Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Welcome to ThirdGen.org!
Welcome to ThirdGen.org.
You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join the ThirdGen.org community today!
The very generic RV cam of yesteryear. If I leave that cam in and swap to the vortec heads, what kind of horsepower / torque potential am I missing out on, compared to say a Comp Cams xe262 or Lunati VooDoo 256?
Car is an 86 firebird, LG4 feedback carb controlled, T-56 swap, 3.23 rear gear. Intake will be Professional Products brand performer knock off. Uh... don't know what else to tell you. Pistons are shallow dish, 4 valve relief cheap-o rebuilder type, block is stock deck height. Heads have been shaved .010 I believe.
If its not already obvious, I'm trying to stay as low budget as possible.
Would the $150 - $200 for new cam and lifters be better spent on gears or traction parts?
Matt- that ain't as bad a cam as you think it is. It's the same one Edlebrock sells as the "Performer" cam and Summit sells as their house-brand #1102 cam. Forget advertised duration numbers- they are misleading. Look at the .050 numbers, the LSA and ICL and you've defined 80% of the cam's performance potential and operating characteristics.
With $200 I'd get some pocket porting done on the heads by a pro who knows Vortec heads real well LONG before I dropped that money into a new cam. Or if traction is really holding you back, buy some DRs or suspension upgrades.
That cam will pin the motor to a range of RPMs where the head flow will do almost no good at all.
The Comp XE cams and the similar ones from Crane and Lunati are known to work well with those heads. Frankly, I'd put $150 into a cam kit a LONG TIME before I'd put money into porting, if it's a "budget" situation. You'll get ZERO bang for the buck out of porting, since the heads are already "too big" for the cam; but upgrading the cam will give some benefit even if the heads are untouched.
With the CC system, either of the 2 cams you mentioned will be a MASSIVE improvement over the old "RV" cam.
3.23 isn't enough gear for a T-56. For that matter, 3.73 is barely enough to take advantage of a motor with some RPMs to it. But unless you can do ALL the work yourself, gears are a much bigger chunk of $$$ than a cam.
__________________ Numquam ponenda est pluralitas sine necessitate. — William of Ockham, from Quaestiones et decisiones in quattuor libros Sententiarum Petri Lombardi
Roughly paraphrased into modern English, and applied to figuring out what's wrong with your car:
The simplest explanation that fits all the facts is probably the right one.
my buddy has a 91 cop car roller 350 with the stock LT1 cam which is pretty similar to that lunati cam you have. vortec heads and i think RPM manifold and 750 carb.
this is in his 83 standard cab shortbed chevy truck with a 350 trans and 3500stall. i think 3.73 gears. the truck runs 13.6s at 97-98mph on average with a best of 13.58 at 99. not bad for a budget build.
but i'd definately lookinto a bigger cam... not too much bigger, but something alittle bigger with abit more duration and just a tad more lift. you should upgrade the springs and such for .500 lift and run a cam with around .470
Damon - I haven't found anyone in my area who has impressed me with their knowledge of porting vortec heads. There's only a couple machine shops to begin with. Both of them looked at me funny and asked me what I was trying to do when I talked to them about cutting down valve guide bosses on these heads. So far traction hasn't been too big an issue, I was kind of hoping it would be after a head swap.
Sofakingdom - The T-56 w/ 3.23 works pretty good now (I like the 25 mpg at 90 mph on the turnpike), but I'm sure it another situation of "If you haven't tried it, how do you know what you are missing?" I plan on a 3.73 swap sometime soon. I would be doing the work myself, haven't done it before, but you got to start somewhere. Obviously I would benefit from both a cam and gear swap, wonder which would give the biggest gain now and later?
I have seen engine builds in magazines that will claim +/- 350 hp and a little more torque out of a vortec head, xe262 or 268 build. I know better than to believe most of this at face value, but just as a reference point, do you have any guess about how much lower hp and torque numbers an RV cam w/ vortec heads would turn out? For some reason no magazines want to do a "Build an Engine out of all the Junk You have Laying Around" article.
Orr89RocZ - Yes, 13.58 sound pretty good on the cheap. I learned quick not to try to build a drag car, someone will always beat you at the track. But that truck sounds like a blast on the street. That's pretty much what I'm looking for. Oh, yea, I've got Comp 981 springs, I figgured those would work with about whatever cam I end up using.
You're building a motor now; concentrate on that. Worry about the gears when you get to that point.
I'd strongly recommend building your motor to where all its parts are "internally consistent"; that is, such that they all work TOGETHER, and don't fight each other. The cam and heads, ABOVE ALL, must agree with each other.
Whatever the "weakest link" is that you install in your motor, that's going to be the limit to its performance. You could get a set of SB2.2 heads from Hendrick, and if you stick that cam you've got underneath them, it's still going to make power only from 900-4800 RPM. Period. No point in wasting money on heads at all, if you're only going to barely crack the valves open, and only hold them open long enough for flow to occur at those verry low RPMs. Heads don't do much good if the valves don't open.
People claim to get over 400 HP on an engine stand, out of "nothing" short blocks with those heads and the XE268. I would expect 350 easily out of a flat-top 350 and those heads with the XE262. Even crippling your motor with the smogger pistons and the lower-than-stock deck height, I'd still expect over 300 from that combo.
HP = torque x RPM x a constant. Study that equation carefully. It's telling you that power (time rate of doing work) = torque (pushing force generated by the engine) x RPMs x a constant (happens to be 1 divided by 5252.11). Torque is proportional to cylinder fill and compression for the most part. RPM is similarly determined by head flow and cam profile. The formula is telling you that to get more power, you have to make more torque at a higher RPM. If you use a cam that limits the RPMs, you limit how much power you'll get. Pretty simple really.
