Cam Suggestions

[Jeff Higgins]

I'm starting to squirrel away parts for my first motor build, and would like some suggestions on cams. Let me tell you what I have in mind, and what I'm starting with.

I have an '81 3.0; it has the small port heads on it. Right now I have it torn down and am starting to send parts out for inspection, polishing, machining, etc. The bottom end will remain stock; crank, rods, etc. I will be running a set of 95mm 10:1 JE's. Heads will remain stock as well.

Here is the kicker: I'll be running it on MFI. I have a set of 2.4 "S" throttle bodies that appear to exactly match the intake port size in my small port 3.0 heads. I have a set of later plastic "T" stacks that I will have bored to match, and a pump that I will have rebuilt and space cam installed to match. I want to send the SC cams out to Web Cam for hard welding and regrinding, plus installation of the pump drive pulley.

It will be going into my '72 "T". The car weighs just under 2200; it has been set up as a DE oriented car, but will continue to be driven more on the street. I'm looking for a good bump in power over my current 2.4, while maintaining its friendly street manners.

I'm envisioning a motor that will spin up to about 7,000 max and provide a flat, useable power curve from about 4,000 on up. Longevity is important, as I really can't afford to do this again any time soon. I'm hoping for a good solid 210-230 hp, or something like that. No 8,500 rpm, 300 hp time bombs here.

So, I hope that's enough info on what I have in mind. Any suggestions on cams?

[SP2]

Hi Jeff,

Good to see you this weekend. I am rebuilding an 81SC Euro right now, sort of. I didn't have to remove the cam towers/P/C, but resealed it and put in new cams. Here are two links that helped me alot:

964 cams in 204 bhp sc

Best Cam Profile For A Stock SC?

I reground my SC cams to 964 profiles. But if you go new billets, I would consider Webcam 20/21. My Euro has 9.8:1 compression stock. John Dougherty (camgrinder) did my regrind and they are perfect. Delta Camshaft did my rocker faces and they also are perfect. (I had pitting issues on both.) I think Webcam suggests high compression to run 20/21's but I think Superman said his CR was 9.3:1 and JW says his engine is awesome. I don't think MFI matters. I know carbs vs CIS doesn't. JD also has a new grind, I think DC17, and that is supposed to be like the 20/21's. I haven't read anything else on them yet.

That was a sweet car this weekend. I loved the wheels and seats!

[jluetjen]

This thread contains pretty much everything that I've been able to learn on the subject.

[Jeff Higgins]

Thanks John; great information. I used 4500 for a torque peak and 6500 for the horsepower peak and came up with some surprisingly mild duration numbers. I got 235.198 intake and 233.909 exhaust. It turns out there really are no cams with that mild duration. Hmm... Raising those respective RPM numbers by 500 gives me 250.569/241.486, which seems more in line with what is available. That's fine with me; moving peak RPM up by 500 still keeps me well within what will work with stock valves and springs, doesn't it?

The popular Webcam 20/21 goes 258/246, with .485/.452 lift. This is sold as a good cam with stock pistons and CIS. This looks just under the GE 60 which has 266/248 duration with .490/455 lift, which is recommended as a "mild race" grind with stock P&C's.

Running higher compression, as I plan to do with the JE 10.5:1's, puts me in what Woods calls "high performance P&C" country. This changes his cam recommendation for "mild race" to the GE 80 (274/256, .500/.470) and relegates the GE 60 to "street / auto-x" duty. Interesting. The duration numbers on that GE 80 appear to place it in an RPM range above what I'm looking for.

The missing piece here is the lift that the ports in the small port SC heads will support. Looking at your flow vs. lift chart for the 2.2's, it looks like the "S" heads continue to improve up to .500" lift. I can't remember the port sizes offhand, but the small port SC's have at least as large of ports, don't they? If so, it looks like the lift figures on the 20/21 and GE 60 should work well.

So it looks like I'm looking at Webcam 20/21's or GE 60's, or other cams in that range. Does that sound reasonable?

Also, with this information, can a space cam for the MFI pump be matched to these cams? I'm a little worried about that. Would a Porsche factory grind be easier to match, or are space cams reground these days anyway? I'm thinking the RSR sprint might be an alternative to keep it "Porsche" and possibly easing MFI pump recalibration. I can't find numbers on the RSR Sprint; does some one have those?

