Bigger cam or not bigger cam - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Newt408 · 03-13-2004, 09:32 PM

bigger cam or not bigger cam that is the question. Im thinking about going with a bigger cam but wanted you fellers input. Heres my setup now.
sb 400 .040 over
30cc dish pistons on 5.7" rods-9.25-1 compression
vortec heads
xe-268 cam
edelbrock performer rpm intake
holley 670 street avenger carb
msd ignition box, coil and recurved distributor
stock fuel pump-about to remedy that
1 5/8 headers to 2 1/2" duals to 40 series flowmasters
BTO 2004r w/2200stall
3.70 gears
295/50s
Anyway i'm thinking of going with the xe 274 cam. Ive got the heads off right now going to get the valve guides clearanced like i should have in the first place but didnt know i needed to until about a year after i built the engine. Its usually better to know these kinds of things beforehand. Anyway this is my daily driver but I sure like to embarass the teenagers in their nice new mustangs their daddys bought them.

*1FaastC10* · 03-13-2004, 09:41 PM

you really need more compression if you're going to go with a bigger cam. i'd say going to a smaller cam could possibly be the direction you want to go. especially so since you've got OD. smaller cam = more torque down low. more low torque means better responce off the line.

MylilBowTie · 03-13-2004, 09:56 PM

If it was my build up I think the xe-268 is a little on the conservative side in a sb 400. Im not sure of the difference in gas mileage though. Im sure I would probably use xe274. Bigger displacement engines tend to soak up what would be a bigger cam in smaller displacement engine and the rpm range they make power in.

Destructo · 03-13-2004, 10:07 PM

For comparison on longer stroke engines, a 350 SB with a XE256 will have about the same torque curve as a 400 SB with a XE262, so a bigger cam in a longer stroke engine will be different than a short-stroke engine.

I am planning on running a XE262 cam in my 406 when I put it together because that will give me the maximum torque all the way from 2k to 3k rpm and will have a nice flat curve.

*1FaastC10* · 03-13-2004, 10:44 PM

mylilbowtie, the thing that concerns me with going to the bigger cam is that he has OD, so his truck will be lower in the rpm range. looking at the cam specs, i guess this souldnt really be an issue for him. what will is the fact that with the XE 268 or the 274, is the dynamic compression ratios are very low. a low DCR will cause it to be soggy down low, which is not a good thing when you're trying to move a 4000# truck. if he could up the static compression a bit, then i'd be all for the bigger cam. since his is so low, i dont see him achieving his goal of making the truck faster. could actually slow it down a little.

Newt408 · 03-14-2004, 01:27 AM

thanks guys. i think i'll just keep the 268. I was just thinking about the specs on edelbrock's rpm combo for a 350 with 9 1/2 compression and a 236 @ 050 cam and thought i might could get away with the larger cam. Dont get me wrong the 408 is pretty salty now but who is ever satisfied?

Tom · 03-14-2004, 08:21 PM

Shave the heads while they are off and then throw on a comp cams XE solid lifter equal of the xe274 hydro.

*1FaastC10* · 03-14-2004, 08:40 PM

shave Vortecs?! sure, why not. GM didnt waste ungodly ammounts of money developing that combustion chamber, they just threw it together.

i still dont like the compression ratio with the 268, much less the 274. how far down the bore are your pistons? how thick and what bore is your head gasket?

Newt408 · 03-14-2004, 10:10 PM

The head gaskets are fel-pro stock replacements I think they were about .043 thick compressed and the pistons are .005 in the hole.

