Latest Wisdom on Mild Cam & Rockers for 3.4pr (Page 1/5)
thesameguy FEB 20, 11:21 PM
I'm gonna be dropping the drivetrain out and thinking maybe putting some effort into the motor. It's a 3.4pr, running the stock ECM. I don't have the ability to change that. What's my best option for a mild cam - maybe a Comp 260? Maybe 1.5 rockers are the same time? Is that likely to push the computer too far out of its comfort zone?
lou_dias FEB 21, 12:23 PM
If you want to save money and get a performance boost, you can get 1.6 roller fulcrum rockers from the Gen2 3.1 and not need extra hardware. I think there is still something about the nut but I wouldn't know as I've never used them. If you do a search, I believe there is a forum post dedicated to their re-use.

You can run narrow body FULL roller rockers (1.6) if you use these crane stud adapters:
https://www.summitracing.com/parts/crn-99148-2

These are the rockers from Scorpion and Crane:
https://www.summitracing.co...-body-style%3Anarrow

You'll also need my 1/8" valve cover spacers as the nut hits the stock valve covers ($130 shipped in the US). I've sold several sets already so you can ask around about them.

So that setup is pricey and that's what I do when I get an engine rebuilt - I buy all new parts... However, I've had zero failures and nice performance. Both me and La Fiera run this setup in our engines. He made his own spacers...others used custom valve covers. With the spacer's you'll need the F-body 2.8 valve cover gasket as the lower gasket...the stock Fiero one still gets inset into the valve cover.

This will get you from .410" lift to .436" on the exhaust and .390" to .416" on the intake if you are using the stock Fiero/3.4 cam.
My 3.4 made 160 rwhp with the stock 3100 roller cam and these rockers when it had a bad old-style distributor. Only other mods was the 57mm throttle body, dawg-modded ported upper intake, ported middle and lower intake and ported heads using Fiero Store SSI valves...and finally Fiero Store short headers and cross-over. I had a 3100 block bored to OEM 3.4 and used F-body 3.4 pistons and kept it's stock roller cam setup. It's probably making 170 now since replacing the distributor and opening up the channel across the ports of the bottom side of the middle intake.

[This message has been edited by lou_dias (edited 02-21-2021).]

Notorio FEB 22, 12:33 PM
Thesameguy, aren't you concerned that the cam/rocker upgrade will fail smog check?
thesameguy FEB 22, 02:49 PM
I am, yes. But the engine is tight, cat is good, and it runs very clean right now. I think I've got some headroom and I'd be interested to see what that looks like. TBH, almost my biggest concern is showing up with a Comp 260 and them failing it because the idle sounds off.... although I've read varying accounts that once it's warmed up it's pretty smooth.

I'm also not sure what's in it right now... it came to me with a 3.4pr, but I don't know whether it's a donor motor, a crate 3.4ht, or whether they did something like keep the stock Fiero cam (which I believe is a bit more lift?)

I'd like to shift the power band a bit higher up the revs, I don't think the Fiero's stock gearing needs all the torque that motor makes. Although tbh I'm not sure how functional that is with the stock intake manifold. I can legally ditch that, but I don't think there are any *easy* options there.

@Lou - Your post recently is actually what made me start thinking about this - that approach is high on my list of candidates!

[This message has been edited by thesameguy (edited 02-22-2021).]

Patrick FEB 22, 04:27 PM

quote
Originally posted by thesameguy:

What's my best option for a mild cam - maybe a Comp 260? Maybe 1.5 rockers are the same time?



What else are you planning to do to improve the engine's breathing? Simply adding more cam lift and/or duration to an otherwise stock engine will not accomplish much if anything... especially if your engine is still running the highly restrictive factory 2.8 Fiero intake unmodified.
La fiera FEB 22, 06:02 PM
I can come up with a cam design to compensate for that restrictive intake system. Since my cams have very short seat timing I can get away with a bit more duration and it wll shift the power higher in the rpm range.
thesameguy FEB 22, 06:43 PM
I like that idea. The old Crane 2030/3.4ht cam seemed like a good option for me, but it's NLA. The Comp 260 seems just a smidge much.

If there's an easy button for the intake manifold, I'm happy to press that button. The only legal requirements are that it maintain the function of the stock manifold, so as long as it has all the relevant vacuum ports and EGR port, I have free reign. It seems like there is no amount of porting - even something like extrude hone - which is gonna do anything useful, and I don't think there are any factory manifolds which are helpful, nor any aftermarket options at all.

The exhaust is a good size aftermarket with a Flowmaster, and the manifolds are WCF "stock replacements." I think the exhaust side is fine. If there's a decent cam & intake setup that won't break the bank, now is the time.
Patrick FEB 22, 07:11 PM

quote
Originally posted by thesameguy:

The exhaust is a good size aftermarket with a Flowmaster, and the manifolds are WCF "stock replacements." I think the exhaust side is fine.



I take it that the WCF "stock replacements" don't have those ridiculous restrictions in the ports that the factory exhaust manifolds left in place?

lou_dias FEB 22, 08:52 PM

quote
Originally posted by Patrick:

I take it that the WCF "stock replacements" don't have those ridiculous restrictions in the ports that the factory exhaust manifolds left in place?



The Fiero Store cross-over doesn't have the D-crimp restrictions...and for pre-88 they offer a larger (2.25") diameter down-pipe section.
La fiera FEB 22, 08:59 PM

quote
Originally posted by thesameguy:
The exhaust is a good size aftermarket with a Flowmaster, and the manifolds are WCF "stock replacements." I think the exhaust side is fine. If there's a decent cam & intake setup that won't break the bank, now is the time.



That's when a good custom cam comes into play. I'd do a reverse split pattern cam to compensate for the intake restriction, that's the same cam profile approach I do for the 2 barrell V8 engines.