well i just took the heads off and measured the valves....1.94 so guess i have the 300 hp 327. so i guess my only option now is to open them up so should i open up the intake or exhaust valves. i want to go to 2.02 intake but my teacher says i can open up the exhaust and get more torque. which will give me more performance 3000-5500 rpm?

 

So now your "327/350" is a 327/300. All bets are off.

Earlier I asked you for the block and head casting numbers, and you did not respond.

So I ask again and would also like to know the stamped data on the front RH deck before I continue to spend more time on this.

Duke

 

the engine is at school now so ill have to get back to you on that later, all i do know now is the drivers side head says GM13 and the passenger head says GM16.

 

Also add the inlet manifold casting number, carb description and number.

Are the exhaust manifolds OE or marine water type? If OE what are the casting numbers? What's the outlet OD. What's the remainder of the exhaust system- open pipe or mufflers? How big is the piping.

GM... are the tooling set numbers. The important numbers are the seven digit casting number and date code number at the top of the head that are normally covered by the valve covers.

Have you driven this boat? What's your take on the bottom end power? Is it adequate for your intended use, like pulling water skiers?

You need to find out what you've got before you can know where you want to go, and you have to match the engine's torque/power curve to the application.

Duke

 

i just got back from class..heres the numbers i got off the heads...3890462, C7, 462, F306. block is still in hot tank. intake, carb, headers are all aftermarket. exhaust is a log style nicson exhaust that goes to 2 1/2 inch hose thats about 2 feet long then through the hull. heres a pic of the new 350 with the exhaust im using http://pg.photos.yahoo.com/ph/purple...4a.jpg&.src=ph

the boat used to haul ***. my dad bought it 15 yeaars ago from the orginal owner who barely used it and took great care of it. 0-30 in 3 seconds...0-60 in 10 seconds, which was its top speed. pretty much hit max rpm instantly, but with a jet boat the last 15 mph are a bitch to get to. i could have 500 hp and be lucky to see 6000 rpm. impellers are kind of like rear end gears, some are made for rocketing our of the water and some are made for top speed. i have an A impreller which is in the middle. C impeller would be like having 4.10 gears but top speed would suffer and engine would rev very high at lower speeds. the boat could pull 4 skiers out of the water. last time i took it out it struggled pulling one skier up. jet is all rebuilt so the power loss is definitely in the engine. it always hit its max rpm very quickly until just recently, when trying to pull skiers or with a lot of people in the boat it struggled big time...so i yanked the engine and here i am

looking at the engine i could tell it was burning some oil, the valves wiggle very little, lots of built up crap in the exhaust ports, crank rockers springs push rods lifters all looked great, valves had a lot of crap on them. so it looks like there was no major mechanical problem...the engine just got all around tired.

 

The heads were cast on July 30, 1966, so it's a '67 engine. 462 heads were machined with both 1.94/1.50" and 2.20/1.6" valves. Heads machined for the larger valves have a tendency to develop a crack between the seats. For this reason I recommend that you NOT open them up to the larger size. Even though the L-79 had the larger valves, 90 PERCENT of the difference in power is the CAM, and it's all over 4000 at the expense of the low end.

The power requirement increases with the CUBE of speed, so even with 20 percent more power and maybe an impeller change to get to it since it's higher up the rev band, top speed will increase only about 6 percent or about 3-4 MPH. In return, "more cam" to achieve a marginal increase in top speed is definitely going to cost you some low end torque and pulling power even with a shorter impeller. Is it worth it? Everything else equal the 300 HP engine makes more torque/power up to the 3500-4000 RPM range compared to the L-79. There's no free lunch!

It sounds like the original configuration was well engineered for the applicaton.

My recommendation is that you keep the engine essentially as is. If you want 10-15 percent more top end power, pocket port/port match the heads, and the power will be pretty flat from 4500-5500, and you'll still have that stump pulling torque. With the OE head machining, power peaks about 4500 and falls off pretty rapidly beyond 5000. Massaging the heads is the best modification you can make. If it ends up wanting to pull past 5500 install a taller impeller.

Discuss with your machinist the valve guide rebuilding and sealing options. Buy the best system for longevity. If the cam shows little wear it can be reused. I hope you kept track of what lifter goes in what bore. Buy a new set of GM 3911068 valvesprings, which were OE.

