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...

[kunsan1987]

it's worse than you know.all 1996 and newer diesels are now to be smogged(retroactive)(and who kept all their original parts?),and all commercial trucks regardless of the model year MUST have a compliant ENGINE installed.to convert a GMC topkick to a compliant engine is going to run $50k each.

[EagleMark]

That's scary! Just within 30 seconds of reading this I can imagine the mass exodus of all trucking companies and jobs from an already bankrupt state... while the radiation and waste from Japan arrives... the air may, I say may get a little cleaner but with the radioactive ocean, bankrupt goverment and no jobs who cares?

[jim_in_dorris]

I don't think that they have set a size yet, at least cat back should be ok, and my cat's predate the calif. only cats. They are 2.5 in which is what my exhaust currently is. i will probably run 2.5 to the cats, then open it up to 3 inch. I don't want to have to buy a calif. only cat ( they cost a lot more than a 49 state cat) I have been playing with all the crane cams, and have not been impressed compared to the comp cams. The other cam that camquest recommends as a great fit is the 8-407-8 cam which as a -11 degree overlap and a 110 LSA. That would give a very strong vacuum signal, peak torque at 2000 rpm is 510 #/ft, so it would fit my requirements, but I am a little leary of a 110 LSA. Isn't that getting into difficult to tune areas?

[1project2many]

Why is 110 LSA a difficult to tune area? What about that number makes tuning difficult?

The difficulties tuning a specific cam for MAP based system typically occur when the MAP sensor signal fluctuates heavily and / or when the O2 reading isn't consistent enough to operate in closed loop yet the ecm is forced to closed loop. The ecm doesn't care about an LSA number. Signal in-->process-->signal out. If signal in is garbage then the chain falls apart. A cam with negative overlap is typically well behaved, regardless of where the center of the lobes are ground.

In contrast, I've had difficulty tuning a TBI added to a stock early '60s engine. The relatively lazy action of the valves created enough overlap to allow exhaust dilution at idle. LSA alone would have suggested the cam should be ok but the grind was designed for a smooth and quiet engine in a time when emissions were little to no concern. When carbed it would run smoothly at a mixture probably bordering on 12:1 with a higher idle than what we expect from today's engines. Trying to wrangle it to run closed loop idle at low rpm was a real learning experience. Ultimately it was the engine, not the tuner, that controlled how the tune would be set up.

[jim_in_dorris]

That's exactly why I started this thread, because up until your post, everything I have read indicated that the LSA was the deciding factor, and 112 to 114 LSA was the ideal spread for a cam, indicating that under 110 and over about 116 were difficult to tune.

[dyeager535]

I installed it so long ago that I am not even sure it's the one I used. But based on what I have online (second DD chart http://dyeager535.topcities.com/miscpics.html) pretty sure it was the 109811.

Here are some vacuum readings if it helps at all http://coloradok5.com/forums/showpost.php?p=2580023&postcount=31

*At the time* when I selected that cam Comp was running what I considered antiquated single pattern designs, so I went with Crane. I think now there is much less benefit (in general, not specific applications) dual pattern cam over a single. I think the dual patterns are better when exhaust flow is "restricted" like when running manifolds or early, poor flowing exhaust port heads.

My goodness those cams certainly haven't come down in price since I bought...I sure thought they'd be more reasonable now, what with roller cams being so much more common!

[EagleMark]

It's funny you mention dual pattern cams for restrictive exhaust port head engines as this is the case with IH engines and the dual pattern is highly recommended.

[dyeager535]

Luckily headers help, and I've seen the light! Even the Small block Olds now has headers made for the G-body, but in reality, other than fitment/reliability/longevity concerns (why they make stainless headers with ball sockets!) there is no real reason not to run headers on just about any application, especially on motors that have poorly designed heads that can't be worked around, or extremely poor exhaust design in general, such as the Olds.

Of course, not fair to fault IH or Olds on how bad their 50 year old designs are, we have much more capability now than they did back then.

On a SBC, if you throw headers on there, I suspect the "need" for a dual pattern cam is much less than if you were running the stock manifolds. Again using Desktop Dyno simply for trending purposes at the time, I remember distinctly how much better an engines specs looked with headers. As I recall it was on the order of 40HP for the motor I have in the graph (which I selected HP manifolds to model), around a 10% gain.

One of these days I'd like to get that motor tuned enough that I feel comfortable putting it on a dyno, and seeing how well the numbers matched up. I've spoken with guys who knew their stuff, and they said that if the numbers input into DD were good (such as the head flow numbers, cam, etc) they were surprised at how close to actual dyno numbers it was.

