potterc32

iTrader: (1)

Needing some serious help here everyone. I have installed a new cam in my 1985 Bird. GM crate 350. Cam specs are attached. These are the specs of the original cam... (.383"/.401" Lift, 194 / 202 Duration @ .050", and 112° lobe separation)

I still have the factory Quadrajet and HEI distributor. After starting it and driving it after the break in period, I'm a bit disappointed in the gains. I am beginning to wonder if the computer controlled carb and distributor are holding it back. I have made no modifications to the carb (have only rebuilt it twice) and no mods to the distributor (other than the brass terminal cap/rotor kits). The distributor has the 7 pin ignition module.

Is it worth my money to go with a non computer controlled carb/distributor setup? I have never had any real problems with the quadrajet, which is the only reason I am reluctant to get rid of it.

Any ideas or suggestions are helpful. Thank you!

sofakingdom

iTrader: (1)

In what way(s) are you disappointed? (yes I already have a pretty good idea; I just want to hear your description)

OrangeBird

iTrader: (1)

I'm not gonna try to play Mr. Zen tuning Master of the internet , cause in reality I have no clue about which camshaft grind profile does what in regards to tuning a car engine . In the world I come from , all but strictly manufacturer approved replacements are not allowed (Aircraft Maintenance) .

But what I CAN tell you , in a very general sense , is that if your fuel and timing delivery curves are optimized for one specific set of engine operating conditions , and you go and change those conditions , well then yea your gonna have to alter things like fuel charge density and timing profile to take advantage of the engine's newfound ability to put more fuel in the cylinders . The ultimate goal of more power comes with the burning of more fuel . You have now put in a cam that will allow that extra fuel to get to the cylinders . But if the carb. isn't putting out more fuel because it's obeying it's ECM's programming , that is why you haven't seen the performance gain you had hoped for . A carb. and distributor tuned to work with your new set of operating conditions that will allow the extra fuel that's needed , along with the right timing profile to make sure it all gets burned , will give you the maximum power gain for the new set of operating conditions you now have set the engine up to run with .

Now bear in mind , this doesn't HAVE to automatically take the form of abandoning the electronic control of the carb. and distributor , your two options here being to get a programmable ECM to be able do the tuning electronically* , or yea , you'd have to abandon the electronic setup and go non ECM controlled and do the tuning mechanically (changing springs in the distributor's centrifugal advance to alter timing curves & such) and all the traditional non electronic carb. tuning that preceded the electronic system .


* personally , I do favor keeping the electronic system if at all possible .

potterc32

iTrader: (1)

It doesn't seem to have much low end power. Won't even break tires loose shifting into 2nd. Throttle response is a little weak unless it is in neutral/park.

sofakingdom

iTrader: (1)

Yup, about what would be predicted for putting a cam that wants 10:1 compression or greater, into a motor with about 8:1...

What that does, is reduce cyl pressure at low RPMs by bleeding off pressure at the ends of piston motion, and by allowing reversion back into the intake during the beginning of the compression stroke. The exh valve opens long before the piston has finished the power stroke. The valve timing is set up to favor high RPM pumping efficiency at the expense of low-RPM compression efficiency. The valves are thus open for too long during both the compression stroke (int valve) and during the power stroke (exh valve), reducing both the period of time that the cyl produces power and the amount of power it makes.

Run a compression test: I'd bet that you're making less than 150 psi cranking compression, as compared to near 200 with the old cam. Simply put, that means that you'll also see about 25% less torque at low RPMs compared to the original.

No amount of tuning is going to make up for that.

That's just simply too much cam for the situation. Or I should say rather, not enough motor for the cam.

You can probably get it to idle better and be a bit less hesitant off-idle with some other carb & dist, but the basic lack of compression as compared to valve timing will continue to limit low-end torque no matter what. That is beyond fixing from outside the engine.

OrangeBird

iTrader: (1)

Now see , aren't ya glad someone who KNOWS the various camshafts stopped by ?

Just so we're clear here , when Sofa says no amount of tuning will make up for the lack of compression that your new cam has caused , that don't mean that tuning won't be required ! Any changes have to come along with adjustments to the various systems , it just sounds like your change was SO drastic that simple tuning alone won't help .

potterc32

iTrader: (1)

So, if you were in my position, how would you go about increasing compression without spending a great deal of money? I have thought about using thinner head gaskets, I hear that can increase my 8.5:1 up to 9.1:1.

sofakingdom

iTrader: (1)

By not buying a low-compression motor in the first place.

I guess now though, to overcome the inappropriate decision-making, a clear-headed, rational, and non-emotional evaluation of goals and resources might be in order. You haven't said anything about what gears and converter you have, what your use for the car is, what your expectations and needs are with respect to gas mileage, emissions, reliability, etc. might be, and so on.

Realistically, just replacing the cam with a choice that's a better match to the rest of the engine, might be the best way to go. You can put the XE274 (a good cam, as far as that goes; I've had one myself, in a 10.4:1 or thereabouts 400, and liked it ALOT) on the shelf and wait for your next motor, if you ever run a flat-tappet cam again, or even sell it.

I wouldn't mess with the head gaskets. You won't get anywhere near 9:1 out of that. Changing from a .028" gasket to .016" in that motor only gets it from about 8.2 to about 8.4:1. That's a real good way to just open a can of worms while only marginally nibbling around the edges of the problem. That will only BARELY tweeeeek the compression but will introduce other potential problems that you might well find aren't worth the hassle. Doesn't make much sense after all, to go out and buy a NEW motor, the ONLY valuable attribute of which is its warranty, and immediately void that. (i.e. throw away the portion of your expenditure related to that)

So, start with a clear description of what you have, what you want, and what you are willing to give up to get it. (both long-term as in gas mileage and decreased utility in some other areas, and short-term as in money and wrenching)

Steve Mack

iTrader: (5)

Well I'll tell you what I was in your exact situation. I had a computer controlled quadrajet carb and distributor in an 87 El Camino. I put a built 400 small block in it.It ran like garbage.The cam, carb and distributor you have were built around your factory set up.Do yourself a favor and buy a carb and vacum advance HEI distributor.You'll find all the missing power and performance your looking for.

sofakingdom

iTrader: (1)

That's one thing...

