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Whats up guys! So I am wondering if I'm nuts or what.... After running the boat this past few months with the new motor( chevy 496 and basic carb tuning, holly 850 dp 79/83 (stats on engine Scatt 638 rods/ 9:25 forged/ Scatt steel crank/ 502 rec port heads/ Rpm air gap/ crane cam Hyd flat 571/553-236/246@50 with a 114. Stock manifolds and risers with custom insert tubes (water) I have not been able to get past 5200rpm and 66 mph with a 24 Mirage 3 blade in 1 to 2 footers. I was estimating 500 hp but I think I might be well short. Fuel press is 6 psi at wot. After talks in here I dont think the manifolds are hurting me a whole lot but I think the motor should pull at least to 5700 the a 24 ? any thoughts? I am thinking about putting a 1 inch spacer on the intake and trying it this Friday for the last time this season.
Boat is a 1988 Scarab Concept 23ft 3500lb boat, small step in hull (1 1/2 inch) 3/4 of the length back

88bullet

iTrader: (1)

ignition system???

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Ign system is good. 33 full advance. I did bump it up to 36/38 put plug readings were showing a bit of splatter from the pistons so back down to 33. On gps, flat water, 62 mph is just about it.

PatriYacht

How deep is the drive? Trying the spacer is a good idea. It's cheap but unlikely to add more than a mph. Check your hull bottom to be sure it's straight.

Wally

iTrader: (1)

Did you have the prop checked to see if its true to spec? I had a set of 25's for my old scarab.....one prop was decient...the other had two of the three blades off by one complete pitch! One was at 24 the other was at 26!

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Ok, So lost 2 mph with spacer. Didn't have a chance to jet the carb up but checked # 5 and 7 plugs and looked good. Bigger problem is oil STILL STILL STILL getting dark after a few hours run time. Thermal temp gun says 190 at oil pan and fittings into remote oil filter sys, cooler after exchanger by 20 . Right where it should be!!!!!!! WTF!!!!!!
170 static cyl pressure on all eight.Fresh motor 20? hrs. HELP!!!!!!!!!!!!!!!!!!!! I'm thinking because of low compression (9:25/1) reason for low rpm 5000/5200. Cam spec called for 10:1 min. This engine is running damn near what the old 496 ran with peanut heads and stock low rise intake! I need a beer..............................

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Looks like lack of fuel (jetting) and lack of timing might be the issue. Was only at 30 full advance. Way light.

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Checked timing today. I have a 24 degree mod. I was at 8 base/ 32 total. Bumped it to 14 base/ 38 total. Going to change jetting to 83/88. Throttle response is WAY better and fires up as soon as I hit the key.
Started fine before, just not as quick. We are gong to have a few days close to 60 here soon ao I'm going to try it out and hope for the best! ( MORE SPEED ) What are your predictions?

nonstop

Hey Wally, Didn't get a chance to get the props labed but I will do so. After making my timing adjustments if I don't see a gain I'm gona call it quits till I get new manifolds and risers.

Sunrocket24

iTrader: (1)

I think your short on your 500hp goal with the stock manifolds. I have basically the same engine but a 468 and not a 496 and a smaller cam Iskey 270/280 mega and 1.7 roller rockers, I went with that cam due to having stock manifolds and not wanting to have reversion problems. I was looking for 450hp on the dyno when I built my engine. My engine made 407hp/460 torque on the dyno with headers but I bet it only makes 365hp in the boat with accessories and stock manifolds.

Lots of people estimate what their engine build will make but not many pay the money to dyno the engine. I payed for the dyno to make sure my engine was broken in and tuned properly but I also wanted to know how good my build was.

Get some good exhaust and let that engine breath!