AdioSS had that on the nose.

The overlap area is what we are concerned with on low rpm high vaccum conditions, like idle and cruise.

Now a 191/196 on a 111lsa is going be a really small overlap. A 230/240 on a 120lsa will not even be close to that small of a overlap. Cam numbers by themselves (duration,lift,LSA,ICL)are only one point of a equation. You can't just pick and choose certain things, those numbers have to work as a combo. In some setups there is flexability the LSA can change 4 deg without changing anything too much. On the other hand it can change it greatly, usually in a very high specific output on a engine.

As for Trey's setup. A 238/246 or really whatever lobes are closest. With heads that don't flow alot on a 383 that might work. I have a problem with matching components up rather than tring to taylor a cam to a system to make it work. There is never a magic cam, but there is a magic combo. And with that is working with the most flow for the right port size for your engine. I can't emphisize the right combo thing enough. The reason I like small cams is because I like really good heads. Give me 250cfm @ .400 and 275 @.600 in a LT1 casting and you have yourself a winner, as long as there is enough port volume, say 200-208cc's. Now I can run a 214/224 in a 350 and be happy knowing that I'm not giving up more than 5 HP up top and gaining TQ down low.

In a engine buildup heads should cost you the most and the valvetrain 2nd. Untill you get to the point where the power developed will break things. That might be beating a dead horse, but you also have to remeber that when you buy heads it's not just the flow but the right port size as well, and $1000 in heads will gain you much more than $2000 in valvetrain.

Bret

 

Mark: there was a time when I would have completely agreed with you about solid v. hydraulic roller. But at the present time, it's almost the reverse. I'd say (for street car) why go with a solid roller? You can get a hydraulic roller setup with as much "area under the lift curve" as you want on a street car. You avaiod the hassle of valve adjustments, and the valve train components needed are, if anything, less expensive and just as durable as a solid roller setup. Valve adjustment isn't trivial on a setup like mine. Close to a days work to get it done, if you saw all the stuff in my engine compartment, you'd see what I mean. Since there's no reason, on a street car, to go higher than the lift/durations you can get with a HR, why?

As far as the bigger XE lobes (or equivalent), I used #3190/3192 for two years and 8,000 miles with absolutley no problem. While these aren't long duration lobes (214/224) they are quite steep (.530/.567" with 1.5 rockers) and I assume that's what you meant by "larger" XE lobes. Good 0.080" pushrods, stock lifters, Crane aluminum rockers, LT4 "extreme duty" timing set, CC #986 valve springs with CC 10 degree locks and retainers - just a basic LT1 valvetrain. Everything was in great shape at teardown, I am reusing the pushrods, rockers, timing set and could re-use the lifters. They have 35,000miles on them though and I decided to replace them. The springs were fine, had seat and open pressures within specs and also suitable for re-use. I need more spring this year, so replaced them for that reason. I sold the old springs and they buyer hasn't reported any problem with them. The cam looked fine and I sold it as well, also no problems from the new owner. This year I am using the biggest of the 31xx XE lobes on the exhaust (#3196) and don't see why it should be a problem.

In case you haven't guessed, I am high on the XE HR lobes. But as far as solid rollers go, to me they are a track item at this point for the reasons above and the issues of longevity. If you are using lifts .0.600", spring longevity is a problem. The lifters often have problems with sustained low rpm operation, valve adjustments are a PITA on a street car, and the only good reason to use them is if you want a power band beyond 6,500-7,000rpm and/or >0.600" valve lift, not where street motors live. Not to say someone who is hard core might not find a SR the neatest thing ever, just not for the rest of us.

As far as LSA goes, a lot has been said. My take: it doesn't make sense to talk about LSA in isolation. The issue is really the timing of the valve events. Optimal valve timing is function of the intended use, fuel, head and exhaust characteristics, static CR, etc. It's the combo of parts. IF you keep everything else the same, and the only reason to consider that scenario is for purposes of understanding the effects of changing valve timing, widening the LSA will make the exhaust valve open earlier and close earlier and will decrease overlap. EVO is not a very critical valve event, it's the least important of the four. Overlap, a function of EVC and IVO, is quite important. But it depends on duration as well. So talking about LSA and not duration becomes almost meaningless. That has already been illustrated in this thread in the disucssion of the very narrow LSA on the iron head LT1 OEM cams. But if you do simply widen LSA and make no other change on an NA motor, the results are as follows. A wider LSA will produce peak torque at lower RPM, increase area under the torque curve, shift the power band lower in the rpm range, increase idle vacuum and improve idle quality, and decrease piston to exhaust valve clearance.

