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PostPosted: Sun Nov 01, 2020 7:23 pm 
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TBI Slant 6

Joined: Fri Aug 16, 2019 8:17 am
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Car Model: custom roadster
Of all the gearhead stuff I don't know enough about, I probably know the least about cams. Read a book about 'em, but it didn't seem to stick. :P

If you had a mind to put a modified, naturally-aspirated ~205ci slant (overbored 170 clearanced for a 198 crank, bigger valves, 2x1bbl Offy intake, Clifford headers*, etc.) into something like this, which cam would you choose? RV15/295 RDP?
https://www.dutra.org/pictures/engine/e ... am60bd.jpg

I own neither the roadster (yet?) nor the photo. The Internet tells me it's from a 2019 A-Bombers event in Uddevalla, Sweden.

* I wanted Dual DD's, but I've failed to obtain confirmation they'll clear a mini-starter on a 170 block. Everybody who runs 'em has the good sense to build a 225! (I do intend to run water under the intake for heat.)

Attachment:
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PostPosted: Sun Nov 01, 2020 9:46 pm 
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Supercharged
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You tell me how good you made the cylinder head and how fast you want to go and I'll give you a range of cams along with a target static compression ratio. With the dual 1 bbl manifold I'm going to assume that it's not intended to be very fast. You're correct that a Dutra exhaust manifold won't clear the high-mounted starter on the 170 block.

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PostPosted: Mon Nov 02, 2020 3:00 am 
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Cam choice will be substantially different for a 170 vs. a 225. Josh is right we need a bit more info before recommending... What are your desired RPM range, static CR, and fuel choice?

Lou

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PostPosted: Mon Nov 02, 2020 7:29 am 
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TBI Slant 6

Joined: Fri Aug 16, 2019 8:17 am
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Car Model: custom roadster
Thank you, Josh and Lou.
Joshie225 wrote:
You tell me how good you made the cylinder head and how fast you want to go and I'll give you a range of cams along with a target static compression ratio.
It's a 1971 head. I'm planning to get seats, bronze guides, and 1.72"/1.45" valves. I asked my machinist to perform the chamber/port work under "Cleaning Up the Imperfections" in Doug's book (p.96). If clearance is needed for a higher-lift cam, I'll ask him to do the stuff under "Grinding the Valve Guide and Seat" (pp. 97-98). This car isn't for racing, and it won't have fat tires, but I'd like to get... I dunno... 0.85hp/ci for all the trouble? I expect the roadster to weigh 2000lbs or less.
Dart270 wrote:
What are your desired RPM range, static CR, and fuel choice?
Premium pump gas, occasional (infrequent and brief) rips to 6000RPM. I was thinking a static CR around 9.5 would be OK?
Dart270 wrote:
With the dual 1 bbl manifold I'm going to assume that it's not intended to be very fast.
I figured that would be the bottleneck. The 1bbl Carters I got flow ~168CFM. If that's a ridiculous mismatch to all the stuff listed above, I think I'd rather cut back on mods and expectations than go to a 4bbl.


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PostPosted: Mon Nov 02, 2020 8:17 am 
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Turbo Slant 6

Joined: Thu Jun 07, 2012 4:29 pm
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Good sense to build a 225? The 170 is a very righteous engine.

If the only pain you feel lies in the exhaust..so what? Make a header that fits, no more problem.


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PostPosted: Mon Nov 02, 2020 9:37 am 
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Turbo EFI
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Location: Desoto Texas
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Do you have the Dutras yet? The Aussiespeed rear outlet it moved around to clear a starter, but not sure about fitting the 170.
I fit my hyper pak exhaust manifolds around a dakota starter on a 170 so I know that fits.
I have a 170 here and a Tilton starter, if I have more time I could check for you.
Doesn't sound like you need to know tomorrow right?

