Bret, is those lobes #s right? You combined the XE lobes on the exhaust and the magnum lobes on the intake. I would assume that you would want the better lobes of the XE on both, seeing that they are faster then the magnum and then would make more power?

Have 2 more questions for you, 1)Why would do you suggest that I run such a large split intake vs exhaust? Is this 10-12 degree seperation something that SBC like? I have seen that cames that run this kind of seperation seem to be making more power then the somes that are closer, liek 6 degrees? 2)Why do you suggest running a cam straight up or 1 degree adv? I thought you could only run single pattern cams straight up bcuz if done with a split cam you would get some neg effect, forget what it was called? I always thought at the MOST you would want to run a cam 2 degree adv for a daily street car.

 

i wont tackle any of the other questions i'll leave them for bret. but i can take a shot at why he likes them straight up. most of the cams that comp sells off the shelf have 4 degrees advance. they do this to boost the low speed tq of the cam. and to kind of move the intake closeing point to a better location. they do this because for some reason a lot of people somehow think they can just toss off and pick the best cam ever made for every engine ever built. they do it without 1/4 of the knowledge that bret has, and without any of the simulations he uses. so anyhow, back to my point, they grind them with advance by default because everyone thinks bigger must be better. and it is to a point. so they boost low speed power to crutch pathetic cam choices with the advance. so now to the ground straight up thing. the 'right' cam for the engine combo will make the BEST power installed straight up. if you retard it you'll lose some if you advance it you'll lose. so straight up is the way to go. i'm sure he'll elaborate on this better but its just something to chew on in the meanwhile.

 

Trey,

Yeah a 6500-6800 is where it will want to go too.

WS6T3RROR,

Yeah that's a good point, lobe area is very important. More area with less duration will hav emore lift but it will also make more TQ.

On the second post, that's pretty dam close. Big cams gain average power with advance, the right cam is good right around straight up. It's all intake closing point. (BTW this is in the pushing the limits situation.) If you need advance to gain average power, you could find a better cam with less intake duration. I do find cases that up to 4 degs advance is needed, but on HR cams it's rare. Solid flat's like some advance, but that's because the lobe area vs .050 duration sucks. The BB 428 FE Ford situation, was working with heads that were way to small for the engine, so I had to tune things differently. If you had more flow a nice easy cam would make some stupid power with that engine. I might not get the best peak numbers on the HP, but my average TQ usually kicks ***, and the peak HP is pretty dam good too.

mastrdrver,

Cam schoool 201. You need to pick lobes you can run depending upon lift. Too much lift and you have a hard time with springs.

1. SBC like more exhaust split. They like it alot more if you have less intake duration than you normally think too. It basically is there to keep the HP up there past HP peak. LS1's like a single pattern much better, but they do respond to a 8 deg split pretty well.

2. See what WS6T3RROR said

Guys,

No need to pick too much apart, there are some good responses out there.

I'm tired


Bret

 

thanks Bret

 

Thanks Bret for answering all our ongoing Qs.

 

So the next logical question to ask is if cam companies can make a cam with less duration make as much power as a larger cam w/o the negative low end driveability issues, why don't they make one?

My best answer is because lope sells cams. Follow me here. They design a bigger cam to allow more overlap to create the sexy lope sound we all want in our cams, but the downside is it really screws low end torque and driveability. So they advance the cam 2-4 degrees (110 ICL, 108 ICL) to boost low speed torque. This has the effect of moving the peak power band of the cam down in the RPM range, but they do get the lope they want.

So the alternative is to keep the cam straight up rather than advancing it. The later valve events boost top end power w/o resorting to big overlap, which means less duration is required and therefore less cylinder pressure bleed-off at low RPMs.

Perhaps this is why most OEM cams seem to have very small durations but are not usually advanced much, if at all.

Am I understanding this right? So rather than looking at an XE224/230 on a 108 ICL I could look at something like a 214/224 on a 112 ICL and make the same power w/o the loss of low speed goodness? I have been reading up and playing around with varying ICL for a couple of months now, but I think I am finally beginning to put all the pieces together mentallly after reading Brett's last post.

 

I was thinking the same thing before I even got to reading this thread again...

I was going to go with 224/236 with 4* advance, however I was going to go with a 115LSA and no overlap at fifty. That would give about the right powerband and a nice lope. However, with 6* less duration (218/230) on a 110 or 112LSA straight up, the powerband would be pretty much the same with a lope that's very similar to the LT4 hot cam.

I can't afford those bad *** simulations, but I do have Desktop Dyno 2000 (doesn't everybody?) In addition to the estimated hp and torque output, it gives the VE and different pressures inside the engine. If you go by the Volumetric Efficiency, then the more duration/more advance cam is higher (by as much as 4.5%.) But if you go by the pressures in the engine, the shorter duration/no advance cam is better. Unfortunately, I don't really understand the pressures enough to really get that part yet


And on the flip side to what I've seen posted, what about if you were to go extra small on the duration, but retard the intake centerline?