[jluetjen]

Using "small ports" with a "wild cam" will may to cut off the peak RPM HP (the last 500-1000 RPM of the rev range) depending on how constricting the ports are. Below that point the engine will be as strong (if not a little stronger at low rev's) then the same engine with adequately sized intake ports.

BTW, you can't really use the 2.2S flow data as an example for the 3.0 SC, because the 3.0 SC's valves are bigger which tend to shift the curve up across the board, as well as changing the shape slightly.

Refresh my memory, how big are the "small" SC intake ports?

[Jeff Higgins]

I checked last night in Bruce Anderson's book; "small" SC ports were 35 intake and 36 exhaust. "Big" ports were 39/36, so only the intake changed. Yes, the intake was smaller than the exhaust; interesting.

Valves in the 3.0L run 49/41.5, so they are somewhat larger than the 2.2/2.4L 46/40 valves. That looks like it might have the greatest affect on flow, if I read some of your other threads properly.

I did go through the archives looking for everything to do with cams, valves, ports, and flow. Your name comes up alot; very impressive work. What I'm beginning to understand from all of that (and please correct me if I'm wrong) is that small ports / big valves flow better than big ports / small valves, at least as a generality, in my target RPM range. With that in mind then, it looks like the small port SC heads are the way to go for my application.

Neither the GE 60 nor the 20/21 goes over .500" lift, so they look to be a little below maximum in your 2.2 L example. With approximately the same port size, and somewhat larger valves, wouldn't they be relatively even further below the max flow the heads would support? The only thing that concerns me is the duration, which appears optimized for a little higher RPM than I was looking for at first. The lift looks like it is in the range I should be considering. Am I on the right track?

[jluetjen]

In your case, if the duration is a little long, the "smaller" ports will tend to help keep the intake velocity up at lower RPMs which will help with the part-throttle running. Sure you might give up a little bit above 6500 RPM, but I doubt that you'll miss it.

Unfortunately I don't have a lot of data on the SC/Carrera heads. In the past Snowman has had access to a flow bench and has been nice enough to flow the heads that provided the data on my chart. If you have a head available, maybe he could help you out.

[Jeff Higgins]

I ran accross Snowman's post on his flow bench during my search as well. You guys have done some great work on this.

I'm kind of thinking the same thing on the small ports as far as keeping that intake velocity up, even with the longer duration.

I spoke with the guy machining the MFI ports into my heads today. He recommends having Elgin put a 964 grind on my cams, saying he has had great luck with that in street/DE 3.0's. I'll have to check the specs on that when I get home today. Wasn't there a discussion on here about the relative merits of the 964 vs. the 20/21 for CIS cars? It seems to me (if I remember correctly) that the 20/21 made more power. I wonder if that even still applies, switching to MFI.

I'm harboring some fuzzy notion of being able to run a little more cam than is normally considered for 3.0's still running CIS. The switch to MFI should open up a little more leeway in selection, with the potential for greater overlap (narrower lobe centers). Off the top of my head (I've been pouring over the cam charts) I think the SC cams, and others meant for CIS, run about 110 degree lobe centers. It seems narrowing that up would be one of the side benefits of switching to MFI. That would steer me towards the GE 60 and away from the CIS friendly 20/21 and similar grinds, including the 964. Am I still making sense?

[jluetjen]

Yes you are Jeff. You might want to communicate with Camgrinder. He helped a lot with my research and I got my cams from him. Given that you're using MFI, I think that you'd be leaving something on the table if you went with 964 cams. Checking some examples that I've collected, it looks like in late 3.0 SC (with 34 mm intake ports), a 20/21 will generate peak torque at around 5200-5400 RPM, and peak HP at around 6100 RPM. So this will be a somewhat "peaky" motor, but within that range it will outperform the 964 cam. Your peak HP should be around 235 HP versus about 205-210 using the 964 cams. The 964 cams will most likely pull stronger below 4500 RPM, but the 20/21's will be all grins above that. I would expect the GE60's (DR60's are Camgrinder's version) will most likely be even stronger above 4500 RPM then the 20/21's. Either way, the MFI will help to fill in the off-cam torque peak so it won't be as noticable compared to the same engine on carbs.

