340 STREET COMPRESSION

[GRUP]

HI FOLKS! I BOUGHT AN AAR 4 MONTHS AGO. IT CAME WITH A REBUILT NON MATCHING T/A ENGINE, COMPLETE WITH THE 915 U HEADS. IT RAN WELL, BUT HAD NO BOTTOM END. I REPLACED THE 312 DURATION CAM. WITH A HUGHES ENGINE HE 3644 AS 509/533/236/244 SOLID LIFTER CAM. WHILE THE ENGINE WAS APART, IHAD A LITTLE LOOK AROUND. TRW FLAT TOP PISTONS. .030 BORE AND BALANCE. HEADS HAVE NEW 3 ANGLE VALVE JOB BUT NO PORTING. I CC'D THE HEADS, 63 CC. THE PISTONS ARE FLUSH WITH THE TOP OF THE BLOCK. A QUICK CALCULATION WORKED OUT TO BE 11 TO 1 COMPRESSION. A COMPRESSION TEST - 170-180 PSI. QUESTION? DO YOU THINK I CAN RUN THIS SETUP ON THE STREET WITH 92 OCTANE AND A LEAD ADDITIVE OUT OF A BOTTLE? (UAP/NAPA SELLS THE LEAD ADDITIVE). ALSO NOTICED THAT THE ROD BOLTS LOOK STOCK. I LIKE TO USE THE ARP BOLTS ON A REBUILD. DO YOU THINK THE STOCK BOLTS ARE FINE FOR STREET USE. WHAT KIND OF HORSEPOWER DO YOU THINK THIS COMBO WILL MAKE. (STOCK INTAKE, EXH, CARBS, ELEC. IGN. 727 TRANNY, 3000 TCI CONV. 8 3/4" 3:91
LIM. SLIP. THANKS FOR YOUR CONSIDERATION
G.C

[HOLESHOT]

THINK YOU'LL BE OK BUT SUGGEST YOU MAKE SURE DISTRIBUTER ADVANCE CURVE IS NOT TOO FAST AND START WITH MODERATE TIMING LEAD (32 TOTAL) ABOUT 4-6 btdc AND GO UP 2 DEGREES AT A TIME .KEEP A CLOSE EAR OUT FOR ANY DETENATION.MAY NEED TO LOOK A YOUR CARD JETTING BUT SOUNDS LIKE A NICE CAR.GOOD LUCK

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[70 charger R/T]

11 to 1 on 92 Octane, I don't think so. but possible, not a good idea though.
But with a thick head gasket to knock it down to 10.5 to 1 sure. I run 92 on 10.5 to 1
Shouldn't need lead additive though.
Should have hardened valve seat by now.
My .02 worth

[GRUP]

I MODIFIED THE STOCK ELECTRONIC DIST. TO HAVE 22 DEG. MECH. ADVANCE, SO WITH 12 OR 13 INITIAL ADVANCE IT SHOULD COME TO AROUND 33 OR 34 TOTAL. I REMOVED ONE OF THE STOCK LIGHT SPRINGS. I GUESS IM WONDERING IF ANYONE HAS USED THE UAP/NAPA LEAD ADDITIVE (OR LEAD ADDITIVES IN GENERAL)AND WHAT IMPROVEMENT IT'LL GIVE TO 92 OCTANE. I'D ALSO LIKE TO SAY I, LIVE IN NEWFOUNDLAND , CANADA. ITS A GREAT PLACE BUT VERY ISOLATED(AND 6 MONTHS WINTER) AND OPTIONS ARE FEW(92 IS HIGHEST) NO ACCESS TO RACING FUEL. THANKS FOR THE AIR TIME!

[HOLESHOT]

GRUP,SUGGEST YOU SAVE YOUR BUCKS ON THE ADDITIVE AS MOST TEST HAVE SHOWN LITTLE IF ANY GAIN IN THE RM NUMBERS FOR OCTANE.I FEEL YOU WILL BE BETTER OFF WITH 13 IN DISTRIBUTER FOR A TOTAL OF 26 MECH. DEGREES BY 3400 ENGINE RPM WITH 8-10 ON THE CRANK.CAR SHOULD REV A LITTLE EASIER WITH LESS LEAD, SO LESS LIKELY TO PING.
ALBERTA ,BOY

[rumblefish360]

At 11.0-1 ,thats to high to run 92. You could run 92 if your retard the distributor back REAL far. Then power would go down alot!!! What you could, and I've done it with ease, is to use the Mopar head shim with a Fel-pro gasket @ about.039 compresed thickness. Total with the .060 head shim would be .099 thick.
That will take a bite out of the high ratio. Then you'll be closer to a point down & run 92 octane with a good start & total advance on the distributor.
The job is easy to do.
As far as the rod bolt, get new HI-PO units. It's cheap ins. Skip the lead & do the heads with the inserts. This price is more up front but, less hassle every time you gas up & over time the constent pay out for the lead additive that adds no H.P.

