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Help picking a camshaft profile
https://slantsix.org/forum/viewtopic.php?t=62286		 Page 1 of 1
Author:  /6 Matt [ Wed May 02, 2018 7:21 am ]
Post subject:  Help picking a camshaft profile
Hello all,

I have a spare engine that I'm planning on putting in my car when I do my 4 speed swap and I was hoping to do just a little work to make it more fun to drive till the day I can finally do a really serious engine build.

The car is a 70' Dart weighing about 3200lbs, I'm going to run an a833od with 3.91 or 4.10 gears

The engine is a stock bottom end 74 225. I'll be doing a little head work just to clean up the bowls and ports bit I will keep the stock valves. I'm going to continue to run a super six 2 barrel and 2-1/4" exhaust for now. A 4 barrel and duals will come down the road. I plan to recurve the distributor and I'd like to shift around 5k rpm or a little less.

I want to send a spare cam and lifters off to Oregon, can anyone recommend a cam.profile? Even though I know my build is mild enough not to really need it, I want just a little bit of lope for really only for purposes of sound.

Also what should i target my DCR to be for 91 octane? On this particular build I will be milling the head instead of the block so that I don't have to tear into in the short block.

Thanks all
Author:  Dart270 [ Wed May 02, 2018 7:34 am ]
Post subject:  Re: Help picking a camshaft profile
Hi Matt,

Sounds like a fun buildup. The cam will depend on your desired static and dynamic compression ratio. I do not normally use DCR but go with my experience, so others can comment on DCR. With your description of your desires, I would:

Mill your head for 9.5 static compression ratio (around 0.080-0.120" depending on gasket, piston-deck ht, etc), and then use something like Oregon #791 on the intake and #1947 on the exhaust.

INT EXH LSA Lift INT Lift EXH
230 224 106 or 108 0.483 0.47

I'm sure others will say this is too big, but it's what I would do. You can use stock or enginebuilder/SI oversize valves. You will want 0.100" shorter pushrods, although you might try with stockers and see if they work. 108 LSA if you want less lope, 106 if a bit more (and a bit more power). Degree it at 100 int centreline.

Happy building,

Lou
Author:  /6 Matt [ Wed May 02, 2018 8:16 am ]
Post subject:  Re: Help picking a camshaft profile
Thanks Lou! My goal is to just use pieces I have on hand and get the motor together for less than $300 bucks.

I have a head that's been rebuilt to stock specs so my plan is to just pop the valves out, do some careful cleanup, measure everything and send it off for milling and then reinstall the valves.

I haven't pulled my donor engine apart to measure piston-deck clearance yet. I'd really rather not shoot in the dark on my milling.
Author:  Dart270 [ Wed May 02, 2018 9:45 am ]
Post subject:  Re: Help picking a camshaft profile
Yep, best to measure with the shortblock you are going to use.

Lou
Author:  DusterIdiot [ Wed May 02, 2018 10:04 am ]
Post subject:  Re: Help picking a camshaft profile
Quote:
The car is a 70' Dart weighing about 3200lbs, I'm going to run an a833od with 3.91 or 4.10 gears
Lou's recommendation will work great, you can go up to 10:1 SCR with that combo and get about 196 hp when the 4 barrel and better exhaust
are added (the stock valves and lack of major port work will strangle it a bit though)...and still run pump gas... if this is a street/strip combination
use 3.91's, it has a better OD ratio and will be less 'granny' in 1st. (If you are going to run the DCR calculations for a street driven hipo build, try to keep
the DCR to no more than 8.1:1).

That being said...

What have you picked out for a clutch for this combination?

In traffic you won't be shifting any higher in rpm than about 3200 rpm (the car will roll on it's own with the rear gear combo with little gas in 1st)... at the drag strip you will need to make a bit more than 5K to overcome the 1st to 2nd rpm drop, and keep the build in the cam powerband during your run (about 3500-4500 rpm)...FYI.
Author:  Dart270 [ Wed May 02, 2018 10:23 am ]
Post subject:  Re: Help picking a camshaft profile
I would run 3.91, 3.55, or even 3.23 gears. 4.10s will be way too much and probably won't run any faster w/that setup. 3.55s or 3.23s might lose you 0.1-0.3 sec on the 1/4 compared to 3.91s and will be MUCH nicer on the street.

Lou
Author:  DusterIdiot [ Wed May 02, 2018 4:15 pm ]
Post subject:  Re: Help picking a camshaft profile
3.55 is a perfect match for that weight and the OD (I daily drove that to and from work and to races in the Hpak duster for years with a similar build)... I would not do 3.23 it's still very ugly in OD unless on a nice long flat road- you would have to modify the carb to lower the rpm threshold for the mains), but much nicer in the first 3 gears...
Author:  /6 Matt [ Wed May 02, 2018 8:03 pm ]
Post subject:  Re: Help picking a camshaft profile
Lots of great info guys I really appreciate the wisdom. A couple of thoughts, this going to be a 99% street car but definitely not a daily driver. I don't really like to go fast so much as I love to accelerate. In all reality the car probably won't see much past 80 mph, I just want to get there really quickly :lol:

That said I think 3.91 might be my best bet despite my head choking things off. Also to be honest I really haven't given much thought to the clutch yet, Im really not going to be dumping the clutch or anything untill I can ditch the 7-1/4" for an 8.8 or 8-3/4". I know in the articles it seemed like the only real options that sounds affordable is to have a modified pressure plate. Anyone have any other suggestions?
Author:  Dart270 [ Thu May 03, 2018 3:11 am ]
Post subject:  Re: Help picking a camshaft profile
Oops, I missed that you were using an OD 833. 3.55s or 3.91s then. 4.10s will mean 1st will be almost useless, and 3.23s might put you too low in RPMs on the hwy, as DI said.

Lou
Author:  /6 Matt [ Thu May 03, 2018 5:39 am ]
Post subject:  Re: Help picking a camshaft profile
Yeah after you told me yesterday to consider 3.91s or higher I started thinking about how ridiculous a 3.09 first gear with 4.10's would be.

I wish it were possible to change the first gearsets to a 2.66 first from a close ratio transmission. I bet it would work really nicely with 4.10's.
Author:  Dart270 [ Thu May 03, 2018 6:52 am ]
Post subject:  Re: Help picking a camshaft profile
Sounds like you are on track. Any chance you will join us for a Slant 6 race or two this year? Radford, VA is June 16 weekend and Wilkesboro is July 21 weekend...

Slant on,
Lou
Author:  /6 Matt [ Thu May 03, 2018 2:46 pm ]
Post subject:  Re: Help picking a camshaft profile
I'll be in Farmington next weekend if anyone may be going that way. I may try to make it out to Wilkesboro but I highly doubt I'll have the car with me this time.
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