GT-40 Heads

[Gehenna]

Does anyone have any recommendations on replacing heads on a 97 GT-40 with a high performance/after market version?

[DavidF]

RE: GT-40 Heads

I really do not think you will gain much as the heads on your engine are already considered high performance heads. If you do change them out, I will buy yours at a reasonable price. New sets of GT40p heads can be found for $450.00.

[Gehenna]

That's good to know. I think we have either a blown head gasket or cracked head. I was thinking about just swapping them both out with something that could get me a few more horse but I wasn't sure if there could be much gained from that.

[bobchris]

there are better heads than the gt-40's everyones all hung up on them and thinks there isn't anything better and that just not true, if it was all of the sportsman racers would be using them instead of the Air Flow Research brand heads. another option is to find some D0OE heads and have the valves increased and a mild port and polish job and they'll perform better as well.

[Mikeski]

Bobchris,

Sportsman racer are interested in power at different RPM ranges than we ask of our boats. Big valves and polish work great over 5k RPM but we don't go there. Pushing the wet exhaust through the transom is handled quite well by the GT-40 heads.

He might see minimal gains with a set of Trick Flow RV biased heads or equiv, but since SkiDim has new GT-40s for on sale I would just stick with them.

[bobchris]

Well I guess if your engine doesn't turn 5K you may have an issue, I don't have that problem and actually I have mine proped to turn 5500 rpm, now if I use a 13x14 it will turn 6K+ not real sure the tach only goes to 6k.

Bigger valves work better with high rpm, but there are other issues besides valve size, like runner length or volume, and the combustion chamber's size, and the quality of the casting it's self.


Even if you stuck with the stock size valves (1.94 int or 1.84 forget exactly / 1.54 ext). which already are quit large, The ARF's will perform much better than the stock GT-40 heads. You really should look into things a little more because you are not very knowledgable about ford heads and the stock valve sizes and comparing apples to apples and when you do that the ARF's are a much better choice for late model engines.

Now if you where trying to use 2.02 int and 1.60 ext then that might be a little over kill with a stock engine, which you would have to notch the pistons to use anyway and are not a direct bolt on, That would be a waste of money.

[ag4ever]

I gotta agree with Mike. I usually run about 2300 rpm most of the time. At that RPM, the GT-40 heads would be just about as good as any other head. If I was running at 5500 RPM all day, beside having to tow a fuel barge with me, I would be worn out from all the pounding I am taking. Even a slalom skier would only be looking at 3500 RPM. That is getting closer to the range where the head would show the additional power, but do you really need the additional power at that level? By that time your up on plane, and the skier is not dragging thru the water, but skimming over it. Where you really need the power is from idle to about 2500 RPM. For that you want long runners with average area. That will keep the fuel mixture velocity up and help produce torque which is what you need in a ski boat.

It appears you think a ski boat is the same as a drag car or even a "stock car", it is not. Those you need high rpm horsepower, and a boat thrives on raw grunting torque down low.

[bobchris]

I'm well aware that torque is the name of the game for a ski boat and the differences betwwen what to use for drag racing and what to use for a boat, sorry your stuff is all stock and you don't every pull barefooter's

[97sport]

Gehenna, You never did say why or what the problem is with your old heads. The GT40 are probably the best. Yes you can get aftermarket ones but it would be hard to beat the GT's. Was there a winter storage/cracking problem?

[core-rider]

Okay, first of all, if your using your boat for sking, wakeboarding, etc. you need more torque in the lower rpm's which means smaller diameter ports and longer runners like the GT-40 heads and intake offer.

Going with a bigger runner and valve size in the heads is going to be almost useless without matching the intake ports size to the head port size. (Air/fuel has to go through the intake to get to the heads) In doing this your going to gain overall airflow, but loose velocity which is what helps create torque.

Now if your looking for top end performance and are not worried about low end then the AFR's would be a pretty good choice. But that being said, you would also need to either port the intake runners to match the heads or go with another intake better matched to them. Also, you might need to change the camshaft depending on the overall combination. Then you have to look at your exhaust manifolds... The combustion gases have to get out somehow, and all that extra air is going to hit a wall at the mainfolds. Basically your creating the snowball effect. To really take advantage of the one part you want to change, you will have to make many other changes.

Another thing... Someone mentioned eariler about using the GT-40P heads. I'm not sure if they would work because that head design moved the sparkplug location a fair amount and gave many car guys problems with clearance for headers. Since our manifolds swing up and not down like most cars do this may not be an issue, but definately something you need to look into before making a purchase. The spark plug change is really the only difference which just un-shrouded the electrode some to give just a few more HP. It won't really be enough for you to notice. On the upside, you might see more improved gas consumption, but not much.

All in all, if your looking to use you boat for the purpose it was originally designed, I would say get the heads rebuilt (assuming they are not cracked) and put them back on. If you really want to gain a little performance, when getting the heads redone, get a good 3 of 7 angle valve job, and have the machine shop clean up any casting flash adn smooth out the bowls a little bit.

Hope this may help you out some.

[bobchris]

you mean your not already using an aftermarket intake and exhaust manifolds on you engine? upgraded the ignition system, replaced the cam and balanced your motors?

[core-rider]

Actually I have done all that, plus I added a twin turbo setup feeding into a water to air intercooler, and finally a 6-71 blower. It helped out a little bit... Still not satisfied though. 8-)

[bobchris]

a blower with turbo's, never seen that before and doubt I ever will.

[core-rider]

You need to take a look at diesel technology over the past 100 years. Nearly every big diesel engine has both power adders. It hasn't been used so much with gasoline engines, but I have seen a few.

The purpose is for the blower to provide low end torque and then the turbo provides top end horsepower. That way you have the best of both worlds for heavy loads like bigger boats, trucks and even generators.

For someone that seems to think they know enough about heads to recomend AFR's or DO0e's, I would think you wouldn't be so close minded to think that a blower/turbo combination could not exist.

But I digress, Gehenna, I think I answered your question well enough and I don't want to take this thread off on another topic. Use the information I have provided wisely young Skywalker.

[DRAGON88]

Lancia experimented with hybird turbo/superchargers back in the group B rally days. It's not really all that uncommon technology.

As corerider also said it's not all that uncommon on diesel motors either.