[Dart]

I have a set of the MOPAR head shims (.060)for the 340. I bought them for my 360 and didn't need them. They are new and still in the original packaging. I would be happy to send them up to you for what I bought them for. I think around $35 US, you pay shipping.

This would lower your compression enough to run pump gas. You could also use the mopar thin head gasket with the shim (shim .060" + P4120094 .024") instead of the Fel Pro .040".

[Dart]

Sorry, I didn't give you my email address:

Blake.Blewitt@valleylab.com

[shannon]

You may want to refigure your compression ratio. 10:5 to 1 340's came with pistons that were .019 out of the block. If there flush with the block, I bet its not over 9:5 to 1 with 63cc chambers.

[PRO]

GRUP,like shannon said your 340 piston should come out of the block approx .020 for a 10:1 comp with a .020 head gasket also your heads will be 65cc unless theyve been milled,the real prob here is 170-180 lbs of comp with a 312* cam!!!or was it with the hughes? either way with iron heads 155 lbs is max with 93 octane.Add what you like but its ALL junk to me,if you cant add a couple gallons of 112 octane to a tankful then lower your comp.Stock rod bolts are fine but if theyre 30 yrs old....get new ones,if your going to do that buy ARP.As far as HP it all depends but you should be capable of 13.5 ets fairly easily but w/o headers you wont go too much faster than that....PRO...

[Hemi Mike]

I put together a 360 for a hot but daily driven M-body. One of my main concerns was the compression ratio. I ended up using the MP 9:1 LA360 shortblock. MP tech told me that they came up with that 9:1 using 69cc heads and a .040 gasket. The flat top pistons were down like .015 in the hole so all looked good. I used stage I heads from Hughes Engines which measured 65cc's and swapped in their 223/230@.050 cam. My cylinder cranking pressure is up around 180. Way more than I wanted. I run 14* initial and 36* total timing with a tight vacuum advance. I must use 93 octane and there is no sign of detonation. Power is awsome and I think the CR has a lot to do with it.

BTW At first I was using Hughes 214/224@.050 cam but detonation WAS a problem, so I swapped in their 223/230 to bleed off some psi.

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Stoplight action in a street fightin' '85 M-body 360ci. or '68 Hemi GTX 4spd.

[rumblefish360]

Shannon;

Kieth black offers a zero deck piston thats suposed to be 9.8-1 with a 72cc head. They also list that @ 62cc it's 10.9-1.

[GRUP]

FOLKS:
I RECALCULATED THE COMPRESSION RATIO, AND CAME UP WITH 10.86 : 1. (WITH FLUSH FLAT TOPS, 63 CC HEAD, AND .040 H.G.). IM CALCULATING THIS OUT BY HAND, NOT USING A COMPUTER PROGRAM, SO IM WONDERING IF IM DOING SOMETHING WRONG. I MEASURED THE HEADS MYSELF WITH A PIECE OF GLASS AND A BURRETTE, 63 CC, AND THE HEAD GASKET IS THE .038 FELPRO PIECE. USING A STRAITEDGE AND A FEELER GAUGE, I CHECKED THE PISTON HEIGHT. THE PISTON TOUCHES THE STRAIGHTEDGE@ TDC. I'D APPRECIATE, THE INFO GIVEN IF, ONE OF YOU FINE PEOPLE, COULD PUNCH IN THE NUMBERS EITHER BY HAND OR THROUGH A SOFTWARE PROGRAM AND TELL ME WHAT C.R. YOU COME UP WITH. THE COMPRESSION TEST WAS DONE WITH THE HUGHES ENGINES CAM, WHICH I THINK( DONT HAVE THE NUMBERS WITH ME NOW) IS 236/244 @ .050.
THANKS

[GRUP]

I GUESS I SHOULD ALSO SAY WHAT MY INTENTIONS ARE. I PLAN ON USING THE TRANS AM ENGINE FOR A YEAR OR TWO. IN THE MEAN TIME, I PLAN ON BUILDING UP A 340 BLOCK/ 360 CRANK 375 C.I. ENGINE WITH HUGHES STAGE 1 HEADS AND THAT HUGHES CAM. THIS ENGINE WILL BE BUILT RIGHT. IN THE MEAN TIME I WANTED TO RUN THE T/A ENGINE ON THE STREET FOR A COUPLE YEARS WITHOUT INVESTING ALOT OF GREEN IN IT. IT WOULD HAVE BEEN GREAT IF I COULD HAVE USED A LEAD ADDITIVE TO SOLVE MY HIGH COMPRESSION/NON HARDENED VALVE SEAT PROBLEMS, BUT IT'S OBVIOUS THE CONCENSUS GAS ADDITIVES ARE JUNK. I'LL AVOID THEM!
THANKS G.C

[72Challenger]

10.925 CR with a 0 deck height, 0 piston volume, .038 gasket, 4.070 bore and 344.5 cubic inches, per the computer.