endeavour32

iTrader: (4)

I'm looking for some advise on valve sizes for my engine build. Its a 454 gen IV block .60 over with a 427 crank for 439 CI's. I'm planning on building up a set of bare merlin 269 ovals. Here is where the confusion starts. My cam guy suggests a valve of 2.190 and my head guy is suggesting a valve size of 2.30. The reason for suggesting the 2.19 is do to the "small bore" and not being able to take advantage of the larger valve like a 4.5 bore can. On the flip side my porter suggests 2.30 for max power? Does anyone have any suggestions on proper valve size?

picklenjim

Personally I would stay with the 2.19's on that set up. Don't know what you plan to use for exhaust but I would deffinately recommend 1.88" Inconel's.

endeavour32

iTrader: (4)

I'm going to be using a set of factory aluminum 496 manifolds. Bob Mandara is designing my cam. We were not sure if these manifolds would work so he made some calls to some engine builders familiar with them... He was told they will work fine for what we are going to do. He was told that they were tested against CMI, stainless marine, dana, gil and EMI. They are close to equal to the Gils and EMIs and only 30 hp off the best choice which I believe was the Stainless Marines. I found this shocking, to be honest. So it looks like 2 votes to stay with the 2.19/ 1.88

OutlawMan

Go with the cam guy. He is looking at actual airflow of the engine which is what the cam dictates. The head guy is simply trying to squeeze every possible CFM out of the head which is great for a drag racer that spins 6500+Rpms. In the lower Rpms that most boats run from getting out of the water to WOT velocity of airflow is also very important. Smaller the valve, the higher the velocity of the air that will enter the combustion chamber. With the correct balance of the two and the properly matched cam, at or near its most efficient rpm your motor will actually draw more air into the motor than could fit statically. i.e. more than 439CI of air will enter the motor. The faster air will also help further mix and atomize the air/fuel entering the combustion chamber.

Also going to a huge valve usually increases the mass of the valvetrain causing valvesprings to lose their closing pressure more rapidly over time.

BillK

end,
I am going to agree with the others on the smaller valves. I would also like to add to what outlaw said about head porting. You can easily go too far with it and hurt performance. Like he said, a lot of head porters want to get maximum possible flow, but this is not always the best for performance. Everything in the engine needs to be matched to cubic inch size of the engine and the intended rpm range the engine will be used in. Too much flow can hurt just as easily as not enough. Make certain that the guy doing your heads is real familiar with marine applications.

Bill Koustenis
Advanced Autommotive Machine
Waldorf Md

KAAMA

iTrader: (1)

What would you guys think about this....what if Endeavor32 wanted make this a roots supercharged application. (???)

Would the reasons given still apply with the smaller valve size, etc? Is there a trade-off between valve size/intake runner size and the port velocity/volumn with a supercharged application??? If so, where does that trade-off begin? It would be interesting to know where thoughts may be on this. Anyone with some insight on this? Thanx

Young Performance

I would still stick with the 2.19 valve even with the supercharger. He has a set of heads with a small intake runner that will not really take advantage of the larger valve. The other thing is the small bore. That larger valve will be shrouded by the small bore. I would be surprised if you saw very much increase in flow if you did both valves on a flow bench using a 4.310 bore fixture. You will also have to clearance the top of the cylinders to clear the larger valve.
Eddie

endeavour32

iTrader: (4)

First off, thanks for all the input so far! The one other thing I failed to mention is that the heads were going to have the runners ported the full length. Again, I'm after max velocity! So would the runners need to be opened up much or just rework the radius on both floor and roof (merlin 269 ovals). Opinions on this?

getrdunn

iTrader: (7)

You have to respect both which I'm sure you do Mike. It looks like I may be out numbered here however I would without a doubt listen to your head guy. The size of the larger valve will certainly dictate flow. I'm not saying bigger is always better by any means however if you truely understand velocity you would understand what he is telling you. There is a bunch of power to be made in your heads. I would think your cam guy would spec your cam given the specific flow numbers. If you do a search most of the Merlin 269's have 2.30 int. I realize that's meaningless but then again...

I happen to know your head guy and would put him up against the best of the best. Trust what he says and go with it. You won't be disapointed. If your cam guy is dead against this then you can always send him out the heads.

Good luck though!

KAAMA

iTrader: (1)

I once had a pair of oval Merlin oval port heads on a pair of 468cid engines only they had 2.30" intake valves installed....which were probably too large for the bore size...but this was back in 1994. The heads were only BOWL/POCKET ported but by what the dyno sheets read was that they (SUPPOSEDLY) made 620hp @5700rpm with some Crower solid roller cams, 1050 Holley Dominator carbs, 9.5 cr, and Dart single plane intakes....this is WITH dyno headers, and not sure about HOW they were dyno'd exactly....perhaps without pullies, etc. (???)

Anyway, I know the intake runners were NOT full length ported on these engines and those engines pushed my boat into the mid 80's with TRS drives....so, perhaps porting the runners of the Merlin oval ports for your engines would NOT be a necessary thing.

By the way, thanks for your input Eddie!!!