Cam Requirements for 3.4

[BillS]

I am using a 1994 3.4 Camaro engine.

Will cams available for earlier version (2.8, 3.1) work with the computer on the 3.4, or is there a home sensor signal that would be missing?

[93camaro_zzz]

You really need a cam with a cam sensor tab on it. The 2.8 and 3.1's in the 3rd gen F-bodies were MPFI, not SFI, which basically means they batch-fire. The injectors dont fire sequentially (according to firing order), the fire bank by bank. (Right bank, left bank, right bank, etc) So in essence you are getting alot of fuel that just puddles up on top of the valves, and that doesnt exactly combust as well as a perfect fuel mist from SFi. This, worse emissions, and worse performance. The cam sensor is what runs the SFI. So if you get a cam without one, the car will still run, and idle well, and wont even throw any SES lights, but it wont be running perfectly. My car has a cam in it without the cam sensor tab, so I can attest to all the downsides of it. lol I basically had to relearn how to drive my manual when I put the cam, cause it ran that rich, I would try to start out in first, and it was trying to die with so much fuel. Now I drive it fine. I would HIGHLY reccomend finding a cam with that cam tab on it.

[BillS]

Thanks Jordan, that's exactly the sort of feedback I needed.

Is the lump on the cam something that passes by a Hall Effect sensor in the block? If so it would seem easy for the cam companies to offer that sort of blank!

[Guest]

You really need a cam with a cam sensor tab on it. The 2.8 and 3.1's in the 3rd gen F-bodies were MPFI, not SFI, which basically means they batch-fire. The injectors dont fire sequentially (according to firing order), the fire bank by bank. (Right bank, left bank, right bank, etc) So in essence you are getting alot of fuel that just puddles up on top of the valves, and that doesnt exactly combust as well as a perfect fuel mist from SFi. This, worse emissions, and worse performance. The cam sensor is what runs the SFI. So if you get a cam without one, the car will still run, and idle well, and wont even throw any SES lights, but it wont be running perfectly. My car has a cam in it without the cam sensor tab, so I can attest to all the downsides of it. lol I basically had to relearn how to drive my manual when I put the cam, cause it ran that rich, I would try to start out in first, and it was trying to die with so much fuel. Now I drive it fine. I would HIGHLY reccomend finding a cam with that cam tab on it.

WTF? Sounds like there's something else going on here.

BTW, the MPFI, from what I have seen fires all injectors at the same time, especially if it uses the 7730 or similar PCM. The injector banks are bridged internally in the ECM.

The fuel doesn't generall "puddle on the back of the valve", the fuel will hit the back of the valve and vapourize, due to the heat that is in the valve from the combustion process, that is transfered into the valve head. this vapourizing helps get a good fuel/air mixture, and has been proven to work well for many years on many applications.

The reason you are running so rich, if that is indeed what it is, is because of you running in limp mode (no cam position signal), the PCM reverts to batch fire (not bank fire), and due to the size of the injector which IIRC was a bit large for batch fire, in addition to limp mode adding more fuel than required as per programming you get a rich condition.

For myself, if I really needed the cam position signal, and the cam I wanted didn't have the tang, I'd add one, a properly selected bolt and careful installation will do wonders.

[BillS]

Uh...not sure I want to be adding bits to the cam if I have the option of just finding a blank with it, or regrinding a stock 3.4 cam. There are enough ways to screw up without me introducing any added variables.....

BTW, looks like you have a similar engine to the one I use in my street Fiero - 3.2 turbo. What size injectors are you using in it?

My latest project is a bit different for me - I am used ot the Fiero era engine management, but this time I am using a 3.4 from a 94 Camaro, and I want to retain the SFI/DIS system when I install it in a different car (a 2000 lb. sports car.

The camshaft options seem a bit limited for these engines, retaining stock compression, and without affecting the PCMs ability to control. The after market handful available seem especially expensive - I was thinking about just trying a regrind on my stick. Problem is finding the sort of high lift limited duration profile to suit this particular situation.

[Guest]

Don't be afraid of adding things like this to a cam, it's done frequently for this purpose.

I added a magnet to a ZX2 Camshaft just a few months ago, no issues whatsoe ever. We are using it to trigger an MSD ignition, but the principal is the same.

Also I'd probably forget using the F-body PCM, it needs either the VATS system to stay in tact, or an aftermarket module that will send a square wave to a particular pin to power up the injectors.

You could use L-body (Berreta) 3100 PCM in it's place, but will have to deal with the auto tranny controls. I don't see any mention of the tranny that you will be using.

Or you could do as quite a few of us have, and that's reverting to an MPFI ECM, which in most cases is the easiest to use, since you can get them without tranny control needs (non-electronic trannies). MPFI works great, and I'm looking at converting from batch to bank fire, to help control larger injectors a bit easier.

