"Hot" cam choice for small port 3.0 with SSIs.
 

In an effort to avoid the slippery slope and preserve some capital I'd like to explore some rebuild options that are limited by my current intake and exhaust.

The car in question is a 1982 US spec SC.

Small 34mm port heads with soon to be installed Weber 40 IDAs. I'm not opposed to doing some work on the heads(valve guides will need to be done anyway) provided the juice is worth the squeeze and the money wouldn't be better spent somewhere else. On the exhaust side I have SSI heat exchangers and M&K sport 2-1 muffler. These are the things I'd like to keep.

The goal is pistons(close to stock compression, single plug) and cams that are able to take advantage of the carbs. Not a track car but I would like a bit more hot rod feel and power higher in the rev range, the car is mostly used for attacking back roads and mountain passes. I love the sound of the engine above 5,000rpm but not much is happening up there power wise.

What would the "hottest" cam I could run giving the weber 40s, SSIs and not wanting to start changing rods, rod bolts, valve springs, retainers, rockers, etc, etc?

Am I limiting myself too much by being unwilling to change the carbs, exhaust, or port sizes?

Again, I'm desperately trying to avoid a soup to nuts rebuild. I'd like to make the engine incrementally better and save the big build and big bill until after the kids are out of the house.

9.5:1, MOD "S" cams and a rethink on the M&K muffler. Historically the M&K sport mufflers have had a terrible harmonic at 5000 and a cost of about 15hp throughout the range.

Gt2 102 grind from DRC

I hadn’t heard that about the M&K, too bad because I like the sound and love the weight savings.

I was thinking DC-40, so it’s good to know I’m on the right track.

I’ve seen this mentioned a few times in my research. Seems like a small step down from the DC-40.

Yep, I'd go the MOD S style cam... and 9.5-10.0 comp. I think with the bigger cam your dynamic compression will be a little lower so you should be safe from knock.
With the cam advanced, torque down low was impressive. And pulled all the way past 7 happily.

I've not had success with M&K mufflers... very limiting on an engine that flows well. Something custom and simple works better. Mine used a GT3 muffler.

How many horse power do you need at the crank to have fun?
If you are guessing , then you probably do not need as much as you think.
I have 230hp at the crank and I can smoke just about any other similar displacement car,
including a 2018 civic type r and a wrx sti 2018 in the 1/4 mile . 14.02 sec
Theses specs with stock cis pistons and 34 mm ports

I do not like the Gt2 102 grind from DRC, it is a cam for your grandmother.
Mike I don't think you liked it either .

Ian

Need or want? The car doesn’t need anymore horsepower and that’s not really what I’m chasing. The goal is to take advantage of what the carbs can offer and make the car perform better above 5-5500rpm. I was reading a post by the late great Gredy Clay and he said the stock 3.0l valve train was good for 7300 on every shift. I’d like to take advantage of that by having an engine that does more than make additional noise between 5-7000. Provided the 34mm intake ports, 40mm carbs and SSIs aren’t going to hold me back, if so I’d like see what I can do within those constraints and identify the limiting factor.

I’ve just started looking through your thread about exhaust. Sad to hear about the M&K, is it the same for all their models? I have an early 2-1 sport and it’s hard to think something that weighs <15lbs is causing that much restriction. I had a Dansk 2-2 and it was over twice as heavy.

Anyone have a graph of that? I have not seen one, and "historically" is a loaded term, as it is known that M&Ks have gone through iterations to address "issues" such as drone. Maybe Brian will weigh in. (I am not an M&K shill, but stating -15hp across the range necessitates some documentation. I'd rather not spend the $700+ if that is a fact).

I second Gt2 102 grind from DRC. Tons of midrange torque and response. Unless you are wanting power above 6500 rpm the GT2 will do the job. I was buzzing my limiter at 7500 rpm last sunday at an AX with those cams.

Also in order to go above 6800 rpm you will need racing valve springs with any hot grind.

