lo po cam dilemma

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brayden_winkles

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lowermainland, bc
I recently re rung and stuffed new bearings in a low mile, low compression rv 440 to replace the one that turned a bearing on break in. the 292 comp that was in the engine will be a little to much for the factory geared 8 1/4 and stock converter that were to be replaced. funds are a little tight right now thanks to this and I would like to get this thing on the road for once. so the question is I have a summit k6400 cam with the lifters and also the stock rv grind that was in the engine what will be better? specs are stealth heads, performer intake, factory 76 bottom end with new rings and bearings, Schumacher tri y's in a 73 duster with a 727 and 2.76 axle ratio with 26 inch tires. what does everyone figure it will run too? would be nice for some educated guesses. can't afford much thanks to this terrible canadian exchange rate and everything listed is just kind of kicking around. thank you for your time.
 
Go hillbilly low buck style...

I think that cam is cut on a 108LSA. Wind that sucker ahead to 100ish installed centerline and check piston to valve clearance. Should be good, but always check. It will make more low end and still have the kick of the bigger camshaft. Done this a lot with low compression 360-400-440 engines. Crank a bunch of initial timing into it and it will be a bunch different than the lazy runner it once was. Doesn't cost anything either, cause you already have it!
 
advancing the cam moves the power band lower correct? retarding it brings it up? it's got a 107 intake centerline according to the cam card. so I would have to move it ahead 7 degrees? how would that affect the power band, or should I just install it and degree it to the specs on the card?
 
If the cam card says 107 ICL, install it that way, and be happy with 106-108.
 
As for me; you couldn't give me a cam that lists the intake at 288adv/214@050. That's a real Dcr killer.
With 2.76s and a stock TC ,She's gonna need all the Dcr you can scare up.

It's hard to recommend the RV grind without knowing anything about it, but since you didn't like the 292, you will like the 288 even less, so by process of elimination; RV get's my vote;no contest.
 
I never even got to drive the 509 cam the engine seized breaking it in. just all the specs Said I would need a 3000 stall and deep gears which aren't in the budget right now.
 
The 509 wants quite a bit of Static compression ratio, or it goes soft from idle to mid-to-late 2000s somewhere. The saving grace for it is that is is ground on a 108LDA.

The6400 has specs of 288/298/112, with .050 of 214/224, and lift of .444/.466.
The straight up installs, put the intake closing angles within 2 degrees of eachother. That means it will be just as soft as the 292. On the exhaust side, the extra duration here,is stolen from the power stroke, meaning when the exhaust opens there is 6 degrees of energy escaping the cylinder,compared to the 292, and that helps fuel efficiency at low revs,not one bit. And to top it off the 050 specs are in the neighborhood of 26 degrees smaller; thats easily 4Plus sizes smaller than the 292.
So what you get with that cam is big-cam idle with little-cam performance,and if your compression is low to begin with; a dog off the line to mid-to-high 2000s, just like the 292cam.And that's why the 3000TC recommendation, and some bigger gears to help it wind up into it's powerband.

So the big questions are; What is your current compression ratio?, and what are the RV cam specs?
If you cannot answer these two questions, and if the cam is out, and if the engine is in-frame, then the only way to answer the cr question is to pull a head off and measure it up.And the only way to figure out the cam specs, if it has no identifier on it, is to fingerprint it. These are not easy or cheap things for a novice to do.
So the hands down,quickest, easiest,cheapest solution,is to slam that RV cam in and see how she runs.And besides,you already own it. And if you don't like it, it's just the gaskets it cost you to find out. And with any luck you can reuse most of those.
You could check all the specs as soon as the cam is nestled in the block;but that requires a tool investment.And the advertised specs will kinda be a guess cuz without knowing who built it you can't really pick a spec to check to.Some manufacturers spec from .006, some from .008, and I suppose some might try to spec at .002.
-But if you are able to provide Scr and cam specs, there are several guys here that can tell you how it might run with those 2.76s and stock TC.I really hope it works out ok for you.
 
so what I'm hearing is it will be just as much of a dog as the old 509 but make less power up top. I'll call some cam companies and maybe I can scare up some dinero for a better camshaft. or any reccomendations from anyone here?
 
brayden
I think you missed something or perhaps I wasn't clear.Without a compression ratio number, or without cylinder pressure results,stabbing a cam in there will be kindof a crapshoot. Since you already have a cam with lifters organized to go back on the lobes that they came off of, then you might as well start out with the crapshoot that you already own.

If you really want to spend money; rent,borrow,or buy, the tools needed to measure your RV cam in the block.Or hire somebody to do it for you. Then install it, degree it, and check the compression on at least one side of the engine before you button anything up.Just make sure the cam stays where it belongs.
Knowing the cam specs and the cylinder pressure, A guy can get a pretty good idea of how she will run.
 
sorry my bad I only read the first part about the 6400 cam. specs are a 1976 cast bottom end with piston .100 below deck. with the closed chamber stealths it should be 8.9:1 with the gaskets that came in the rering kit. but I've read the chambers are not quite as small as advertised. I measured the deck height with a sled gauge and dial indicator so it should be accurate.
 
Now you're half way there. And I can already tell you that

It is my opinion that with just 8.9Scr, both of those big cams would have been very soft on the bottom. The Dcr would be 6.5ish with cylinder pressure of near 122psi.Can you say; disappointing?
For a strong bottom end to pull those 2.76s, with just 8.9Scr, you are gonna need a very early closing intake valve, to trap as much of the charge as early possible and compress it for as many degrees as possible. Some RV cams do just that.Perhaps yours is one of those.

