|09-02-2012 11:54 AM|
fyi 6000 rpm is not really that high of rpm.
The limiting factors to rpms(for dependability) is piston speed and valve train stability,at least at 8000 rpm and lower.So a 350 with a 1/4 inch longer stroke than a 327 will not love to rev as much.
Look back to the mark 1 big blocks,the valve train was not reliable past 5000 rpm,the mark 4 was much better and revved freely to 6k in some factory applications. The 283 would rev 7,000 no problem with not much more than cam,manifold,carb and headers,3 inch stroke,piston speed not as high as a 327,its all math.
forged pistons will last longer than cast in high rpm situations,we all know this. New valve spring technology(last 20 years) allows higher rpms without spring failures and last longer than what we had in the 70s. factory forged GM cranks are very good items,no worries there.Ive seen 1 rod failure in a 283 back in the 70s.street guy (Doug Hall,predator rep in western Canada back then) had a street car that rarely was under 5,000 rpm. That engine was from a full size car with unknown history that had a cam ,manifold ,carb and headers put into a chevy2 with 4.11 gears,and it lasted 2 years of daily abuse.
what ap says is partially true,most cars are not operated at high rpm for long periods of time,but if you do decide to run 7,000 rpm with modern cam springs and good valve train it will last and not likely come apart. Any engine can come apart and its usually the faster guys that lose an engine,,,
list a few cars that rev past 7,000 now,,,BMW/Honda both make power through rpm,anything over head cam(valve train stability)
|09-02-2012 11:30 AM|
"love to rev" and "6000-6500" are not words normally associated with street engines.
stock 327's don't "love to rev" more than a stock 350. and if you plan on driving it above 6000 rpm then you should get a well built short block that can take some abuse.
Since you realize this is a street application and big cams are counter productive I would go with the VooDoo 262 cam or one very similar. With an RPM intake, a 750 carb, shorty headers, 9.5:1 compression and that cam I would expect peak power to be around 5700 rpm at about 375hp. A hair more compression and better headers and the 268 cam would put you at 400ish.
Remember you need "optimum power" where you will be using it, NOT at the peak RPM.
The previously mentioned XE268 or the solid cam I mentioned will both also work fairly well but give up some low end torque and mileage- if you want more of a hotrod sound it may be something to consider though.
|09-02-2012 10:14 AM|
|Malibusurfer||I have stated at least 3 times I don't want to race this motor, just have fun and get as optimum power I can for the parts I have... That's not pretending to be anything else than what I have stated repeatedly.... I do appreciate all the help.|
|09-02-2012 08:22 AM|
You can spin that engine as high as you like, you're just wearing out parts though. 400hp at 5500 RPM is NOT any better than 400hp at 7500 rpm. The XE268h cam would work okay for that combo but a smaller cam would be a little better. While still a little too big if you really want to be able to spin it and have an old school solid cam sound the Lunati 60140 would work, it's critical to use the proper springs though.
FWIW, those heads really don't ever need more valve than 1.94/1.6, the valve size is NOT the restriction, you can get 250cfm+ around a 1.94 valve. Going to a larger valve will actually hurt power, but it's one of those "bigger is better" old wives tales that just won't die.
Instead of pretending you have a race engine build according to what you really have and your results will be much better.
|09-02-2012 02:58 AM|
327 power questions
Your engine will make more usable power over a wider RPM range with a XE268H. That's because the larger cams will be hindered by those 461 heads at higher RPMs where it's designed to shine. So all you'll be doing is giving up low-mid RPM torque for nothing more at high RPM. Now, if you had some modern heads with 180-200cc intake runners, that would be different. Just comment from a guy who used a few "too big" cams over the years. You could call Comp Cams and get a custom ground XE268H on a 108 Lsa for a more lopey idle. One more thing as the duration increases you will need larger converters also. For instance a 12-243-3 X4270H 1800-6000 .480/.498 lift 226/234 duration, 397 hp @6000 torque 402 @ 4000. XE268H .447/.480 lift and 224/230 duration @ .050 396 hp @ 6000 torque 401 @ 4000. Your compression ratio compliments the XE268H also. You got to remember you are using stock rods too.
|09-01-2012 10:59 PM|
|vinniekq2||if its a hydraulic flat tappet cam,expect 6500 rpm.For HEI,you need to have a much better than stock coil to support over 5500 rpm.|
|09-01-2012 10:57 PM|
I just want something that gives me a smile when I stomp on the gas and I won't hurt the motor... 400hp would be plenty I would think... At .60 over, motor is on borrowed time anyways, and I don't want to speed it up..
