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Old 11-15-2004, 10:52 AM
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Cam selection 400 sbc help

Hey guys great site, i've been lurking for quite a while, this is my first post. I want to know your opinions on a cam selection. Here is my info:

400 small block chevy, motor was out of a '74 chevy caprice
The stock pistons are dished
TH400 trans
Stock converter
Polished but not ported the ports on the heads
Alum Edelbrock dual plane performer intake
Hedman headers
Holley 650 carb

Its going into an 87 Jeep CJ with stock gears
Used mainly for off roading and a daily driver.

I'm staying with the Hydraulic flat tappet style cam...

1. Whats the max Lift I can run with this motor without getting into bigger springs / coil bind / or valve clearance issues

2. Whats the max Duration I can run without getting to problems with a stock converter or other issues.

I see summit has some cams for $60, are they any good for a deal like this?

Ex: SUM-1103 Camshaft, Hydraulic Flat Tappet, Advertised Duration 272/282, Lift .442/.465, Chevy Small Block

Thanks for any help! Gary
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Old 11-15-2004, 01:52 PM
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First off, I would not recommend using the old lifters. I would get a cam and lifter set from comp or some other cam company. As far as the springs go, that is kind of hard to say without knowing the specs on your stock springs. I would call comp and see what they suggest. www.compcams.com

Adam
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Old 11-15-2004, 02:14 PM
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cam for SBC

I dont recommend using the old lifters. Thats a good way to destroy a good camshaft in a hurry. The used lifters have developed a wear print on the old cam and to use them again will cause premature wear on the new cam. Unless you are running roller lifters, always use new lifters with a new cam, and if you are using an old cam in an engine and not sure which lifter came off of which lobe, install new lifters on the old cam.
I would recommend a cam of 210-220 degrees @ .050", and with a lobe separation of 108-110 degrees. Duration dictates the rpm range the cam is most effective in, and lobe separation dictates at which end of that rpm range the cam is most effective. The narrower the lobe separation, the more torque that is generally produced within the power band and lower in the rpm range.
Some side effects of narrow lobe separation cams:
The narrower the lobe separation, the less tolarance to lower octane fuels.
You will have a more lumpy idle with a narrower cam as a rule, due to the higher volumetric filling of the cylinders.
You lose less hp off the top end going with a narrow lobe separation cam than you generally will gain using a wide lobe separation cam.
Wide lobe separation cams are generally easier to get by exhaust sniffers for smog certification.
There are trade offs to everything, but it seems that general concensus is that 110 degree lobe separation is the best compromise for low end and hi end power throughout the power band.
Vertually all of Comp Cams street shafts are ground with 110 lobe separation. This does not mean that I particularly indorse Comp Cams, just that it is a referance to their tech. I have used Comp Cams and have no complaints about them.

I would also recommend installing new valve springs on the engine, and use the pressure springs the cam grinder recommends for their shaft.
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Old 11-15-2004, 02:31 PM
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right, I was planning on buying new lifters with the cam, sorry forget to mention that, mainly just looking for limits to keep me out of trouble. Its a low buck deal, so i'm trying to keep away from buying new (stronger) springs, or a converter with more stall... Thanks very much for your help so far, any other suggestions?
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Old 11-15-2004, 02:53 PM
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cam for a 400 sbc

You are welcome. You failed to mention what you are running for intake etc, that being aside, even with a 2 bbl carb, you would notice significant gains with a cam as I recommended, and would only be hurt on the very top end by not having quite enough carb to feed it. If you are planning to go to a 4 bbl carb, I recommend a dual plenum intake like a Performer, and a carb of up to 600 CFM.

Carburetion formula:

CID X rpm desired divided by 3456= CFM needed.
Example:

350 CIDX 5500 Rpm divided by 3456 = 557 CFM.
Unless you plan to turn the engine over 5000 rpm a lot, I would go with a 500 CFM 4bbl carb.

