Hibbs

Hey guys,

I've found a ton of good info on the is site and tried to research as many old post as possible to educate myself. A lot of the info I've found is around roller 350 (Vortec) blocks but I'm looking for a flat tappet cam recommendation for a small block 350 I'm building for a project jetboat.

Not something you want to take Offshore but it is my entry into "performance boating". Here is a quick shot of the project boat:




The boat has a small block 350 and I am hoping to get between 300-350hp out of it to run with a B/C impeller. 350hp on a B/C impeller should turn just over 5000 rpm.

The engine I have came with the boat and is a early 70s Gen 1 350 that is a 4 bolt main. It was rebuilt with .030 stock type pistons and everything looks pretty good. I’ve purchased a set of Vortec (906) heads that are just rebuilt with the following:
-Stainless steel valves
- Machined bases and spring to accommodate .550 lift
- Drilled and tapped with ⅜ studs and a set of guide plates included

I want to swap on the Vortec heads and have a Edelbrock 7516 SB Chevy Performer RPM Air Gap Manifold that I plan to use with a Holley marine 600 CFM carb.

I was looking at the Xtreme 270 (12-240-4 with RPM range of 1600 - 5800) cam but realize that is most likely a little too much and chances are this engine is going to be spinning too far above 5K for any extended periods of time. This boat will run across the cove (going with a closed loop system for salt water use) and too the beach but won't see extended periods of high rpm use. I’d love to know any thoughts on using the Xtreme 262 (12-236-3 with RPM range of 1300 - 5200) with this combination or recommendation for another cam?

Either way I am planning on going with the cam/lifter/timing chain combo.

I contacted Comp Cams and they recommended the 270 but I am interested in the thoughts of those here who have first hand experience with similar setups.

Any opinions or recommendation are greatly appreciated.

mike tkach

iTrader: (3)

i agree with comp cam,s recommendation of the 270 cam.im thinking you may need to upgrade the exhaust because you may have some reversion.with the vortec head and 270 cam you will see an increase in power.

Hibbs

Mike,

Thanks for the reply and I am hoping that going with the 270 makes sense but I don't want be the guy who just goes for the larger cam and ends up missing torque on the bottom end.

When you mention upgrading exhaust can you explain? I am currently planning on using a PCM setup that I purchased with very low hours and fresh water use. It has the heat exchanger and the manifold/risers that I'll connect to the thru hull exhaust.

Here is a pic of the engine the setup was take off of:



Thanks,

Kent

SB

iTrader: (1)

A 196°/206° at .050" (109°LSA) HR makes 300hp-310hp at approx 4800rpm with Vortec heads, therefore the 262 HFT will break that no sweat. The 270 will absolutley needed long talipipe (ie: water introduced very late) aftermarket exhaust.

If your 600 is a vac secondary carb, you'll thank me for this, lol, get a quick change secondary spring kit and start going softer until you are happy. Chances are you will end up within the last two softer springs. The softer the spring the quicker they open.

The 262 HFT is 218°/224° at .050" and will pull to 5000-5200 rpm on your motor.

The 270 HFT is 226°/236° at .050" and really needs 9.5:1 -10:1 compression to make it work well. This will pull to approx 5600rpm or so.

Don't listen to boogie, and make sure to run 15-40 to 20-50 for those hyd flat tappet lifters to run well over 5k.
Obviously oil with lots and lots of flat tappet goodies in them.

Get ready to here people say get hydrauklic roller cam/lifters for your motor. I'm not saying anything other than I'm in that camp also. Do it if you can.

FIXX

iTrader: (2)

Hibb's,,just a heads up,,im using that exact cam but i took 2* out of it because i wanted to rev higher..my motor dynoed @ 434 hp with that cam but i have 6'' rods and also running aluminum heads..my friend ran the same cam in his 18' donzi,flat top pistons 58cc chamber vortec heads,air gap intake and a 750 cfm holly..he would spin to to 5600 all day long and get 72 mph out of the boat...i spin mine to 6000+ at times and i get 78 out of my donzi in the rite choppy conditions..its a read good cam..and a little choppy..im also running emi exhause with the standard non stainless risers,,they made more torwue on the dyno then the stainless ones i had.. this is what that cam sounds like.. http://www.youtube.com/watch?v=dLdeNiyk0Ew

Btw,,you want to use a crower cam saver lifter,,ask mike tka
ch for the part number,,i forget but i turned him on to them,you also want the ones that have the r in the part number.they have a snap ring instead of the wire ring holding the plunger in and are a little stronger this way..

mike tkach

iTrader: (3)

no more listening to boogie,he did the boogielou,gone-capoot.

FIXX

iTrader: (2)

here are the ones you want to use,,i have been reving the piss out of mine since 1998.. http://www.crower.com/lifters/flat-t...iling-821.html

FIXX

iTrader: (2)

Btw,,looking at your engine pic it looks like you might already have vortec heads.. is their 2 boalt at each corner of the intake total of 8 holding it on the engine?

Hibbs

I LOVE THIS FOURM !!

You guys rock and thanks for all of the responses!

I would love to go with a roller cam/lifter set up but I've already capped out my small budge on this project with the Vortec heads, intake, and carb. If it turns out well I'm sure there will be another motor in it's future.

I can't say for sure because I don't know the exact calculations but I'm pretty sure the motor was stock at 8.5:1 and had 76cc heads. I am going to a 64cc Vortec heads so from what I've read I can be expect to be just over 9:1. I don't think it would be as high as 9.5:1 or even 10:1

SB is your recommendation to go with the Xtreme 262 based on my compression and the exhaust?

FIXX - LOVE the Donzi! It sounds awesome and those performance number are impressive. Are you saying that you are running the 270 or the 262? I took this boat on as a bit of a low budget project to learn about working with fiberglass (have rebuilt a few old Jeeps) and build something from the ground up. I had to gut the entire inside and I am just getting to the point where the stringer / floor are all rebuilt and I've finished the floor. If I ever do another project boat which I'm sure I will .... it will be (1) in better shape when I start and (2) an 18 or 22 Donzi.

Thanks for the tip on the lifters.... I will definitely go with those!

Here is where I am currently:

I build a cradle so I can work on her in the garage (another reason she had to be 18' or less)




Here was the stringer / floor build:



The photo of the engine is just from the guy that I purchased the manifolds, risers, and heat exchanger from. When I got my boat the engine wasn't running but after replacing the starter and cleaning the plugs I got her fired over. She was running a bit rough because the carb was a mess who knows about the cap/rotor/wires but at least I was able to confirm strong compression in all 8 cylinders for a decent budget bottom end.

https://www.youtube.com/watch?v=8aWexrdPgCs Here she is now in preparation for the Vortec heads and the previous owner was actually telling the truth that it was recently rebuild with .030 stock type pistons.

79formula

I ran a 355 in my 79 Formula. I had flat top pistons with 4 valve reliefs, 262 flat cam, vortecs, air gap intake, 750 sea demon carb. I gained 12mph over a stock 260hp. My vortecs did not have an open center port like yours.