Dizzy I'm thinking just simple HEI with Davis unit in it or similar to gets a few more rev's out of a stock deal....
Would a magnum cam 268, 270, or 280 be in the ballpark?? Not stuck on Magnum cams, but am I thinking right???
|09-01-2012 10:48 PM|
back in the 70s we ran a sig ersom high flow 2 solid cam in 327s.There are better cams available now. All we had then were 11:1 pistons(dont recommend that now) 750 holleys, 4779, torker manifolds,long slot stamped steel rockers,194s with screw in studs or 202s same castings. I worked at a gas station that had 7 ,,57 chevy belairs.I had a 65 acadian.
All the 57s that had solid cams revved to 7200 and the hydraulic cams all went 6500. All the cars were street driven and bracket raced. We all had problems with points.not cams. WE used dual point mallories or GM off road points. we changed the points about every 6 weeks to 2 months.
You are not asking much from your engine,good ignition,moderate cam,decent carb and intake and try not to shift at 7k and try not to grin every time,,,,
|09-01-2012 10:33 PM|
The 462 heads are what I have for now, but would eventually like to bump to aluminum's eventually...
The 462's have been ported pretty good and polished by reputable guy in my area... They are fresh cut to 2.02 /1.60 (from 194's) screw in studs, guide plates, etc... They are getting done right to handle the most they can flow for their vintage....
I'd really like to get to 6-6500 or more if possible just for some adrenaline or even take to track to see what she does in 1/4, but mainly truck is a street cruiser...
Am I limited to my high rpm's by cam and trans and rear setup??? Would a built 350turbo be a better deal??? Truck will not see lots of highway miles, but now and again......
Frame on truck is getting boxed in and crown Vic panther front suspension, etc... So chassis should be able to handle what I have for motor....
|09-01-2012 10:04 PM|
In the late 70s when there were very few good heads,there were a lot of engines making power way beyond 7500 rpm. The 327 mouse has been doing this since it came out and is not, was not, and wont ever be limited to 5800 rpm or anywhere near there with stock heads. The 283 had even smaller heads and it can make close to 400 hp at 8,000 rpm and it does not use a 225 duration at 50 cam to do this.
There are better heads than old factory heads,no doubt!!!
Factory heads from the sixties will make power past 7,000 rpm in a 327!!!
|09-01-2012 09:42 PM|
As for the math, on those heads you need to notice a few points. Flow, compression, and choke. Even assuming those 160cc heads were heavily ported and taken out to 180cc's you'll be choked around 5800 RPM in the pushrod pinch, assuming you flow enough to make power at that point (225cfm would be adequate and relatively easy to hit) and you have enough compression to make power at that RPM (9.5:1 is about right for that RPM and those chambers) then to make the most average power at those RPM you need to match the duration.
Since you're not working with a restricted intake nor a really good exhaust a 220-225 duration would provide about the duration you need for that RPM and power. With a good thorough job you can easily get over 400hp.
There is more definite math involved than these generalities but I don't feel like putting the effort forth to show it. A great basic website for related calculators though is Wallace Racing.
|09-01-2012 08:06 PM|
|vinniekq2||ap sometimes you make very good posts,sometimes you dont. 300 "advertised" and since when does time( duration) become not effective with any head? show the math,,,,|
|09-01-2012 07:59 PM|
The absolute BIGGEST I would go is 225/230, the smallest I'd go is about 210/210. Get all the lift you can with reasonable durability.
|09-01-2012 04:29 PM|
|vinniekq2||If you want a true 375 hp then use a solid lifter flat tappet or better, advertised duration will be close to 300 with .500 lift, intake centre line and lobe displacement angle tbd. for a truck,the RPM air gap is good enough and use a 750 carb,1,5/8 headers.|
|09-01-2012 02:38 PM|
Yes, the explanation makes sense... Motor is a standard hyd. Flat tappet deal... Truck is gonna just be a cruiser/driver, and very rarely tow my v-drive boat..
I know 327's love to rev... I,m thinking of about a 25-27 inch rear tire (265/50/15) and with a 700r, should I bump up gear to 4.??? I want to get the benefit of why I chose the 327... 6-6500k revs
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