt you will run into a cam w/ enough lift to hit the pistons on lift numbers. I am sure that you could find a cam w/ large enough duration to have the timing events possibly hitting the pistons, but I doubt you would run that cam on a stock short block due to the rpms it would require.

Are you going to leave the shortblock stock w/ the supercharger? You need to find a cam to match w/ that blower, so do some research on that... What SC do you have??

 

Not completly true. The L98 short block I rebuilt was out of a police car. It shared many things with a L-98 except that it was a high nickel block and it had (drumroll) Flat top four valve relief pistons. Granted it was out of a 91 police car so there are differences, but to my understanding, a L-98 could be ordered with the options my short block had.

It would not hurt to pull the heads and look. It sure surprised me.

 

Dang... would have surprised me as well... Guess you learn something new everyday...

 

vortech s trim.... gonna use stock shortblock and heads till it blows.....

 

Keep in mind, lift isn't the only thing that effects VP clearance. Duration and valve timing are 2 more factors.

Sure, a cam may open up a total of say .575", but if it's peak is when the piston is still quite low in the hole, then no issues, but if it is installed bad or degreed wrong, then you can be in for a world of trouble.

Just food for thought.

 

what cam would u recomend with stock heads... supercharger.. long tubes. 3800 stall yah i know kinda big.... everything pretty much stock...

 

something with around 210 @ .50 and around 220 @ .50 on the exhaust with a 113 or wider LSA. I ran a comp with these #'s and the stock ECM was fine with it. I also ran it with 1.6 rockers which gave it around .533/.544 lift and no piston to valve clearance issues. But keep in mind the stock L98 heads have probably almost reached the flow/stall point at this lift.

 

can an LT4 hotcam be run in an L98 with 1.6 rockers?

 

Said that in my original post...

yes

 

Hold up. My L98 has FLat top 4 valve relief pistons. Is that rare? I never thought to question it?

 

Guess not. Tore into a buddies L98 and I thought it had dished pistons, but didn't pay too much attention to the pistons cause several rods were destroyed!!!

 

Yes it can, but it will put you above the operating range of the stock runners and intake, possibly even aftermarket ones.

 

I never said it was rare or barely happened. I just meant that I MYSELF usually don't hear or see much of them at all from the factory. So I guess that they are just less common? Or now are they more common?

 

I just figured they'd all be one way or another.

 

That was my assumption too. Been wrong before and will again...:lala:

I dunno. Guess there are some of each though... since some guys say they have flattops and others dished.

 

I don't think there is anything unique about your L98. It is my understanding that all L98's came with four valve relief flat-tops. My stock L98 had them, so did my buddies 1988 Notchback GTA, and my friends '87 Iroc L98. Also, I know another guy who purchased a L98 out of an '89 Iroc to swap into his '88 Fiero GT and that motor had the four valve relief flat-tops as well. I think they are pretty common.

Also, I know that "police packages" had differences in them to make them faster and handle better, but this is the first time I have heard someone mention that the bottom ends of the motor would be different?

 

They did not all have flat tops. speed 88. Chris89GTA was not. Mine was different and not rebuilt. The different block numbers help to illustrate that to me at least.

 

Is there a benefit one way or the other?

 

My 88 L98 had 4 valve relief pistons.

As for the hot cam, you can run it, but youd be pushing it with that lift and the stock heads. It would be fine with 1.5 rockers because that would keep the lift under .500".

 

valve springs seats on stock heads are not big enough to install springs that can handle that much lift...correct ? though tyou had to have them machined to fit a larger diameter spring

 

Stock spring diamater is 1.25". IIRC, the LT4 hot springs are 1.37". Aside from machining the pockets, youll need to machine down the guides as well.

 

The pistons on my original L98 motor had 4v reliefs. I have pics from when I tore it apart after it blew if anyone wants. They are NOT pretty though.

Also, my rebuilt long block has 4v reliefs as well.

 

supposedly the lift is rated at .525 with the 1.6 rockers. read somewhere max clearance is about .600. i don't know that for a fact, just what i saw, maybe understood it wrong?

KAM

 

I checked in my chiltons book and L98's through 1990 had 9.3 to 1 compression. It said that 91-92 had 9.5 to 1.

Could this be the difference between motors with flat tops and dished pistons? I noticed here on the site, it says only 9.3 to 1 on all. Which is right?

 

You can buy 1.25" spring that will hadle .600 lift from any place that sells performance parts.

 

I don't know, but, maybe the moderaters would let us take a survey of members(?).

 

yeah! I would like to know which is the right ratio.

 

If you are going to run the hot cam,you can use stock z28 valve springs. They have a seat pressure of 100-110 which is enough to handle the lift.And they'll fit in the stock seats with out any machining.