G'day everyone

Ive just scored a wrecked 08 Dyna. The damage isnt that bad, just a bit of paint and a few bits on the bars etc and it'll be all good. Im new to the forum, but have always enjoyed a lurk every now and then. Thru the search function ive started to learn about corrected compression ratios and stuff which is all interesting.

 

I thought about building this engine using S&S gear. 106 kit, 89cc heads and maybe 625 cams. Punched all the numbers into big boyz and it came up with a very low corrected compression. Changed it to 82cc and got around the 9.2. This is a good number for a street engine hey??

 

Is it normal to have to reduce the cc by so much? And how many thou would you mill off to get it? I know there are other brands of cam and head porters etc but ive used S&S gear before and a friend of a friend in the states can send it over at a good price.

 

Thanks in advance for any help, and if im totally on the wrong track, let me know. Ill be doing the work, which ive done before, but not this performance level. I just wanna have a bit of fun, then ill probably get rid of it and but something older again.

I would say your not that far off.

The 106 should have enough torque to carry the lower compression.
The 625 should be OK anywhere from 10:1 to 11:1 static.
Toss around some numbers using the 79cc super stock heads with a .040 gasket.
Maybe less hassle than trying to mod the 89cc heads.
That's if you want to stay with S&S.

go 107 with bored stock/seasoned barrels and run the 625s at no less that 10.8/1 with ported stock heads

Like Ando says, the 625s need at least 10.8:1 compression. S&S 585 or maybe their new 635s maybe a better choise. Get the cams with the EZ start feature. - Rob

I kinda put the cart before the horse and ordered the bits before asking the experts and didnt want to embarass myself......im old and impatient.

So can the 89cc heads be milled down to 82cc, which should give the 10.8 comp, with 9.2 corrected. I have ordered the ezy starts, and i went with the 89cc over the 79 because they have the bigger valves.

I want something a bit angry and thought the 625 would be good. Maybe next time i will go for some different brands, but for now im gonna have to make this work.

One thing i havent thought too much of is the intake. is the SE 58mm throttle body the may to go?

Go 55mm HP I TB with 1.8 intake runners and 4.9 injectors
Gets a domed piston . Leave heads as is

Thanks Ando. Where do i get HP I throttle body?

Who does a domes 106 piston? Cant find any in S&S catalogue. Will a different piston mess with the piston to cylinder clearance if the S&S vbarrels are honed to suit their pistons?

If you want angry, that cam in a 106 ain't going to do it. A lot more compression would be needed, requiring a big chunk off the head surface to achieve the compression needed for what you want/need. As Ando recommends, domed pistons would be better in this case. 55mm throttle body is a good recommendation also, 58mm is a bit big. - Rob

M & M Cycles for the HPI 55mm TB

HPI told me you only need bigger injectors if your engine needs more fuel. I am using the stock injectors with the HPI 55m TB and the engine seems to be getting enough fuel. Ando is in a better position than me to make that call.

Only my 2 bobs worth but the guy putting my 106 together recommended the 50 mm SE and taking out the bigger injectors and putting back in the stock injectors ... has the 79 cc heads with 585 cams .

His reasoning is the 58 is way to big for every day ride ability and by taking out the bigger injectors it makes it far easier to tune and stay in tune if that makes sense ... bit early yet to put on Dyno but seat of the pants so far is very nice indeed .

Has shown me figures for very simular build and he was getting 120 to 123 Hp and from memory torque was up around 115 to 118 ... I`ll have to check that last figure ... compression is in the 10.5 to 1 area .

All I know it feels bloody good but it is nice to know it`s getting the best all round performance after getting it Dynoed down the line .

Thanks speedzter, thats what i wanted to hear. i figured it must be workable. the S&S 79cc heads are probably decked 89cc heads? either way, ill make it work. ive done plenty of piston to vlave, valve to valve and deck height checks on v8's and evos and shovels before. Ill keep yas posted when i get it sorted.

The woods and tman cams seem very popular on this forum. Are they big horsepower cams only, or do they do bolt-ins too? probably drop a set of cams in the young blokes 96cu softail slim soon.

keep ya heads as is and run. If not what ya want look at different cam better suited to comp, on sell the 625s or keep them for future upgrade

Time to update I spose. Been on an trip down a river with the cook over seas. Dispite what everyone said, I did it any way......sorry to those who gave advise, but it all worked out ok.

When the parts turned up it turned out to be S&S new 107 kit. These had CP pistons with the cool new locks on the piston pin. Wasn't a easy as the video whith my old hands. The pistons also had a little dome on them, so the machinist didn't have to take as much off the heads. Told him to make it 10.8:1, and he did. Don't know what he took off them.

Its all run in. Did heat cycles like I read on here which ive never really done, and used assembly lube on rings which is new toi me too. Starts and runs mint. Changed oil at 50km and 500. Goes good, pretty happy. done about 2000 now and another oil change. May be using a bit of oil. Was down to bottom of the scale when I changed oil. Maybe still bedding in or are these big motors prone to using a bit. Plugs are spotless and no oil in intake to speak of. Oh well, keep an eye on that one.