If it was me, I would open up the intake ports to something like 36-38mm. Not hard to do. Match with the manifolds. Otherwise your power will drop off above say 5500 with 34mm intakes.

Oh, and by the way, I tried a M&K a couple of weeks ago. The drone was SO bad I took it off right away. Did not seem to hurt my power, though.

Why not email John at DRC???? Ask him what he thinks.....

It is what he does. We rely on him often. And he has made a couple of grinds specifically for our builds and we have been very pleased.

Cheers

How is weight related to flow?

This is true. I guess in a broad sense, one might think that "less metal" = "less dense".. but we know that isn't the case!

In my case, the M&K droned so bad, it gave me a terrible headache. First time I'd ever experienced this... weirdly, other people claim it's the best thing they've ever had and that their cars don't drone... I cannot begin to explain the difference in results...

Brian tried to help by making me another set of tips with baffles in them. They did reduce the drone but the flow was so heavily impacted, the power was quite low.

I sold the muffler to someone who ended up enjoying it, with no drone!

I don’t want to waste his time. If I was ready to order a set of cams right away that would be a different story but I’ve got a few more ducks to get in a row before that point.

I started this thread with the hopes of getting some recommendations from people that have been down this path before and educating myself so when it’s time to talk to someone like John or if a great deal pops up in the classifieds I can be a more informed consumer.

Thanks to everyone for their help so far.

It was just an observation made when I had both mufflers in front of me. The M&K is so light it can easily be picked up and carried around with one hand. I doesn’t seem like there could be any baffles in it compared to the much heavier Dansk.

It’s a 2 to 1 so there isn’t an issue with drone. I love the muffler but not if it’s costing 15hp vs ???

I wish Harry would return to the thread to give a little more insight.

When it’s all said and done I’ll get the car tuned on a dyno and maybe I can take the muffler off between runs to get some actual data.

Henry,

Not to hijack the thread, but what exhaust do you recommend for a SC 3.0 mild mod short stroke (Max Moritz 9:8:1) with a slight cam bump (M1) with SSI’s and early (‘79) CIS?

I assume a 15 hp exhaust bump should benefit the original post question since that 3.0 has carbs and he’s looking for cam recommendations.

The worst part of my ‘82 SC is that it “dies” at a little over 5k RPM - heck, my high mile Benz W210 OM606 diesel revs higher!

I have almost your exact same build in my car. John recommend the gt2 102 when I gave him these specs. Highly recommend.

Daniel

You would not be wasting his time. Its what he does. You may end up getting the cams and rockers ground by him in the future. If you do, answering your email questions are a great use of his time.... He is very knowledgeable, and helpful.

And despite what you may have read/heard about lead times, the last few sets we had John do were back to us before we needed them.


Cheers

Call and ask John if the GT2-108 is right for your build. My engine is coming apart soon and I'm trying some top secret cams and my GT2-108’s are going to be available. Less than 10K miles.

5200 rpm
 

Chassis Dyno graph shows a power loss centered at 5200rpm that may be what Henry is describing.
Engine is 3.2 SS
120/104 cams, 46mm pmo carb tuning, or M&K 2 in 2 out.
Could be one or a combination of all above.

Curious to hear others experiences with those cams with other combinations. They are very similar to DC 60, GE 60.
The funny thing is everyone loved the feel of this engine. The kick from 5400 to 7000rpm was impressive but data would show it could be much faster eliminating that dip.
Wish I had the opportunity to explore some changes.

http://forums.pelicanparts.com/uploa...1654352793.JPG

And the greater missing variable not accounted for in that graph is the afr trace.

One cannot throw 5 variables into the mix and claim that a particular one is the issue without isolating the other 4.

As to the Henry's claim, that was conditioned as across the range, and not at a particular rpm. Do a pull without the m&k and one with, all with an afr readout, then we'll all know where the issue lays.

so above 5500 w/ 40IDAs
 

my 3.0 w/ carbs, 9.5:1 comp. sing plug, SSi w/ a Bursch exhaust - running a 906 set of cams and on thru 7000 still has me asking, are you sure ? Everyone said S cams but man 80Kmiles w/ these 906's and you can't get the smile off my face - until I pull up to the pump.

