will this run on pump gas ?

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AdamR

AdamR

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Im planning a 360 build for the Duster down the road. Must be street friendly pump gas motor. Stock 73 340 intake and Thermoquad, Stock 340 exhaust manifolds. I will be running a 904 with a low 2.77:1 first gear and either 3.23s or 3.55s with a 26-27" tall tire.

My plan is

360
KB107s
Scat I beams
RHS Heads, 62CC chambers
Crower 271HDP
ADVERTISED CAMSHAFT SPECIFICATIONS:
INTAKE: Duration: 271º Lift: .485
EXHAUST: Duration: 284º Lift: .495


INTAKE Opens: 3.0 BTDC
Closes: 39.0 ABDC
EXHAUST Opens: 53.0 BBDC
Closes: 1.0 ATDC

LOBE SEPERATION 112º

Duration at .050" Intake: 222
Exhaust: 234
LOBE LIFT Intake: .323
Exhaust: .330

I ran the numbers through the compression calculator on KBs site and came up with 10.88:1 static and 9.32:1 Dynamic.
 
Nope. My limits for pump swill and an iron head with quench is a dynamic of 8.5:1. Dynamic will go up as the efficiency goes up with rpm. So you need a little room to account for that or you'll find yourself with detonation issues. I'd have the chambers enlarged by 2-3ccs when they are put together, and look at cams that have another 10 degrees on the intake and exh sides. Another though would be to go with a dished forged piston which allows for the use of a decent quench and lowers the static and dynamic.
The KBs were developed before the rise of the closed chamber heads. So they really are best for an open chamber head. With the costs of RHS, it might be similar or less to have a set of LA heads done well and forget using quench because they'll make similar power ( a little less overall but you're not looking for huge HP numbers) and you can run pump fuel with them. Using LA heads at 70ccs and the 107s gives you 9.9:1 static and 8.4:1 with that Crower cam. It's still a little high but you can always just run a slightly thicker gasket.
 
Thanks Dave, Maybe I will just stick with a set of LA heads then. Should I consider a different cam ? May be then one up ?
 
Its the KB107 that will be the issue,I know a few around here that have pinging problems,if your good with the dizzy you can dial it in,around here they don't seam to get the program lol.
 
No it's not going to run on pump.

Not enough cam duration to bleed off the static number. That's going to need a cam in the 240 at .050 to get it low enough unless you want a total timing number in the mid 20's.

Unless someone has cut rhs heads to 62 cc's, they have been showing up with chambers in the 68cc range most of the time, IIRC. Brian may be able to answer that better.

I agree with Dave, open the chamber up to get your static down and put a bigger cam in it.

Brian built a couple of 360's with RHS heads and XE275HL cam that run on pump gas. Don't recall the particulars but I'm sure they were KB107's.

Here' it is.
Stock 360 block .040 over
stock rods with arp bolts and resized
KB 107's
balanced
IMM RHS heads, no porting
comp is 10:1
comp 275HL cam on 112 lca advanced 2°
stock pan
PRW 1.6 rockers
rpm airgap
Holley 750DP
1" open spacer
TTI 1 5/8 step headers

425ish HP 440TQ
 
Thanks Rob, I got the chamber volume off of Hughes Engines site. If they are actually at 68ccs that would put me at 10:1 static and 8.7 dynamic
 
If I can get the RHS heads to 68cc and go with the next cam up that will get me to 8.5:1 static

INT/EXH - Dur @ .050” Lift: 227°/237° RR: 1.5/1.5 Gross Lift: .480”/.503” LSA: 112° RPM: 1800 to 6000 Redline: 6500

Cometic has a head gasket with a 4.040 bore that is .060" but they are $123ea

Or I can just do some LA heads. This is also all assuming the 107s are at zero deck
 
AdamR said:
Thanks Rob, I got the chamber volume off of Hughes Engines site. If they are actually at 68ccs that would put me at 10:1 static and 8.7 dynamic
Click to expand...

Most of the 340/360 heads that I've cc'ed have been 70 cc.
 
I don't buy into the add 15* to the .050 numbers like KB suggest.


107's and stock heads = no quench.

ENTER YOUR DATA CALCULATED DATA
Cylinder Head Volume (cc) 65 Cylinder Head Vol (cubic in.) 3.965
Piston Head Volume (cc) 5 Piston Head Vol (cubic in.) 0.305
Gasket Thickness (in.) .040 Swept Volume (cubic in.) 45.892
Gasket Bore (in.) 4.10 T.D.C. Volume (cubic in.) 4.798
Cylinder Bore Diameter (in.) 4.04 Gasket Volume (cubic in.) 0.528
Deck Clearance (in.)Note: Neg. nubmer above deck, Pos. number below deck 0 Deck Volume (cubic in.) 0.000
Stroke (in.) 3.58
STATIC COMPRESSION RATIO 10.565

OPTIONAL DATA
Rod Length (in.) 6.123 Adjusted Stroke (in.) 2.814
Intake Closing Point (degrees)ABDC @ 0.050 lift plus 15 degrees 63

DYNAMIC EFFECTIVE COMPRESSION RATIO 8.518
 
crackedback said:
I don't buy into the add 15* to the .050 numbers like KB suggest.
Click to expand...

They do that in order to be able to get a figure off the base circle without being too concerned with the various take up ramp designs... There isn't really any difference in using the .050 numbers, but you have to make sure whatever you're basing the final decision on is based off that same set of numbers because the dynamic ratio you calculate will be much different than one based on "base circle" calculations. I always use the KB site, so my experience is based on those figures.
 
I'd go with the RHS and open them up to 68cc and do it on the intake valve side to help unshroud the valve.
 
With lowering it to 10.1 it would be VERY temperamental at 190 something psi, close the int in the 40's and u can get into that 175-185 psi range. Jmo good luck bud.
 
I didn't mean take it all out of the intake side but use the opportunity to do some unshrouding the intake valve.
 
Just a thought based on experience, I know a closed chamber shrouds quite a bit, curious what the effect would be with this particular port and how much u could get away with.
 
Dusterguy said:
My kb107 was ~0.020" above deck..
Click to expand...

I normally run flat tops proud of the bore too - especially when I'm building with a dished piston and closed chamber. So there's another option for the open head version. But as I said - it does noting but gain static compression - which is already a problem.
 
Adam. Your going to need to know exactly where the piston sits in the block. I have has 2 engines with the KB-107's and they both came in at different spots. 1@ zero, 1@ .010
Moped has told me that most (if not all IIRC) of his 107's were below deck on stock blocks.

Of course you all ready mentioned thicker head gaskets and opening the head up. InJUST start on the short block set up and the. From there, we can see exactly what you got. Unless you have a machinist blue print it all out. Block, crank, rods.
 
I will be running 91 octane with 8.8ish DCR, but I will have a cam of 251 Int and 260 Ex @50 and 10.18 compression. Its a setup Brian did for another customer possibly Mad Dart, but not 100. Your ABDC is too low, I think with magnum heads a DCR around 8.5 is good like others have said maybe even 8.7 like DGC33 runs with his setup
 
Im certainly not going to run a cam that large. I can always run the dushed KB pistons.
 
I ran into the same problem building my 360. I am using kb107's with 62cc heads. I just ordered custom cometec gaskets to match the compression I wanted. I can't remember the exact thickness, I think they are around .098. They are EXPENSIVE though. I think I paid around 180.00 for each one:(
 
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