Once the block is back you can determine if it needs to be bored oversize. I recommend Magnaflux inspection of the crankshaft and rods. Fortunately you should have the last design small bearing rods, which are okay. Look for a little hump of material near the bolt seat. Take a photo and post if you can. All the earlier small bearing rods are WEAK!

Sounds like you didn't measure deck clearance, so who knows what the CR is, but with the OE pistons, typical machined deck height, and a typical composition gasket it probably will be in the range of 9-9.5, and it should be okay with premium fuel and a fairly aggressive ignition map.

I'd still like to know the block casting number, date code, and stamped data from the front of the RH deck.

Run a good street dual plane manifold like an Edelbrock Performer, and you absolutely, positively DO NOT need more than a 600 CFM carb., even if you install more cam, which I don't think is a good idea, and you still haven't divulged the make/model of the installed carb. Is it a family secret?

The Carter AFB is the the most reliable and trouble free four-barrel carbuetor on the planet, and that's why Edelbrock still makes them. The Quadrajet is okay, too. Since neither has any "wet" gaskets, like Holleys they are much less prone to leaks, which is a definite safety feature in either an auto or marine application.

Duke

 

so is this a 300 hp 327? ive also read about a 325 hp. but i always thought it was a 350 hp so now i am lost haha all i know for sure now is that they are definitely camel hump heads.
ill get the block numbers to you on monday when i get back to class...someone took my head stand so i had nowhere to put the block today so i just left it in.

the boat came with a 650 holley double pumper which went bad and was replaced with a 600 carter, which i sold last year because it never put out quite the power of the 650 holley which screamed at wot! the engine wont go in until the end of summer, and i have a 750 eddy, 750 holley dp and 650 holley dp to switch around between my dodge charger and the boat...so whatever carb works best ill use on the 327.

i currently have an old edelbrock performer intake and a brand new non-name brand single plane intake, was either gonna use the eddy with an open spacer or the single plane with a 4 hole spacer.

could i open up the exhaust to 1.60 valves for a little more torque? all the labor and machine work is free, im doing it so if it will help ill do it, if you dont feel its necessary ill just let it be.

they are 64 cc heads correct? from what i looked up this engine came from the factory with 10-1 compression. im definitely boring and getting new forged aluminum pistons, only reason i havnt purchased yet is becuase i dont know what compression to get. and im also replacing the whole valve train, everything is 39 years old so i feel it needs replacing. ill clean up the valves and leave them in if i can, or replace the exhaust with 1.60 if you recomend it. im leaning towards a cam made by comp cam's for marine/4x4 that produces a ton of torque starting at 1800 rpm and keeps making power to 5500 rpm. i read up on a 327 build that highly recomended this cam

ill keep posting with my million questions haha, thanks for all your help SWCDuke!

 

No, installing larger exhaust valves won't "increase torque". As OE machined the E/I flow is about 0.65. If you pocket port the heads the E/I ratio will increase to about 0.85, so it doesn't need bigger exhaust valves.

The two Corvette engines were 327/300 and 327/350. If it has 1.94/1.50 valves it's a 300. The 350 used larger valves.

What's the number on the cam????????????????

Aftermarket cams have too much overlap for manifolds. Stick with the OE cam. They have overlap that is suited to manifolds.

Don't use a single plane manifold. They are designed for engines cammed for top end power with peak torque at 5000 or more. Use the Performer with NO spacer.

If you want a power band between 3500 and 5500, with stump pulling low end torque a blueprinted 327/300 with massaged heads is the way to go. If you massage the heads it will have a ton of low end torque and keep making power to 5500. Isn't that what you said you want. Do you want a proven combination, or do you want to do and R&D project? Your choice.

You don't want more CR that about 10:1, and you need to get educated and start taking some measurements if you want to end up with a targeted CR.

Get David Vizard's books and "How to Hotrod Your Small Block Chevy". Get an engine simulation program and start doing some system engineering. You should had started all this before you tore the engine down, but it's never to late to make up for past mistakes.

If you just listen to "guys" and read hotrod magazines, you're going to end up with a kluge.