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PostPosted: Mon Nov 02, 2020 11:52 am 
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TBI Slant 6

Joined: Fri Aug 16, 2019 8:17 am
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Car Model: custom roadster
Thanks, GregCon and Hyper_pak.
GregCon wrote:
Good sense to build a 225? The 170 is a very righteous engine.
Oh, I know. I was just kidding. I mean, there's more power-per-dollar in a 225 build, but I love the idea of a low-deck "205."
GregCon wrote:
If the only pain you feel lies in the exhaust..so what? Make a header that fits, no more problem.
The Clifford shorties will clear my starter. I don't know how my steering stuff will sit in the roadster, but I imagine I'll have some options, so that shouldn't be a concern, either.
hyper_pak wrote:
Do you have the Dutras yet? The Aussiespeed rear outlet it moved around to clear a starter, but not sure about fitting the 170... if I have more time I could check for you.
Thank you. Correct - I'm in no rush. I don't have Dutras; I just have the Cliffords. From Josh's reply earlier, it sounds like he's already determined Dutras won't clear the starter on a 170, but I'm not certain he's talking about a mini-starter. (Judging from photos I've seen, DDD's are very snug on a 225 with a mini-starter.)


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PostPosted: Mon Nov 02, 2020 1:50 pm 
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Turbo EFI
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I can't speak for the regular mini-starter, but I have the "super-mini" planetary drive starter that tucks the motor up close to the block. On my 225, the rear Dutra (non-Aussie) manifold flange has about 5/8" clearance before it hits the starter solenoid. So this combination would not work on a 170.

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PostPosted: Sun Nov 08, 2020 6:50 pm 
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TBI Slant 6

Joined: Fri Aug 16, 2019 8:17 am
Posts: 164
Car Model: custom roadster
Going back to the cam question:

Goals/application/expectations
This will go into a no-frills, street-driven custom roadster with a T5 trans.
The car will weigh about 2,000lbs.
170hp at the crank would be just fine. 190 would be great.

Parts I've accumulated or ordered:
2x1bbl Offy 5041 intake
Carter BBS 7044s (matching pair)
1971 head
stock cam and matching oil pump
170ci block
198 crank
170 rods
1.72" intake valves
1.45" exhaust valves (1.50's that will be turned down to 1.45)
JP5613 double roller timing set
Ishihara-Johnson crank scraper
Rick Covalt's windage tray
Clifford 55-0010 headers
Stock water pump
Remy 16054 mini-starter
OD bellhousing adapter plate for T5
NGK ZFR5N spark plugs

Parts I'm looking at:
Hot water plumbing for intake manifold
Y-pipe to single exhaust pipe
Silv-O-Lite 1461-1-0MM pistons?
GM HEI conversion

Planned work/modifications:
~0.060" overbore
Clearance work on 198 crank
Clearance work on block for 198 crank
Head work per Doug's book ("Cleaning Up the Imperfections" and the intake port work shown in the photo)
Oiling system improvements per Doug's book
Bronze guides
Head shaved and block decked as needed for a 9.5:1 or 10:1 static CR (if that's sensible on premium pump gas)

The engine will be slightly undersquare, with a bore of about 3.46" and a 3.64" stroke.

I've kept the stock cam and oil pump as a matching set in an effort to avoid gear failure. Given the parts/plans/application described, do you have any recommendations for regrind specs?

(I have not chosen rearend gears. I actually haven't picked a rearend.)

Attachment:
intake port work.jpg
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PostPosted: Tue Nov 17, 2020 4:23 am 
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Many many factors here, and thanks for giving more info.

9.5-10:1 static comp means you will want a relatively big cam to get the most out of this and run on pump premium. The closer you get to 10:1 (or more), the more finicky the tuning (ign curve and fuel) will get on pump gas. If you don't want to worry so much about that, then go with 9.5:1.

The Oregon 346 would be a great mid range cam with 9.5:1 and will not require fancy valve springs or retainers. 340 springs/retainers will work, just check valve keeper does not hit valve seal or guide top at full lift. Oh, I see you are using the longer chevy valves, so you will have plenty of clearance (but still check). This cam has more intake duration than exhaust, which fits well with the Slant head, which has more exh flow relative to int flow than most heads out there.

You are using a low deck block with a 198 crank, so it is still an undersquare engine, between the 170 and 225. So, I would go for a lobe separation angle (LSA) around 110 instead of the 106 or so that the 225 likes. Oregon can easily do the #346 with 110 LSA. I would degree this cam in at 104-106 intake centerline, again to move away from the 225 likes, which is around 100.

If you want more top end HP and are good with a rougher idle, then I would suggest using lobe 1727 intake (244 @ 0.050", 0.516" lift) and lobe 1475 exhaust (236 @ 0.050", 0.495" lift). Again, and ask them to grind it with 110 LSA and on an 104 centerline. You will check/adjust the centerline when you install it. I would run 10:1 static comp with this.

