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Old 05-28-2018, 10:40 PM   #1
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What is the best compression ratio for nitrous use?

This is where I am at, I have 9:1 forged je pistons. I want a decent run around off the juice too. Im not going crazy on spray but, on occasion I might run up to 100 shot. I have a few options for higher compression. One that seems to have people get mad at is, svt head. I like this option for the valve terrain and size of cam and valves.
I could also have the head milled.
Ive heard detonation is an issue with the zetec head. I havent heard anything on the svt head.
So, nitrous guys and gals, whats your thoughts?


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Old 05-29-2018, 08:29 PM   #2
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I never saw anyone get mad about adding the SVT head , My opinion is it isnt worth the hassle of adding SVT Head only to have about the same performance

Add cams to your Zetec and end up with the same performance

Do you have a SVT Header on now ?

The SVT head is just as prone to spk knock / detonation as the Zetec

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Old 05-30-2018, 01:18 AM   #3
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Old 05-30-2018, 11:46 AM   #4
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I do have cams and the svt header now. The compression and bigger valves have to be a better starting point. Even you, Tom, say the zetec needs more compression. This is one of those things that doesnt make sense to me. Id rather port a head than do 1mm over valves, shave the head and port it.
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Old 05-30-2018, 12:29 PM   #5
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Perfect time to ask a question here and Tom the guy likely to know.

The question being, when Ford made the SVT valves bigger, did they open the pocket ID directly under the valves the same amount?

The reason I ask is that many engines will put bigger valves in a head but NOT increase the pocket ID whatsoever, it being a bragging rights thing and done on the cheap, AND then the bigger valves having no pocket ID increase actually LOWER head flow as the bigger edge becomes an impediment to flow being it is too far out. Having a matching seat is not the only thing there to consider.
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Old 05-30-2018, 10:21 PM   #6
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I would love an answer like that. Just stating it doesnt work is kinda upsetting. Numbers all look better. I'd love to understand why the superior numbers wont be beneficial.
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Old 05-31-2018, 09:22 AM   #7
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Yes the complete SVT Intake runner is bigger then the Zetec head from Valve seat to where the intake bolts on
Everyone thinks because the SVT is 170hp vs the Zetec 130 that its all in the head and it isnt
Higher compression
SVT header / larger Exh
SVT larger Cams
These 3 things is where most of the HP/TQ gains for the SVT comes from

If you have a Zetec head with Cams and a SVT header and bigger Exh already then surface the head you have and get the compression to about 10.5 and let it go , good time to add bigger cams why head is off , if you add the SVT head now you might gain 8-10 hp to the wheels about the same thing you will gain going to 10.5 compression with your head

If your not going to 11.5-12+ Compression , 3 inch Exh , custom intake , larger TB , 95-105+ octane all the time then use your Zetec head and keep it simple with about the same results

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