Moparts Tech Archive
Big Block
"Default 500hp" (525hp) BB combo??
im freshening up a street/strip type 446 for a customer, and it will be on the dyno early next week.the bottom end was done several years ago, but was in pretty good shape overall.
all im doing to it is clean, hone, rings, bearings, etc.
it had bowl ported big valve 906's, but one was cracked, and they needed hardened seats...so the decision was made to just put some E heads on it now.
it had a MP509 cam, but a few lobes were starting to show excessive wear, so a new mild solid cam is going to be replacing it.
the motor already had TRW L2295's in it, and a Milodon low profile pan, Crane Gold 1.6 rockers, and he is running Hooker Competition headers(which are going to need a few extra dents put in them for the angled plugs on the new heads).
he was running a std Performer with an 850DP carb, but the intake is getting replaced with a Holley SD, and the carb is getting overhauled.
the single bolt Cloyes True timing set was still nice and tight, but since it was the one bolt variety, i wanted to use a cam with pretty smooth valve action. also, with the 1.6 rockers, i wanted to make sure it would work with the as supplied Edelbrock springs.
the heads also recieved "stage I" type prep and the one port i tested was 292/210 @ .550 lift.
the pistons are down the hole .050, and the heads are 84.5cc, which works out to 10.1:1 compression with a std Fel-Pro blue gasket.
the cam selected is an off the shelf Comp street solid, grind number 294S.
the catalog specs are 294/294@.020, 248/248@.050, 110lsa, and .525 lift(with 1.5's).
the cam card shows 250/250@.050, and i'll be checking the actual measurements later today.
i told the cutomer it should make around 525hp on pump gas, and that the torque should be better than the HP(im thinking around 535ft/lbs).
i'll post more info as i have it....and the motor should be on the dyno by Tuesday.
cam has been degreed in, and checked for size.
a correction of my original post about the advertised duration of the 294S cam.
on the Magnum street solids, the advertised duration is rated at .015, not .020, but i did take a reading there so its easier to compare the cam to other cams where the duration is taken at .020.
duration @ :
.015-298
.020-287
.050-251
.100-213.5
.150-183
.200-155
.250-125
lobe lift-.354(1.5=.531, 1.6=.566)
installed dot to dot, it came right in at 106 intake c/l.
Andy, we've run these cams in several motors and have had pretty good luck with them.
maybe that particular combo just wasnt a good match for this cam.
we'll see how this one works out.
a few notes:
-the E heads did require clearancing for the 1.6 rockers
-the off the shelf Crane pushrods will work, but are really too short by about 2-3 threads on the adjuster.
IMO, this overall combo would be a better package if it were built around a zero deck, flat top short block that utilized lighter pistons.
as for the intake, IMO the Holley SD is a perfect match for this combo, and will fit nicely under the hood.
a low deck 451 would certainly be similar.
the difference in bobweight/rotaing weight makes almost no difference on the dyno where the acceleration rate is held constant, but it should/might make a difference in the car.
Jim, im sure the customer will be happier if the motor makes your HP estimtate rather than mine, but 540hp from this mild combo would be pretty good.
the high lift area of the cam isnt like the typical cams most guys are running these days, although that will be made up for to some degree by the 1.6 rockers.
my guess is with the 1 7/8 headers and mild high lift area of the cam, the VE numbers will fall off too early in the RPM band to allow the motor to make the "big" HP numbers.
however, i'll admit that when i quote a HP guesstimate to a customer, i try to lean towards the conservative side.
if you say 525hp, and it makes 540...everyone is happy.
if you say 540hp, and it makes 525....everyone is less happy.
TRW L2295F 1067g 2.029" dome piston
TRW L2355F 872g 2.061" 4 valve reliefs
TRW L2266F 876g 1.991" no valve reliefs
the piston weights for the 2355 and 2266 are shown without the pin. the 2295 weight is with the pin.
they all weigh about the same with the pin.
the 2295 piston is actually about 25g lighter than a std piston.
they use a 25g heavier pin to offset the difference in piston weight so they could theoretically be used without rebalancing the crank.
all the std replacement 383/440 pistons use a 225g pin. the 2295 and 2293(383 domed piston) use a 250g pin.
