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Old 05-12-2010, 12:20 PM
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which cam to use? xe274 or xe284

I have a 468 big block with forged SLP 10:1 pistons, forged eagle rods and crank, GM polished and ported with 3 angle valve job (2.19/1.88), Edelbrock RPM air gap, Holly street avenger 750 carb, 1 7/8 headers to true dual 2.5" exhaust with flowmaster mufflers, th350, 3000rpm stall and 3.42 rear gears. I know i have inquired about the xe284 on here before but i need help making a decision.i could lock out the timing if needed for the 284 to help with idle and vacuum but i also like the more streetable power range and sound of the xe274. Its a street/strip car with mostly being street. Which cam should I get comp xe274 or xe284?

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Old 05-12-2010, 12:37 PM
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The XE284H-10 will make you go faster. You can lock out the timing or recurve the distributor for 26deg at idle and 38deg at max advance. ( a 12deg advance curve)

then 10-12deg of vacuum advance for cruising.

its very hard to over cam a 468. you worry too much.
The 750 carb is going to limit it. Get a 850 cfm carb for max performance.
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Old 05-12-2010, 12:45 PM
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Quote:
Originally Posted by F-BIRD'88
The XE284H-10 will make you go faster. You can lock out the timing or recurve the distributor for 26deg at idle and 38deg at max advance. ( a 12deg advance curve)

then 10-12deg of vacuum advance for cruising.

its very hard to over cam a 468. you worry too much.
The 750 carb is going to limit it. Get a 850 cfm carb for max performance.
well the xe284 will only add around 20hp and 30tq over the 274 with my combo. haha yeah i know i worry too much lol i just don't want to use the wrong cam. isn't a 850cfm carb too much on my 468 build for mostly street use with some strip?
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Old 05-12-2010, 12:48 PM
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Quote:
Originally Posted by Jason7504
well the xe284 will only add around 20hp and 30tq over the 274 with my combo. haha yeah i know i worry too much lol i just don't want to use the wrong cam. isn't a 850cfm carb too much on my 468 build for mostly street use with some strip?
Do you want to go fast,,,,or not as fast?/// neither are too much.
Both are just right. 750's are for small blocks. If you already own this 750cfm carb upgrade it with a hp style main body (holley/proform) at minimum. The xe284H-10 is a baby cam in a 468.

The idle sound is boss.

The flowmaster mufflers have only 1 thing going for them. Sound at idle.
All the other high perf mufflers ( eg: dynomax or magnaflow) will outperform them and have a lot less interior noise resonance when driving.
If you want a car with streetability (that you can and will enjoy actually driving) change the mufflers.

Last edited by F-BIRD'88; 05-12-2010 at 12:59 PM.
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Old 05-12-2010, 01:21 PM
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Quote:
Originally Posted by F-BIRD'88
Do you want to go fast,,,,or not as fast?/// neither are too much.
Both are just right. 750's are for small blocks. If you already own this 750cfm carb upgrade it with a hp style main body (holley/proform) at minimum. The xe284H-10 is a baby cam in a 468.

The idle sound is boss.

The flowmaster mufflers have only 1 thing going for them. Sound at idle.
All the other high perf mufflers ( eg: dynomax or magnaflow) will outperform them and have a lot less interior noise resonance when driving.
If you want a car with streetability (that you can and will enjoy actually driving) change the mufflers.
ok well now im leaning towards the xe284
would a 750 Holly street HP carb be better than the street avenger? or just go with a bigger street avenger?

yeah i do notice noise resonance more at idle. So magnaflows would be a better choice? most mufflers don't contribute that much to power, so the main difference would just be sound. i kind of like the old school, rumbling sound of the flowmasters though lol

EDIT: i guess my carb is a 770 not 750

Last edited by Jason7504; 05-12-2010 at 02:07 PM.
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Old 05-12-2010, 02:06 PM
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I've got a fairly similar build, with lower compression.

454 +.030
Forged flat-tops
781 heads (stock 3-angle valves, no porting.)
RPM Air Gap intake
TH400 Trans
2600 Nitrous Holeshot Converter
3.73:1 gears
66 GMC pickup

It's a toy, and it's not finished yet ... hasn't turned a wheel under it's own power yet.

