Comp XE275 HL 440

[Mike67]

I was wanting to get some input from some of you seasoned moparnatics.... I bought a short block last year for my 67 Coronet, .060 KB step pistons, stock stroke steel crank and it came with the XE275HL K kit (not installed). The pistons look to be .010-.015 out....the guy told me this ought to be around 10.2-10.5 cr with 906's. Does this sound right???
The heads I have, they are rebuilt & have some mild pocket porting, bee as valves & springs, locks, guides but I have not cc'ed them to verify they are 84 either... This will be a weekend street car Doug's 2" headers,Crane adjustable rockers- non roller, 727, 2800, 3.73 gears. Will this be a decent setup? What problems can I expect?
The kit it's brand new and if possible I would like to use it to avoid having to spend a bunch more $$$$$ as I am a low budget kind of guy.... Two daughters are a blessing but man are they expensive!!!
Thanks to all!

 

[cudadoug]

There is no way to know actual CR without knowing the head cc and what gasket. 906's can be up up 88cc depending on seat depth, etc.

 

[Mike67]

I was kind of worried about it and until I get them measured I was taking the guys word for it, so I figured I would probably be running a .041-.060 gasket just to be safe especiall with the step pistons. I want to run pump gas but I really don't want to leave any compression on the table if I don't have too.... I'm more curious about the cam....110, 275/287 @.05 231/237, 525/525...
Thanks

 

[lewtot184]

the step piston should be around .050+" out of the hole. the step has to match up with an open chamber head. if those are the 10.5:1 pistons then they'll make too much cylinder pressure with that cam for pump gas. try to find the exact part number for those pistons.

 

[Mike67]

The short block is assembled, minus the cam, which I plan on taking apart just to make sure the clearances are all correct... but the number is next to the wrist pin on those so I will have to get back with you when I just it apart... I've read here that the KB's have little margin of error on the gaps... I'm not running spray or any adders but I figured it would be easier/cheaper to check now than wait on a catastrophic failure...

 

[PurpleBeeper]

Lewtot is a lot smarter than I am, but honestly that sounds like a pretty good combination to me as is. If what you mean by "step pistons" is something like a TRW L2295, then you might be up around 11.5'ish compression and that's pretty high for 93-octane with a .030" head gasket. I do see that Cometic has some REALLY thick BB head gaskets, up to 0.120" so you might be able to get away with those pistons. In the old Direct Connection book, you didn't have to check piston to valve clearance until you got into the 292/509 purple cam (or larger) unless you had one of those 383's with the positive deck height ('68-'69?) + you've got valve reliefs in L2295's, so you're good for sure in that regard. FYI- my pistons are L2295's with the "step" milled off & when I clay checked piston-to-valve clearance with a 292/509 cam I had at least 1/8" clearance. Why not cc the heads, put check the piston-to-valve clearance with some clay & some old head gaskets & do a little math for your static compression ratio? I think you might be OK. If not, just clean the cam off with some carb cleaner, sell it & find one with more overlap. Just my 2-cents.

 

[lewtot184]

The short block is assembled, minus the cam, which I plan on taking apart just to make sure the clearances are all correct... but the number is next to the wrist pin on those so I will have to get back with you when I just it apart... I've read here that the KB's have little margin of error on the gaps... I'm not running spray or any adders but I figured it would be easier/cheaper to check now than wait on a catastrophic failure...

if those gaps aren't correct the piston will break up by the top ring land. it's not that big of a deal to check. there are two step pistons; kb184 9.3:1 and the kb 236 10.5:1. that cam will make a lot of cylinder pressure even with the kb184 piston. should be north of 200psi with the kb236 piston; too much for pump gas. the cam will have 4 degrees of advance ground into it but can be set back the 4 degrees to help a little on cylinder pressure. check how far the step is above the deck and measure the depth of the combustion chamber where the step fits to get the quench.

 

[Mike67]

The motor is at my father in-laws and I can't get over there until Saturday, but going off of just looks ,they look like the KB236KTM, but what doesn't make sense to me is that ,if my memory serves me, the valve reliefs are "troughed". Mancinni, Jegs & Summit only describe this on the KB184KTM & and when I look at that image the raised step looks a lot bigger that what I have...Mine have the smallish looking step that's why I think they are the 236's....as far as the cam goes I have never opened up the kit, lifters,springs , keepers &cam are all still packaged up like it was shipped....
Thanks for the help!

 

[lewtot184]

the kb 184 has .140 step, the kb 236 has a .075 step. the 184 has a 1.992 pin height and the 236 a 2.057 pin height. the piston in the pic is an earlier style 184. later pistons may have "eye brows" rather than a "trough".

 

[Garys1969RR]

You can use the United Engine and Machine C/Ratio calculator, to determine your C/R. For instance, the KB 236 piston has a 6 cc dome, then 88 cc cyl heads, .015 below deck, (not counting the dome) .020 head gasket, is going to put you at 11 to 1 C/R. At .025 below deck, your at 10.8 to 1. Going to a .040 gasket puts you at 10.3 to 1.

