OK. i tore down my L98 to the block recently, and it needs a timing chain bad. Its a 88 GTA L98.

Anyways, Down to the block. I dont think i got the dough to splurge on my rotating assembly, but i want to at least get somthing done while im poking around inside. Since it needs the timing chain, i figured, Hey, why not dump a cam and some new roller lifters in there while i change the chain.


The problem. CAMSHAFTS CONFUSE ME!!!! I have read so much tonight and the more i read the more confused i get as to what is best.

heres what my engine is right now:
stock L98. ported intake, gasket matched, Air foil.

what it will be:
383 (30 over, 3.750), GMPP Vortec Heads, Ported Vortec FIRST injection setup, custom CIA, Dons shorties into dual cats and some kind of cat-back. somewhere just north of 10:1 compression. definitly less then 11:1. Trying to build it as a low-mid range torque monster just north of 400hp.

So what kind of cam am i looking at here guys? All these numbers are confusing me. The engine will probably be in its current configuration for a fair amount of time but i have every intention to make it what i have planned, and i dont want to swap the lifters and cam AGAIN when i do.

So what cam will give me good strong low-mid RPM power (high is obviously good but i want it to work with the engine i think). These numbers just have me lost. Would a custom cam be best? Or Comp Cam? Lunati? I really dont know enough about this black magic of camshafts


Cliffnotes:
fairly stock 88 GTA L98. minor power mods
want to swap cam for somthing really good for low-mid RPM
Have plans to make the same engine a low-mid RPM 383 torque monster over next 2 years
Dont want to change cam when i make the 383.
numbers and black magic confuse me!!!!


please help !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


edit: btw, i get GM stuff at a discount so if a GM cam is a possibility please tell me. Just so i can consider it.

 

While it'd be a bit racy in the stock L98, once you go 383, the Lingenfelter 219 cam or Comp's XE276HR (#08-503-8) would be a pretty good choice for your final goals. Either of those cams would give you gobs of low end and midrange in a 383 motor. You'd have to budget in some work to your heads to run either of them though. You'd definitely have to upgrade the springs and you'd also have to get the valve guide bosses machined down to clear the lift. It might be a better idea to pick up a used LT1 cam for dirt cheap to throw in your L98 for now. You could run one of those without any additional work to the heads, although I would recommend putting new, LT1 springs in at least. If your lifters are working fine, I wouldn't bother putting new ones in. You could always get new ones as a finishing touch for the 383 build. I guess what I'm trying to say is that it'd be cost prohibitive to do much more than the used LT1 cam in your motor until you're ready to do the 383. Another cam that would work great in your L98 if you can find a used one for cheap would be a Crane 2032 Compu-Cam. That one would work great with nothing more than a valve spring change too. The affordable ZZ4 crate motor cam is also great in a L98, but it requires some machine work to your heads to handle the .510 exhaust lift. All three cams mentioned above will be far too mild in a 383 though. So yeah, bottom line is just get a cheap cam to throw in there for now, and spend the money for a really nice cam once the 383 is going together.

 

Is it a roller motor? What year is the motor?

Cams arent that complicated, trust me.

Duration is how long the valves are open, or how big the lobes on the cam are. Duration at .005 or .001 or whatever tehy choose is basically a total duration number. It's not nearly as important as duration at .050. Duration at .050 is sort of a real world duration number. That's how long the cam lobe's lift is taller than .050 ... inches I guess?

By how long, you'll see numbers like 212, 240, 230, etc. That's measured in degrees. So these numbers are basically "How many degrees of rotation of the cam is the lift more than amount X and amount Y".

From there the important thing is just to know what relative numbers mean to each other.

Another set of numbers you'll hear is lift. That's how far open the valve is at its highest point, or how tall the cam lobe is at it's highest point. That's important for getting a better idea of how the profile looks, but it's not mission critical to completely be able to visualize that or anything. It's more important for most people just to know that so that they know their valve springs can handle it and that their heads can handle it. You have to get valve springs that can deal with the kind of lift your cam makes, and with higher lift cams you run into bad problems with parts binding and so on.