A carb will continue to feed your engine quite well even after the peak RPM, as much as 15-20%, so your 400 turning 5000 rpm only needs a 578 CFM, so that means that carb would effectively feed your engine up to 6000 RPM with no problem.
The NASCAR guys run 390 CFM carbs with a restrictor plate and turn 7000 rpm and build upwards of 600 hp.
750's etc make for impressive numbers bench racing but dont help much when it comes to a standard bread and butter engine.
One other note. The smaller carb makes for higher fuel air flow velocities and better fuel air mixture, making for both better throttle response at lower end and better mileage as well.
Aslo consider just how tight you do plan to wind the engine on a regular basis.

back in the early 70's, I ran a cam with 226 degrees duration in a 69 302 Mustang. This was the upper limit for a cam in an engine that size with a stock converter. You should have no problem with stall speed with your 400.
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Old 11-15-2004, 02:56 PM
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Re: cam for a 400 sbc

ok cool, I have a dual plenum edelbrock performer intake, and a holley 650 carb. And being used for mostly off roading, I want alot of low to mid range torque, cause i'll spend most of my time down there...
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Old 11-15-2004, 03:07 PM
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i just put a comp cam in my blazer 4x4 350/350.

everything is stock, with cam and lifters, chain, headers, 4 bl carb, intake, and accel dist.

the cam grind # is cs 268h-10
im real happy with it. it has a real cool idle. and alot of power.
its designed to work with lower compression ratios by building higher pressures.


http://www.compcams.com/Technical/Se...umber=12-210-2

oh yeah, you will definatly want to get some new intake gaskets. unless you like water in your oil.
i like to get the ones with no heat crossover hole.

Quote:
Originally posted by Max Keith
You are welcome. You failed to mention what you are running for intake etc, that being aside, even with a 2 bbl carb, you would notice significant gains with a cam as I recommended, and would only be hurt on the very top end by not having quite enough carb to feed it. If you are planning to go to a 4 bbl carb, I recommend a dual plenum intake like a Performer, and a carb of up to 600 CFM.

Carburetion formula:

CID X rpm desired divided by 3456= CFM needed.
Example:

350 CIDX 5500 Rpm divided by 3456 = 557 CFM.
Unless you plan to turn the engine over 5000 rpm a lot, I would go with a 500 CFM 4bbl carb.

A carb will continue to feed your engine quite well even after the peak RPM, as much as 15-20%, so your 400 turning 5000 rpm only needs a 578 CFM, so that means that carb would effectively feed your engine up to 6000 RPM with no problem.
The NASCAR guys run 390 CFM carbs with a restrictor plate and turn 7000 rpm and build upwards of 600 hp.
750's etc make for impressive numbers bench racing but dont help much when it comes to a standard bread and butter engine.
One other note. The smaller carb makes for higher fuel air flow velocities and better fuel air mixture, making for both better throttle response at lower end and better mileage as well.
Aslo consider just how tight you do plan to wind the engine on a regular basis.

back in the early 70's, I ran a cam with 226 degrees duration in a 69 302 Mustang. This was the upper limit for a cam in an engine that size with a stock converter. You should have no problem with stall speed with your 400.


thats assuming it is 100% efficient though, but its more like 80%.
i dont think a cam that big will be that good for low end power.

i would go with a 750 q-jet carb for offroad use. edelbrock or rochester are good.

Last edited by blazinwest; 11-15-2004 at 03:07 PM.
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Old 11-15-2004, 03:38 PM
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What you can get away with for lift depends a lot on if you have had shims put in before you and if you have rotators. I have run trouble free up to .480 with no rotators or shims a lot of times. It seems that for some reason the .500 line becomes a risky point,I tried to get away with a lot of low dollar combos years back and found a lot out the hard way. This by the way is assuming you still have the stock heads on it. For a cheap cam that will work nice,check out the summit k1103 214-224 .442-.465,if you have a few more bucks check out the comp cams I would say,also I like the speed pro anti pump lifters.
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Old 11-15-2004, 05:43 PM
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400 sbc

The cam you are looking at with the 445/465 lift should work fine.
As for the carb, since you already have the 650, I would run it, as you wont lose that much over the slightly smaller carb for low end, but in any event, I sure wouldnt go any bigger at this stage.
As the old saying goes, a little bit is good but a lot aint always better. To my experience, it doesnt seem to matter what brand carb you are running, if its set up properly, it will work just as good as any other.

In an engine of 400 CID, a cam of 210-220 degrees duration is still well in the class of a torque cam. Once you get over 230 degrees then you are getting into the high rpm cams and you start losing your low end torque.

One thing to consider, a hydraulic cam of 200 degrees is duration wise equal to a 210 degree solid lifter for rpm range.
Other axiums:

10 degrees duration plus or minus changes the rpm range of a cam shaft 400 rpm up or down.

