C3 Engine rebuild

[Tim anderson]

I'm rebuilding the L81 engine in my wifes 81. She says she doesn't need the horsepower, (but she did ask about nitrous oxide today ) and I want her to be able to ward of punks in mustangs! Stock at 190 HP sounds like a waste of machinery to me. I would like to jack it up just a bit. But wasn't to sure how the ECM would feel about such a move. I don't really want to change to a conventional carb and distributor. Will the ECM even care if I slip a cam in on it?

I was thinking about 9 or 10 to 1 pistons and a cam in the 450 lift 290 duration neighborhood.
Does anyone have any suggestions for jacking up the power in a semi computer car? Or should I leave well enough alone.

Thanks.

[Gerry Proctor]

Re: Let me see if I understand this right...

You want to completely change the character of a car...compromise driveability, emissions, economy, longevity, and value so your wife can street race Mustangs? You can do whatever you want but you better do some research on how your proposed changes are going to affect the package.

First, you better start talking about cams in terms of valve timing events at .050" lift. Advertised duration is subject to generous marketing pitches and is really very meaningless. You also need to understand lobe centerlines and lobe separation angles and how they affect the engine's manners. Lift isn't very relevant in this regard but more isn't better since most factory smallblock heads show very little gain over .450" lift. There is considerable balance between the cam, compression, flow potential in the intake and exhaust, transmission type, a rear gear ratio. You can't make significant modifications in one area without due consideration of everything else.

You better believe that you can screw up your ecm by selecting a camshaft that operates outside the lookup tables in the computer. Your proposed advertised duration of 290 degrees will ensure that your wife will become very familiar with city bus schedules.

The changes you're proposing will only allow you an expedient pathway to another car, perhaps a new Mustang, that your wife can actually drive.

[Jim T.]

Re: Let me see if I understand this right...

If you have room to store your 81's engine you could buy the 350/330 HP crate engine that GM sells for a very reasonable price for the torque and horsepower this engine delivers. About all you will need is a intake that will bolt to the vortec head bolt pattern that comes on this engine. This was a 300 HP engine until GM switched to the vortec heads which upped the HP to 330.

[Joe L.]

Re: Let me see if I understand this right...

Gerry----

I TOTALLY agree with your perspective.

[Walt McGaw]

Another perspective.

Tim,

If hte engine you currently have is running fine, you may also consider leaving it alone and going after a Bowtie Overdrives 700R4 transmision instead. In the 81, I believe you are still running a 3 speed automatic. The 700R4 gives you gear reductions for 1st and 2nd, and even 3rd and an added bonus of an overdrive 4th. My car is a 72 with a TH400 and 3.08:1 rear end ration. The 700R4 swap would be the same as changing the 3.08:1 gear to a 3.73:1 and I've been told by many that it would get me more seat of the pants performance increase than dropping in a new crate motor.

You may want to visit www.bowtieoverdrives.com and take a look.

Regards,
Walt

[tim anderson]

Re: Let me see if I understand this right...

Yea Gerry your first sentance sumed it up pretty good. I had thought about a crate motor and saving the original. But the original motor needs rebuilt anyway.

[Tim anderson]

Re: Let me see if I type the right #

Jim I did look at the 330/350. Thanks for pointing it out to me. It's a great price and I might repower my M715 with one. (Anybody have a M8 2WD transmission to sell?) Just a bit to much HP for the wifes car though.

Gerry I made a mistake on the 290 duration (advertized). That would'nt be very streetable now would it. But you got to admit a cam with that much overlap would sound GREAT! 260 was the figure I should have typed. I could see why you freeked about driveability.

If I remember correctly the Crane cam I used in a SBC/Jeep was a part# 268 H and it had a REAL (.050 lift) duration about 215-220. It was a very nice steetable cam. I drove that jeep for 10 care free and reliable years. From what I can gather those figures ain't to much differant than a L82 cam.

Back to the ECM. I see lots of chip companies but who's who in that world? The ones I have found seem to only cater to Grand Nationals or 85 and up Vette.
Thanks

[Gerry Proctor]

Re: Let me see if I type the right #

Your best bet for a replacement cam is to talk to the manufacturers. They all have tech lines and will give you their recommendations. My preference is either Crower or Crane who do have cams that are designed for use in feedback cars (not cams that WILL work, but cams that are DESIGNED for them). Others have their favorites. It gets real iffy with durations over 215-degrees. The wider the lobe separation angle, the better for idle quality and vacuum signal. I don't like CompCams for this very reason. My impression is that their grinder doesn't have a setting above 110-degrees LSA. Keep your compression around 9.0:1, be conservative with the cam, forget the street racing and you'll end up with a driveable package that doesn't require you to pour crutch money into it.

[tim anderson]

Re: Let me see if I type the right #

I noticed that Comp cams had smaller lobe angles. Thanks for the heads up on them. I'm still kinda laughing at 290. I didn't find the page at Crane on feedback cars but I'll look again.

Thanks.