Get rid of the crappy cam, it WILL disappoint you, and you WILL NOT get the full benefit of the head properties that you're paying for, if you leave it in there.
__________________ Numquam ponenda est pluralitas sine necessitate. — William of Ockham, from Quaestiones et decisiones in quattuor libros Sententiarum Petri Lombardi
Roughly paraphrased into modern English, and applied to figuring out what's wrong with your car:
The simplest explanation that fits all the facts is probably the right one.
Sofakingdom - The T-56 w/ 3.23 works pretty good now (I like the 25 mpg at 90 mph on the turnpike), but I'm sure it another situation of "If you haven't tried it, how do you know what you are missing?" I plan on a 3.73 swap sometime soon. I would be doing the work myself, haven't done it before, but you got to start somewhere. Obviously I would benefit from both a cam and gear swap, wonder which would give the biggest gain now and later?
you have no idea what you're missing.. the T56 has a really tall 1st gear...
you'll want atleast the stockish 3.42s to have the car be normally geared... for performanceish daily driver, 3.73s will show almost no diff in MPG, but alot when you punch it..... 4.11s will knock a tad (not much) off your MPG, but its a heck of alot of fun.... better have some suspension/tire under the car if you want to punch it from a stop.. lol.
That cam will pin the motor to a range of RPMs where the head flow will do almost no good at all.
That's a claim without merit.
You don't need a big, or even moderate cam to make power so long as the heads flow well and you have a decent burn speed. That's why the L31 Vortec makes 250-255 fwhp and 330 ft ftlbs with a 191/196 deg duration .414"/.428" lift cam i/e... because the heads flow so well and because the burn speed is fast (30 to 32 degs max ignition advance at WOT). The numbers are nearly the same for the iron Bcar LT1 engine from 94-96, because the (reverse flow cooled) heads are essentially the same as the Vortecs, and the stock Vortec cam was taken from the Caprice/Impala parts bin.
That same Vortec engine combination, using the so-called peanut TBI cam, was rated at 230 fwhp and 330 ft lbs with factory TBI in the mid 90s and used in medium duty GM trucks (source for this info was Fast355). 230 fwhp may not sound like much, but from the peanut cam & TBI combo, it really is... especially with a factory restrictive exhaust.
The use of a seemingly mild cam in an engine with very good heads (good flow, good burn) means it will still make decent power and it will also lug well at low rpms. That type of combination is perfect for a moderately heavy vehicle (Bcar, light truck, towing) or for street/sport use in a 3rd gen. It will also get fairly good fuel economy, something that will be reduced the larger overlap the cam has.
The cam specd is slightly warmer than an F/Y car LT1 cam, and those engines were rated at 275-285 fwhp @ 5000 rpm when new. So with proper tuning you can expect slightly higher numbers. And the cam is mild enough that it ought to idle well. So it may be a generic cam from yesteryear but it will still run very well in a budget-build engine with Vortec heads.
On porting: the intake side can be improved but not by much... and frankly not worth chasing given the cam choice. If you do anything at all to the heads, clean up the casting flash, make sure the valves are backcut, and do some mild porting to the valve guide boss on the exhaust side. If the Vortec heads have any weakness at all, it's that the exhaust side doesn't proportionally flow as well as the intake side does. HTH.
Heres a members ride from a message board I frequent. He really has a strong motor going with the vortec heads. Thats a low 12 sec car without nitrous. Its not an even comparison but it gives you a good idea what little has to be done to get those heads to work well.
I'm afraid i'd also have to recommend a cam swap. The current combo will net you essentially a vortec motor. Sure, nice heads, but the cam is basically a stock truck cam right? I dunno about you, but trucks aren't camaros, and i'd rather be driving my sports car. (camaro)
I've ran both lunati 60103 ("The best 268 cam ever") and the compxe268. Both are quite tame in manners, and i'd recomend either. The specs on the 268 style of cam is commonly used in magazine buildups with vortec heads. Why? 'Cuz it works! Someone slapped it together a while ago, and found that that cam compliments the vortecs VERY well. Same deal with the xe274, but lets not go too big right?
I think the cam will give you the most bang for the buck where you are now. I think your gears are fine for what they are now. A posi unit and steeper gears can be in your future, but I wouldn't put them top of my priorities. Not like you have 2.73's !
Sonix what would you recommend as an upgrade cam since Im running the comp 268. I was checking out the voodoo cam which looks promising but Im assuming a 114 lobe sep would cost extra.
I run a vortec 383, and use the 08-413-8 comp cam.
Cam Style: Hydraulic roller tappet
Basic Operating RPM Range: 1,500-5,500 RPM
Intake Duration at 050 inch Lift: 220
Exhaust Duration at 050 inch Lift: 224
Duration at 050 inch Lift: 220 int./224 exh.
Advertised Intake Duration: 270
Advertised Exhaust Duration: 274
Advertised Duration: 270 int./274 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.474 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.474 in.
Valve Lift with Factory Rocker Arm Ratio: 0.474 int./0.474 exh. lift
Lobe Separation (degrees): 111
I was lucky with the head work, the machine shop in the area here knows a lot about them and do a lot of work with them. The cam was suggested by comp and matches the rest of the car very well.
As for doing the cam swap or the gear swap first....cam definately. After you get it running you're not going to want to go back into the motor to swap out a cam, or take off the heads to have them ported/polished larger valves and good springs put on, you can do the gears any time. Finish the motor, then deal with the gearing and traction problems that you created.
Sonix what would you recommend as an upgrade cam since Im running the comp 268. I was checking out the voodoo cam which looks promising but Im assuming a 114 lobe sep would cost extra.
Why do you want a 114 lobe sep?
I think the xe268 is pretty good, I can't really recommend an upgrade without knowing more about the motor, to see if a cam swap is really worth the extra bucks...
