Big CFM 914 Heads In U.S.A.

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cal 67
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Re: Big CFM 914 Heads In U.S.A.

Post by cal 67 » Mon May 29, 2017 4:57 pm

Ok. Well I know the 75% rule: exhaust should flow around 75% of the intake. Intake cross section for a street engine should be no more than 85% of the intake valve size.

Yes, a D-port should be used on the short side. I was also thinking the chamber wall nearest the short side should be more shrouded than the other sections of the wall.

cal 67
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Re: Big CFM 914 Heads In U.S.A.

Post by cal 67 » Mon May 29, 2017 5:28 pm

Here's the new AA heads. They're currently out of stock. They made a small batch, and sold out quickly. The verdict is still out with the people that have them.

European added the guides and seats in these.
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cal 67
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Re: Big CFM 914 Heads In U.S.A.

Post by cal 67 » Mon May 29, 2017 5:35 pm

Some more pics of what's been done. Going slowly. I have some CB connecting rods showing up this week.
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Piledriver
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Re: Big CFM 914 Heads In U.S.A.

Post by Piledriver » Mon May 29, 2017 9:43 pm

:twisted:

How's the material around the intake ports? Same as stock or added some?
cal 67 wrote:
Mon May 29, 2017 4:57 pm
Ok. Well I know the 75% rule: exhaust should flow around 75% of the intake. Intake cross section for a street engine should be no more than 85% of the intake valve size.

Yes, a D-port should be used on the short side. I was also thinking the chamber wall nearest the short side should be more shrouded than the other sections of the wall.
I am personally a bit dubious on that classic I/E ratio rule of thumb at least...

Pro Stock heads typically run at 60% or less I/E, and Larry Widmer insists an oversized exhaust port (even port matching to the exhaust) absolutely destroys low end>midrange Tq. Mind, these ports support supersonic flow, and have a very carefully developed cross sectional area progression. Might be possible on T4 exhausts with a D port, plus the added material might help prevent the ex seats sinking into the port.

His PS SCJ 429 head exhaust ports were about the exit diameter of a stock T1, if that.(largest cross sectional area)
The intakes you could probably stick your whole hand in.

I realize we aren't building unlimited Pro Stock monster motors but it's still a fine example of something.
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Re: Big CFM 914 Heads In U.S.A.

Post by wreck » Tue May 30, 2017 3:02 am

http://www.shoptalkforums.com/download/ ... w&id=19279

I'm building a similar combination ,except using a 78mm AA crank and Deutz cylinders machined down to suit 103mm JE pistons , the same rods . Using a pair of 48mm trijet dellortos .

I've gone with 47mm inlet and 40 exhausts ,When I researched the inlet /exhaust ratio I realised most of the info is for water-cooled engines that have a cylinder head temp of under 100C , our air-cooled heads run 60% hotter , so I figured that the higher temp would lead to a higher volume of exhaust gas for the same volume of intake gas . If you look at aircooled Porsches , they run around the 85% ratio .Also all the high po after market type 1 heads all have a ratio over 85% . I'm guessing that some scavenging is promoted to help cool the heads .
I'd be interested what the guy from CB comes up with .
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Re: Big CFM 914 Heads In U.S.A.

Post by cal 67 » Tue May 30, 2017 2:48 pm

Wow! Those Deutz cylinders are nice! Piledriver, they appear to be exact replicas. When I called, the representative responsible for having these heads made told me they didn't change anything other than the exhaust guide size.

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Re: Big CFM 914 Heads In U.S.A.

Post by Piledriver » Tue May 30, 2017 11:32 pm

They look pretty good.
There's a couple spots they could have added material so welding wasn't needed for bigger valves, or make the deck a little thicker, but any source of decent stock 2L castings is welcome. They are already a huge win as the chambers and plug location are right without welding.

To get "2L" heads from AMC castings, the mods probably costs more $$$$ than the Chinese 2L heads outright due to extensive welding and machining.

How much did they go for?
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Re: Big CFM 914 Heads In U.S.A.

Post by trapnm » Wed May 31, 2017 4:07 am

Pm sent pile. Prices so low they're inssaaaaannnnne.

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Re: Big CFM 914 Heads In U.S.A.

Post by Piledriver » Wed May 31, 2017 1:29 pm

Whoa.... I think I see some new heads in my future.
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wreck
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Re: Big CFM 914 Heads In U.S.A.

Post by wreck » Wed May 31, 2017 4:55 pm

How much and when are they going to be available ?
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cal 67
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Re: Big CFM 914 Heads In U.S.A.

Post by cal 67 » Wed May 31, 2017 9:59 pm

2-3 months, $225- $250 each.

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Re: Big CFM 914 Heads In U.S.A.

Post by trapnm » Wed May 31, 2017 11:41 pm

279 was the retail quote. That's for a bare head. They sell them complete typically. They were supposed to be in this week but maybe a delay. I'll contact them tomorrow.

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Re: Big CFM 914 Heads In U.S.A.

Post by Piledriver » Thu Jun 01, 2017 2:19 am

How much are they getting for seats/guides etc?

The valves/guides/seats etc all cost the same as T1, and the machining required is ~no different...
Porting will still cost, but a pass in a CNC mill and the rest shouldn't push ~`a $K/pair, finished, if that.
No welding etc required on these AAs as they appear to be a good 2L 914 copy.

Certain places that charge ~4X std rates for run-of-the-mill T4 headwork should be driven out of business:
They're not that freaking special.
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wreck
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Re: Big CFM 914 Heads In U.S.A.

Post by wreck » Thu Jun 01, 2017 3:16 am

Murphies law , just getting a pair of new AMC's finally finished with bigs valves etc and something better pops up . I may still get a pair to put on the shelf .
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Re: Big CFM 914 Heads In U.S.A.

Post by Piledriver » Thu Jun 01, 2017 12:30 pm

The jury's still out on "better", but they should cost significantly less, and have zero welding.
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