These are all educated guesses, but should work quite well. I have not spec'ed a cam for a 198/170 engine before or had direct experience with that combo.

A probable limiter will be the Offy 2X1. My experience is that this setup will not pull much past 4500-5000 on a 225. A single eddy 500 4bbl or holley 500 2bbl on a Clifford or Offy intake will get you better performance. Clifford wins up top, Offy down low. If you are set on the Offy 2X1, then definitely use the Oregon 346 and 9.5:1. The bigger cam+CR combo will not work well with that intake, so there is no reason to add ragged edge if you will get equal or lesser performance.

Hope this helps, and happy building!

Lou

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PostPosted: Wed Nov 18, 2020 5:38 pm 
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TBI Slant 6

Joined: Fri Aug 16, 2019 8:17 am
Posts: 164
Car Model: custom roadster
Dart270 wrote:
The Oregon 346 would be a great mid range cam with 9.5:1 and will not require fancy valve springs or retainers. 340 springs/retainers will work... I would go for a lobe separation angle (LSA) around 110... I would degree this cam in at 104-106 intake centerline... If you want more top end HP and are good with a rougher idle, then I would suggest using lobe 1727 intake (244 @ 0.050", 0.516" lift) and lobe 1475 exhaust (236 @ 0.050", 0.495" lift).
Lou, many thanks for the detailed recommendation.

Joshua also sent me some great information via PM, including tire height, transmission gearing, and rearend ratio suggestions. He recommended Oregon #1694, with intake and exhaust lobes swapped ("273/265° advertised and 247/239° @ .050" lifter rise with .563/.539" net lift"). Like you, he mentioned that the 2x1bbl setup would be the limiting factor.

I think I'm leaning towards the 346 now, with the option to go bigger in the future?


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PostPosted: Wed Nov 18, 2020 6:04 pm 
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I agree that Oregon Cam Grinding #346 would do very well and would be a bit easier to accommodate in terms of valve springs and tuning. I see that Lou's 'hotter' recommendation is exactly 3° shorter in duration than my choice at .050" lifter rise, but those two lobes have a relatively long advertised duration (both 282°) and I expect it would idle worse than #1694R.

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PostPosted: Thu Nov 19, 2020 5:22 pm 
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TBI Slant 6
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Car Model: 66 Valiant, 82 D150, 94 Ram 2500 TCD, 69 Dart
Just a thought on your intake situation. If you think your Offy 2x1 intake will be the choke point for your build, have you considered modifying it for a 2x2 setup? I have that manifold that I got from a guy on FABO that hogged out the carb mounting area to take a pair of Weber 2-bbl downdrafts. It came from his daily driver so it's been street proven.


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PostPosted: Thu Nov 19, 2020 5:37 pm 
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I have seen guys put a pair of BBDs on that intake too. Not sure how it works, but could be useful. Hard to say whether the intake is the bottleneck or the carbs.

Josh: I have not had tons of luck with the fast ramp cams, and Tilley in Oz said he did not find them to work very well in all his dyno testing. I pick my lobes to have somewhat larger specs on the valve lash, like the original Slant 6 performance cams, and I basically ignore duration at 0.020". Not sure all of that is "right" but it's just my feeling about what has worked for me and some others.

Lou

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PostPosted: Thu Nov 19, 2020 10:31 pm 
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Lou,

How fast a ramp is too fast? When it leads to more valve lift than we can use? When the .050" duration number is about right, but the overlap is insufficient? Theory seems to be that for a given RPM range the advertised duration will be a little less, duration at .050" will be a little more and lift will increase. My relatively small number of builds doesn't include one with especially high lifter velocity so I'd really like to have some good information. The Mopar Performance cams seemed to have decent velocity for their vintage, but I have found it hard to compare those grinds with other, newer cams as Mopar Performance left out duration at .050". Yes, they say that you can multiply the advertised duration by some factor to get .050" lift duration but that yields a duration number far short of what the cam's behavior indicated.

Duration at .020" means something if that's close to the running lash, but more or less lash will change the seat duration. OCG #346 is listed at .012" lash. I'd like to know where you run yours.

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