Not a 3.2, mine is a 2.2 E engine with S pistons, John's Mod-Solex DC30 cams, 40 PMO's and Ben's header and sport muffler. Feels like the earlier graph, pulls great from 5 to 7,000. Great sound with some drone around 3.500. Mark

Cam Selection
 

If you want to kick-a$$ in the 1/4 mile - buy a Mustang ;)

If you want your 911 to have more torque at 2,750k RPM - buy the GT2 102 // and Grandma will greatly appreciate your headrests when you stomp 3rd gear at 2.5k RPM :D

Call DRC - he's a great resource to talk to. I called him over a year out of starting into my rebuild and he really helped me narrow in on achieving the kind of performance I was looking for.

Good luck, Gordo

--------------------------------

Side note: I agree with 917 regarding RSstop's graph showing 5k RPM performance dip. Install a wide band / Air Fuel Ratio (AFR) reader and you will know exactly what's going on.

Lacking AFR readings, it appears your idle circuits are providing primary fuel up to ~ 5k when your carbs transition to main circuits.

Idle to main circuit transition is difficult to smooth out on carbs. If you currently like how your engine runs and accelerates, I suggest you leave things alone. Otherwise - study up, experiment and enjoy the the learning curve.

The OP asked for a hot cam , The GT evo 102 or 108 is a came based on an emission based cam .
I am working with a very fun 3.2 with the gt2 108 cams in the car now , yes it is lots of fun and smooth pulls to 7200 rpm, making about 230 hp at the crank. I do not consider this a hot street cam
It is a better street cam than stock . There is no question this is better than stock . 50 hp better
It is just that I would trust my grandmother with my car if it had this cam in it
A stock 911 s 1973 2.4 is much more of hot street cam, wow , tuned well this cam rips ! and lots of low end torque , as I said , tuned well.
Just my thoughts, as for my 911 drag car , I drove that car 65,000 miles in three years,
getting 28 mpg and it rips , 146 mph, It also has 10 track days of playing, all on my fav mini van tires!!! wink wink
It's an Opinion
I like having FUN !
Ian

Ian, I think it’s possible that you’re getting hung up on the words “Hot Cam”. I know what KY asked 4, but I think he clarified in his post that he wanted “the hottest” cam that would work with his current set up.

It’s like the lady that went through the MD drive through and ordered “hot coffee” then got scalded, she really meant “the hottest coffee” that she could drink safely.

Given the small ports and Weber 40’s a hot cam for KY would be a GT EVO cam.

And OBTW you get 28 mpg because you have a cheater knob.

Enlarging small ports to bigger ports is not a really involved operation.... If the OP is interested.

Like Henry said the DC40 is a good choice for this engine. For a 4000+ RPM powerband.

Back in the 70s, a cam guru [Harry Weber] took on the task of making a cam that would fit in a CIS engine [back then, a 2.7] that would offer performance and the clearance needed to work with the squish chamber piston. He came up with a Web 2021.
The interesting thing about the cam is that it offers a stable vacuum for idle but increases vacuum on light throttle acting very much like an accelerator pump. The cam has good performance into the low 6000 rpm. John at DRC has his version of this iconic cam I believe he calls it the DC21
This cam is even a great choice if carburetors are fitted to a stock SC or 3.2 Carrera engine.
On a side note: the CIS air flow meter has a tendency to run lean on light throttle cruise. This phenomenon is caused by a transition from turbulent air flowing across the metering plate to a laminar [high volume/low pressure] flow at cruise. This reduction of plate lifting force/pressure causes the lean running condition. Clean exhaust flow helps but it is always a concern when considering compression increases..
Lean running at cruise makes acceleration through max torque [high cylinder pressures] a detonation nightmare.

As for exhaust: there are a plethora of muffler choices but we like the Dansk Sport muffler for performance and reasonable decibel levels.