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D3 head questions

3K views 11 replies 6 participants last post by  rmcomprandy 
#1 ·
I am putting together a 521 for my jet boat. It had D3 heads on it originally, with the exhaust valves upgraded to 1.725 exhaust valves and not much else.
I realize these are probably the worst heads I could start with, but I will probably run them one year and go to alum.
The question is: Are there any substantial gains to be made by porting these? Does the Mad Porter's guide to head porting cover these heads?
Or should I just bolt a piece of chain to them and use them for an anchor?
The engine probably won't see 5000 rpm's, gonna be around 9:1 compression.
Input on rocker arm suggestions and cam suggestions (flat tappet) would also be appreciated.
I am leaning toward a Stealth intake and an 850 Holley for the intake side, it has log type wet exhaust on it.
She is a pretty heavy boat, not looking to build a racer out of it, but more power is always nice!
Thanks for the help!
Tim
 
#2 · (Edited)
I have a set of ported D3VEs on my jet boat and it goes 85 mph gps. And I know a guy who has run ported D3VEs on several 557 jet boat engines. They may not be on top of the food chain but once ported they have can certainly their place.

A 28cc dished piston will net you about 9:1 compression ratio. If you shave the heads to abut 91 ccs you might get 9.25. Definintely don't go any lower than 9:1 as it will cost significant power--keep in mind that if your boat uses an open cooling system then you can get away with more compression on pump gas since the typical jet boat engine operates with a water temp of 140*-160* F. Consider a 22cc dished piston (9.4:1) if you can find one.

The D3 heads respond very well to porting and The Mad Porter's site is very effective for D3VE heads. There are other things to consider such as valve guide height and maximum amount of cam with the OEM valve train. The Stealth and 850 are good for now, even if the engine may run better with a larger carburetor but we don't know the exact application of the engine yet. Such a build as you are describing could be a reliable and economical cruiser boat build.

Paul
 
#3 ·
Where did you ever get that wrong idea that a D3 head was not a very good head...? Those heads are just as good as any other non CJ regular port head, (other than the D2OE-AB P.I. offerings), if high compression ratio is not required.

In my opinion ... the Stealth is the wrong manifold for what you wish to do. I'd use a Torquer II.
 
#5 ·
I guess I assumed that since they were smog era heads, they would be lacking in performance.
Thanks for the input on the Torquer 2. It has a Torker 460 on it now. Is there enough difference to warrant the upgrade?
Any thoughts on cam or rocker selection? I will have the rotating assy here next week, and will drop the whole mess off at the machine shop. The valvetrain is the next batch of stuff to order. I will gladly support the vendors on the forum.
Thanks for the help!
 
#7 ·
If you are going to use hydraulic lifters then converting to studs is almost useless, (sometimes even a detriment), and cost more money to boot.
I would recommend the Ford Racing Performance Parts rocker arms #M'6564-C351 or Scorpion equivalents.

The "Torquer 460" is a low performance MILEAGE type manifold and is completely different than a "Torquer II".
 
#10 ·
Pay very close attention to the advice given in this thread...

Properly ported D3's even with just 2.11" intakes / 1.65" exhaust valves will support enough HP to take an A impellor to 5400 rpm with just a 460. A 557 will do even better.

For a juice cam the stock rockers are fine until you near the larger cams which require dual springs with more than 330 pounds open. I would then graduate to a bolt down roller rocker as suggested elsewhere.

In oem form they are pretty miserable. Well ported they perform amazingly well...

Oh an Lem is too right. jet boat / Torquer 2 / match made in heaven...


:D
 
#11 ·
I appreciate the advice more than you know.
I had been looking at the Scorpion rockers, I just didn't know if that was the route to go.
I have 3 different impellers here I can try once I get the engine done. I have an A, an AA, and a 4A (long story). I also have a diverter to go on it.
So, what is the magic behind matching the engine to the impeller? With the previous engine, it would top out at 4700 with an A impeller. MPH unknown.
Thanks again!
Tim
 
#12 ·
Matching the impeller will depend upon how much you actually already know.

When you go immediately to wide open throttle the RPM should go slightly above the peak torque of the engine ... that will get you close.
 
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