- - - Updated - - -

We are running a similar cam in a 383, the 274HL. And at 12.5 to 1 C/R we need to use a mix of race gas and 91 octane premium.

 

[Mike67]

Well I went by the shop this weekend to measure my compression height and was having problems with my dial indicator ( inconsistent readings). It looks like the top of the piston is anywhere from.025-.032 below the deck. The step/quench was where I really had some problems measuring, appears to be .038-.045 out...which looking at Campbell Enterprise & all things being equal if they are in fact 236's on a 85cc head should yeild 10.5cr and the 184's 9.3.... That being said with the measurement I took it does seem to add up to what the specs are saying as for them being the 236's... 236 have a .075 quench, 2.057CH and the 184's have 1.40 quench, 1.992CH so it's either my math or the measurements....1.40-.045=1.355 out?, .075-.045= .03 below deck , which is in the neighborhood of my measurements...???.... Right??? I want to thank everyone for helping out with their comments, it's really appreciated!!!!

 

[lewtot184]

you probably have a math/measurement issue. to find TDC i use a dial indicator and feeler gauges to square the piston up in the bore. then i use a depth mic to check the piston deck and quench dome heights. i'm building a kb184 engine now, third time with these pistons, and the numbers are always very close to the same as previous builds. dome being .055" out of the hole and the top of the piston .085" in the hole. your piston should be around .020"-.025" in the hole and the quench dome should be close to .055" above the deck. there will be some variance due to rod lengths and stroke variance but shouldn't be any big differences.

 

[Mike67]

Thanks lewtot, I have an assembled short block so the pistons should be square, shouldn't they? My plunger on the dial kept sticking is the reason for the variance, I don't have a depth mic and used the dial indicator to measure the deck-piston-quench.... With the measurements you have (184s) & the specs I read for the 236s (.075 quench) minus my measurement of .045 above the deck , wouldn't that give me the top of the piston at tdc (.030)? I still plan on having the heads cc'ed and checking the clearance....I'm also going to pick up a depth mic as well just to be safe. Sorry for all the questions....I guess when I get an exact cr we can discuss more about the cam.... I spoke to Comp yesterday and told them what I was doing and of course they said it was fine...thanks again!

 

[lewtot184]

the pistons are never square at TDC due to rock. they have to be squared at TDC with feeler gauges inserted between the piston and the cylinder wall. usually something like a .010" feeler slipped in between both sides of the piston and cylinder wall perpendicular to the crankshaft.

 

[Mike67]

Did not think about that, thanks!

 

[Mike67]

Reading/researching threads regarding rod bolts and haven't found the answer yet, the rotating assembly is put together as I bought it. LY rods with stock rod & cap bolts, my question is should I send it out and have the rods resized and fitted w/ arps? Or more over do I need to? Would they have to turn the crank and resize? What is a stock bolt good to hp/rpm wise?
Thanks

 

[Garys1969RR]

If it's just a mild street cruiser, the stock bolts should work fine. If you disassemble it, then you should check all the parts and clearances, plus put in new bearings and rings. You may just want to pull off 1 or 2 rod caps and a main bearing cap to check for grooves in the bearings, or oil starvation. You just never know what you have on a used motor, unless you can hear it run. Or take it apart and inspect everything. How much did you pay for this motor?

 

[Mike67]

I gave $1000 for it..supposedly a new build that sat in his shop for a few years. It had the heads on (906 w bigger valves) at one time but he pulled them off to show that it was fresh. Cylinders look like a fresh bore, no ridge or vertical marks, cam bearings are new as are freeze plugs. Came with the heads, valve train, unopened comp cam kit , lifters, springs keepers ect and a bunch of other parts.
I was planning on breaking it down just to clean it and put everything back together as it was....if the motor was only spun by hand on the stand I wouldn't think there would be a problem using the same bearings...??? The motor sat for so long and it appeared that it was covered but I have seen some dirt and the asembly lube is pretty sticky from sitting. And on top of that there is old head gasket material that needs to be cleaned off.
I'm going to ditch the 906 and buy the Sidewinders, CR should be like you said, in the 10.3 range and it will be a street car 99.9% of the time...

 

[Garys1969RR]

Well if it's a new build, all the parts should be re usable. The best way is to disassemble the motor, check clearances, clean and re assemble. Use all the correct torque specs. I have always used factory specs. Stock rod bolts should be OK if you don't go past 5500 RPM. If it's going to see severe duty, use high strength aftermarket rod bolts.

 

[Garys1969RR]

First thing we need to know is exactly what piston you are using. From there we can determine the best head gasket thickness, and head cc. Also you will want to have about .040" clearance between the step head on the piston, and the flat area of the cyl head. This will give you the ideal squish effect, which makes the mixture burn more quickly and evenly, reduces the likelihood of pre ignition, and detonation. Plus it improves throttle response. I use .037" squish clearance in my 451 at 13 to 1 C/R, 509 cam, at 5600 feet. And 98 octane fuel keeps it from pinging. Soon as you hit the throttle it takes off immediately, at any RPM above 1500. Runs low 12s. Build proper squish in your motor and you will love the results.