The first cam I had was a Clevite 229-2305.
224 / 234 Duration, .529 / .553 lift 114 Lobe C/L
Everything I read said that was going to be perfect.
In actuality ... meh, not so much.

It would idle at 600 with a barely discernible lope. It was "lazy" when you blipped the throttle. My impression: "RV cam?"

Unfortunately (or fortunately?) I experienced a lobe failure with that cam and decided I wanted something significantly "lumpier".

Enter the Comp XE284H.
Oh yeah, it's "lumpier" alright!
Downright "snotty" when it's cold ... needs babysitting while it warms up in my 50 F shop. Once the needle comes off the bottom peg, it will idle at about 800 RPM and smooths out quite well at around 150 and 1000 RPM.
After it's reached the 160 or so range, it responds very well to the throttle, and gets that snappiness when you throttle it back to the stop.

My neighbor comes over once in a while, drools a little, and says "That's going to be a monster! Can't wait to see it."

Yeah ... that's kinda the reaction I was lookin' for.

Edit:
One more thing. I'm sure the vacuum will be lousy ... but I don't really care.
Hydroboost brakes, baby!
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Old 05-12-2010, 03:26 PM
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10:1 piston with how many cc heads? and how many cc's are in your cylinder heads?

what is the deck height? (how far is the piston below the deck at tdc, not counting the dome).

10:1 cr is too high for a 274 degree cam in a BBC.

3000 stall and a 3.42 gear is a little of a mismatch on the street.

I would avoid XE flat tappet cams. too aggressive and tend to go flat, especially on a BBC. make sure to use an oil additive like zddplus (www.zddplus.com).

With a 10.1 cr BBC, I would use a compcam 292H, 3000 stall and a 3.73 gear. 25 initial timing and 38 to 42 total (test for best results).

I have used over cam oilers on BBC with good results. BC engineering sells a kit for $50 but it is easy to make for less than 20.
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Old 05-13-2010, 01:13 AM
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Quote:
Originally Posted by 454C10
10:1 piston with how many cc heads? and how many cc's are in your cylinder heads?

what is the deck height? (how far is the piston below the deck at tdc, not counting the dome).

10:1 cr is too high for a 274 degree cam in a BBC.

3000 stall and a 3.42 gear is a little of a mismatch on the street.

I would avoid XE flat tappet cams. too aggressive and tend to go flat, especially on a BBC. make sure to use an oil additive like zddplus (www.zddplus.com).

With a 10.1 cr BBC, I would use a compcam 292H, 3000 stall and a 3.73 gear. 25 initial timing and 38 to 42 total (test for best results).

I have used over cam oilers on BBC with good results. BC engineering sells a kit for $50 but it is easy to make for less than 20.
im not sure off hand what the cc is for the cylinders or heads. Why is 10:1 too high for a 274 cam? well i just wanted to go with 3.42 so my BBC isn't cruising at too high of rpms. When i contacted Hughes, they said the 3000 stall is a better match with the 3.42 gears with the xe284 cam. you don't think a 292 is too much for it? and according to CamQuest,the comp cam 292H will have around 20 less hp and 35-40 less ft/lb torque than the xe284.

Last edited by Jason7504; 05-13-2010 at 02:10 AM.
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Old 05-13-2010, 01:38 AM
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or how about a comp cam xtreme energy roller cam instead? like this one http://www.compperformancegroupstore...=MARKIVCAMHRXE
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Old 05-13-2010, 03:21 AM
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I think xe284 is better to use
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Old 05-13-2010, 04:49 AM
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I have the following setup
- 468
- 10.25:1
- .340 domed pistons
- 336781 oval 118cc heads
- 850 carb
- Edelbrock performer RPM intake
- 3000 stall
- TH400
- 3.55 gears
The cam selection was a "nightmare" - ask 10 people and get 15 answers!! The guy that built 3 engines with the very same specs insisted on a thumpr cam with 235/249 @.050" (comp 11-601-4). The engine is not in the car yet, but sounds good and should be as powerful as it sounds...
I agreed on this because it's always easier to go back than to install a more agressive cam...
One question: what do you mean with the vacuum problem for the brakes? Is this a big issue?
thanks,
Peter
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Old 05-13-2010, 10:03 AM
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what is the piston part number?

what is the head casting number?