03-13-2004, 09:32 PM	#1
Newt408 Registered User Join Date: Feb 2004 Location: west texas Posts: 71	Bigger cam or not bigger cam bigger cam or not bigger cam that is the question. Im thinking about going with a bigger cam but wanted you fellers input. Heres my setup now. sb 400 .040 over 30cc dish pistons on 5.7" rods-9.25-1 compression vortec heads xe-268 cam edelbrock performer rpm intake holley 670 street avenger carb msd ignition box, coil and recurved distributor stock fuel pump-about to remedy that 1 5/8 headers to 2 1/2" duals to 40 series flowmasters BTO 2004r w/2200stall 3.70 gears 295/50s Anyway i'm thinking of going with the xe 274 cam. Ive got the heads off right now going to get the valve guides clearanced like i should have in the first place but didnt know i needed to until about a year after i built the engine. Its usually better to know these kinds of things beforehand. Anyway this is my daily driver but I sure like to embarass the teenagers in their nice new mustangs their daddys bought them. __________________ The way of a fool is right in his own eyes:but he that hearkeneth unto council is wise. Proverbs 12:15

03-13-2004, 09:56 PM	#3
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	If it was my build up I think the xe-268 is a little on the conservative side in a sb 400. Im not sure of the difference in gas mileage though. Im sure I would probably use xe274. Bigger displacement engines tend to soak up what would be a bigger cam in smaller displacement engine and the rpm range they make power in. __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

03-13-2004, 10:07 PM	#4
Destructo Registered User Join Date: Sep 2003 Location: Lewisville, NC Posts: 1,836	For comparison on longer stroke engines, a 350 SB with a XE256 will have about the same torque curve as a 400 SB with a XE262, so a bigger cam in a longer stroke engine will be different than a short-stroke engine. I am planning on running a XE262 cam in my 406 when I put it together because that will give me the maximum torque all the way from 2k to 3k rpm and will have a nice flat curve. __________________ 1985 Scottsdale Shortbed 4x4 Stout 350 with some "upgrades"-700r4-33x12.5" Mud Tires, Warn 8274-50 winch. 2005 Chevrolet Colorado Regular Cab 2wd 4-banger, 5 speed, Street Pack with 3.73 axle.

03-13-2004, 10:44 PM	#5
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,399	mylilbowtie, the thing that concerns me with going to the bigger cam is that he has OD, so his truck will be lower in the rpm range. looking at the cam specs, i guess this souldnt really be an issue for him. what will is the fact that with the XE 268 or the 274, is the dynamic compression ratios are very low. a low DCR will cause it to be soggy down low, which is not a good thing when you're trying to move a 4000# truck. if he could up the static compression a bit, then i'd be all for the bigger cam. since his is so low, i dont see him achieving his goal of making the truck faster. could actually slow it down a little. Last edited by 1FaastC10; 03-13-2004 at 10:48 PM.

03-14-2004, 01:27 AM	#6
Newt408 Registered User Join Date: Feb 2004 Location: west texas Posts: 71	thanks guys. i think i'll just keep the 268. I was just thinking about the specs on edelbrock's rpm combo for a 350 with 9 1/2 compression and a 236 @ 050 cam and thought i might could get away with the larger cam. Dont get me wrong the 408 is pretty salty now but who is ever satisfied? __________________ The way of a fool is right in his own eyes:but he that hearkeneth unto council is wise. Proverbs 12:15

03-13-2004, 09:41 PM	#2
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,399	you really need more compression if you're going to go with a bigger cam. i'd say going to a smaller cam could possibly be the direction you want to go. especially so since you've got OD. smaller cam = more torque down low. more low torque means better responce off the line.

03-14-2004, 08:21 PM	#7
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	Shave the heads while they are off and then throw on a comp cams XE solid lifter equal of the xe274 hydro. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

03-14-2004, 08:40 PM	#8
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,399	shave Vortecs?! sure, why not. GM didnt waste ungodly ammounts of money developing that combustion chamber, they just threw it together. i still dont like the compression ratio with the 268, much less the 274. how far down the bore are your pistons? how thick and what bore is your head gasket?

03-14-2004, 10:10 PM	#9
Newt408 Registered User Join Date: Feb 2004 Location: west texas Posts: 71	The head gaskets are fel-pro stock replacements I think they were about .043 thick compressed and the pistons are .005 in the hole. __________________ The way of a fool is right in his own eyes:but he that hearkeneth unto council is wise. Proverbs 12:15



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