Baldie

First off, thanks for any help in advance, as I have been battling this for a bit.

I have a 1977 Scarab 300, and know it is no speed racer by any means, but something isn't adding up. Here are my mods..

350 Chevy, 10.0:1 Compression, Trick flow heads 195cc intake, 62cc combustion chamber, Holley EFI single plane intake, 1000 cfm throttle body, FAST EFI, Comp cams, I want to say around 230 @.050 duration, .480 lift, 110 lsa, stock cast iron manifolds with dry 3" free flow exhaust, TRS drives, Bennet trim tabs, 21p Michigan prop 3 blades.

Right now, I am at about 54mph and 4500 rpm, but something doesn't seem right. The motors are fresh, and good, I can't say anything is wrong with them, but it doesn't seem to want to get over the hump. The props are spinning out. I threw a set of Mirage 25p+ on it, went 52mph at around 3400 rpm and won't get past that barrier. The boat seems to be pushing a lot of water, like the transom seems to not be lifting out of the water much, as I trim up I gain tons of speed. Do I need a different prop?

Any advice is greatly appreciated!

hullofjustis

iTrader: (1)

you need a smaller prop and take 1000 cfm throttle body off way to big for a 350 ci. you may be at most, making 400hp. the exhaust needs to go as well you may be sucking water back in at idle. what kind of cylinder heads do you have? what is your timing at full advance?
trs drives are burried in the water as well,
so yes you are pushing water. new hulls and drives are designed to have the propshaft level with the bottom of the hull if not an inch or 2 higher than the bottom of the hull on most performance boats for the most part.
what power was in this before?
the 300 that i have seen have usually had big blocks in them. i think small block would make the boat run great if they were putting out 500 hp

Gh700xx

these heads

phragle

iTrader: (3)

Thats some hefty compression for a boat.... Im not a motor guy, but seeing as how you are in toledo, you could talk to Brian41 he is right up the road and has a pretty good handle on motors and efi plus he has a dyno.

I dont think the TRS setup is doing you any favors with smallblocks. I think you would see some definite improvemnt in speed going to bravo's and raising the X a bit.

cigboat1

You need to try some old school tricks... That boat with 280trs motors and drives would run 61 mph right from the factory;The big blocks later would only run 66 but only if they were trimmed correctly----- throw the Michigan wheels away or sell them and try some 21 or 23 cleavers and then try some 23 mirages... Then you need to learn how to trim the drives the right way. there is nothing wrong with trs drives , they just need some trim to surface the props. you have a lot more horse power than the stock 280's so they. should run a lot better than it is now....... good luck

jim

hullofjustis

iTrader: (1)

I would not worry about the compression with aluminum heads. that kind of compression is used quite a bit around here. cigboat1 is correct about the cleavers however higher drive faster and the better the attitud of the boat my opinion. I have an 86 scarab panther and removed the trs's and put bravo's on after replacing transom and stringers.

FIXX

iTrader: (2)

+1...you need a surface prop to lift the hull out of the water..if you can find a set of 22 pitch revolution prop to try..could work well on that hull..

Baldie

The exhaust is dry to the tip, so I doubt I have any water reversion. The 1000 cfm throttle bodies are the smallest I can get in a 4150 flange... I have the timing at 32 degrees, with 12.5:1 AFR, leaning around 13.2:1 and 34 degrees at cruise.

Baldie

You think some 23 clevers would run better than 23 mirages? Or the revolution props?

FIXX

iTrader: (2)

you need a prop that will lift the stern,,if you can get a hols of a set of revolution props try them,,you might be suprised ..