compression with 274cam

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360 heads ported later on
xe274
kb107s
rpm air gap
flow tech headers
750 vac carb
273 rockers or roller rockers
2.5 exhaust with flowmaster 2 chambers
4.10 gears
3200-3500 converter
904 tranny
sure grip
fbo ignition or msd
 
Ok I take you don't have it built yet so that is good. If you have 273 rockers I would go solid cam. They are not a pain to set lash. I run one everyday and don't mind the noise and honestly I like it. I think you could run more compression with a few things done. One polish the combustion chambers and the pistons. Some aftermarket valves can have too much of and edge on them for my taste so watch that. Other things you can do to help out is a cold induction, plastic or wood carb spacer, lower thermo stat, 34-36 timing all in around 2800 and a proper tune on the carb(very big one).

As for cam you can run the one you picked out but I've always been a fan of the solid flat tappet. http://store.summitracing.com/partdetail.asp?part=CCA-CL20-248-4&autoview=sku

It's bigger then you need but I can't find one equal to your hydralic. If you have the extra cash have comp build you one based on the FL lobe series. Hope this helps.
 
One more to think about. Even with the cam up picked out your going to run close to retainer to valve seal contact. If you got some aftermarket retainers with added installed height and turned down valve guide stems for positive seals you would have alot more valve spring options and the ability to run a bigger cam later on.
 
naw once its built its done also i forgot the head work

ported bowls
gasket match the heads
bowl blend back cut valves
75 degree dut on the bowls
and a valve job
 
DusterBoy15 said:
heck no haha its not a dailey driver its a weekened warrior i have the 274 cam
but i asked whats the best compression to run with this cam because i can get higher octane fuel by making it
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Well then if money is not the object I would go around 11:1 static but you need at least cometic head gaskets and around 100 octane points depending on gears car weight etc as others mention. Also altitude makes a huge differance too. Closer to sea level requires more octane due to thicker air IE has more O2 in it.

For more wallet freindly I would stay no more than 10:1 may just need a little booster, but you do not want to have to back the timing way back to make it live on poor full, this will result is less power than if you ran more spark advance and less compression. it is a balancing act. Also iron VS aluminum, heads make a diff to, but that is more of another topic..

PS I did this against many reccomendations years ago when 100octane wa still at the pump, but I needed 105-108 to make a 12.5:1 motor live on the street, it got real old real fast, and that was gas was .50 a gallon.

good luck man!
 
DusterBoy15 said:
sunoco sells 114 from what i heard in pasadena CA

so 91 is fine for 9.5??? why were 10.1 cars able to run with 91 in the 60s?
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Octane ratings are 4 points from what they were back then for starters, there is a research method and convention method of testing, so the scales differ 4 points. Also LEAD techraethyel lead makes the engine cooler in the combustion chamber too.

Todays cars run hotter to burn cleaner, the cams are smaller so you end up with more static low end compression, hence less wasted fuel out the exh less= les smog.. egr valves etc etc.
 
I would stay around 9.5 with that cam-its designed to build lower end which equates to more cilinder psi,also the gain from a half point or so doesnt really equate to much h.p. in a street engine and your not always on the edge of detonation.If you really wanted to build something serious with alot of compression then iI would go with a bigger cam anyway.
 
also i jsut found a gas station selling 100 octane for almost 6/per gallon not bad considering 87 is almost 3.50
 
DB15

Todays computer controled cars can handle higher comp. ratios along with everything else the engine has built into it. Lessons learned over the years are slow to show up, but there showing up.

The open chambered 360 heds are the biggest problem of the combo. While there fine for certain levels of performance, octane and timing issues cn crop up with cm selection.

The open chamber vs closed chamber is something to consider when building an engine. Closed chambers and a zero deck piston can provided a good quench area. A good quench engine can run less timing, higher octane and larger cams than normally seen in an open chamberd head.