If the intention is a play car/DE car where the peakyness will be fun, I'd go for the GE60's. If you're going to be pottering around town on the at 2000 RPM most of the time, I'd go with the 20/21's.

[Early_S_Man]

GE60s

The WebCam 20/21 grind doesn't have much overlap, so the GE60 have the benefit of a classic wild cam sound ... and additionally, the overlap will lower effective compression at lower rpms and reduce octane requirements somewhat.

[Jeff Higgins]

This is definitely just a play car / DE toy at this point, so day-to-day manners in city traffic is a non-issue. Some level of peakiness will definitely add to the fun on the DE days. I guess the more I think about, and look at various options, a 3.0 "S" of sorts is kind of what I'm drifting towards. Not as peaky as the 2.0 "S", but maybe along the lines of a 2.4 "S" on steroids due to the added displacement. That long-overlap, lumpy idle and raspy exhaust note would add to the fun as well.

I have heard and read references to using cam timing to "fool" the motor into thinking it has less compression at lower RPM's and higher compression at higher RPM's. It makes sense with the little bit of innefficiency introduced at low RPM with some of the intake charge going out of the exhaust port, and the momentum of the exhaust charge sucking in a bigger intake charge at higher RPM.

After my conversation this morning with the guy doing my cylinder head work, it looks like the JE 9.5:1's will be what I will use, as opposed to their 10.5:1's. I'm afraid even the longest overlap cams would still result in too high of an effective compression ratio at low RPM's to be safe without twin plugging. I'm not ready to spend the additional outlay to twin plug; this isn't a race motor.

It's my understanding that the "supercharging" affect of long overlaps cannot be utilized on a CIS motor, and that is why the cams are compromised with wide lobe centers / short overlaps. So I agree, I think any CIS cam would leave something on the table in my application. It looks like I'm narrowing in on that GE60, or an equivelent grind from Elgin or Webcam.

It's great to be able to run these thoughts past guys that know what they are doing here, and that have so much more experience with this. I kinda sorta think I'm on the right track, but it sure is nice to do a sanity check with you guys. Thanks.

[Eagledriver]

I love the idea of using the MFI on your engine. I'd say the biggest compromise to your engine is the small ports. With a 3 litre and hot cam with open intake like the MFI your going to lose a lot of top end power potential. I don't think you can safely run to 7000 RPM with stock springs and any of the cams you are looking at. If you want to keep stock springs you should use something with slow valve acceleration like a 911S cam. Better yet put in Camgrinders stronger valve springs. He has a street version that I'm using that will give you enough spring to run safely to 7500 or so. I've been told by one of our local race engine builders that the stock SC valve train will float at 6900 RPM and that is with stock cams. With the cams you are looking at they will float even sooner.

My suggestion if you are keeping the stock ports is to use GE 40's. They will give you lots of torque at the lower range and will match your small ports strengths.

If you open up the ports then GE 60's or even 80's would work. Of course you'd also need to open up your MFI throttle bodies. All this gets expensive.

-Andy

[Jeff Higgins]

I've heard that about the stock SC springs as well. My original goal was a motor that would never go over 7,000, so I'm still fine with that. I can see where more lift would mean earlier valve float, too. I don't have the cam charts I've been pouring over here in front of me now, but if I remember correctly the GE 40 does not offer substantially more lift than the stock SC (I think it's around .470" vs. around .450 or so for the SC's) where the GE 60 has .490" lift on the intake. Is that extra .020" over the GE 40 enough to push it past the limits of stock springs? If so, I could probably live with the GE 40's instead. Or the Elgin Mod S.

I have a set of 36mm throttle bodies already, so they should work well with the 35mm intake ports on my small port heads. I see on Supertec's web site that they bore them up to over 40mm for the 3.0 and up motors, but like you say, my ports don't support that anyway.

I guess the ultimate 3.0/MFI set-up would have 40+mm ports, throttle bodies to match, GE 60 or 80's, race springs, and a 7500+ red line. Like you point out, getting there gets expensive. My budget restricts me to stock heads and springs, and the throttle bodies I have. Those parameters will have to drive cam choice as well. So if the GE 60 is pushing it with regard to valve float, even in a sub-7,000 rpm motor, I need to rethink that. Maybe the GE 40's or Mod S is a better choice for me. Thanks for the input - there is a lot to consider here, and your help is much appreciated.