Rich Krause

 

Thanks for your time guys. I can actually read your responces now without getting a migrane , whereas I probobly couldn't say the same a month ago

With that said, I'm going to see how the heads come out. For a free port job, I really cant complain.

Being how this was my first motor, I really didn't know what I was doing. I did some reading and decided i wanted a longer stroke, 6'' rods and the basics- but never as deep as this thread goes. Unfortunaltly, i never took the "Double your estimated price" rule seriously. Obviously, now you can see why I have billet steel connecting rods and stock heads.

I Should have Flow Numbers for my heads at the end of this semester (4 or 5 weeks). I'll dig this thread up then and ask you guys for your two cents then. We are expecting 250's @ .550ish lift with more emphasis on lower band RPMs. Unfortunatly (or fortunatly , depending on how you look at it) I have SBC heads and hes a BIG ford guy, some of the head work hes done is absoutly gorgous. These are the the first chevy heads hes worked on so we'll see how it goes. Figured might as well since i had a set of castings laying around. At this point in my life, I just more important finacial obligations than gaining 40hp- Like student loans, rent, food, truck payments and becoming more financially independant all together.

Enough rambling-
Thanks again

 

The gist is that a 112 vs a 114 will have crisper midrange but less vacuum and a rougher idle quality. The 114 will also drive a little smoother given duration/lift vs. duration/lift with better emissions but simply not feel quite as “snappy”.

What’s one man’s trash is another’s treasure and frankly I vacillate back and forth as to which I prefer. Ask me on a Tuesday and I’ll give you a different answer than on Friday. With proper tuning and a little common sense in cam selection, they both will do a good job with good drivability.

No question regarding heads. A great set of heads can do wonders with just a good cam vs a great cam and mediocre heads. A prime example is the LT5 motors. I’ve seen 430 rwhp from stock block, stock cams and full exhaust with a hot motor. It revved up to 7400 rpm making good power with very little drop off. But the car also had a **** pot full of head work.

Get me great head any day, and I’ll forget all about the little stuff with cams.

Denny

 

I just want to point out that the LSA's being discussed here are too big for an NA motor. I like 110 for a hot street/strip 350 and 108 for a 383. LSA in that range with a slighter shorter duration lobe will work much better than a longer duration lobe with a wider LSA. The big/wide combo closes the intake too late, leading to lower DCR and opens the exhaust too early, bleeding off cylinder pressure. Both will kill hp.

Rich Krause

 

The big reason I like lower durations and better heads is due to this, but in reality the LSA is trivial unless it's a extremely sensitive motor. 2-4 deg of LSA can be tuned in with a adjustable timing chain and advance/retard. Even though that's a little hard on a LT1. One reason you see the C30 ground in 4 deg advanced is to move the intake closing point to the right spot.

I gotta agree with Rich above on the Solid vs Hyd Roller. A Solid is better for higher RPM, from 6,000-7,000 than a Hyd will be mostly due to the lifter and pump up issues. A Solid Roller is not the best setup for everyone, it will work for some, but I think it is over recomended on here. Don't get me wrong, you can do a bad *** setup with one and make it a street car, but guys really need to look into the fact that they have to adjust those puppies every once in a while and what it takes to do that.

Bret

 

Trey: this was too long to PM, and I thought it might be of general interest. I will now go out on a limb and put my "LT1 Cam Selection Ideas" out for criticism/comment. Enough of vague talk, here's "how to do it".

You don't want any of the valve events too late or too early, but just right. Did you ever drive a car with a race cam on the street (or even in the pits)? You wouldn't like it.

There is no black magic here. Keep in mind, people have been experimenting with cams in NA SBC's for many years. It is well known what is too much cam, to narrow or too wide an LSA, etc. Stick with what works, unless you have the time and $$$ to experiment.

Here's the story on valve events.