The only other number to deal with is Lobe separation angle. Im not entirely sure what this means, I think it's basically how far apart the centers of the intake and exhaust lobes are on a given cylinder. The more important thing to remember is that for a fuel injected car it's much better to use 114. You'll see anywhere from 106 to 114. 106-110 is usually better suited for carbs, 112 can be done on EFI, and 114 is the best for EFI usually, especially stock style EFI that's barely tuned for a cam, if at all.

I've told you all those things, so the cliffnotes are:

Duration @ .001/.002/.005(Whatever they pick) = degrees of duration above that lift number, a "total duration" number.

Duration @ .050 = degrees of duration above .050 lift. In the real world, this number is a much better barometer of what you're dealing with than the total duration number. This should probably be the first thing you look for when picking a cam.

Lift = The max lift at hte peak of a given lobe.

Lobe Separation Angle = Since you've got a stock TPI now and a glorified TPI later, go with 114.


As far as what those numbers mean for you, the buyer, I will give you a quick run through. THe more duration at .050 you have, the more horsepower you will have. THe more horsepower (or high end power) you have, generally, the more low-end power you lose. So the game is to pick a cam with as much duration and power as possible while still having enough torque down low to fit your needs for the car. That's really what it's all about. Around 230 duration at .050 is where you start running into streetability problems. That's from my anecdotal research. If you want to work with stock TPI and then Fancy TPI, consider keeping it below 220 or maybe even closer to 210. I'm not an expert on that all so I'd be curious to see what everyone else says.

But also, you probably have a roller block, and roller cams are a bit different than flat tappet cams as far as relative measurements go. It's hard to compare them to each other.

Anyway, if you've got ar oller cam, there's a lot of stock GM cams that would probably work well for you that I dont know eough about to recommend one. I know the LT4 Hotcam is pretty popular.

But if you get any kind of serious cam, expect to change the valve springs.

 

Thanks! i hink i understand a bit better now.

Anyways, my father works for GM and told me that it is a roller cam. it is half the reason he practically demanded i buy this engine for my Iroc. I havnt had the cam out yet (plans for saturday) but i trust him. he is also where i get my GM discount from, and im guessing he could get me a LT1 cam for nearly free if thats honestly what it would be best to do.

Would it really be that poor of a performer if i put the good 383 Cam into the 350?? By the way, I definitly think i dont want anything over 6250RPM. Im definitly thinking somewhere from idle or 2000 up to 5600 or maybe a tad higher at the most like the torque band. My FIRST system will flow alittle more at the high end because it will be ported, however with my limited knowledge im thinking any cam over 6200RPM would be a giant waste.

My engine should be built very similar to this engine, which is a 383 with similar compression and the FIRST system. I figured this would be helpful. This engine is running a Comp HR Extreme FI cam :

 

That manifold still appears to retain the TPI style of long-tube runners, and will suffer (or enjoy, depending on your point of view) the same RPM range type effects as TPI. While it may flow more, the RPM range that it will work best in, will be similar.

Meaning, look at cams that, in your size motor, will give peak torque in the 3600-4200 RPM range; and expect engine output to CRATER above about 5400 RPM.

The "perfect" cam IMO would be a Comp XFI276. However, they don't seem to have that, in their catalog; it goes from the 268 to the 280. And on top of that, they don't have the master lobe list in the catalog any more, which means it's about impossible to design a custom grind.

Call Bullet Cams www.bulletcams.com and get them to cook you one up with a HR276/340 intake lobe and a HR280/340 exhaust lobe; set up with the ICL at 106°, and LSA of 114°. Use 1.6 rockers.

Don't bother with a GM cam, with the possible exception of the 846 or 847 (which are really Crane cams that GM re-sells). Out of those 2, the 846 might not be too bad.