typical weights for .030 over bore in my piston catalog are:
440's-
2266-876
2295-825
2355-872
2388-819(loooooow compression piston, C/H-1.926)
383's-
2315-786
2293-765
note:
the 2293 and 2388 are no longer in the newest catalog
there is also a new addition to the 440 line up, a "LW2355", which is a coated "light weight" version of the 2355. for a .030 over bore its 818g, uses a 1/16, 1/16, 3/16 ring pack, and can use either pressed or floating pins.
the catalog doesnt indicate what the pin weight is.
i checked the actual "loaded" rocker ratio today.
most Crane Golds seem to run about .05 over the advertised ratio, and these were no exception.
lift with "0" lash was .580, which works out to a RR of 1.638:1 with a lobe lift of .354.
lash is going to be around .022 hot, so the net lift will be just about .560.
tomorrow the tin goes on, and a coat of paint. then i just need some spark plugs, oil, filter, etc...and it'll be ready for the dyno.
i would think clearancing the pushrod tunnels would likely be necessary with any 3/8" pushrod and a 1.6 rocker arm.
the motor is basically done, just need to install the damper and pulleys.
today i recurved the MP distributor, and overhauled the 1984 vintage 850DP carb.
not sure if i'll dyno it tomorrow or Wednesday(customer is in no hurry for it).
I havent used the Comp Cams .525"/253 deg. shaft but have heard of its poor street manners
my guess is youre referring to the 305H hydraulic cam.
in the motors ive run the 294S cam in previously, its had better low speed engine characteristics than the MP509 cam.
the MP509 cam has an actual advertised duration(duration @.006) of around 305 degrees(not 292), and a 108lsa.
the 2deg wider lsa of the 294S cam, and the loss of 7deg of seat timing(305 vs 298), results in a decrease in actual overlap of 11 degrees compared to the MP509 cam.
also, the Comp Magnum series street solid lifter lobe designs are able to be run with a wide range of lash settings(.015-.030) to further taylor the cam to a specific combination.
And then the MP .528 is 284 on 112 so it is 10 degrees less duration and spread apart 2 more degrees. Same lift though so it is a more agressive grind (same lift less duration) than the Comp grind.
I've switched them back and forth and find the MP .528 to be a lot friendlier on the street than the Comp. 294S I haven't done back to back dyno runs or 1/4 times. I have run the MP .528 on the dyno a fair bit and it easily makes 525 hp with the box stock E heads in a zero deck 10:1 motor.
more aggressive? maybe, maybe not.284deg duration @ what lift?
actual duration @ .050?, .200?
MP's cam specs dont tell enough about the cam to determine which one is more or less aggressive. it would need to be put in a motor(or checked on a "cam doctor" type machine) and measured.
NONE of the MP cams ive checked have ever had the duration numbers work out with any industry standard checking point.
its going to have to be closer to spec than the 590 or 620 cams ive checked to actually be .528 lift too.
590 cam actual lobe lift= .389(.5835 w/1.5)
620 cam actual lobe lift= .410(.6150 w/1.5)
Comp 294S cam actual lobe lift= .354(.5310 w/1.5)
since the Magnum series cams are pretty much the slowest grinds Comp offers, it is likely that the MP528 is more aggressive.
however, my guess is the reason it seems more streetable is because its just smaller(the motor sees it as smaller).
if its actually 28deg smaller than its bigger brother 590 cam(284 vs 312), then it should be around 242 @ .050, since the 590 cam is 270 @ .050.
Numbers I have on the MP .528 solid are 243 duration at 0.050 and 152 @ 0.200.
From the little digging I did on a project a while back, I deduced that the MP cams were ground around a Ford lifter diameter (.875) which is why they are a tad bit more agressive than the Chevy grinds (294S is a Chevy grind if I recall my Comp Catalog numbers correctly).
