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Raising CR on L28 worth the effort?


Guest Anonymous

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Guest norm[T12SDSUD]

Increasing your compression ratio from 8.3:1 to 10:1 will give you a solid 6-7% power increase across the board without changing ANY other variable except maybe a slightly richer mixture to avoid detoantion.

 

There are no drawbacks to increased compression except the possibility of detonation and the requirement to always run 93 octane..

 

You will get more torque and HP across the rpm band and BETTER gas mileage as well.

 

My 11.6:1 motors always broke ringlands when in 3rd gear above 5500 rpm under hard acceleration. The 11.3 CR motor lasted 3 months before racing it on a hot day under load in 3rd gear above 5500 rpm.

 

My 10.6:1 CR motor performed flawlessly for three years and is performing well again at that CR level.

 

As long as you do not exceed 11:1 and you have an aggressive cam with a slightly rich mixture you should be just fine with cast pistons.

 

BTW, a higher rod to stroke ratio of 1.8:1 to 1.9:1 has been proven to defeat detonation.

 

HOT ROD magazine built a Ford and Chevy V8 with 1.9:1 rod to stroke ratio and ran 87 OCTANE with NO pinging!!

 

 

later

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yo2001, there's the rub...you know you could make more power if you advanced the timing more with the open chamber or lower rod/stroke engines...but you can't because of detonation. I'm limited to the stock cam in the autocross car (F54/N42) and this really brings out detonation tendencies. The car is quick but I know it would be faster if I could advance the timing (faster, that is, until the ring lands are fractured or there is a hole in a piston).

 

The rod/stroke ratio of the LD28/N42 has the potential to be higher because of the huge 46.5mm comp. ht. Every decrease made in comp.ht due to piston selection allows a longer rod and thereby an increase in rod/stroke. The choice of L28 piston (38.1mm) and 148.6mm rod (Z22E) makes for a readily available and economic (compared to buying custom pistons) combination yielding 148.6/83 rod/stroke. If r/s is the key to minimizing pinging, then a combination like this should allow use of any type head with a stock cam. DAW

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  • 5 years later...

alright guys....i hate to bring up an old thread but was reading this one and ive looked....i wanted to know the set up on norms 11-6-1 motor....im going all motor...and i have a 78 with a fairly stock motor...i need to check timing but other than that everything runs great. i went to the 1/8 mile track and not being able to launch (even with a burnout on street tires) i pulled a 9.9 second pass at 72mph spinning a little off the line, my friend in a honda hatch (gsr motor) on slicks went 8.9 @76 and on street tires were pretty damn even from a dig till 80+. i was pretty happy, but i want an all motor setup and got a line on some 40 over flat top FORGED pistons....and was wondering what cam would be best (im looking at msa's ofcouse cause theyre only $600 a kit (cam,lifters, springs,etc) and wondered what grind you guys find best im looking at the stage 3 or 4. and im going to have a slight port and polish done to my head along with bigger valves and hardened seats (machine shop is determining size) but what could i safely get to with premium (93oct) cause im wanting 11-1 or higher, oh and ill be on megasquirt standalone also and ofcourse bottom end will be balanced and rods shot peened

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