IVC: most important 'cause it determines DCR.
EVC/IVO: important because of their effect on overlap.
EVO: least important (but not unimportant).

How to pick a cam for a HR NA LT1:

1. Chose IVC based on desired DCR. Aim for ~8.5-9:1 depending on what fuel is available, etc.

2. Decide how much overlap is needed based on the intended use. Rules of thumb for a NA SBC based on advertised duration for hydraulic roller cams:

Daily driver: ~50-60 degrees
High performance street: ~70-80 degrees
Race car, occasional street use: ~90 degrees or more

3. Chose an intake duration based on head flow and desired rpm range. Better heads need less intake duration to make hp and the converse. You can't compensate for poor heads with more intake duration beyond a point. Excessive duration will kill low end torque. In general, think of 270 degrees as "small" and 300 degrees as "large". Bigger motors can use more duration. Here are general guidelines for what constitutes a small, medium, or large intake lobe at 0.050" (correlate with the advertised durations above):

Small: 210-220 degrees at 0.050"
Intermediate: 220-230 degrees at 0.050"
Large: >230 degrees at 0.050"

4. Chose an LCA based on the following.

350 stock heads ~114
350 good heads ~112
stroker, good heads 108-110

5. Chose an exhaust duration based on exhaust flow and intake duration. If your heads have killer exhaust flow and a good exhaust system, exhaust and intake duration shuld be the same. Most LT1's need at least a couple of degrees more exhaust than intake duration.

Intake center line: not enought time to go into it now. Usually, 4 degrees of advance is good, which means on an LT1 that the cam is ground with an ICL 4 degrees less than the LSA.

Lift: get as much lift as you can "afford" within the limits of HR technology. More lift = more spring = more stress on the valve train = need for better parts = more $$$. Rule of thumb: limit lift on a street HR to ~0.600". If it's not a street car, use a SR.

Voila - you have a cam.

Note: much of this does not apply to blower or N2O optimized cams. N2O cams follow the above pretty well except that they need a lot more exhaust duration. Blower cars are quite different. The need more exhaust duration and less overlap as well as a later IVC point, depending upon the static CR and fuel used, etc.

Nits, picks?

Rich Krause

 

Rich,

That is about as good as you can get on informing people on how to pick a cam in 2000 words or less. This will help ALOT of people that insist on picking their own cam and trying wierd LSA's, duration, overlaps, lifts, etc and end up with the WRONG cam bercause of it.

The best info was to "stick with what works unless you can afford to expirament".

For the people that do not understand everything that was written there, get someone to help you with cam selection. You will be happier.

NightTrain66@msn.com

 

One "nit pick"

As i was reading above,
as a rule of thumb, more LSA = broader band with less peak power.

Using my 4L60e- is that not more desirable? I could see using the smaller LSA on a 6speed, but my 1-2 shift goes from 6600rpm to like 3400 or something like that

 

It sounds like you need more converter.

With my stock iron head LT1 with the baby cam specs I posted earlier in this thread along with the 4L60E/ 9.5" Vigilante 3200 stall/ 3.73 gears I've been shifting at ~5500 and it never drops below 4000rpm. Not even on the 1-2 shift. I expect even less of a drop with the 4.10s.

 

Like I said, it's hard to talk about any of these things in isolation. But maybe going a couple of degrees wider on the LSA is worth considering for an A4. But that's one of the reasons for the "~" before the sugested LSA's.

Rich Krause

 

Vigi 3400 stall- prob going to flash a bit higher...

Rich, I think i might go with your suggestion on a 110 (as u said)..
btw, where to you expect that to rev to?

 

I found that Vigilante's converters are seperated by 400RPM. They've got a 2800, a 3200, a 3600, and so on. I was told that my converter was a 3500 stall, but when I called Vigilante with the number on the box and on the converter, they said it was a 3200 stall. I'm betting you've got the same one as I do.

What gear are you running?

 

3.73:1

 

Rich, this is going by advertised, duration, right?

Quote:

Here are general guidelines for what constitutes a small, medium, or large intake lobe at 0.050" (correlate with the advertised durations above):

Small: 210-220 degrees at 0.050"
Intermediate: 220-230 degrees at 0.050"
Large: >230 degrees at 0.050"

And this is by duration@.050, right?