03-09-2009, 01:01 PM #1
After Market Head Question for my 98 XPL
I'm looking to buy some new after market heads for 98 XPL and i heard Rossier and Miller are good, but what should i look for as in CC and stuff, im looking to get more speed. is one will 47 cc good?
Thanks for the help
03-09-2009, 03:15 PM #2
They are all pretty much the same.. Miller and Buckshots are the same mold, then there is rossier and ADA.
I ran a miller and ADA heads on our XPL's.. Both were fine. The domes for the ADA's are cheaper though. 47cc's are fine, 50+/-cc is stock...
A head is no going to give you more speed, it will bump your compression and allow the motor to HIT harder, giving you more holeshot. Going with too agressive of a dome will actually decrease your speed, but give you a HELLUVA hard hit from idle..
We are going to have one of our ADA heads with (I think) 48cc domes for sale here in a few days.
PM if interested..
03-09-2009, 07:26 PM #3
thanks man, i know that it doesn't produce more speed but i want to get a skat trak 13/21 impeller and some say that the prop might put to much pressure on the engine and fuck it up so i wanted to get an after market head just for the prop so i can get more compression so i don't mess up the engine
03-09-2009, 10:04 PM #4
i got an ada with 50cc domes. +15 in compression. just got a new oring set for it but never put it on my ski since im selling it. the head has like 10 hours max on it. practically new. ill let it go for 150+shipping.
03-09-2009, 10:16 PM #5
can you guys tell me the difference from ada 48 cc compared to the ada 50 cc?
03-10-2009, 07:20 AM #6
I have an ADA head on my XPL.
The comp with 48cc domes was 155. With 50cc domes it is 150.
Engines will vary somewhat and comp readings will vary based on time on the rings, altitude, weather, battery, starter, ect.
IMO, an aftermarket head gives you better cooling and tighter squish without having the head machined. Tighter squish can give you more pull on top while the compression, as Dan said, gives you a harder hit on the bottom. But, tighter squish requires higher octane as it can deto in the squish band, even if the overall comp is not too high. This is a BAD situation, trust me.
To do what you want, pull a more agressive prop on top, you would be better served by porting the cylinder or running a pipe (or pipes, if you are adventurous).
In the end, I went with a thicker base gasket to put my squish in the .070 range and the 50cc domes to ensure that I would be safe on 93 octane. I can pull a stock prop to the rev limiter and run it WOT all day long if I want. It has run 63 with just a splash of gas in the tank and that is enough for me.
A running ski is more valuable than a fast ski that needs constant wrenching and applications of cash. At least to me. The Speed God has gotten all the sacrifices it will get from me.
03-10-2009, 09:12 AM #7
so would the 48 cc be better then the 50 cc because it has more compression
03-10-2009, 12:01 PM #8
It would generate more compression.
Better? That is up to you.
Higher comp is higher stress load. The higher the stress load, the shorter the engine life and the greater the catastrophe when something lets go.
As long as you understand, and can afford, the price of failure, you can enjoy the fruits of modification.
I suppose I should have also stated that there was no discernable difference in performance between the 48cc domes and the 50cc domes. Sure, the comp was higher, but you could not tell it while riding the boat.
03-10-2009, 06:15 PM #9
Ok you say there is no difference really in riding but what will help if i buy a skat trak impeller to turn properly?
03-10-2009, 07:18 PM #10
Probably not. As Dan said, higher comp will not increase your top end RPM and can in fact reduce it (the very thing you are hoping to avoid).
They are telling you that the more aggressive prop may overload your engine. You will see this as a drop in RPM at WOT. Comp does not help you much at WOT. Porting the cylinder and a performance pipe DO help WOT.
In the end, just what do you hope to gain by running that prop? More speed? Well, in that case you will need an engine that can pull it on top (pipe, port, rev limiter, water injection). Better hole shot? Higher comp, tighter squish, timing adjustment.
Keep in mind, all of these things stress the engine and even running race gas may not save it if the conditions are right.
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