Cam differences - vacuum, lift, overlap etc.

[jim_in_dorris]

So as not to muddy up Rally's post, I decided to start a new post. I use DD2003 a lot to model my upcoming build, I have been playing with different combo's for several years now, and I think I hit the sweet spot for my build, but I am alway open to something new. I opened my build and stuffed in the spec's for the cam Mark recommended to Rally, and it was a little less HP and a LOT less torque than what I think I have settled on for my build (I know DD isn't absolutely correct, but it shows me trends). I have tried modeling a lot of different cams; Comp, Lunati, Howards, LT4 hot cams, Crane, Summit, and now Edelbrock. I want a torque build, and I have to stay smog legal, so that dictates my heads (193's, or really expensive AFR's, or World Torquer S/R's) and after getting some numbers from a set of 193's Fast305 ported, I decided to stick with 193's. That dictates my top-end even ported, so I chose a cam accordingly. The block is an 88 350 with the bosses ready to go. I think I want to use the Comp 8-464-8 Hydraulic Roller eXtreme Fuel Injection cam. It specs a Seat-to-Seat duration of 252/264 I/E with a lift of .550/.545 I/E an intake Centerline of 109 degrees and a Lobe Center Angle of 113. That gives me an very narrow Overlap of 32 degrees. It also requires 1.6 ratio rocker arms. I think that with that narrow overlap, I should get good vacuum, and the Lobe Center angle of 113 ought to make it reasonable to tune. However that being said, the last time I did a performance build was 13 years ago, and I didn't do that good a job with the cam for that build (way to big for a 283 and really tall gears). According to DD2003, my combo should see peak HP of 351 at 5000 RPM and peak Torque of 422 at 3500 RPM with over 400#/ft from 2000 to 4000 RPM. Has anyone tried tuning this cam? I really don't want to struggle with the tuning after I build this 355. Does this look like a reasonable build?

Compression Ratio of 9.5
Quench height of .044 (.005 in hole with .039 crush height gaskets)
DCR 8.15

[gregs78cam]

Have you tried Comp's Camquest?
http://www.camquest.com/
It seems to be modeled after DD, but should be a 'little more' accurate, I would think. That cam sounds good to me, but is that the most duration you can get while keeping overlap small, and LSA large? Still seems sort of small.

How does 8-305-8 stack up? More Duration, 1* more LSA. If I could get Camquest to load I would check it.

As far as tuning, my cam is 270/280 seat-to-seat, 219/224 @ 0.050, .526/.525, 106 intake Centerline, 110 LSA and was not that hard to tune.

[jim_in_dorris]

Actually, camquest is where I got that cam. Yes that is a very short duration cam. With that software, using the same flow data for the heads, camquest gives me 405 hp @6000 RPM and 510 #/ft of torque at 2000 RPM which I find interesting, considering that the cam RPM range is 1000 to 5000 RPM. I don't think that my engine will spin over 5000 RPM's if I try.

I tried using small tube headers on both models, and got these numbers

DD 346 hp @ 5000 RPM , 419 #/ft torque @ 3500 RPM

camquest 387.8 hp @ 5000 RPM , 507.6 #/ft torque @ 2000 RPM.

If I believe the cam quest #'s, then I need to run my 90# injectors at 17 PSI and set my BPW to 79.
Gonna have to run a vacuum referenced AFPR

If the DD numbers are close then I need 13.5 PSI on my 90# injectors with a BPW of 88 with no AFPR, just a quarter.

[jim_in_dorris]

I can't get the camquest software to work in firefox, but I downloaded it from here;

http://www.compcams.com/downloads/register.asp

and it works fine.

the 8-305-8 cam doesn't even show up as a recommended cam for my truck. I will try it in DD if the profile is available.

Okay, 378 HP @ 5500-6000 RPM and 396 TQ @ 4000-4500 RPM. Not good for my truck, maybe a light car.

[1project2many]

What's very difficult to model correctly with DD or any other software is the lobe lift rate. Having grown up around solid roller racing cams, I naturally thought the hydraulic roller cams had more agressive lift rates than flat lifter counterparts. Come to find out that many of the cams are not so and some are very similar to the flat tappet versions they replaced. Faster lift cams tend to have lower total valve overlap when considered over a range of engine rotation than a cam with a lower lift rate but same lobe specs @ .006". I know DD has some ability to estimate lift rate using both the .002/.006" specs and the .050" specs so I'd get those wherever they're available.

Now here's a funny note. I googled that Comp cam number looking for specs and I found this neat post by some guy named Jim on thirdgen... the only thing I would say in reference to that thread is that a low rpm cam with fairly restricted exhaust is more likely to suffer from exhaust gas diluting the fresh intake charge during the overlap period than from unburned mixture exiting and affecting O2 readings. This can be ok as it provides a self-EGR effect which can help emissions. OTOH it can be extreme enough to prevent smooth idle at low speed but the overlap you're considering is fairly small. That combination should be tunable without major issues.

For comparison I'm using an old Speedpro TP240 grind in my '57 under the Crossfire intake. .443 lift, 117 deg lobe center, 64 deg overlap, 288 adv duration. It's a copy of the even older 350 hp 327 cam and it still manages to idle well plus achieved 18 mpg when lean cruise was enabled.

