Pismo10

While you are in there, How's your transom?

gmgearhead454

Glad to hear about the valve shrouding before I bought new valves! Lol, well that will save some money. I've built dozens and dozens of engines before, but this is my first Vortec BBC, so I'm still gathering info. And as far as the transom goes, I pulled the engine last weekend, and it was suprising clean and solid. Looks like someone had already been in there and painted it too, unless Formulas were painted grey inside from the factory

Gimme Fuel

The chevelle forums have more info about making something out of these heads than on here. Most will say they are junk on here. Exhaust runners flow great so just some clean up is needed. Intakes have ski jump "vortec design" and causes swirl into the chamber but hinders flow. Be careful porting too much as the castings are thin. If you want to run premium pump gas, they will make good power around 34° timing but you will find many tell you that is too much. Depends on source as always here on internets. I have found a few articles about porting them but they dont go into deep detail and are scarce or are not backed up with flow results being as most applications for them are very budget oriented so the expense of flow tests is forgone.

The small chambers are a bonus and are hard to achive a budget minded replacement casting to maintain close to the same CR. I was going to ditch them for 781 castings but didnt want to loose all that compression or have to change pistons and rebalance. Trying to just do simple rebuild with good bearings and gaskets so I decided to run the vortecs.. I have one money pit of a motor that gets best of best. This one just has to work as a spare to get on the water and hopefully be able to reach what my hull used to do when it had a stock 502 mpi.

It will be interesting to see how our motors end up performing. These heads can make very good torque on a 454 i understand. Keep us posted!

dandercam1

iTrader: (1)

As far as the timing and compression you will find that boat motors are run more conservative because of the excessive heat generated by the longer duration under high load that a marine engine has to deal with.

Gimme Fuel

Here is some good reading for you.

http://www.chevelles.com/forums/show...highlight=l-29

http://www.hotrodders.com/forum/bbc-...cs-171714.html

http://www.fullsizechevy.com/forum/g...g-results.html

This seems to be about the best porting information I can find on these heads. With a little work they can flow close to stock 781's Worth a shot if you have time on your hands to hold a die grinder.

gmgearhead454

That was a great article! Its nice to see some actual data and results from the exact head I plan on using. The way those were ported look IDENTICAL to how I've always done my heads, and how I planned on doin these: smoothing and shaping the valve guides, opening up the bowl and smoothing out really good (especially the first inch of the valve seats, and smoothing out and shaping the short turn radius). Ill gasket match it, but not take much out in that area as that's not where heads get choked up. Ill re-use the stock valves after reading this too. Dyno tuning was an idea I was kicking around too, but we'll just have to wait and see what accesable dynos and cost permits. I figure if I can get this anywhere close to 500 horse, I will at least be able to keep up with the majority of what's out here on the rivers. (Not tryin to be a LOTO hero... that will never happen, lol)

dandercam1

iTrader: (1)

I would do some research around these forums before sticking with the stock valves. Im not sure what valves GM put in the vortec motors but I do know that performance marine engines are very hard on valves. Most builders spare no expense in that area. Consider that merc uses inconel exhaust valves in their motors starting at the hp500 on up.

Gimme Fuel

Most of the late model GM truck engines came with Inconel valves due to towing/emissions compensation exhaust temps. The 96 7.4 I just took apart has them and except for some carbon buildup that has been removed, they look good.

tpabayflyer

I did this....... Rebuilt my gen 6 7.4 with 279 vortec heads. Put in 2.19/1.88 valves and ported and blended as much as I dared. Don't mess with the ski ramp. Used the GM .510/.540 lift hyd roller cam from the 7.4 magnum... Got it cheap....... Excellent cam with great torque. Uses all stock valvetrain........ I don't think I gained that much with porting and the larger valves. Dont even think about using a single plane intake. You will be giving up power right where you need it. Air gap will outpower any intake with your combo. Oval port heads make lots of torque so add parts that build on that..... Motor will be out of breath by 4,500..... Single plane does not start making better power unil about 5,400pm on up. I cruise my 26ft wellcraft at 3,700 rpm at 40 mph all day long effortlessly.... 3,000 Rpm is 32 mph with a bravo 3 24P...... Gets up on plane quick and easy and has torque out the wazoo!

endeavour32

iTrader: (4)

I built a 242 a few years ago and I would say that if you make the power you think you will make, you should hit 63-65 MPH. I had around 530 hp in my 242 and I would hit 68 mph. Honestly though I don't think you will make over 425 hp I think with your combo you will will hit 61 MPH on the GPS. In order to make the power you want you are going to need to spin it to 5100-5300. As for props get a Mirage plus 21 pitch. There is no need for a 4 blade on a 242, yes you MAY gain a little in the midrange but it will kill your top end. My experience with props is that as long as your going to build the same cubic inch engine you will typically spin the same prop, only now it will spin more.

Also I would stick with your original Performer RPM. You are not going to gain anything by going to a single plane, you are simply not turning enough RPM's to take advantage of the upper RPM power they make.