MPFI, doesn't require a cam position sensor, or even the 24x crank position sesnor. Just the 7x crank position sensor, for the DIS ignition.

What kind of car are you putting this in?

[BillS]

Also I'd probably forget using the F-body PCM, it needs either the VATS system to stay in tact, or an aftermarket module that will send a square wave to a particular pin to power up the injectors.

What kind of car are you putting this in?

Apparently the guys that I have been talking to get the original PCM to function with the engine when putting it into MGBs, a popular swap.

I will be running a 1988 T5 behind it in a rebodied 1957 MGA


The advantage of having the engine in that sort of car (sub-2000 lbs.) is that I don't need to go crazy with engine mods to get the sort of power to weight ratio I want, as I had to do with my heavier Fiero (turbo). I'll be happy to settle for anything north of 200 BHP for this application.




More pics at http://www.rhodo.citymax.com/Jamaican.html

[Guest]

Yeah, I'm not saying that you can't get the PCM to function, just that it seems to be more hassle than it's worth, especially for an unhacked PCM (not many guys seem to hack these PCMs, so not much documentation is available). There are products available to get everything to work, or a lot of effort to get the VATS system installed in the vehicle.

Enh, I'l be using a completly different ECM anyway, either a 7727/7730 or a 7749, depending on what works best.

[93camaro_zzz]

Hey raven, I have scanned my car at my old work, let it run on his snap on scanner, and it was not in limp home mode. So I know that, and when I was installing the cam, someone told me that about the screw in the cam thing, but I didnt do it, and I didnt know if it was going to run perfect, hadnt researched it enough, so I justs stuck it in. I mean, the car doesnt run bad, just like they way I used to drive I drove it for the first time and almost killed it. Its running rich for sure you can smell it behind the car. I would like to get another cam soon. I personally like SFI tons more than MPFI. JMO though.

[BillS]

Well, after checking with most of the cam manufacturers, none of them seem to have blanks with the SFI trigger on them.

I've decided to go with an earlier batch fired ECM and system, retaining the DIS, which solves my cam problem - I will probably go for the Crane 272.

One question - my understanding is that 3.4 rockers are 1.6 ratio while all the earlier ones are 1.5. If you go with a cam designed for the 1.5 ratio, not remembering that you have the higher ratio, one could get into trouble with spring bind etc. As it happens I will probably go for 1.5 roller rockers and that solves that problem.

[geoffinbc]

You will only have problems with stock springs. And even at that you cannot keep stock springs with a 272 cam. So you MUST change to Crane Cams recommended springs and retainers or use the stuff off the crate 3.4L.

Oh and the old oil sheilds on the exhaust valve will not fit on the new retainers so you need new sheilds too. Or dont use them at all and you can choose to install exhaust valve stem seals.

With either the Crane or Gm springs you can run 1.6 rockers if you wish.

[BillS]

You will only have problems with stock springs. And even at that you cannot keep stock springs with a 272 cam. So you MUST change to Crane Cams recommended springs and retainers or use the stuff off the crate 3.4L.

With either the Crane or Gm springs you can run 1.6 rockers if you wish.

I'll be using Comp Cams springs which do work with stock retainers I believe.

I don't think you'd want to be running 1.6 with the Crane - it would put you at over 1/2 inch of lift and you'd need to be looking for different springs again - you'd hit coil bind wqith the ones I will be using on the 1.52 rockers.

[geoffinbc]

Yes they will fit the retainer but is the install height correct for the spring? NO

That is the only reason for the revised retainer. Comp specs their spring at 1.7 install height which is what you should be using. The revised retainer achives this height.

The comp spring maxes out at 440 lift
The crane spring maxes out at 547 lift.

Thes specs are right at coil bind so you cant push it right to that limit. Also the comp spring has less pressure so I would go with the Crane or a different comp spring.

I just noticed Comps 270 cam maxes out at 440 lift. How can they do that that is max coil bind for their springs??

Edit: I was just looking and the 981 spring looks like a better spring. it is comparable to GM or Crane springs

[BillS]

I just noticed Comps 270 cam maxes out at 440 lift. How can they do that that is max coil bind for their springs??

Edit: I was just looking and the 981 spring looks like a better spring. it is comparable to GM or Crane springs

Yes, I already went through the same line of reasoning you did. The springs I ordered are indeed 981 - the same ones I used with my Fiero turbo, because on that I was using 1.6 rockers. On the 3.4 I will be using 1.52 as I choose not to go over 0.500" lift for the street.

I like Comp's magnum rockers and am convinced that the lowered side-thrust will pay dividends in prolonged guide life.

[geoffinbc]

Side thrust? Explain?

I would suggest Comps PRO Magnum rockers. Very nice rocker and gurenteed for life. Well the body is anyway. Plus it is full roller where the magnum is only a roller tip.