[jluetjen]

Jeff; it's not the lift that drives the need for the stronger springs, but the valve acceleration. The other factor is the heavier valves in the 3.0's compared to the earlier 2.0's and 2.2/2.4/2.7's since this extra mass means more inertia. If you're going to stay with stock valve springs, I'd go with something like stock "early S" cams. Camgrinder may have some other options since he'll have the detailed cam charts which include the accelerations. E's might work, but it will take a little investigation and flow data to determine this. They don't flow enough air in a 2.7 (with the smaller 2.7 sized valves) to support rev's much past 5700 RPM. The good news is that in a 2.7 it makes over 170 lbs/ft of torque from 2800 RPM to 5600 RPM. Your 3.0 has even more capacity, but larger valves too so I would expect the results to be similar.

[NY65912]

Jeff, I'm running a 3.0 with intakes opened up to 38mm, 10:1 CR, PMO 46mm carbs with Dougherty DE40 cams.

I make power up to 7000 rpms (set limit) with MSD ignition. I use 100 oct fuel.

The cams make power in the correct rpm range for me. The car is 95% DE and 5% street.

I would contact your cam grinder for sure. Here is Dougherty's link. http://www.drcamshafts.com/


I love the way this car runs.

[joetiii]

Originally posted by NY65912
Jeff, I'm running a 3.0 with intakes opened up to 38mm, 10:1 CR, PMO 46mm carbs with Dougherty DE40 cams.


The cams make power in the correct rpm range for me. The car is 95% DE and 5% street.

Mike,

Where on the tach do you find the power range?

I've got PMO 40s on a stock SC engine and am looking at Camgrinders bump sticks. I'll end up doing P&Cs and opening up my small ports. My time in the car is opposite of yours. 90% street, 10% AutoX.

[Jeff Higgins]

The Dougherty chart sure is very enlightening. There is one thing that stands out that I had not considered. Because of the radical difference in lobe centers on my SC cams vs. some of the ones I'm looking at, they would have to be hard welded before being reground. No wonder the 964 or 20/21 is so popular; they don't require hard welding to make them from 3.0/3.2 cams.

So it looks like I will either buy new, like a GE 40, or hard weld for an equivelent DC 40 / Mod S. It looks like any of these three offer substantially more duration and overlap than the SC. The intake lift does not go up much; .450" on the SC's to .470"-.474" on these three. The exhaust lift does increase significantly, from .395 on the SC or .399" on the early S to .440" on these three.

With the same springs on intake and exhaust valves, and the intake valves being much larger, the intakes must be the limiting factor. It looks like this increase in exhaust valve lift is "free" in that it won't drive the need for valve spring changes.

So it looks like my search continues to narrow. Something in the GE 40, DC 40, or Mod S range seems to make sense. With a moderate increase in intake lift, and much longer duration to achieve that lift, it seems valve accelerations should stay within what the stock springs should handle. That said, it would be nice to confirm this by checking out camgrinder's excelleration chart. How do I find him? Is that his handle here on Pelican?

[jtkkz]

I have a question on heads (porting )

I am in the process of rebuilding my motor 2.7 off my 74 carrera.

specs:
2.7 (NO boring)
PMO 40 carbs / manifolds
Elgin Mod S cams
JE 9:8 pistons

what is the best size porting should be done to the heads
PMO recommends opening them to 36mm to match port the manifolds...

Any other suggestions....

thanks

[NY65912]

Joe: The cams come on strong about 4300 rpm and pulls like mad to 7000 rpms.

jtktz - 36 mm on the intakes should be the right opening with 40 mm carbs.

Jeff: give John Dougherty a call, he'll steer you in the right direction.

[jpnovak]

There was a thread long ago on the engine board about port sizes. John Luetjen posted some empirical formulas regarding intake air speed at peak HP for factory engines. Anything over 100 m/s gives a reduction in power. 36mm ports should give ~104 m/s at 7100 rpm (peak HP of Mod_S cam). Anywhere from 36-38mm should work great with the lower number favoring lower speed torque curves and the higher favoring high speed HP.