 

you are 100% correct in assuming its similar to the TPI. In fact, it is simply a larger TPI plain and simple. a novice could not tell them apart.


Ill look into those cams. Any other ideas??? What operating range am i looking at besides 3600-4200 (remember, im porting my intake so HP should be a bit more aggressive in the higher end but still)


edit: also, what about Voodoo cams. They seem like the right cam will take me all the way from like, barely touching the gas to the end of my power band/shift points/ 5400 RPM

 

Just looked on Summit's website and it looks like the only hydraulic roller cams in the Lunati Voodoo line are for the 1998-2002 LS motors. Sofa has a good point in recommending a custom grind. You could get pretty close to optimal with the right "off the shelf" cam, but you could get it perfect with a custom grind. Just keep in mind that you're running a long tube type intake, and you're shooting for low to midrange power. It's real easy to "overcam" it. I'd still have to say no matter what, you're still looking at two different cams for the 350 versus the future 383 you're going to build. If you pick a "compromise" type cam, it's a good chance that it'll be a bit too much in the 350, and end up being too mild in the 383. If you put the new, upgraded heads on the 350 now, that'd narrow the margin quite a bit. I went through a similar dilemna with the motor I'm building. I was going to run a ZZ4 cam with ported 083 heads and SLP runners, but I ended up buying a set of AFR 190 aluminum heads and a Super Ram intake, sooooo I scrapped the idea of the ZZ4 cam in favor of a larger one.

 

the problem with the heads is that im using a vortec setup. However, i think there is a way to drill the TPI to accept Vortec heads. If this is true i may try that becaue i may be able to route some of my paint funds towards my heads if that is the case. Also, I've been bouncing around the idea of making it a 355 while i have it down even though i cant do the whole 383.



Anyways, for the 383, what would you consider the "perfect cam" to be. Im not worried about the 350 running well on the cam because i can get a LT1 cam for free through my father and run that till i can up the displacement. And it seems my roller block is actually limiting my options which is odd and makes me think it would be best to go with a custom grind, so whatever you think is the perfect cam, leme hear cause ill consider custom grinds.

Thanks so far guys!
~LMSkyliner

 

Drilling isn't the main problem.

"Vortec" is GM-speak for "we moved the intake ports". Specifically, they moved them UP, by at least ¼", from where older heads located them. That's where their great flow comes from. Alot of older intakes (I don't know about the stock TPI base, or the F.I.R.S.T. one either) don't even cover the Vortec intake port, let alone match it. In fact, the port mismatch is SO BAD, the combo of a "drilled" intake (if it even works at all) will probably flow WORSE than what you had before, meaning the Vortec heads will result in a NET LOSS of performance in that situation.

Kind of self-defeating to pay money to get these heads with all that nice flow, and then shackle them that way.

Get the right base, or select an intake that does offer the right port location, or use different heads. With the ports mismatched, it won't matter what cam you pick. Or, whether you end up with a 350 or a 383.

 

ok thank you. Ill have to think then what i want to do. And the FIRST injection system has a vortec option that the company just completed recently.


so i guess ill just see what kind of custom grinds you guys think are best for the 383 and go with an Lt1 cam for now. That seems easy cheap and safe. So what's your guys opinions?

Thanks!
~LMSkyliner

 

Just a quick note about LSA:

The separation angle alone cannot give you the information you need to
tune the desired RPM. It also has nothing to do with EFI, or carburetors.

Overlap is a function of lobe separation and duration at the lobe. Then
you have valve size, rocker ratio, valve angle, etc. which also effects the
overlap at the valve.

You could literally have a high duration lobe with a wide LCA and have more
overlap than a low duration lobe on a tighter LCA.

IE: 300 degrees duration on a 114 center will have more overlap than a
260 degree duration on a 112 center.

The overlap tunes how far into the RPM range the motor will produce power.