Although the peak power level isn't nearly as high as the Comp cam, I have always like the GM 12353914 cam for trucks. The low end torque on these things is incredible and with a typical 4 speed '80s truck trans having only three streetable gear ratios this cam allows excellent pulling and towing power without those annoying 5000 rpm downshifts on long highway hills. Installed straight up the initial torque calculation at 2000 rpm is a full 26 ft lbs greater than the Comp cam straight up. It's $133 from GM and with my current thoughts to revisit the engine in the '57, it may be time for a change.

[jim_in_dorris]

When you brought up ramp rate, you reminded me that one of the things I played with was adjusting the ramp rate and lift using DD. I increased the ramp rate and lowered the lift while trying to hold the HP and Torque the same. If a custom grind wasn't so expensive, that looked interesting. I can't model that GM cam because I can only find partial spec's for it. I really think I want a roller cam however as I don't want to be stuck remembering to add stuff to my oil to prevent premature cam failure. (Us old farts sometimes have trouble remembering stuff like that ;) ).

[EagleMark]

I really think I want a roller cam however as I don't want to be stuck remembering to add stuff to my oil to prevent premature cam failure. (Us old farts sometimes have trouble remembering stuff like that ;) ).

That is why I only have an use one oil on everything I own including the lawn mower. Amsoil 10w/40 Full synthetic with Zinc and phosphorous. But then again I have nothing OBDII that it may hurt either... my LT1 is roller but I use it in there too.

[1project2many]

I really think I want a roller cam however as I don't want to be stuck remembering to add stuff to my oil to prevent premature cam failure. (Us old farts sometimes have trouble remembering stuff like that ;) ).

Not so sure you're much older than I am. Use Delvac 15W40 or another oil with plenty of EP lube and you don't have to add stuff. Buy plenty ahead of time as well so you're somewhat insulated against changes.

I can't model that GM cam because I can only find partial spec's for it.

It's a Crane cam grind number 2010 part no 114102.
Adv. duration 244I 254E
Dur @ .050" 184I 194E
Lift w/ 1.5 rocker .378I .401E
Valve events @ .050" IntOpens -12BTDC IntCloses 16ABDC ExhOpens 21BBDC ExhCloses -7ATDC
http://www.cranecams.com/56-67.pdf

Similar cam in factory hydraulic roller is Crane 104201. Dyno specs with generic 5.7 engine show 70 ft lbs greater torque (467 vs 391) over comp cam previously mentioned. Again, top end is significantly lower so the deciding factor for me would be the rpm range where the truck will spend most of its time. Anything running manual trans below 3100 rpm on the highway will feel stronger more often with the Crane.
http://www.cranecams.com/88-89.pdf

Low zinc oils are to help catalytic converters live longer. If you're past 150k miles you're past the "longer" they've got in mind.

[jim_in_dorris]

Thanks, the only thing I see with the 104201 cam is the 106 LSA. Would that cause tuning problems? I have 2 new cat's (true duals that will be getting changed back to a single exhaust due to a new change in smog rules that california is implementing). I just DD'd the 104201 and 104211 crane cams and compared them the the comp 8-464-8 cam. They are surprisingly similar, although the 201 doesn't hold torque as long or flat as the other 2. The crane cams have negative overlaps, the 211 is -23 degrees and the 201 is -5 what's with that, did I get something wrong when I entered the values?

[lightning-jr]

For a Crane I suggest a 109811.

http://www.cranecams.com/90-93.pdf

You might go one step higher but I know that cam works great in 4x's.

[1project2many]

Negative overlap represents the intake closing before the exhaust opens. Positive overlap is intake closing after exhaust opens. Those cams will have very strong vacuum signals. With carburetors they provide a strong signal and are very responsive. With TBI you should have little trouble tuning although the timing table will probably look very different from stock when you're done.

For a Crane I suggest a 109811.

This is a nice choice. It's essentially the same cam as the two I recommended in a hydraulic roller retrofit version. All the notes I've seen say the cam core is different for the retrofits and cannot be swapped with later cores. I've never tried the swap myself so I don't know if it can be used in the later block. DD puts torque output of this cam between the two I mentioned which is still not too shabby.

[EagleMark]

I have 2 new cat's (true duals that will be getting changed back to a single exhaust due to a new change in smog rules that california is implementing).

What did they do now? I haven't lived there in 20 years and it was horrible then... my stories could be a whole thread on a decel valve on a VW carb that no longer exists or made or reproduced and they would not let the one with bad diaphram pass...

You really have your hands tied trying to make all these choices as you not only have to pass emissions tests but every part changed has to have a CARB number.

[jim_in_dorris]

Mark, the rule change says that if the vehicle came with a single exhaust, it must have single exhaust or it will automatically fail.
I hope to sneak the cam past, because they don't disassemble the engine to look, and I am doing it myself. All the rest of the parts however must, that's why I will probably stick with my 193 heads, and just port them (again, not telling the smog guy). The only headers worth anything with a carb EO is Doug's triY's, and they are spendy, but I will bite the bullet on those. I may go with a carb manifold with an adaptor (eddie makes a CARB EO manifold IIRC 3706 that has EGR).

[1project2many]

Mark, the rule change says that if the vehicle came with a single exhaust, it must have single exhaust or it will automatically fail.

Does it have to be stock diameter? Single 3" pipe flows better than two 2.25" pipes.

[EagleMark]

Wow they really just suck the life out of car enthusiasts! Really what can a dual exhaust hurt? Anyway sorry you have to live there.

So back to the bigger diameter I nicely built y pipe to muffler 2 in one out (easy CARB cert.) and 3 inch back would be single, flow as good as truck needs with engine being built to pass smog nazis...