BBC Valve Size
 

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?

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.

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

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.

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

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

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

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?

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!

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!!! :)

I agree that all of the assembled merlin heads have 2.30intakes, bare castings are 2.19". I also agree that the guy I'm talking to about porting is one of the best. On the same hand so is the cam guy! :readinghelp: So I need to call and make sure he knows this is for a 439. Bob's thought in this was that there would be to much shrouding in the bore with the bigger valve. He said he has never seen any improvement on a dyno with that big a valve on a 4.31 bore. Maybe with bore notching that would resolve some of the issues here. I'm not bashing anyones opinion on any of this, I just am a firm believer in getting other opinions before I make a decision. I really hate spending money on stuff I don't need. Also PM me your e-mail so I can send you the info we talked about.

If I remember correctly those 468's I once had DID have the cylinder bores notched....and I am a firm believer in that! I have always liked getting other opinions too....but sometimes it can become a bit confusing. And spending good money after bad is something I never liked either. I wish you the best with you project...and have FUN! Mark

I see the dilema your in. Good thing your doing the assm. or you'd with out a doubt have a 3rd opinion. LOL.....

lol- Tell me about it! Sometimes it's a can of worms that you shouldn't open.

Performance is in the Details
 

If you already own a good set of 2.19" valves, stay with them and don't just hog out those intake ports. do most of the work in porting at the bowls and throat of the valve.
If you've got to buy new SS valves you could also use 2.25" because they are the most popular size and can be usually purchased at less cost per valve. You won't need 2.30" on those heads and it will be difficult to blend bowls and have good transitions into the chamber and pretty good shrouding of the valve on that bore size.
Have the head rework person keep the bowl throats at 87% of valve diameter and use a good 4-5 angle valve seat and throat job. This is where your velocity and power will come from with those Merlin Oval Ports. Also have a 20degree back cut made on the intake valve to improve the low lift flow numbers. Big flow numbers on a flow bench are not the last word in marine engine performance, the really productive work is in the little details! Bob knows his cams and he knows that bigger is not usually better in these type of engines, he won't steer you wrong!

Best Regards,
Ray @ Raylar

I kinda look at this a different way. Are you building a cam to match you heads? or are you porting heads to match a cam? The heads dictate how the air is distributed to the cylinders. If the heads only flow so much air at certain lifts then the cam has to be designed to achieve the the best efficiencies at these lifts. If you have a cam designed for this (X) duration and (Y) lift but your heads don't work their your F'ked.

I assume you are matching a cam to the heads. Give your cam guy your head flow #'s and have him go from there. You are going to be spinning the RPM's to be making the power. Rule of thumb from what I have been told. As big of an intake valve that will fit and as small of an exhaust valve that does not hinder flow.

And don't forget to the Bore Notch, that is 15-20HP on a built 468 when you unshroud the valve.

http://i43.photobucket.com/albums/e3.../borenotch.jpg

Heads first- then cam!

Where is our boy?

Use a system approach
 

With the kinda domes you're showing in those pictures, the valve unshrouding would be critical as you show, but I am thinking Endeavors engine will have flat tops and the bore notch is good but not as critical and won't net that much power with a flat top piston on pump gas especially if he is using a 2.19" or 2.25" intake valve size. The intake probaly starts opening about 4-10 degrees BTDC and At about 10 degrees ATDC that intake valve is really chasing the top of that piston down the bore for awhile. The notch tends to really help the hopefully swirling air/fuel mixture spiral down the bore with the piston and not create a vortice at the top of the block deck to combustion chamber joint.

When we have done BBC intake air flow shots around the intake valve seat where the charge enters the chamber its amazing to find out that about 75-80% of the air charge actually exits over only about 25% of the total valve seat diameter!!
This why air charge direction in the port ,swirl and tumble are so important to packing an air fuel mixture into a cylinder with a piston on the way down. The more you can pack into a cylinder, the more you blow up! and that makes more power!

As for cam or heads I would say its important to get a good head/cam package match taking into consideration the rest of the air tract like induction system and exhaust system. Once all these parameters are covered and known, I still think Bob Madera will get it right for this guy. Again this the best system approach that will net the best overall results based on Endeavors needs and wishes.

Best Regards,
Ray @ Raylar

In reality I think what he is looking for is the most power he can get out of a 439 CI and stay within his budget.

Back in the mid to late 80's I ran a single BBC 24 Challenger. One of the early on boats. This was shortly after Valako started raising the floors on the intake ports among other things. I remember straping on a set of his reworked Darts, while my out of the box ones were on his bench, with no other changes and was completely amazed. The mid range and top end was exhilarating. As years went by I would always try and duplicate his work however the only thing I would get is a good laugh and a chance to catch up while he would attempt to clean up my work.

Thanks Ray!!! I love reading all the experts technical stuff with in depth R&D. I wish I knew half of what all you guys have forgotten.

Thank You. Most of us old Motor Heads are just here trying to help some of your appreciative individuals steer your engine projects in the right direction with the minimum of expensive learning lessons we've already had.
Good Luck on your build out, with Bobs help and good parts it should be a nice piece!

Best Regards,
Ray @ Raylar

Thanks Ray, I appreciate yours and everyone elses input.