the cam you use makes a huge effect on the dynamic compression ratio. The intake valve closing point is what effects that. a 274 degree cam will close the intake valve fairly soon which caused more cylinder pressure as compared to a larger duration cam (284, 292,....). I feel that 10:1 static compression ratio in a BBC with a little 274 degree cam will make too much cylinder pressure to run pump gas and full ignition timing.

a 292H cam would be a much better match for 10:1 cr in a BBC, as the intake valve closes later to bleed off some cylinder pressure. which will allow for pump gas and full timing.

sure the XE cam make more power because they have more aggressive ramps. But theses aggressive ramps tend to eat cams and make noise. when a cam goes flat, it isn't pretty, as it eats up the crank and engine bearings along with the cam and lifters. I don't think 35 or 40 ftlbs extra is worth it if the cam goes flat soon after start up. been there and done that.

3000 rpms with a 3.42 gear and 28 inch tires is 73 mph (not including 10% slippage). plus a bbc will stall higher that 3000 with a 3000 stall due to more torque. converter are typically rated with the torque from a 350, not a 454. On the highway, a 3000 stall and a 3.42 will make extra trans heat until 80 mph.
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Old 05-13-2010, 10:13 AM
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Quote:
Originally Posted by Fonti
One question: what do you mean with the vacuum problem for the brakes? Is this a big issue?
thanks,
Peter
My little brother had a '72 Chevy pickup 350 engine, "350 HP 327" cam. I don't recall what the specs are for that, but it was "rough idle".

REALLY nice truck, lots of power ... but a real PITA to paralell park!

At idle, the engine didn't make enough vacuum to provide any power assist which you usually discovered or at least remembered ("Oh ya!") when you were like 12" from the front bumper of the vehicle behind you. I'm not the kind of driver that likes driving with one foot on the gas and the other on the brake ... so like a said ... a real PITA.

With Hydroboost brakes and a stall converter, the engine powers the PS pump and braking assist ... so it will retain a consistent pedal feel.
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Old 05-13-2010, 10:25 AM
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the 350hp 327 cam has very soft ramps (designed by GM). The cam will last a long time but the soft ramps really kill power.

If i remember correctly, specs are around 300 degrees advertised duration with 224 at 0.050" duration with 114 lsa with 0.450" lift. this cam needs lots of compression to run decent on a sbc. at least 10:1 and as high as 11:1 with pump gas. a 3000 stall and 4.11 gears are also a good idea for this cam.
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Old 05-13-2010, 12:48 PM
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Quote:
Originally Posted by 454C10
what is the piston part number?

what is the head casting number?

the cam you use makes a huge effect on the dynamic compression ratio. The intake valve closing point is what effects that. a 274 degree cam will close the intake valve fairly soon which caused more cylinder pressure as compared to a larger duration cam (284, 292,....). I feel that 10:1 static compression ratio in a BBC with a little 274 degree cam will make too much cylinder pressure to run pump gas and full ignition timing.

a 292H cam would be a much better match for 10:1 cr in a BBC, as the intake valve closes later to bleed off some cylinder pressure. which will allow for pump gas and full timing.

sure the XE cam make more power because they have more aggressive ramps. But theses aggressive ramps tend to eat cams and make noise. when a cam goes flat, it isn't pretty, as it eats up the crank and engine bearings along with the cam and lifters. I don't think 35 or 40 ftlbs extra is worth it if the cam goes flat soon after start up. been there and done that.

3000 rpms with a 3.42 gear and 28 inch tires is 73 mph (not including 10% slippage). plus a bbc will stall higher that 3000 with a 3000 stall due to more torque. converter are typically rated with the torque from a 350, not a 454. On the highway, a 3000 stall and a 3.42 will make extra trans heat until 80 mph.
well im not home now but i will let you know what the head cc's and cylinder cc's are when i get home.
when the intake valve closes later does that mean it loses some low end power? i just don't want too much duration so that it will limit my low RPM power. they really can go flat right after start up? thats crazy!

the guy at hughes said it would flash stall to like 3100-3200 with my combo. well if i do go with 3.73's, i will be at like 3300 with my 26.5" tires. So you think i should go with a 3.73 gear ratio and a 3000 stall?

what do you think about going to a xtreme energy 294HR cam? (http://www.compperformancegroupstore...=MARKIVCAMHRXE)

i heard you can go roller with more duration and still be more streetable. it would be like an extra $550, do you think i would be worth it in the long run?
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