Moper (I think) has a modest build pumping out excellent street power and can get away with a lower octane level than most builds. The Magnum heads are part of this combo.

It looks like (IMO) a similar mech. XE cam would do well with the 273 rockers. Have the heads ported and tell the machinest your lift so he can do them right. I myself would look into a HI lift version. The Xe HI-lift series cams are stout.
 
ya i was going to go xe284 but then i would have to get a double spring and cut the heads and run higher compresion
 
The XE274 requires double springs too. I went with the XE268H because so I wouldn't have to deal with double springs.

FWIW, I am running 10.6:1 compression on 89 octane mid grade gas, might even run on 87 but haven't tried. The key is the zero deck KB107's, closed chamber magnum heads and 0.040" compressed head gasket.
 
actually i found a strong enough spring so i dont have to i cross refrenced it with the mopar how to hot rod a small block book
 
Being that the "How to Hot Rod" book is pretty old and does not have any info on the newer fast ramp rate cams like the Comp XE series i would be very hesitant to go by what's in it in this case.
 
I was wrong, it was DGC333 with the engine I was thinking off.
 
well i did talk to BJR about it and he helped me find a spring with dampener that will work for the xe274 and xe284 but im thinking now about returning the xe274 and just getting the xe284 cam so that i can run the 10.1 compression with it


what do you think???? keep xe274 or trade it in for the 284???? also might have found a deal on magnum heads
 
I ran a 284 extreme in my old 360 with 10.4 compression. I only had 10 inches of vacuum though with 155-165 cranking psi. I also had clearance issues with the retainer to valve seals on a set of 308 heads. I eventually just ground the crap out of them with a 2inch grinding disc and cleaned them really well. Also I used a set of crane single springs with the new cam and was running close to coil bind with it; not on all just some because of production differences. One more thing I busted two of those springs within 16 months but very very very lucky neither of the valves dropped.
 
do you remember the specs on the cams or what springs they were so i can get stronger ones??? thanks or what the seat pressure was 110? 120?
 
I've looked for the card and I'm not seeing it but it's just the comp cams extreme energy 284 with 507/510 lift. I did have comp promagnum rockers and remember the lift being very close to the advertise but if your running stock rockers then you should have some extra room. As for springs they were 99837. Around 125 seat and around 295-310 open. I'm sorry but I don't remember my installed height but I do remember that they were all over the place. I run higher spring pressure in my 340 but I spin that to 7000 and my 360 only saw 5900rpm. Some people like big cams and think 10 inches is more then enough. For me 11 inches is the lowest I'll go anymore and still drive it on the street.
 
You can get away with the 284 if you run them 4:10 gears but if you have 2:94-3:21's you won't like the bottom end. Same thing for the compression if you keep the motor spinning faster you can get away with more compression.
 
IMHO,if you must have a bigger cam for your combo go with the comp xe275hl or the lunati voodoo series 60404 for off the shelf grinds,I would consider these the best match for a hot street setup.Its all about the rpm range and cubic inches,they go hand in hand.I have ran a few of the comp xes and I had the xe284 in a couple engines but they were 400 and larger cubes and the cam was still pretty radical for the street.Im also a guy who considers 8 in. or better vaccum fine for power accesories on the street,but its all about the whole package and you cant have it all,there is a trade off and you will be giving up a ton of torque/driveability for a single peak horsepower number.If you really want to build a single purpose engine then port the heads,run 11to1 or better compression,big tube headers with 4.10 or lower rear gears and then you can utilize the xe284 to its full potential in a 360,or go bigger cubes to get the power in a usable range-either way big money when compared to a basic hot street 360.I say this not to discourage you but hopefully to avoid the pitfalls alot of us have encountered-everything I do is on a budget so I have to make each dollar count!.
 
well i heard i can run both cams with a stroung enough single spring
and i am getting the 4.10 gears but i would have to run 11.0 compression meaning higher octane like 96? 100? or even 91 but i still dont know if i should get it. what would be the power diff between the 2
 
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