Author Topic: Compression for FED  (Read 423 times)

Offline nitroscott

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Compression for FED
« on: March 25, 2021, 12:13:56 PM »
Hi, I have a 350 SBC to put in my FED. The problem is that I was going to use nitro as the fuel so I bought flat top pistons. Now I am going to use alcohol. I need to raise my compression ratio for the alcohol. What is the best way to raise compression on the engine and still use the flat tops? Thank you.

Offline Paul New

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Re: Compression for FED
« Reply #1 on: March 25, 2021, 02:05:39 PM »
Easiest way is to add a blower ;D. But in all reality the only way to do it is zero deck, thin head gasket, and small combustion chambers.  Other than that new pistons

Offline JEFF/21C

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Re: Compression for FED
« Reply #2 on: March 25, 2021, 04:37:06 PM »
What heads are you using? like Paul New said zero deck, steel or aluminum rod? steel rods.035 piston to head clearance if your are running tight piston to wall clearance if you run the pistons loose the pistons will hit the heads need more because they rock, really check valve to piston clearance,and check it with the cam your are planning to run because the specs change the clearance even advancing or retarding the cam will effect it.  building for max compression you just have to be more careful

Offline masracingtd1167

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Re: Compression for FED
« Reply #3 on: March 28, 2021, 10:21:36 AM »
If you have a small cc head you should still be able to get at least 11 to 1 out of it ! When I started messing around with 20 percent nitro I went to a flat top piston to drop compression down ! To my surprise it really didn't slow down much on straight alcohol ! The best it ever ran on the higher compression straight alky was 7.24 and with the lower compression straight alky 7.32 ! If you need to make a little more power just put a little nitro 10 to 15 percent and that will wake it up !

Offline hemidakota

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Re: Compression for FED
« Reply #4 on: April 02, 2021, 09:38:16 PM »
If you have a small cc head you should still be able to get at least 11 to 1 out of it ! When I started messing around with 20 percent nitro I went to a flat top piston to drop compression down ! To my surprise it really didn't slow down much on straight alcohol ! The best it ever ran on the higher compression straight alky was 7.24 and with the lower compression straight alky 7.32 ! If you need to make a little more power just put a little nitro 10 to 15 percent and that will wake it up !
How much of a compression change and from how high of compression? Just interested, thanks
If it jams force it, if it breaks it needed replaced anyways

Offline masracingtd1167

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Re: Compression for FED
« Reply #5 on: April 03, 2021, 12:43:41 PM »
If you have a small cc head you should still be able to get at least 11 to 1 out of it ! When I started messing around with 20 percent nitro I went to a flat top piston to drop compression down ! To my surprise it really didn't slow down much on straight alcohol ! The best it ever ran on the higher compression straight alky was 7.24 and with the lower compression straight alky 7.32 ! If you need to make a little more power just put a little nitro 10 to 15 percent and that will wake it up !
How much of a compression change and from how high of compression? Just interested, thanks
      With the high compression it was 13.8 now down to 12 to 1 !

Offline wideopen231

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Re: Compression for FED
« Reply #6 on: April 06, 2021, 05:13:30 PM »
Good news is lower compression motor have huge tuning window and normally respond well the MFI, Unless you are looking to get every thing you can out of motor I would sweat a point or so on compression. Plus just allow you to run higher percentage of nitro w/o worry of detonation.
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Offline Curly1

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Re: Compression for FED
« Reply #7 on: April 09, 2021, 05:39:58 PM »
I have ran alcohol on low compression 9.4 to 1 motor and it really picked it up. Just run it on alcohol as is and if you want to add some Nitro you can. From my experience you can not run much Nitro with high compression.

As for raising compression, thinner head gaskets, smaller chamber heads or bigger dome pistons.