That's ENTIRELY a different matter.

The experience with the one, however good OR bad, doesn't translate to the other.

Sticking a cam meant for a high compression motor into a low-compression fleet vehicle replacement mule is a surefire recipe for no torque, poor low end, no leave, fuel consumption in the gallons per mile, and any number of other CLASSIC problems I've been trying to keep people from inflicting on themselves since the 70s. I cannot begin to count the number of times I've seen this same mistake made, always with the same predictable results. No amount of mixture or ignition timing help will fix the ills caused by low cyl pressure.

potterc32

iTrader: (1)

It is not a daily driver. It has headers and exhaust cut out, and edelbrock rpm intake, and the valve springs came with the cam kit. Monster 700r4 trans with their 2000 stall converter. 3.42 rear diff from a 96 z28. Electric dual fans.

It gets out of the garage maybe a dozen times a year. I intend to do some racing with it, but I do drive it around town occasionally.

Am I just missing some 64cc heads? 😀

OrangeBird

iTrader: (1)

If you increase the compression enough to make the cam worthwhile , from your present 8ish to 10ish , even if you could accomplish raising the CR with just heads alone* , won't that leave you needing lower end work , like better made pistons and maybe a forged crank instead of cast , to have the engine have a somewhat normal lifespan ?

* I ask this cause I figure if you COULD get out of this by just replacing the heads , I'm sure Sofa would have told you that . When he said you have too much cam for the engine , or more properly not enough engine for the cam , I'll bet he meant the entire engine , and not just the heads ?

potterc32

iTrader: (1)

Please forgive me guys, I never have had any real hands on experience with high performance building, nor do I know anyone close by to guide me, so a lot of what I have done has been trial and error.

That being said, I'm not shooting for anything wild and crazy yet. The goal is around 400-450hp when all is complete. You guys don't think this lower end can handle that?

OrangeBird

iTrader: (1)

No No my friend , I didn't say your lower end for sure wouldn't hold up , I asked if it would hold up to the increased stress of a two plus point rise in compression ratio . Sofa is the guy to answer that , and I asked my question based on the fact that he said the entire engine was not up to that cam , and he did not mention being able to change just the heads . I know a fair bit about engines but not about modifying them for increased power , which is why I'm asking questions myself . You have my apologies if you took my post as saying for fact it won't hold up , my intent of my question was to see if Sofa would say whether it would hold up or not .

sofakingdom

iTrader: (1)

OK, so I'm hearing a sunny-weekend-day cruiser kind of a deal, that you can take out for a little fun with your SO once in awhile. Not a racer. Having a SO myself, I can assure you they HATE a car that's unreliable; any significant risk of having trouble with it while out on a cruise is UNACCEPTABLE. We want a nice peppy car with a bit of excitement, but no broken parts, blown head gaskets, overheating, day's worth of prep work the day before every time you want to turn the key, yadda yadda yadda. Correct me if I'm wrong.

What you have is a long block that was intended as a budget replacement for an already substantially depreciated (aka worn-out, used-up) fleet vehicle, designed to get it back on the road earning revenue for the limited remainder of its life.

What it is NOT, is anything resembling any kind of "performance" or "racing" engine.

Keep that picture FIRMLY in the front of your mind as you evaluate your options: knowing your STARTING OUT point is as important as knowing your DESTINATION. Just try using your GPS to guide you when it doesn't know where you are now, and see what happens.

This lack of "performance" adaptations starts, in 2016, with having a flat-tappet cam. It continues with dished cast pistons that fail to reach the top of the block ("deck clearance"... the number most people leave out of their compression "calculations", but which in fact makes as much difference as chamber volume), shoddy machine work (you'll probably find that the "deck height", which is the distance from crank centerline to deck, is AT LEAST .010" different from least to most among the 8 holes and possibly as much as .020"), cast crank, emissions heads, lame valve hardware, ... the list goes on. To take what you've got and turn it into a "performance" long block would cost EXACTLY the same as going to the junkyard and getting a $50 block core and starting a fresh rebuild. Crank, pistons, probably rods, CERTAINLY heads, would ALL go into the trash, as step 0 of the rebuild (before you even got started good).

400 HP is not too much of a stretch with a 350 in general, but is out of reach and unrealistic for what you've got, without treating it as just a bare block and starting over from scratch.

You MIGHT get to 300 or even 325 HP with good head and cam choices. Past that, it's short-block tear-down and start-over time.

I'd suggest at this point that you lower your expectations for that engine. Get better heads and a Comp XE262 cam for it. It won't wind out as high but it'll be AHELLUVALOT more responsive to the throttle. A set of Vortec heads and a new intake would max it out, that'd be by far the best choice as far as results vs cost. (you can get somewhat more results by other means but at a MUCH greater cost) You might need different valve springs for that though; once you find a pr of heads, we can revisit that. At the power level you will get with that combo, your existing short block should suffice as far as "hold up" is concerned. Much past that, ... not so much.

potterc32

iTrader: (1)

I really appreciate all the input guys!! I will definitely re-evaluate my case, and see what I can do with the budget I am working with. I know this is nothing to get too deep into without having deep pockets. But we'll see what I can make of this thing!!