[Cruzer Dood]

I don't know if this will help any, but when I was looking to upgrade the 350 in my Land Cruiser, I played with DD some. The one cam that made some decent numbers in reguards to my needs, was an old Crane Energizer that spec's 204/204@.050, .427/.427 on a 110. I was running a Comp XE 4x ( 210/218, .447/.462 on a 111 ), but didn't like how noisey it was and the power was up higher ( carb'd setup ) than I wanted. While I had the TBI setup on the Cruiser that Comp cam started, idled and rev'd ok, but I never got to drive it due to some engine problems that surfaced. The engine is now fixed, running a Harold Brookshire recomended Lunati single pattern ( 207/207@.050, .442/.442 ( w/1.52 rockers ) on a 112. Since the #193's are supposed to have very good exhuast ports you might consider a single pattern cam. Those were the heads I was going to use until I weighed the cost to rebuild vs new World s/r Torquers, difference was less than $100. I need to get my TBI/'7427 system back on there. I'm at 13.5-14 mpg with my Holley, might improve some w/EFI. Hope this made sense, wife kept calling dinner time as I wrote this. Al

[jim_in_dorris]

Started thinking some more about overlap. If you have no overlap, then your SCR and DCR will be the same. I am set up for 9.5:1 compression, and I don't think that you can run non-race gas with that DCR. Also, given the smog nazi's in Californikate, I would't put it past them to measure vacuum to test for a changed cam. I wonder what the stock TBI cam has for overlap?

[1project2many]

Plenty of stock cams have zero or negative overlap. Stock vacuum on an 80's to 90's TBI engine is 17-18 inches of vacuum. Try setting ICL and valve separation angle to 130 degrees and figure out what that does to DCR. Even with zero overlap you're going to have a DCR around 5:1 thanks to poor cylinder filling.

I believe DCR is a poor way to describe the effects of cam timing on cylinder filling anyway. It's an attempt to relate the results of changing valve events to the spark and fuel requirements that develop from those events for old school guys who can't relate to an engine through anything other than old rules about compression and fuel requirements. In order to be truly accurate people should be describing DCR as a D event... large overlap would be similar to lower compression ratios at low rpm but the CR would increase as RPM increases. Cams like the ones we are discussing would be higher compression at low rpm but would decrease rapidly as rpm exceeds 4500. In essence the DCR is nothing more than a description of the torque curve. Actually relating spark and octane needs to the cam really should involve some understanding of chamber efficiency, bore, and rod to stroke ratio at the very least. Chamber efficiency generally indicates more speed and completeness of combustion while larger bore engines tend to require more time for combustion to finish. Long stroke, short rod engines also tend to require more advance because piston velocity increases faster as the crank comes off TDC. Rapidly increasing cylinder volume quickly works to decrease cylinder pressure so you want to get cylinder pressure as high as possible early in the cycle. All of this means a large bore, long stroke, short rod engine with old tech heads is going to be more likely to require higher octane fuel to make power. The goal is really to get the fastest combustion and start timing as late as possible while still building high cylinder pressure at 12-18 deg ATDC. Old school engine builds don't usually favor this.

In regards to the cams we've discussed, I've built a few engines using the Crane I first recommended and all were similar configuration with great results. Quadrajet carb, aluminum intake, swirl port 86-95 heads, 10:1 "flat top" pistons, 350 cid + a small overbore, stock length rods, stock metal head gasket with roughly .030" quench height, rapid mechanical spark advance to 2500 rpm and stock vacuum advance can. All engine were able to run low octane fuel without severely retarding the timing. This was several years ago and with what I know today I might consider ceramic coating the chambers and piston tops to keep heat in the chambers and help increase combustion efficiency.

[EagleMark]

I had this in my favorites and it has a DCR Calculater.

http://cochise.uia.net/pkelley2/DynamicCR.html

[jim_in_dorris]

1project, Thanks for your input. I don't claim to understand 10% of how to get an efficient engine built. I have seen ceramic coated pistons, but never a combustion chamber. I think that although it might well yield excellent results, my budget wouldn't support it. Oh well. here are two tables from DD2003, the first is the Crane 104211 cam, and the second is the comp 8-464-8 cam. I think for me the biggest question is why the Crane cam has such a small VE in comparison to the Comp cam. As you can see, the Comp cam appears to beat the Crane cam all the way around. I still can be convinced that the Comp cam is not the best for me. I am going to try another Howards Cam from Summit in DD.
21912192

[jim_in_dorris]

Here's the Howards 180-225-12 Cam. 112 lobe CL with 260/266 duration and .450/.465 lift and an overlap of 39 degrees
2193

[1project2many]