 

With regard to your last question, I played with that in desktop dyno. and the problem is there appears to be a diminishing return to further retarding the ICL. It appears the low end starts to drop off again, probably because valve events are happening too late.

I'm also looking at a 218/230 using comp XE lobes. I'd love to hear some expert opinion on this.

 

I have seen to many hotcam cars and cc306 cars on stock heads running the same trap speeds and MPH. so i went with the XE224/230 since it seem like the prefect cam. just slightly larger than the hotcam and cc305 but with better lobes and little more intake duration. i also went ahead and had it ground on a 110 LSA so with the 4 degree advance typically found on LT1 cams i have a 106 ICL. my purpose however was not to find a choppy idle but to get the maximum DCR and still keep the cam streetable with the ability to pass emissions if i ever have to. with the XE lobes even that cam on a 112 only has 51 degrees overlap which is only a degree more than the XE230/236 on a 112 so it SHOULD have comparable steet manners IMO. of course only after i can get the cam in will my logic prove true or false.

 

Well, since I had some personal experience with this very matter, I will offer my history here:

I did not have an LT1, but I had a 350 SBC with a bone stock TPI intake and TFS Twisted Wedge G1 aluminum heads. This engine was born and run with a GM Performance Parts LT4 HOTCAM. To put it in a nutshell, that 350 TPI was the best TPI engine I have ever felt, to date. It ran a 13.45 in the 1/4 in my 3500 lb Monte Carlo and a stock GM 2000 rpm stall converter.

After coming into some money, I bought a TPIS Miniram intake. (I know, too big for my 350, but I planned on building a 383 or 400 later on). Anyway, I installed the Miniram and the car got SLOWER. Had all kinds of top end power, but only after 6000 rpm. Far too much for a basically stock bottom end.

I was on the phone with TPIS for a number of days trying to sort out my performance problem. To sum up their opinion, the tech I talked to said "the HOT LT4 CAM is junk and no good for any application" to put it mildly. They suggested that I run one of their $350 bumpsticks for the maximum amount of power. In fact, they wanted me to run a smaller cam than the HOTCAM. Funny thing was, I had a Comp Xtreme Energy unit already in my garage from a previous project that was almost identical to what they wanted me to buy. I installed it per their advisement.

Well, I installed it and guess what....THE CAR GOT SLOWER AGAIN. I called TPIS and their only explaination was the Comp unit I installed was not their "approved" design and that is why the engine was not responding.

To make a long story short, I put the hotcam back in and tweaked the computer to the max but it never did run a 13.45 again, with the miniram intake at least.

I am currently running a SuperRam intake on the same basic engine but with the Comp Xtreme Energy cam that is one step bigger than the HOTCAM. My heavier GTA ran a 13.1 @109mph spinning like hell. Not bad for a 350 engine with the same 2000 rpm stall converter.

I helped my friend build up his LT1 with the LT4 heads, intake, and hotcam and his car feels almost as good as mine. I seem to remember reading a magazine article that came out a couple of years ago that did the same buildup and attained 429HP and 430TQ at the crank or something like that, out of a stock bottom ended 350ci LT1. I wouldn't doubt he is making those same power levels the way his car feels.

Like someone said earlier, there are a lot of aftermarket vendors that want you to buy their stuff. I have had great success with the LT4 HOTCAM in every application that I have used it in. It is a great street cam, but you need to have 3.73 or 4.10 gears and a 2000+ rpm stall converter if you are running an auto and 350 cubes. In my opinion, it is a relatively small cam for a street/strip application.

I think it really burns a lot of vendor's butts that GM offers a cam that can be purchased cheaper than most other units that perfoms better in most cases. One nice thing that I have always liked about those GM roller cams was they are machined from a steel core, not a cast one like most aftermarket camshaft manufacturer's use.

 

The hotcam has really lazy ramp rates though. That's my major gripe with it. You can build a cam with Comp's XE lobes with less adv duration yet more .050 and .200 duration and the car will make more power with less loss of low end power/torque.

In fact, I came across Crower's website yesterday and they have some interesting hyd roller grinds, with fairly intense lobes (as measured by .050 duration divided by adv duration).

 

I agree that there are better cams out there. But you have to remember that the HOTCAM was probably designed before the LT4 came out in 96 (which would put it in 94 or 95 depending on development time). I don't even think the Xtreme Energy line came out until 98 or 99. We are really comparing apples to oranges here. To be clear, it is my opinion the HOTCAM is a great piece for what it is. Sure there are better things out there. I still think the LT4 cam performs well for the wholesale price I can get one for.

 

I can agree with that

 

so what is this LT1 hotcam you speak of

 

I think they meant LT4 HOTCAM; GM p/n: 24502586. I have never heard of an LT1 HOTCAM.