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Discussion Starter #1
Just trying to get some opinion or experience with the swap. All I know if that it puts less stress on the mains , makes the crank vibrate less, and is suppose to give more hp? My question is how much hp are we taking about? I have heard 8-10hp, then someone says that they say peak hp can go up 38hp. here are my specs;

4 bolt 454 bored .060 over
eagle crank-cast steel
eagle rods-cast
Kb hyperutetric -25cc domed pistons
390 heads which are oval and 98cc chambers and they are ported and polished.2.19/1.88 valves
harland shrap 1.8 roller rockers
weiand stealth intake
1 7/8 long tube headers
holley 3310 carb
I was planning on running the comp cam xe274, but then I saw the xe274 with 4/7 swap for less than $100 more.

I think the compression ratio is going to be somewhere around 12.5:1, so will this swap relieve some stress on the bottom end? any info would be helpful
 

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I was unaware that they made a 4-7 swap for a BBC. On the sbc cylinders 5&7 fire right after each other, by swapping 4 and seven it is suppose to prevent 7 from starving for air at higher rpms
 

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Just trying to get some opinion or experience with the swap. All I know if that it puts less stress on the mains , makes the crank vibrate less, and is suppose to give more hp? My question is how much hp are we taking about? I have heard 8-10hp, then someone says that they say peak hp can go up 38hp. here are my specs;

4 bolt 454 bored .060 over
eagle crank-cast steel
eagle rods-cast
Kb hyperutetric -25cc domed pistons
390 heads which are oval and 98cc chambers and they are ported and polished.2.19/1.88 valves
harland shrap 1.8 roller rockers
weiand stealth intake
1 7/8 long tube headers
holley 3310 carb
I was planning on running the comp cam xe274, but then I saw the xe274 with 4/7 swap for less than $100 more.

I think the compression ratio is going to be somewhere around 12.5:1, so will this swap relieve some stress on the bottom end? any info would be helpful
It will rid some of the strain on the bottom end but your motor isnt anything special..Honestly ask yourself how long do you want out of this engine..I mean its not at the ragged edge of its components, if it was then to me the 4-7 swap would be worth it to help it last a season..On paper seems like a simple budget build to me..The cast crank can handle the miniscule added vibrations and harmonics than say something from Bryant.


Spend the extra cash on a full solid roller..Great lifters and rocker arms (you already have)and you wont have to worry about adjusting valves..You will get more hp from that alone..A lot less friction and internal heat too.

Ive done the 4-7 swap and yes it builds power if your comparing apples to apples engines..Most of the time ive done it due to crappy intakes that id have to run,one time it was lack of plenum room on a turbo motors sheet metal intake..The latter engine we never dynoed but the first one we gained 14 hp or so iirc..That was on an engine dyno.But both engines were hardcore quick 8 motors that had to freshened up once a year..

Solid roller is way far much better of a cam to run..But again spend good money on lifters if your gonna drive it daily..Or at least run a hydro roller with a decent set of roller lifters..You will be far more happy with a full roller valvetrain..Save the fancy smancy cams for the gas ported pistons, vac pumps and the guys who coat every damn thing to gain power. At your power level its way easy to get the added hp, and the lessened strain is a can of worms for a never ending argument.
 

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Way too much compression, you will never be able to run pump gas through that motor but maybe you don't plan to. With that compression and the other components listed you should only run maybe 10.0:1 if you want it to be reliable. Even then you need to have it tuned properly to avoid detonation. The 4/7 swap alone is not worth anything close to 38 hp.
 

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Discussion Starter #6
I bought the engine how it's set up. It's definitely a budget build. The guy I got it from told me it was 10.5 compression ratio but I ran the casting numbers on the heads and found out they are 98cc chambers. The kb website has a calculator I used to get the compression ratio. How much would it help if I use a thicker head gasket? The engine won't be ran much bc it's going in a beach toy. It wont see over 5500 rpm and short sand drag runs
 

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If it really is 12.5 compression you will detonate at part throttle and low rpms. You should not calculate compression ratios based on what a website says your combustion chamber cc is. This is just one piece of information needed to truly know where you stand. You need to actually measure the volume of the combustion chamber because you don't know what has been done to the head in the past. You also don't know how far down in the hole the pistons are and this will need to be measured. You need to know gasket thickness and piston dish or dome volume which you don't need to measure as it is a pretty accurate spec from the piston manufacturer. Unfortunately for you it sounds like this motor is already put together. Lots of people have a bad habit of believing the compression ratio that is advertised by the piston manufacturer and sometimes they get lucky but most of the time when all of the components are put together you could end up a full point higher or lower than you intended maybe more. I suggest that you tear this down and verify some of these things and correct any problems before you destroy what could be a pretty decent engine.
 

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That xe274 could be a great cam for this build and will have great torque at low to mid rpms in a motor that size but I would knock compression down to 9.5 to be safe. I have used this cam in a 455 Oldsmobile so I have some experience with it. I understand that there are differences between Olds and Chevy but the cam itself has the same specs and opening and closing points for both and I feel it will perform similar enough to recommend it. I am also assuming that you will be running pump gas 91 octane.
 

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Discussion Starter #10
I already took the engine completely apart because I bought it with a blown head gasket. I have checked the part numbers on the web to get the info I have. I guess it would be a good idea to have the chambers measured. I did choose the xe274 because of the low end tq. I didn't want to go too big on the cam bc the heads nothing special
 

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I already took the engine completely apart because I bought it with a blown head gasket. I have checked the part numbers on the web to get the info I have. I guess it would be a good idea to have the chambers measured. I did choose the xe274 because of the low end tq. I didn't want to go too big on the cam bc the heads nothing special
then you need to lower the compression to match the application.
 

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i have a custom grind cam in my 454. it has the cylinder swap.
my poor motor has 11.5:1 compression and anything under 100 octane and ill come apart. of course, my machinist hogged the heads for the domes of the piston to come in cause im using 97 vortec heart shaped chambered heads. I can stand on the rev limiter at 6500 rpm all day without worry.

the only bad part is 12 gal of 100+ octane doesnt get me far or last long when i stand on it. My stock bore 454 has dimple rods, forged crank, hyd roller cam 600+ lift ,roller lifters,roller rockers yadda yadda yadda.

at 2500 rpm it puts out 520 ftlbs torque and at 5500 rpm puts out a little over 600. horsepower is 340 @2500 rpm and [email protected] 5500 rpm.

I love this setup, but not good for a trail rig or street truck. I drove it 2 miles the other day and burned 4 gallons of fuel. did 3 passes on a 200 ft mud track and burned 5 gallons of fuel.

but the cylinder swap helped a little I guess, but my machinist said it wasnt enough to really matter.
 

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4/7

need kick-ass heads and alot of rpm to make the swap worth while, reher-morrison has the 4-7 swap standard on all their big inch motors, the swap works and makes power, just usually needs killer heads and intake to take addvantage of it. the milder the motor the less you'll notice the gain
 
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