Just so we're clear, I'm not arguing for or against a specific cam. The Comp may make for a noisier valvetrain due to faster lift, but it's closer to the theoretical goal of instantaneous valve opening and closing. Crane flat tappet cams used to be relatively cheap but the rollers have always been expensive. I also would run a roller cam when the cost isn't prohibitive. The few people that I know who have run Howards cams have been very happy with the bang for the buck results, but these guys also tend to be the guys who rarely spend big money on the latest stuff. I only presented the Crane example because I have had good results with it. Your concerns about California emissions testing are valid and I have made no recommendations in that area due to distinct lack of experience. Any time we notice California emissions from the east coast they always seem to be questionable. :laugh:

The first time I applied ceramic coatings I bought a $30 cheapie paint touch up gun, a $15 cheapie sandblaster, about $25 worth of wood to build a sandblasting box, and a can of oven cleaner. The oven cleaner was because I had to agree to clean the oven after baking my pistons and heads in them. The first batch, on the pistons, scared me because I didn't think it looked like the pictures of properly cured coating. I proceeded to sandblast all the coating off and do it again. Whether or not it was applied correctly, it sure was tough to remove. Years later when having a machine shop open the heads for larger valves I had to remove the coating in the chambers. That time it took new "black beauty" sand (very sharp), 150 psi air pressure, and I had to hold the tip of the blaster about an inch away from the coating to break it up. Very tough stuff and definitely well applied even though it was done by an amatuer.

The point of the argument against DCR was that it may not be the best way to relate to the cam. Plan for small quench distance using thin gaskets and/or proper piston height, pick a decent set of heads (the swirl ports aren't bad if that's what you're forced to use), keep overlap to a minimum to prevent exhaust dilution, and you'll probably have no troubles. Any of those three cams will produce plenty of go power for you so it might just come down to price.

[EagleMark]

I think for me the biggest question is why the Crane cam has such a small VE in comparison to the Comp cam.
That's only 3-4% change in VE which is not that big of a change. Don't know why but must be do to specs of cams?

[jim_in_dorris]

Actually I think 3-4 % gain in efficiency is huge, I would love to get more, but how to effect cylinder filling with a cam is beyond my abilities. 1project will certainly understand it better than I do, I am learning a lot with his posts. I don't know if my budget will support it yet, but I found torquer s/r heads with SS valves for $700 pair on ebay, and that's almost cheaper that rebuilding and porting a set of 193's.

[jim_in_dorris]

1project, I plan on having the block decked to a piston height of .005" in the hole, and using an .039 felpro head gasket giving me a .044 quench height, does that seem reasonable? I understand that you were making recommendations based upon what worked for you, and appreciate it. That was why I tried more cams. How did you paint the ceramic paint in the combustion chambers to prevent it from intruding onto the surface of the head, yet completely cover the combustion chamber? I don't know if the torquer flow numbers are accurately posted on the ebay site, but I saw the same #s on two different sites, so that must be what world posts. It is different from the DD #'s however.

[EagleMark]

Actually I think 3-4 % gain in efficiency is huge, I would love to get more, but how to effect cylinder filling with a cam is beyond my abilities.Well yes any gain is better but I don't think that is huge. If you read that page I linked the DCR, filling cylinder for compression ratio is determined by intake valve closing at BDC for static CR but the cam specs and cam timing can allow piston to be already on upward stroke reducing CR. So a 10 to 1 CR may only be 8.5 DCR.

There is also some info on quench and head gasket thickness, deck height and chamber CC. It really made me understand the hows and whys.

[1project2many]

The first rule to remember in engine design is that everything is a tradeoff. If you look at each gain with an eye for what may have been lost it really helps get a feel for some of the balance game that's constantly at work in the engine.

The big time engine builders like to keep quench below .035" so that's the target I aim for. Less is more in that regard but you're on the right track compared to the large distances found in those trucks when new.

The coating I use is applied like paint using an airbrush or small touch up gun. Mask the gasket surface using tape then use a small hammer or the handle of a screwdriver to tap very gently around the edges of the chamber so the tape gets cut and can be removed. I removed the valves from the chambers before coating and very carefully applied a light coat of grease to the seats. You have to be careful because any grease in the chambers prevents to coating from bonding. The heads need to be around 100 deg IIRC when spraying so the water carrier dries fairly quickly. After the initial drying and before oven curing, any tape is removed and overspray is cleaned up with steel wool, razor blade, scotchbrite, or equivalent, and the grease on the seats is removed with a solvent coated rag. Coating pistons is just a matter of taping the outside of the piston up to the crown. Spraying should be done at low pressure and with light volume. If you've sprayed paint you can spray the coating.

Then again, the entire process including turning on the oven is probably illegal, immoral, and just plain mean to your neighbors in California.

[Cruzer Dood]

Jim, I payed $630 for the heads from a machine shop who builds sprint car motors, perf builds. If you have something like that in your area, you might ask them about priceing you a pair, you might save shipping costs that way. A good website that explains quench, and it's affects in plain language is Speed o motive, look for engine building with S O M in the collum on the left of the page. HTH, Al