Your TBI/TPI engines don't breathe well at high RPM , so installing a high
duration lobe and tight lobe center works against you. That is why the
general rule comes with installing cams with wide seperation angles.

For another example, the motor in my current car uses a 110 LSA and
it's fuel injected. It peaks HP at 6100 RPM.

Similar cubes, and injection type, but different manifolds, heads, exhaust, etc.

There are some decent primers on camshafts on Comp Cams, or Crane's
site. Once you grasp those concepts, try getting into some basic cam
design books for some intense reading.

 

OK thanks guys. I think i understand alot better now!


just a question, would somthing like these cams be what im looking for for my 383?
http://store.summitracing.com/partde...3&autoview=sku

http://store.summitracing.com/partde...N&autoview=sku


that seems to be the best i'm coming up with for mainstream cams. Both are from Lunati. They are also the hydraulic roller tappet and EFI cams and the like, so i think they would work well though they are extremely expensive in my mind. Maybe getting a custom grind to those numbers would even be cheaper

any better ideas than those cams? better numbers i should search out? Just get a custom grind? numbers for that grind? Im worried about going too high and losing the cruisability at like 1200 - 2000 but i dont want to lose any power its still making at 5400 - 6000 yanno?


anyways, thank you guys so freaking much. Making sense of these numbers was not somthing i was good at but you really helped!

~LMSkyliner

 

For best results, you should really know what pistons you will be using
and final compression ratio.

If you're serious, I can direct you to a guy who designs cams for
Lunati and he will spec and grind one for your needs.

PM me when you're ready with your parts.

 

wow thatd be great thanks alot. We were just talking about pistons today because we will replace them with the 30 over that the engine needs (166k miles). Would rod length matter because we werent sure if we wanted 6" or 5.7" ? Other then the rotating assembly and cam we were pretty sure with what we were going to build so thats no issue.

 

Rod length makes little difference for spec'ing the cam.

I do suggest going with a longer rod as the piston weights will bring down
the total weight of the assembly, aside from other benefits.

 

Ok so il probably do some kind of Lunati or custom grind setup for the final build.



but what about my current 350/355. Should i go with that free Lt1 cam? Maybe a cheaper comp cam or somthing? It wont be a 383 for a good 18 months minimum. I need some good power now, and i still need that timing chain. Suggestions? Any good cheap 350/55 roller cams out there?


Thanks!
~LMSkyliner

 

They do have the LT4 hotcam *grinded by aftermarket companies* on ebay for cheep alot of the time.

I dont know how that cam would work for your TPI 350, but I do know that it sounds mean as hell in all the LT1's. Look on google video and youtube for "LT4 Hotcam" and listen to it.


I was wondering for all you engine genius', what is it that makes a certain camshaft sound "lopey" or "lumpy" at the low RPM's?? Because I have seen cars make great power on cams that sound stock at idle, and cams that barely run at idle.

 

Hmm. The hotcam is 218/228. That might be alittle high but should still work much better than what i have now i would think. Would this be a good idea for my L98??? And i was just thinking, why is one cam for my 350 not just fine for my 383? With the intakes having nearly identicle curves (albeit the FIRST will have everything a good deal further up the dyno chart) shouldnt the cams work the same as long as the rest of the valvetrain is the same???

I really want to have the L98 pull hard till i can get the 383 in there, and i dont want to buy 2 cams, so any cam that would work for both really well, or a GM cam i can weasle out for cheap would be great. I just dont want to button this engine up with the silly production cam in it, and with so long until the 383 i cant justify leaving it alone or spending big $ on a cam that wont work.


Does that make any sense? All im trying to say is i wish these fancy cams that i would use for my 383 would work just as well on my L98 because i cant live with a dead engine for the 2 years till it will be finished.

 

im gunna tell u like i told someone else. go to compcams and download a program called camquest. its free and very helpful. just enter your engine specs and how u will be using the car and it will recommend a couple cams that are just right for what u got! give it a shot! its very helpful!

