When is too much cam ? How spaz will the computer make a motor run with too big of cam? May be what is wrong with my 91?

altradine 530 50deg ctr 223 intake 230 ex 108 intake ctr 112 lobe seperation . That's all I know.

 

Based on the extensive information about setup, mods, vehicle purpose, and description of the problem, I would say you do need a new cam, or not.

Dig in and let us know how it works out

I don't mean to be a jerk, it is not my style, but come on, you can't really expect a good answer giving us nothing to go on.

 

I'll take a shot at an answer.......

Too MUCH cam is one that:

(1) Moves the power and torque curves of the engine up to a range that is not pratical for the REST of the engine or the use of the vehicle.
(2) Causes driveablilty issues because of (1) as stated above.

The engine is a 'system' comprised of many parts and the cam is just one of those parts.

 

you've got a '91, so you've got speed density. not much tolerance for big air/fuel modifications (like intake, cam, and/or heads), you'll need a custom chip to compensate (as eluded to in post above). with speed density, you normally can't go more than one "step" up (about +7 degrees duration on the intake lobe) on the factory cam without major changes in fueling partial throttle and PE tables in your chip.

to answer your question directly a cam with 220 degrees duration for example, will "spaz out" your computer.

 

Most would say my car has "too much" cam, but I kind of like it. It lopes at idle, bounces at stoplights, scares children and animals and generally puts a smile on my face. To each their own.

 

There is an old saying about selecting a cam that goes: Study cams,your engine,your goals, pick the very smallest cam you feel you can live with--------


Then go one step down. Odds are if you think your cam is too big, it is.

 

What are the specs of your current cam? Has the tune been modified? Hot Rod 90 is correct - Speed Density is a lot less forgiving than MAF.

 

YES!!! A most eloquent description of which I'm in total agreement.

 

what cam do you have? what about the rest of the build? (i usually don't ask and bug people to death about what their combos are)

by the way, i LOVE your avatar (as you know) perfect

 

it is 530 altadine 50 deg. d 223 intake 230 exh. 108 intake ctr 112 lobe seperation.

 

it is 530 altadine 50 deg. d 223 intake 230 exh. 108 intake ctr 112 lobe seperation

 

BG, in your case thats waaay too much cam, assuming a non-tune and an otherwise stock engine. Way out of the ballpark. I'd either sell the cam or decide what you want out of your car and set aside $7k for an overall engine buildup (heads + exhaust + intake + custom chip).

 

The ECM spaz can be tuned out.
I have one of those shaker cams in my '73 Chevy truck and I'm running the 727 ECM with it.
It's easily tuneable but the cam has a very noticable lope.
I crank it up just to listen to it sometimes.

With SD the MAP is the numero uno input for the ECM fuel tables.
The MAP is an accurate way to approximate the amount of throttle opening on an engine where the VE or volumetric efficiency is known.
So, that's what the engineers that designed it used as primary air flow input to the ECM.
If you CHANGE the VE by changing engine intake components the system has to be 'recalibrated' .
A cam with greater overlap reduces the manifold pressure at idle.
The lower manifold pressure is reported by the MAP to the ECM as the throttle being opened, therefore the ECM responds with more fuel.
It's no big deal to tune SD.

MAF systems use the actual airflow so are a bit more lenient with changes that affect the manifold pressure.
But the ECM can only adjust a percentage +/- of stock so if there are major changes with the MAF system, the same recalibration must be performed.

That's a basic description of the difference in the two systems.

I like my SD systems. When I converted my truck I used the SD system and the same ECM that's in your Vette..

I think someone posted above that the max 'reccomended' duration for our EFI cars is around 235* with all the lift you can get before the valves kiss the pistons.
220* is probably a more reasonable value unless you plan on running the engine way beyond the RPM the TPI system can supply airflow for.

The LT1 is a good example of a system approach by the GM engineers..
Compared to the L98 it was designed to make power at a higher RPM.

It's best to think of the engine as an air pump. There are bottlenecks to the airflow. If you remove one of them the next one becomes the limiting factor. Removing the restrictions to airflow is pretty much a matter of spending money.
Decide how much you want to spend and go from there with your modifications.

 

don't modify with just cam. you'll waste your time and money, and it will hurt your low end grunt. and that includes a tune just to accomodate the cam.

for L98 apps, you need to better maximize by modding the intake (yank the stock TPI altogether -- its woefully inadequate to begin with) and exhaust (LONG TUBE headers, etc.), as well as better heads (preferably good aftermarket, and recoup some of the cost by selling your D113's).

and yes, that custom chip tune is critical, otherwise you'll blow lean and blow up your engine.

 

Hold my beer...

Edit:
.490, 218/218
P&P'd '91 heads with 58 cc chambers (about 11.0 CR)
1.6 roller rockers
Ported and matched intake
Forged TRW pistons

I'm working on getting some headers and and possibly ported TB's.

That's what $1000 buys you I guess.

 

looks good

and by the way, your avatar motivates me to take another wonderful opportunity to say --- ***** NOTRE DAME!

 

Thanks.
Yeah, that's a lot of cam.

 

.218/218

THat's right in the 'good' range.
Considerable more than stock but not too much more.

IIRC the stock cam is around 204* square.
Can somebody post the stock cam specs if that's not it?

Most any duration more than stock starts to take away HP and torque from the lower end.
Throw in more overlap and the resultant intake reversion and the low speed power suffers even more.

 

Nowadays thats not considered alot of cam. Both the lift and duration are fairly mild. Its the duration and LSA, together they dictate overlap, that make it do all the stuff its doing. Low manifold vacuum @ or around idle, thats interpreted by the MAP as load, so in goes more fuel.
It can be tuned to run real good. They (lumpy camshafts) take alot of work in the VE tables.
Whos doing the tuning?
FWIW 114 LSA seems to be the fine line when it comes to cam selection. What do I mean by that? Depending on duration, of course, 114 degrees of lobe seperation seems to be about the limit for anything that may be considered smooth idle. In other words 113 and lower and shes gonna lope. Almost regardless of any other of the specs. 230 deg of duration is completely different from 114 LSA to 112 LSA

 

the OP never said anything about the rest of his setup, so i assume stock. and i'm saying its WAY too much cam for an otherwise stock setup. and i'm also saying its a waste of time and money -- and will only serve to hurt his driving enjoyment -- if the cam is the only thing going on...........tune, or no tune.

and i don't get the "nowadays" line......we're talking about a GEN I smallblock, that aint nowadays. it was 1991, and the tech is older than that.