As an example;A cam with an ICA of 50 degrees might bump your Dcr to 7.8 and cylinder pressure might climb to 155
I must warn you tho that a 50*ICA is a pretty small cam and will be done very early. This is not necessarily a bad thing, cuz with 2.76s, 5500 at the top of first gear will be speeding, just about anywhere in Canada. And with 150Plus psi, she would be snappy, hang on tight!

I did a little math; to get a 50*ICA might require a 252/262/108 advertised cam,in at 104.If one can assume fast ramps this might be;212/222/108 at .050. now compare this to that 6400Summit at 214/224/112.....See what I mean about that 6400?;all bark,no bite.
 
I recently re rung and stuffed new bearings in a low mile, low compression rv 440 to replace the one that turned a bearing on break in. the 292 comp that was in the engine will be a little to much for the factory geared 8 1/4 and stock converter that were to be replaced. funds are a little tight right now thanks to this and I would like to get this thing on the road for once. so the question is I have a summit k6400 cam with the lifters and also the stock rv grind that was in the engine what will be better? specs are stealth heads, performer intake, factory 76 bottom end with new rings and bearings, Schumacher tri y's in a 73 duster with a 727 and 2.76 axle ratio with 26 inch tires. what does everyone figure it will run too? would be nice for some educated guesses. can't afford much thanks to this terrible canadian exchange rate and everything listed is just kind of kicking around. thank you for your time.

"low mile, low compression rv 440", "I have a summit k6400 cam with the lifters and also the stock rv grind that was in the engine what will be better?"

I read this as the stock cam from a 440 motor home engine.

"funds are a little tight right now"

So, there are probably 30 different cams that are even better........but.....of the two you have, the K6400 is the best.

How much money do you want to spend and we can all help you spend it. A stroker would be better!
 
How much money do you want to spend and we can all help you spend it. A stroker would be better![/QUOTE]

I could probably scrounge up enough money for a set of lifters and hydraulic cam and the stuff to go with it springs, timing set. but nothing exotic like a mechanical roller or that needs an adjustable valve train.
 
I'm all for spending money on our hot rods.

But to me there is a difference between, I can afford.......and "I could probably scrounge up enough............"

When somebody tells me they want a 600HP engine, that's fine. But the next question is, "Great, what money is in the budget?"

Sounds like the budget is spent if you are scrounging. The K6400 is paid for.
 
ok scrounging makes it sound worse than it is. I can afford a new cam and I got the summit lifters unopened, and I have a new timing set so I should only need the cam itself and the springs for it.
 
I think I'm missing something here....with 2.76s, and an automatic;
-In first, you are geared for 12mph per 1000 rpm. So 2500=30mph,and 3500=42, and 4500=54, and 5500=66.
-In second you are geared for 20 per 1000 rpm. So 2500 =50, and 3500 = 70, and 4500=91
-In Drive you are geared for 29 per 1000;so 2500 Would be 72.5mph

What speeds will you be typically driving at, when you need torque?, and what will your rpm be?
If you answer 30 mph in Drive; Well, first the tranny will have to downshift, and if the governor allows first, your tach might hit about 2500; Got Torque? Got all 4bbls? A big cam will not help you; the bigger the cam, the worse it will be.
But if you answer 60mph in Drive; Well it's hardly likely the gov. will allow first so in second, your Revs will be about 3000 rpm; Got torque? Got all 4bbls?
But if you answer 45mph in drive; well the downshift into second will put you around 2500; Got torque? Got all 4 bbls? But suppose it shifts all the way down into first, giving you 3750 rpms. Got anything there? Well, actually you do. But in about one or two seconds you will be speeding, and almost out of revs.
So, where are you gonna cam that beast; for horsepower at 5000Plus,or for torque from idle to 3000?
 
"I can afford....." There ya go! Sounds like AJ could come up with a cam recommendation for you.
 
I don't recommend cams cuz it ain't my money. Occasionally I do recommend what cam not to buy, or not to install, when I see a recipe for disappointment, in a certain combo.
It is my opinion;
that the 6400 needs an Scr over 10.5 to be truly effective below 3000, When saddled with 2.76s, and a stock TC..
IQ knows facts. Way more facts than me,for sure.
 
I don't choose cams for others for the very same reason. I do design cams for the engines I build for others.

Here are the facts. He has the stock motorhome cam and the 6400. Of the two, which would I run? The 6400. Maybe that is choosing him a cam.

Facts, a 7.5:1 440 with stock 906 heads, headers and the 6400 cam will make 427 lb-ft of torque at 2,500 rpm and 287 HP @ 4,400 rpm. I have dyno'd this exact setup. That will move an A-body with 2.76 gears away from the stop light. Plus he has heads that flow another 30-40cfm and 1+ points more compression. He's got all the parts, and the springs on the heads will work forever with the 6400.

The torque converter, gears and intake manifold are for grandma's 318........but they are what they are.

Put it together and save for a better setup down the road.

If somebody wants to tell him a better cam to buy for an obviously temporary setup, please do. I won't argue with you.
 
Yeah I suppose I'm stuck in small block mode. I read your build, in the link. What I saw was; with almost every single change, after the headers went on,low end torque just kept on disappearing.
What I know is; 250 to 300 ftlbs at 3500 in a SBM, is enough to blow through 295s like nothing with street suspension, even at 40Plus mph,when geared at 12mph per 1000rpm. I suppose 400 at 2500 is even funner.
I wasn't thinking big block. Plus, I don't know why,but,I was picturing a big Chrysler 300 in my head.
-So Brayden, upon reflection,Facts trump opinion.I am wrong. I still believe everything I opined holds true; just not for a BB in an A-body.
And to IQ; saying sorry ain't saying enough.Thanks for the schooling.
 
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