 

Basically, as I understand it, the more displacement you have, the more torque and power you have. Since you have more torque and power, you can basically get away with a cam that runs crappier at low RPMs than another cam, but with the extra displacement, you make up for it.

Another way to look at it is the more displacement you have, the the more tame a given cam becomes. A cam can be way too much cam for a 305, and put in a 400 and presto change-o it's nice and streetable... at least in comparison.

If my first paragraph explanation is wrong (It wouldn't surprise me, that's just what I managed to logically conclude a while back) the second paragraph is still mostly correct. The more cubes you have, the smaller a given cam will seem.

 

hotcam and gm 846 cam would work great for a 350 and then the 383.

there are many Lt4 hotcam motors making well over 400hp with modified TPI and other intakes. Highest i've seen was in the 370-380 whp range on a HSR 383. that FIRST intake should support near 350whp on a 383 with the hotcam. thats well over 400 on crank but will have ALOT of torque

LT4 hotcam would be mild in a 383 and only alittle aggressive in a 350. you cant go wrong with it, or the bigger 846


BUT CONSIDERING a cam is a MINOR cost component of a engine build, compared to pistons/rods/crank, bearings, machine work, balancing, balancer, flexplate, etc.... you might as well buy another cam down the road for the 383.. preferably spend the money and get a custom grind

 

Ok thanks so much. I think ill just go with a LT4 Hotcam since i can get one close to $150, That should work GREAT for the 350 (though i think its gonna be a 355 before its in the car. Even better.)

And for the 383, I'll just go custom grind by that guy with Lunati!


Thanks so much guys. Much learned! Much Thanks!
~LMSkyliner

 

well, to make a 355, that means you gotta bore it (.030 I think) over. Which means you gotta pull all the stuff out the bottom end, and get new oversize pistons, and all that other stuff that needs replaced.

Now, wouldnt it be more cost effective to wait untill you are gonna make the 383, and then replace the pistons and bore it out?

 

make sure you get the vortec heads machined to handle the hotcam lift. you dont have to run 1.6 rockers if you dont want to. it wont make much of a difference in power on vortecs.

 

my dad wants to pick up the tab for the 355, so why complain


Anyone have a cam that wouldnt require machining? how are Crower or Cower or w/e cams? I didnt realize there was so much work required for the Hotcam...


Thanks
~LMSkyliner

 

its not just for the hotcam, its for ANY cam you will run on those heads. Vortec heads just arent any good over .480 lift or so. Just dont have the ability without having alittle machine work done. It wont cost much more than 100-150 bucks i'd say to have a shop grind down the guide boss and install new seals for more lift

there also is the possibility of running shims under the springs, and run .050" offset locks with 10 degree retainers. that may be cheaper to do and may give you roughly .520" lift. Perfect for hotcam with 1.5 rockers

 

As for cam specs the amount of overlap and IVC timing has the most effect.

In terms of the motor, it would be piston speed at idle (not RPM), firing
order, and how the pressure pulses mix within the exhaust vs. pressure
at the intake ports.

If you break it down to a single cylinder engine, think of how a late closing
exhaust valve with an early opening intake valve would be destructive at
low RPM. The piston during the overlap period is near TDC and not moving
quickly at all.

The piston is responsible for varying pressure in the cylinder. During the
overlap period, there is very little pressure change produced by the piston.

This leaves intake and exhaust pulses to mix at random and result in a gain
(intake charge enters), or loss (reversion - exhaust gas enters) of
charge in the cylinder.

As for the other question about displacement and camshafts at idle, it has more to do with piston speed again.

A 355 has a slower piston speed than a 383 with the same bore size because
of the stroke length.

The faster the piston moves from TDC to BDC, the more vacuum produced
at the same RPM. So a longer stroke must move the piston more distance
in the same amount of time. That is how a larger cam seems more tame
with big cube (longer stroke) engines.