Swede

Whats the most cost effect to get 700 to 800 hp?

I need to pull the engines from my 30' Spectre this winter and atleast freshen them up or possibly set them up to accept blowers this spring depending on finances. I'm no engine expert so let me know what you guys think.

Heres what I know about the engines I have now. They are 509 short decks, with GM ported heads, Elderbrock intake, Dominator 1050, Elderbrock cam(non-roller). Speedpro pistons, Stellings Exhaust. They put out 550hp on the dyno at 5500 this spring. I believe they are at 9:1 c/r.

I know its hard to get the best of both worlds but I would like to get the engines to were I could run naturally aspirated or add a small blower(671) or whipples at a later date. I do not need to be any more than 800hp. 800hp would put me bewteen 135 and 140mph.

My thinking is to go ahead and put a roller cam and do something to get the compression ratio down. My questions:
What compression ratio should I be at?
What cam should I install? Crane 741?
What type of pistons?
Would the roller cam make up the difference in the power lost by reducing the compression ratio in a NA situation?

I guess the other route is what could I get out of Stroking it to 540? What would I have to do to get 700hp?

Sean H

I would think that lowering the comp from 9:1 without adding the supercharger will really hurt power in n/a form. If you are gonna run low boost numbers, leave the 9:1 ratio or even up it a little but keep it under 10. I am no engine expert either, but pumping out 550 now you should be at 700 or so pretty easy with the whipples and you can always turn it up and run some race gas when you wanted too.

I am looking at the same thing, I got a 30' Spectre w/ 500HP (carb) and I am looking at putting whipples on them and hoping for around 120-125 when done (107 now). I am going to just freshen up the heads a little, new ignition system and slap on the whipples and see what happens.

tomcat

Cheapest way to 800 HP is a blower, but you need modified carb and an excellent fuel system to go there.

OK, this is a shameless plug, but true. The Rtech supercharging system would be a great package for both of you. It can easily produce 800 HP and will be easier on the drives than any positive displacement blower. Low profile, low boost and low intake air temperatures from the most efficient intercooler setup available.

9:1 compression is OK with our system, not likely with positive displacement blowers. Spend some time on the exhaust ports. 741 cam is a good choice but don't be afraid of the stock HP500 cam. Keeps the low end torque up; let the blower do the work up top.

We have tested other systems that were supposed to be 700 HP and they only made 650. That's a long way from 800 HP. You can see this for yourself when speed gains are in the 10-15 MPH range. Our system took a vee hull from 63 mph to 85 mph. That's a 22 mph gain in a vee hull. Boost was 7.5 psi, intake air temperature was 90F using 70F lake water.

That's my two cents worth. I'd be happy to answer any and all tech questions at the number below.

Tom
(416) 709-8714

Attached picture is from our display at LOTO shootout.

BgBoost1

I have over 2 seasons on my HP500efi Whipple Combo without any problems at all. It pushes my 26' Eliminator to a best of 104gps, and an everyday 95-98 on GPS.

As far as reliability and performance goes I don't think that you can beat the whipple!!!

StrikinLightnin

BgBoost1,

Nice of you and your girl to give us a place to sit at Big Dicks!
We had a great time!
Don't mean to step on anyone's post.........

mikes280

you can go to a good roller the 741 is good just keep it under 5800 head work will help or a good set of aluminum heads and that would help with your 9 to one comp. and a whipple would get you to 800 plus with ease

Swede

Here's my current cam specs. What do you guys think? I haven't learned how these numbers effect an engine. How does this compare to your typical marine engine cams?

Edelbrock Performer RPM
adv(.006") 300/306 @ .05 240/246
Lift at Cam .330/.337 Lift at valve.560/.573
110 ICL
112 LSA

I also found the flow test on my pocket ported heads. How do these look?
.3 214/147
.4 269/184
.5 314/205
.6 340/220
.7 348/229

mikes280

not bad but a roller would wake it up

tomcat

The intake ports look good; the exhaust side could be better. Something like 255 @ .600" would give you an ex/in ratio of 75% and really help the engine get rid of all the extra exhaust from supercharging. I'm not sure if that much exhaust flow is possible from GM heads but whatever you can get is worth it and cheaper than switching heads.

Roller cam would be better because of higher lift AND lower duration, but you have good intake flow numbers in the heads so I would try what you have now. You don't need the Dominator. It would be good on a small Roots blower like a B&M 250, but that isn't going to get you to 800 HP. Neither the Whipple or the Rtech use the Dominator carb or the intake that you have now.

If you decided not to supercharge I would say, by all means, go to ported aluminum heads and a roller cam, keep the Dominator and make 650 HP. But I have seen guys make 800 HP with our system using GM heads and mild roller cams (228/[email protected]"). With well ported GM heads and solid roller cams (240/[email protected]") we have made 1000 HP. This required more boost and lower compression so I don't recommend it for you because it would require tearing the engine down.

Just take off the heads, port the exhaust, change to Inconel exhaust valves if you don't have then already, and reassemble with good head gaskets. Keep your big duration hydraulic cam; it will keep your effective cylinder pressure lower so that the 9:1 compression ratio isn't an issue.

I have attached a clearance drawing for the supercooler so that you can check the fit in your boat. The front stbd corner is the one to check. It is 17" forward of the carb's air cleaner stud and 11" to the stbd side. Depending on the compressor used, the top of the box is 7.5 - 8.5" above the block where the front of the intake manifold sits. This obviously depends on the intake manifold; our measurements were taken with a Dart single plane or Edelbrock Victor Jr.

Swede

Thanks for the info guys. It's amazing how much I've learned from just reading this website over the past 6 months.