gt-40 heads and performance

Yeah 79 is right the old ones are more simpel,and boat dr is also right about the outboard settings.how would know were to start to recalibate,how could tell what the idel is?but if you want this one for a test - my email is-MADDMARXX@AOL.COM    #321-231-6041

teleflex should have a rotary dial @ 4 oclock at the rear.yours should be set to 8c/4p=8cyl. or 4 pole[outboard]. the new tachs do have a calibration screw located @ about 10 oclock,but you have to have a "master or known to be correct" tach to adjust yours to.........tachs are cheap insurance for your motor.plan on spending 100.00 for a good one or bite the bullit and buy quality,Gaffrig or Auto Meter.....boat dr

What could the tack be set to, to make it run low? 10?

Anything but 8 would read too high.

Let me investigate!

STANG -this one has a swich on the back for 2-4-6-8 did you check to see if yours is on the 8? I dont think you can recalibrate.

You can have it,just pay the shipping its a black VDO.

Stang-I have an extra tach if you need one, its never been used, its out of an 85.

Yeah...it has to be...with the federal 13x13 before the 540...same thing low rpms...it sounds like it's rappin out pretty well.It's an old tach.

It does run pretty strong...I'm trying to reach close to the 50 mark with it with out major machine work...that would be pretty good for a 302!
I figure the rpms should be closer to   4400-4500 at that speed .I think I will put on another tach and see.

Soaked foam was removed everywhere..but it was not heavily soaked...once I got started, I just got it all out...even up under the bow.

That's pretty consistent with what Ive seen. With stock sized props, both 1:1 and 1.23:1 boats seem to run pretty close on RPM vs. MPH. You can see some differences due to hull efficiency though. Once you start changing prop sizes, that can skew everything as well. Before my mods, for example, I was seeing 43MPH @ 4600RPM.

Boat Dr, I see that Cam Research did your cam- I have been impressed with mine. Did you have to source them the reverse rotation blank? When I ordered from them they said they could not get them.

46 is no slouch for a 302 in a Ski Nautique, thats for sure. Strange that it was faster before though... Where was the soaked foam? Ive noticed that we can pick up a solid MPH by putting a few people in the back seat.

I bet that the heads, intake and a full tank of gas will get you there!

Oh, and I would say its a pretty good bet that your tach is off. With a new 540 and 46MPH on GPS, 4k RPM doesnt make much sense.    

Tim,

On the gps...I am seeing 46mph...tach reads 4000 and is most likely off a bit(original tach 1972).
Hole shot is great and midrange too...0-40 is fast, but top end is not there like I want it! 49- 50mph for a 302 in a SN would be nice! Funny thing is...in the fall last year right after I brought it home, it was hitting 47 and that was before I removed 300lbs of soaked foam and drained two year old gas out???
I also switched to an EI ign...reset timing. I think the carb can be fine tuned a bit as well as minor timing tweeking.That with the head and intake should get me there!
Or just go out and find some old gas!

Great info and thanks! I am keeping things somewhat simple...swap heads and intake!If I pick up 2-3 mph it's a success!Low end and mid now are strong.

Actually, the chart shows flow from .100 to .600 of lift. I agree that a race motor that turns high RPM is not comparable to our boat motors that generally turn 5k max. However, I dont think that low end torque is the most important factor on our motors either- I think its all about the midrange power. The cam I chose for my boat makes power from 2500-5200 and it works great. Holeshot is much stronger than stock, and the midrange power is terrific- a great ski boat motor. Since I get 3k+ RPM out of the hole, I dont see the need to make huge amounts of power below that point. The 400+ RPM I picked up on the top end can be attributed to the higher flowing heads and intake (and the cam that can support them).

How many RPM do you turn with your new setup?

I agree that the slight increase in CR helps- but I dont think its the biggest factor. The GT40's outflow the stock heads all across the board by a pretty significant amount. I would think that the better breathing is what allows you to pick up several hundred RPM at the top end.

To see a good side-by-side comparison, check out the Ford head flow chart here: http://www.allfordmustangs.com/Detailed/630.shtml