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Author Topic:   13:1 with flat tops possible? 355 sbc
nice_guy_wi
Dirt Maniac

Total posts: 120
posted January 28, 2005 09:48 PM  
Is it possible to get to 13:1 compression in a 355 with flat tops? We have a good set of Vortec heads that would be used.

[This message has been edited by nice_guy_wi (edited January 28, 2005).]

racin78p
Dirt Freak

Total posts: 333
posted January 29, 2005 12:25 AM  
Small chamber heads, the thickness of your head gaskets, after market flat tops (I don't know about OEM) and you can get more than that. I'm not sure of the exact chamber sizes, pistons, ect. to use, but I have modified buddies who do get well over 13 to 1 with this set up (they run alky). Race on.

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racin78p
if it ain't fun, then don't run

2nd2none
Dirt Forum Champ
Total posts: 755
posted January 29, 2005 06:42 AM  
its possible to get 15:1 with a flat top. You just have to spend about $2000 having the heads milled.

BCracing
Dirt Full Roller

Total posts: 32
posted January 29, 2005 09:41 AM  
you can get Dart Iron Eagle heads that are 49cc which with flat top pistons should come out to right around 13 to 1

racin78p
Dirt Freak

Total posts: 333
posted January 29, 2005 02:58 PM  
Talked with a local engine builder that puts together the flat top motors with Pro heads, for some mod guys around here; wouldn't give all the details (job security) but he's getting 15 to 1 + comp, running alky as I posted before. I checked on this just to make sure I wasn't leading you astray. Good luck! Race on.

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racin78p
if it ain't fun, then don't run

[This message has been edited by racin78p (edited January 29, 2005).]

sledgehammer
Dirt Forum Racer

Total posts: 94
posted January 29, 2005 06:08 PM  
With a two valve relief piston 15 to 1 would require about a 42 cc camber on the head, is that even possible?

Somebody have an answer?

B36
Dirt Roller

Total posts: 20
posted January 29, 2005 06:11 PM  
38 is possible if you got the cash!!!!!!!

nice_guy_wi
Dirt Maniac

Total posts: 120
posted January 29, 2005 07:16 PM  
We have to use OEM heads. Of which we are running Vortecs now. Anyone know if the Vortecs can safely be milled to the 49cc ballpark? We also have to run either pump gas or race fuel. And from reading off here most race fuels are good to about 13:1 so that is why 13:1 is the goal. Does that sound about right as well?

sdhnc29
Dirt Forum Champ
Total posts: 934
posted January 29, 2005 09:38 PM  
sledgehammer,

Yes it's no problem. We take the 64cc Iron Eagles and angle mill them .385". Of course this is quite labor intensive, and it gets expensive. Once the head's are angle milled this far, the intake and exhaust face angle need's to be corrected, the head bolt holes in the cylinder head's need to be corrected, and the head bolt holes need to be spot faced. If there is any core shift in the casting's at all, then some will need to have the head bolt holes between the intake runner's sleeved.

As B36 stated, 38cc is most common. But we do have some down to 35-36cc using larger diameter titanium valves that have been cut down to 2.055". This of course gives us a thick valve and help's get rid of cc's.

Custom pistons will also be in order for this combination to work correctly, if you are running a roller of high lift flat tappet cam. If using a lower lift cam, you can usually get away with correcting the valve pockets in shelf stock pistons.

We have been doing this procedure to Iron Eagles for many year's now, and I HATE it!! I really wish these lame promoters would get a clue and stop trying to save racer's money with their flat top piston rules!!!! In my opinion, this does nothing but further the gap between the "haves" and "have-nots". The first promoter to actually make sensible rule's that are enforced equally, might actually make thing's affordable for everyone.

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

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