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| RPM limits https://slantsix.org/forum/viewtopic.php?t=32206 |
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| Author: | 2 Darts [ Tue Nov 11, 2008 10:14 am ] |
| Post subject: | RPM limits |
I have a 73 Dart with a /6 & 904. This is my first time to do something more to a /6 than drive it. I'd like to end up with a good highway cruiser. 1. What is the RPM limit for a 225 with the stock intake & valve train? 2. Does adding more air (cam and carb) raise the limit? Or, is the 225 limited rpm wise due to lack of air. 3. I have a Comp Cams 260H and an AussieSpeed 4 bbl manifold that I plan to install. Should I change out the valve springs? I have not decided if I want to go to the oversize valves. 4. I have heard that the Achilles Heel of these engines is oil starvation on the camshaft at high rpm. (whatever that is). Comments. 5. If you've grenaded one of these engines, how did it happen? |
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| Author: | Force Fed Mopar [ Tue Nov 11, 2008 4:58 pm ] |
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I am also searching for a similar answer: What is the highest rpm anyone has reliably turned a Slant 6 to? I've heard that the stock oiling system is good to 7500, is this true? Has anyone consistently run/shifted at this or higher rpms, stock or modified? |
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| Author: | slantzilla [ Tue Nov 11, 2008 5:08 pm ] |
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A stock Slant starts sucking wind around 4400 or so. Like any motor, the Slant will respond to add ons. The more you do, the better the results. I shift mine around 62-6500. That is aboot the safest upper limit. I would be frightened to be around one much higher than that. Probably the most common destruction would be tossing out the #5 rod. I have killed one when my Mopar cam ate the oil pump gear on the tollway. The car ran low 14's at the time and I was driving 3 hours to get to a race track. The most important thing aboot doing a Slant is to use your head and keep everything working together. It is real easy to fall into the "bigger is better" trap. With a 225" engine it just won't always work. |
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| Author: | THOR [ Tue Nov 11, 2008 5:20 pm ] |
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IIRC theoretical redline for a stock slant (1bbl, straw-sized exhaust) is/was 5500 RPM, but as Slantzilla said, they won't spin much past 4400, and even if they do, they aren't making any power. I've spun mine up to 5500 on my '71 Dart, but I had a large exhaust, and a modified 1bbl holley to make it do that. Betcha I made a few people wonder what engine I had in an old crusty car doing 85 in second gear trying to pass a truck.. UPHILL!  ~THOR~ |
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| Author: | DusterIdiot [ Tue Nov 11, 2008 6:16 pm ] |
| Post subject: | You what? |
If done properly, I've been OK up to 6200 or so on the 'stock' oiling system with a 'stock' replacement melling pump...bigger air inlet in and better outlet makes for a higher winding motor (stock 1 barrel kind of runs out around 4K at best... BBD 2 barrel is good for more, but it kind of goes 'flat' at a certain point... 4 barrel you'll probably throw a rod before you see 7K). Not to ask... but you have a 1973 dart.. that should have a solid lifter camshaft stock and you have specified a Hydraulic comp cam number (260H... not 252S, 264...256X)...did some one swap out your original engine with one from 1981+ ? Just checking... -D.idiot |
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| Author: | madmax/6 [ Tue Nov 11, 2008 7:33 pm ] |
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Learend in Redding,you need 10 lbs of oil pressure for every 1,000 rpm.went tru the traps at 13.91,94 mph with about 40 lbs of pressure,Knock Knock,whats that noise,I now know you need more pressure at higher rpms,wish I knew this before,race and learn,mark |
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| Author: | Nathan in MN [ Tue Nov 11, 2008 7:38 pm ] |
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Quote: Learend in Redding,you need 10 lbs of oil pressure for every 1,000 rpm.went tru the traps at 13.91,94 mph with about 40 lbs of pressure,Knock Knock,whats that noise,I now know you need more pressure at higher rpms,wish I knew this before,race and learn,mark
What was your engine speed at that point?
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| Author: | THOR [ Tue Nov 11, 2008 7:48 pm ] |
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He had to be running close to 6k on that run. IIRC, that was the run against me that this happened. ~THOR~ |
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| Author: | Rob64GT [ Tue Nov 11, 2008 9:39 pm ] |
| Post subject: | Re: RPM limits |
Quote:
3. I have a Comp Cams 260H and an AussieSpeed 4 bbl manifold that I plan to install. Should I change out the valve springs? I have not decided if I want to go to the oversize valves.
I have one of the AussieSpeed manifolds with a Holley 390, it works much better than my Clifford manifold. The only problem with it is that I had to spend about 3 hours with my die grinder to get the triangle washers to fit. If you don't have a die grinder (I have 3) or the time to fit the manifold I would get a Offenhouser 4 bbl manifold for ease of fitment. The Offy manifold will work with your stock manifold, headers or Dutra duals. The Aussie speed manifold will work with headers or Dutra duals...I have Dutra duals on mine and the current Clifford manifold will only work with headers. Headers can be a pain in the rear on a slant six. I could have made the Clifford manifold work with Dutra duals but I would have needed to do lots of grinding and Tig welding on the manifold to make it fit.
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| Author: | madmax/6 [ Wed Nov 12, 2008 7:37 pm ] |
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I was running tru the traps at 6,100 rpm,I have 456 gears and 26 inch tires,this car will do 98% of the time on a local 1/8th mile track,and driven back and forth to work,,,,only 1 mile each way,Vegas is 1/4 mile,I will have taller tires,same combo,WITH higher oil pressure,reground crank,new bearings,hopeing everthing else is ok,want to do a semi patch job on this,Mark |
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| Author: | madmax/6 [ Wed Nov 12, 2008 7:46 pm ] |
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On the run that it failed,it was probabably under 6,000 because of spun bearing,went tru the traps 14.80 ish knocking,shut it down in the pits and it was done,stuck tighter than a frogs butt.mark |
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| Author: | Volare4life [ Sun Nov 16, 2008 10:21 am ] |
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it wa the #5 rod for me, put a hole in the bolck the size of my head lol !!!! also twisted the bottom of the piston off, was very nasty. but still drove it to a "safe" *ie 7eleven* about 1 1/2 miles down the road, even ideled for a minute before it shut off. But I sent it to the grave, drove with a rod knock for about 2 months, -Mike |
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| Author: | Russell Cable [ Sun Nov 16, 2008 10:19 pm ] |
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I hade my car on a dino and it stoped makeing power at 5300 rpm but I was tearing up oil pump gears and hurting cams at 6000 rpms so I set the reve limiter at 5600 and had no trouble sence. The car had 148 hp at the rear wheels and 229 foot lbs of tq and with the nitrus 220 hp and 315 foot lbs of tq |
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| Author: | Rug_Trucker [ Sun Nov 16, 2008 11:01 pm ] |
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My stock bottom end 198 was 4200-4400 on the power. I did actually spin it to 5900 on the dyno rollers.  M1 2bbl, BBD that was really running rich! |
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| Author: | Slanted Opinion [ Mon Nov 17, 2008 4:01 pm ] |
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My best friend's slant also lost the #5 rod years ago. Why is this the one to go? Why is it the weak spot? And can it be prevented when rebuilding an engine? -Mac |
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