I suppose that the MP guys weren't willing to go all the way to a .904 grind back in the day when the MP cams were first designed but they were willing to get a little bit agressive.
well...its been on and off the dyno twice now.the motor has a chronic rear main seal leak(actually, "leak" doesnt quite describe it....its just running right out).
i pulled it off the dyno, pulled the pan and seal, found nothing wrong....installed a new one....still leaks.
and its REALLY leaking. its just getting pumped right out.
its so bad that the first time i thought i had to have screwed up and installed one half in backwards.
got a few pulls in before it got too messy...enough to play with the lash and timing a little.
at this point, its:
532TQ @ 4400
521HP @ 5900
i dont expect it to get much better than this...maybe a few hp/tq.
at this point its going to have to come apart so the seal surface of the crank can be measured as well as the diameter of the recess where the seal sits.
the second time i just ran it long enough to see it start to really leak, but didnt make any pulls.
i wanted to be able to see just where it was coming from when i got it off the dyno.
its leaking right from the seal. the only thing thats wet on the back of the motor right now(after being all cleaned up before putting it back on the dyno) is a little trail running right down the rear seal cap.
ive never had BB Mopar leak at the rear seal before, and this is a huge leak...twice...so something is not right back there.
its got too much oil pressure(just over 100psi), and while im sure that isnt helping the leak...it shouldnt be causing it either.
i have a customer with a 493 that runs 100psi all the time....no leaks.
i reused his old HV pump, and even took two coils off the spring after i saw it had so much pressure...and it still had over 90psi, so im going to install a std volume pump on it.
getting the pressure down to 65ish, and reducing the amount of oil flying around should free up a couple of HP.
well, i finally got around to re-testing the 446 street motor that
had the big rear seal leak.
i have to admit that after 3 tries at it, it still has a little drip coming
from it once in a while.
my feeling at this point is the rear seal channel and the main line
must not be concentric with each other.
without pulling the whole motor down, theres no way of knowing
for sure....but ive done all im going to do on my dime.
ive never had one leak before....and this one leaks after 3 tries at
fixing it, so something out of the ordinary is going on.
anyway, i was able to do some testing on it and have a few numbers.
the timing seemed best at 35-36deg, and the lash ended up at .026 hot.
all testing was done with Citgo 93 octane pump unleaded.
all tests were done using the customers Hooker 1 7/8 X 3 Competition headers.
for those who didnt see the first post, the basic combo is:
440 +.030, TRW 2295's .050 down the hole, E heads with stage I prep, Holley SD intake, 850DP Holley carb, Comp 294S cam, in at 106, Crane 1.6 Rockers.
A-Holley 850DP on 1" 4-hole spacer
B-Holley 850DP on 1" open spacer
C-HP950 on 1" open spacer
D-HP950 on 2" "Super Sucker" spacer
TQ/HP
rpm------A--------B--------C--------D
3500--436/291--440/293--437/292--446/297
3600--447/306--452/310--450/308--451/309
3700--468/329--469/330--466/328--469/331
3800--503/364--507/366--509/368--511/370
3900--509/378--515/382--517/384--519/385
4000--516/393--518/395--524/399--526/401
4100--522/407--526/411--528/412--529/413
4200--529/423--526/421--528/422--535/428
4300--524/429--528/432--536/439--535/438
4400--531/445--531/445--533/446--540/452
4500--527/452--532/456--537/460--539/462
4600--529/463--528/462--533/467--537/470
4700--527/471--527/471--532/476--537/481
4800--522/477--525/479--529/483--532/486
4900--518/483--519/484--524/489--531/496
5000--513/489--516/491--520/495--523/498
5100--513/498--514/499--521/505--522/507
5200--506/501--509/504--515/510--521/516
5300--499/504--502/506--511/516--512/517
5400--497/511--497/511--501/515--504/518
5500--486/509--491/514--497/520--498/522
5600--481/513--487/519--487/519--491/524
5700--479/519--477/518--484/526--484/526
5800--471/520--471/520--477/527--480/531
5900--464/521--467/525--468/526--475/533
6000--452/517--456/520--457/524--462/527
6100--443/514--446/518--450/523--448/520
6200--432/511--437/515--437/515--439/519
i made a few pulls to 6500 and it wasnt showing any signs of valve float with this cam, the 1.6 rockers(measured 1.65), and the E head springs.
power was still solidly 500+ hp at that rpm.
i'll be running another similar combo in the next few weeks only with flat top pistons, HS 1.5 rockers, and a more aggressive cam profile that has more high lift area.
the heads also have the same stage I prep, and the intake is also the Holley SD.
the customer is getting TTI 2" headers, which may or may not fit the dyno.
if they dont, i will use the dyno headers, which have a 4" collector(which is a bit too big to make big tq numbers below the tq peak).
that combo "should" be in the 550hp range.
Tech Index