speedtigger

iTrader: (16)

I can certainly help you pick a better camshaft, but before we go there, I want to point out that your heads could be a lot better. There is probably 40+ horsepower available just in some better heads. The other thing is that a 4 1/8 crank in a standard deck block creates a lot of rod angle and pistons that come out of the bottom of the bores when at BDC. This leads to piston rock, cylinder lubrication shear, oil control problems (oil in the combustion chamber) and accelerated piston wear. Especially in a constant high RPM application like a boat. Nitrous oxide is going to make this much worse as when the oil gets in the combustion chamber with nitrous, it induces detonation and often piston failure. I feel like you are on borrowed time already.

What is your compression ratio? What fuel are you using?

OkieDave

I appreciate the concern about the long stroke and I the associated problems but it is what I have.. I would like some better heads and if they were too pricey maybe I get them or maybe I might just port the ones I have. I haven't done the math for the compression but I suspect I'm over the limit for pump gas which is what I run. the motor does run a lot cooler in the jet boat then it does in the car so I think I can get away with a little extra compression and also I have pretty tight quench with the pistons 5 out of the hole and 41 thousands head gaskets. most of my experience is with 4 and a half inch stroke big block Fords.

speedtigger

iTrader: (16)

With the longer stroke, you will want something with more duration. With the nitrous, you will want something with more exhaust duration to get the spent gasses out better. Your intake lobe center will need to be pretty early to help feed that long stroke and yet still keep the power focussed in your 4000-6000 RPM target range. Since you have an unusual combination in a little different application, your camshaft will look a little different than most.

For a 50-200 shot I would pick a cam that looks like this: 236/246 112+6
You can order this cam from Cam Motion as this grind: XA236/365-XA246/350-112+6. For your application, I would use a good double spring like this one: http://store.cammotion.com/catalog/p...cbfba573238628

OkieDave

Thanks man! What would you think of a 108 or so with 250 duration or so and .650 or so lift?
Too much for under 6k rpm?

OkieDave

My buddy has a cam from commotion. Its xa246. 246\254. .646\.629. I think its 112 lc.
He says its a nos spec custom cam. Wants to trade for the turbo cam that I have.
Also who and how much$ for porting my 243 heads vs. Buying some better heads? Thanks.

speedtigger

iTrader: (16)

Those larger cams will start to make more power than the smaller cam that I suggested at about 5500 RPM, so if you are limited to 6,000 RPM, you will lose average power in your 4,000-6,000 range.

OkieDave

Is a 108 lc vs. a 112 better for mid range vs. Upper rpm? Same question only more vs. Less duration? And what about advancing the cam timing when install? Thanks.

speedtigger

iTrader: (16)

If you really want to understand these numbers and be able to project how the changes might affect your engine's performance, download this camshaft event calculator and start studying the 4 valve events:

http://www.cammotion.com/cam-timer.php



When people create "tighter" lobe center camshafts, typically two things happen. 1. They add more overlap. 2. They advance the intake lobe more creating earlier intake open and often earlier intake close.

Look at these two camshaft's specifications @ .050" lift.

First, the one that I suggested: 236/246 112+6
IVO 12
IVC 44
EVO 61
EVC 5
Overlap 17 degrees

Second, a same duration camshaft on a 108 ICL: 236/246 108+4
IVO 14
IVC 42
EVO 55
EVC 11
Overlap 25 degrees

IVO = Intake valve open
IVC = Intake valve close
EVO = Exhaust valve open
EVC = Exhaust valve close

If you notice, the intake centerline on the tight lobe separation camshaft is more advanced, so the IVO and IVC happen 2 degrees earlier. The exhaust centerline is more retarded, so the EVO and EVC is 6 degrees later.

On the intake side of the tight lobe separation camshaft, the earlier intake valve closes will tend to move the powerband lower and increase torque while the earlier intake valve open will tend to increase midrange and high RPM power by filling the cylinder better. However, the earlier intake valve open will also increase overlap and low speed reversion. This will make the engine idle rougher, consumer more fuel and be less efficient at engine speeds below about 3000 RPM in this case.

On the exhaust side of the tight lobe separation camshaft, the later intake valve opening will in general be better for low speed driving and idle characteristics while the later exhaust valve close will increase overlap which typically bolsters high RPM horsepower.

I might make an argument for the tight lobe center camshaft for your boat if: 1. You were not using nitrous, 2. You do not care about fuel consumption, 3. You do not care about a stronger fuel/exhuast smell during operation.

