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Safe Compression Ratio


Guest Stoker3.0Z

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Guest Stoker3.0Z

I have been reading alot about the differant rod/piston/gasket/head combos you can use to gain compression for the strokers. With the 280Z rods and 280ZX Flat tops you can get 10.6:1 compression with a 2mm gasket and 1mm mill on the pistons. But is this safe to use on the street as a reliable caburated car on pump gas? Or should I go with 240z rods with the 720 pistons and keep it around 9.5:1? My mechanic told me that the differance between 9.5:1 and 10.5:1 is only 4% HP gain, I'm not sure that is worth it to have a possibly unreliable car for only 8-12 HP.....whats your opinion?

 

Mike

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Guest Stoker3.0Z
Check this link......

 

http://zhome.com/rnt/L28conversion/3031FAQ.html

 

LARRY

 

I read all that, thats where I got my info from..but I was wondering what a good streetable ratio is...all that says is how much compression you get from what set-ups. I was wondering what a good compression ratio I could have to use pump gas and have a reliable car.

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well, you can easily run 10.5:1 on the street, of course you would want to run pump gas, but what your mechanic was telling you about only a 4% increase is false. The good thing about raising the cr is that you can get the most out of a big cam. If you put a big cam on a low cr motor, it will lower the dynamic cr too much by bleeding off pressure in overlap and actualy hinder performance. The increase you will see by switching to a higher cr and larger cam will be alot more than 4%. If you just do one or the other you won't see such a noticeable increase. I am running 10.3:1 on my engine and just use premium, and with the stock cam, and 2580lb I ran 14.8s in the 1/4. Obviously the compression did something over the stock 16s 1/4 of the 280z.

 

you won't start getting unreliable until higher than 10.5:1. that is the highest you can run on premium on these engines. That is the general sentiment on this board.

-Oliver

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Guest Stoker3.0Z
you won't start getting unreliable until higher than 10.5:1. that is the highest you can run on premium on these engines. That is the general sentiment on this board.

-Oliver

 

 

With Diesel Crank from the maxima 280Z rods and 280ZX Flat top pistons the compression ratio is 10.6:1 with 2mm gasket and pistons milled 1mm. Is 10.6 pushing the limits of pump gas or is that close enough to 10.5:1 to be "safe"? I don't want to worry about ping every time I drive the car and would like it to be fairly reliable and not give me problems every other day.

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good tuning will get you around the ping issue. Other things you can do to make it more reliable is to use a header (duh) to keep the gasses flowing and smooth the combustion chamber, like spark plug threads that aren't needed, stuff like that.

Check out the detonation post in misc. tech I recently revived. It has alot of good info.

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Guest iskone

My setup nets 11.7-1

 

N42 Block

240 rods

5cc Domed pistons 1mm over

.080 shaved Early E88 with 45cc chambers (I think)

278* .580/.580 108 cam

1mm MHG

 

I run pump gas (92) without any problems. Chamber design and a big cam are the keys.

 

Isk

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