Duke

 

thanks for your advise, im just going by what the teachers are telling me and we havnt gotten to measurements yet, ill learn soon though. i think im gonna sell both intakes and go with a edelbrock performer air-gap, i put one on my charger and it kicks *** at all rpm levels. does that sound like a good choice to you? and i will definitely pocket port the heads and port match everything.

ill get all the numbers from the cam and block to you on monday.

my goal is 10.1, but ive just been looking at what the piston companys say the compression will be instead of measuring myself and all ive seen is 9.1 and 10.35-1....so ill do all the measuring and find a way to get just below 10.1

one concern i have is that i will have over transum headers within a year...or once i get the money haha. every jet boat owner ive talked to only has one thing to say...HEADERS. and i dont want to have to change out cams when i switch over to headers.

i appreciate all the advise your giving me. up until now all ive gotten is opinions and not reason, ill actually listen to you haha

 

Your following statement caught my attention:

"Jet is all rebuilt so the power loss is definitely in the engine. it always hit its max rpm very quickly until just recently, when trying to pull skiers or with a lot of people in the boat it struggled big time...so i yanked the engine and here i am "


I have a question for you. I used to race NJBA with a blown 496 Chevy, so what exactly was done to your pump? Was it blueprinted and clearanced? Was a nozzle reducer installed, was a new pickup "loader" installed? If so, you could be simply overloading your pump for the HP of your engine. Same with the impeller (I assume you swapped this one in) it may be loading up too much for the HP you have with the 327.

 

You keep rewriting the equation. Headers are a whole new ballgame. In that case you need a cam with more overlap and maybe a single plane manifold - more compression and forged pistons would be advisable. The torque curve will move up the rev range, with peak power in the 6000-7000 range. A mechanical lifter cam would be the way to go. Low end torque will be lost, so you need a shorter impeller. The OE rods are not adequate for sustained revs over 5500 so you better contact Scott Marzahl and get in on the program for a set of Crower Sportsmans.

Headers aren't going to make that much more power even with a cam that has enough overlap to exploit wave dynamics, and they need at least 24" of tailpipe length to get a good midrange boost. They're mostly cosmetic and noisy. On Dave McDufford's engine headers dynoed about 8 percent higher on peak torque, but about the same power. The torque peak is 4500 with peak power at 6500-7000, but the 20 percent increase in power of his configuration is only going to get you 2-3 MPH more speed, and the low end torque loss is signficant.

You need to do some serious system engineering on your project. You first have to understand the application and propose a realistic and achievable torque curve that provides acceptable performance from initial acceleration including pulling waterskiers out of the water to top speed. Then you select complimenatary componets to achieve the torque curve objective.

If you change a component architecture it effects everything else, and as you move the torque curve up the rev scale, you need better bottom end and valvetrain components to achieve decent reliability. Picking parts *****-nilly out of catalogs is not going to yield good results.

Duke

 

we didnt add anything or even change the impeller. we took it to G&C in riverside and he rebuilt it, i think just a standard rebuild. still has the normal grate....not a loader. doesnt have any snoot or ride plate. we didnt notice any rpm loss after the rebuild thats why i think the engine was the main problem. i mean 39 years in a jet boat...how long can and engine last?? haha and i looked up a hp graph that berkley has and according to the graph i actually have a C impeller, which will hit 5000 rpm with 300 hp.

 

I would consider a Demon 500-650. I don't see the need for a dble pumper. I don't know what kind of water you are running in but you will see more at around 6200-6500. Otherwise push the torque curve some to the left. You won't get much out of it since the engine comes on after 4500. I have some worked 461 heads for that engine that should get you a good bit more flow with bigger valves, unshrouded, some bowel work and some secrets he won't tell me port wise. I would definitely run Racor see thru filters. Let me know the dates on the block as well as the suffix code. I might want to trade you if you are interested. The L79 cam/30-30 are hard to beat. This is a good place to consider a hydraulic roller as well.

Michael

 

sorry, i want to keep the boat as original as possible so im keeping the whole engine. ive got all the vette guys telling me to stick with the L79 cam and all the jet boat guys telling me to go with comp cams exteme marine 278 cam....who am i suppose to listen to!!

 

stick with the stock L79 cam if possible. If you start changing things from want or wear then ask a tech at someone like Comp cams and fit it all together. You will get all u want with a cam that still works well with the orig setup. chevy did amazing work then and they still do.