But, since you are running nitrous, the camshaft the I suggested will be more efficient on nitrous due to the earlier exhaust valve opening. This earlier EVO lets out the increased exhaust produced while using nitrous oxide which reduces pumping losses, reduces residual heat in the combustion chambers and leaves the combustion chamber cleaner for the next cycle. The earlier EVC reduces overlap which reduces the amount of the nitrous oxide that is needed to make a certain amount of additional power as overlap allows a certain amount of air and fuel and nitrous to escape out the exhaust unburned.

You can use the above calculator to play with these numbers and explore all kinds of ideas. You could even come up with your own and have it ground just to see what would happen. The suggestion that I gave you I feel is a good combination of performance characteristics for what you want your boat to do.

OkieDave

Thanks for the reply. This is the conversation I'm looking for. An old jet boat guy told me a long time ago to run a 108 lc with plenty of duration. My best na bbf was a 557 with 14-1 compression and a 108 .685lift 256 dr cam and good heads. It made 800 at 4900 and 843 @6200. Perfect jet boat motor with an impeller that held it down enough to leave room for nos. I'm trying to get an Ls motor to work as best as possible with less c.I. I don't care much about driveability since its mostly wot or idle or cruise..cruise is pretty flexible as is idle. Wot is most important and with the big impeller it means grunt from 4600 and up. Nos will help but I need to get all I can before the nos.

speedtigger

iTrader: (16)

How big of a shot of nitrous are you running? And, are you limited as to how much nitrous you can run?

OkieDave

150 so far. I think my limit will be my pistons. Would like to go 250. At 150 my AFR was 10-1. Probably could lean that a little and get more power. Its off season now so boats are down for winter. Just finished ceramic coating my headers and also my turbo exh system
off my other boat.

speedtigger

iTrader: (16)

Yeah, I would say you could lean that out a lot. LOL

You want your nitrous tune to be nearly the same as your N/A tune. Many run thiers the exact same as their N/A tune. Mine is typically 1/4-1/2 point richer.

eversmann79

iTrader: (1)

i dont know if this is the right spot for this but i have a question for the single plane guys.

Im building a 69 camaro with a 08 LY6 engine. Im going with a single plane 4150 EFI setup.
I am wondering with the heads milled .030 and .41 gaskets how much of a dog is this thing actually going to be on the street with a properly spec'd cam? The car will be a 3.73-4.10 rear gear 3500-4000 stall 90% street car.

Thank you guys, and if you can recommend a cam or cam guy please let me know.

speedtigger

iTrader: (16)

If you mill the heads .030" you are going to have to fly-cut valve reliefs in the pistons to fit any decent sized camshaft in there. If you have not milled the heads yet, don't. You can go fast with LY6 compression.

eversmann79

iTrader: (1)

i was going to flycut them anyway. i was recommended a 234/246 on a 108, but if you dont think that is needed i wont. I just dont want it to be a dog down low.

BTW nice to talk to you Tiggs, ive seen you alot around here and on YB.

Im just trying to race on a budget, i wish i could to a solid roller like you, just cant afford it or the cubes yet.

speedtigger

iTrader: (16)

If you are willing to flycut, then no problem. With a 3500-4000 stall, it will get rolling no problem as long as you don't get crazy with the camshaft.

Two choices:

This one will be all about the midrange power. I had one similar to this and it drove great with nice lope to the idle for the hotrod sound:
http://store.cammotion.com/hot-stree...reted-camshaft

If you want to be a bit more aggressive, you might go with this one. I know it says it is for cathedral port heads, but if you flycut the pistons, it will work great. It will have a bit more lope at idle and will want to rev more. Still fine with a 3500+ stall converter though.
http://store.cammotion.com/junkyard-...plane-camshaft

I have had cams similar to both of these in 6 liters and both are great. I preferred the bigger of the two, but I tend to like the more aggressive stuff.

This one is in between the two above and is great too. You could not lose with any of these 3 with your setup:
http://store.cammotion.com/junkyard-...-port-camshaft

eversmann79

iTrader: (1)

will i still need to flycut with the first cam you suggested?

speedtigger

iTrader: (16)

You should not need to flycut if you do not mill with either of these two cams below:

Hot Street Carbureted Camshaft - http://store.cammotion.com/hot-stree...reted-camshaft

Junkyard Dog "Single Plane" - Rectangle Port Camshaft - http://store.cammotion.com/junkyard-...-port-camshaft

eversmann79

iTrader: (1)

thank you so much for taking the time. HOw much am i leaving on the table do you think if i dont mill the heads and use tighter gaskets, the car will probably never see nitrous, and if it goes boosted ill build a shortblock

speedtigger

iTrader: (16)

Using the thinner gasket will decrease your piston to valve clearance too, so if you are going to try to increase compression, I would go the whole way and flycut if it were mine. Compression does make a nice difference for sure.