IE: a 200 degree cam will operate in an rpm range 400 rpm lower than a cam with 210 degrees duration.


50 cubic inches displacement plus or minus changes the effective operating range of a cam by 500 rpm up or down.

IE. A 2000-5000 rpm cam in a 300 cubic inch engine will be a 1500-4500 rpm cam in a 350 and 1000-4000 in a 400 cubic inch engine.

That is why a cam in a small displacement engine may well have a lot of rump rump to it and be very docile idling in an engine 100 or more cubes larger.

In 72, we put a stock 70 351W cam in a 65 260 Falcon. Its unbelievable what it did to that engine. The power band actually went up 1000 rpm. Due to the 109 degree lobe separation it gave the engine a mild lopey idle, which had an awesome sound to it.
The cam a 196 degree 416 lift. Not much of a cam in a 351 but was pretty torid in that 260.
We also put on a Holley 500 cfm 2 bbl carb and headers. This engine would easily wind 6000 rpm and ask for more, this with a 3.25 rear and 4 speed.

Last edited by Max Keith; 11-15-2004 at 05:43 PM.
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Old 11-15-2004, 06:31 PM
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Your compression ratio will also significantly dictate bottom end and torque. I run an 11:1 400, with a 230o duration cam. It has more bottom end than my suspension can take. The idle quality is good, and the mileage is good.

Look for the Holley 4778-2 and 4778-1. They have the skirted truck type boosters. They will keep all of your torque, and give more top end. They are both 700 cfms. I got mine brand new on Ebay for $125.
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Old 11-16-2004, 07:11 AM
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Re: cam for SBC

Quote:
Originally posted by Max Keith
Duration dictates the rpm range the cam is most effective in, and lobe separation dictates at which end of that rpm range the cam is most effective. The narrower the lobe separation, the more torque that is generally produced within the power band and lower in the rpm range.
Some side effects of narrow lobe separation cams:
The narrower the lobe separation, the less tolarance to lower octane fuels.
You will have a more lumpy idle with a narrower cam as a rule, due to the higher volumetric filling of the cylinders.
You lose less hp off the top end going with a narrow lobe separation cam than you generally will gain using a wide lobe separation cam.
Wide lobe separation cams are generally easier to get by exhaust sniffers for smog certification.
There are trade offs to everything, but it seems that general concensus is that 110 degree lobe separation is the best compromise for low end and hi end power throughout the power band.
Not exactly.....

Narrow lsa causes the engine to be more peaky in its power range and will generally put up better peak numbers while the wider lsa tends to have a smoother torque curve with a little lower peak numbers....but as always it depends on the combination.

Narrow lobe separation causes the engine to bleed off cylinder pressure in the low RPM due to the increased overlap of the open ramps of the intake and exhaust valves. What this does is lower cylinder pressure. This is further complicated with increased exhaust contamination of the intake charge in lower RPM which necessitates a richer mixture to get a good burn. All of this causes the nasty idle and eye watering fumes on an engine with a tight lsa/wide duration cam.

Additional effects of this overlap is increased resistance to detonation. Detonation is caused by cylinder pressures exceeding the fuels ability to burn at a stable rate. By decreasing cylinder pressure we help this problem somewhat. As the engine revs to the higher RPM the valve overlap effects cylinder pressure less and less. Additionally, as RPM goes up the combustion process gets less and less time to burn and less likely to detonate.

For a crawler, I aggree that a 215 range duration with 110-112 lsa is a good candidate for that engine. You have to be careful that you dont run too small a cam with too much compression or cranking pressures will be out of site. With the dish pistons and factory head you are likely around 8.5:1 CR so you should be fine. Lift is really not near as big a deal as duraion and lsa when it comes to the characteristics of the cam.

Chris

Last edited by TurboS10; 11-16-2004 at 07:16 AM.
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Old 11-16-2004, 07:46 AM
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ok got it. thanks everyone for all your help. this gives me alot better idea of what to keep an eye out for.
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Old 11-16-2004, 08:28 AM
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Say,for reference sake,I put that same summit cam in a friends 350 1/2 ton truck with a stock stall and stock 69 cast iron Q-jet intake,it had a nice lope and ran real nice,even got fairly good mileage. It could have used a little more stall,but with your extra 50 cubes,it should work perfect,remember,no rotators though.
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