SBC upgrade issues.

**mardonzi** · 04-19-2009, 03:17 PM

I got a call from a friend up in Provo asking for some help on a conversion that he did on a boat of his. It was a mid 90's 5.7 l. 225 hp SBC that he worked over, changed the cam, pistons, etc.. and is supposed to be getting 300 hp out of it now. The only issue is, he is only getting about 4000 rpms out of it and then it's topping out. It's a Thunderbolt IV system.

I know this is vague, but it's all the info I have. If someone has a lead on a shop or mechanic in that area, I'm sure the help would be appreciated (and compensated)

**scarabrick** · 04-19-2009, 04:08 PM

SOUND LIKE TIMING. iS IT GETTING FULL ADVANCE? THE THUNDERBOLT ONLY ADVANCES TEH TIMING SO MANY DEGREES. hOWS TEH FUEL PRESSURE? Is it fat or lean?

**Wet** · 04-19-2009, 04:15 PM

We all know the obvious answer, but it's probably best to let this thread play itself out without influence.

Ultra26 # 1 · 04-19-2009, 04:17 PM

Originally Posted by scarabrick

SOUND LIKE TIMING. iS IT GETTING FULL ADVANCE? THE THUNDERBOLT ONLY ADVANCES TEH TIMING SO MANY DEGREES. hOWS TEH FUEL PRESSURE? Is it fat or lean?

X2 on timing

**Beer:30** · 04-19-2009, 04:42 PM

Too little info.

Did he change the carb/injection to match the new HP? If not, it is still calibrated to the lower HP and now is acting like a restriction plate.

Did the cam go in straight up? +4? -4?

**mardonzi** · 04-19-2009, 06:13 PM

I appreciate the responses.. and know that the info is vague.

**bigdave196** · 04-20-2009, 09:42 AM

Hello everyone, I am the friend up in Provo. Here is all the info I have.
The engine is a 95 (pre-Vortec) SBC 5.7L with about 225HP before the rebuild. Edelbroc 600CFM carb 4 BBL(no choke), Thunderbolt IV ignition, Accell 8mm wires, AC Delco Iriduim Plugs, MSD Blaster Coil and thats about it. Outdrive is a AlphaOne Gen II, Prop is a Stainless 19Pitch 3 Blade Quicksilver. Last season the motor was able spin to 5700RPM and pushed the boat to 60ish-mph on the water. Fuel is always 91-93 octane and has been since its first tank.

Reciently I had a very reputible machine shop rebuild the engine (who we have used over a dozen times for work trucks and play vehicles) rebuild the motor after the #4 Cyl last year had an ignition failure eating up the piston. All the internals were upgraded/replaced and only the Block and Heads were reused. Block was punched out .020 over and flat top pistons were used. Compression ratio is believed to be really close to 9.5-1. All Valvetrane and short block internals were replaced. The kit was a 300HP kit ( I do not know the manufacturer).

All wiring was marked and replaced back into the same locations that they were when I pulled the motor. Everything basically fell back into place during the reinstall.

The motor was set to TDC upon reinstall and when it was time to start the motor it basically fired up and we timed it right then and there. Timing is at 8*BTDC.

I spoke with 2 Edelbroc Techs and both said that the 600CFM 4BBL carb is sufficient to handle the HP increase and that its reccomended to almost 400HP and under 6000RPM. Breaking either of those specs would result in needing a 750CFM or Larger pending the application (PER Edelbroc). The Secondaries in the carb open mechanically and do so in gear and in netural. The Helm throttle controll is correctly set up and at WOT on the Helm you acheive WOT on the carb. I even took off the linkage to veryfi this and had my wife steer while I controlled the throttle manually.

Fuel is delievered thru a mechanical fuel pump on the side of the block. The motor shows no signs of a starvation problem ( no surging or cutting out at WOT) nor does it backfire in the upper rpms ( that means 3800 is my max rpm as of now). In Netural the motor revs al the way to 6000rpm.

Ignition is a Thunderbolt IV with 4 wires coming off the back. (Purple, Grey, White with a green stripe, White with a Red stripe). When I had a basic timing light ( no dwell settings) at 650-700rpms the timing was at 8* btdc. When the motor is reved it advances almost 3 times the distance from TDC to the 8* mark on the indicator. To give a rough idea where the mark is think of a clock. 8*btdc is at about the 1:30 area of a clock face, under rpms the timing advances to just about the 12 O'clock position.

The actions of the motor is this. Pulls hard out of the hole as expected for the HP increase and just tops out at 3800 RPMs. The time to plane is not entirely noticeablly different from the previous year, but I am thinking it should be a little faster.

Now I do not know if this is related but the exaust manifold on the left side of the motor is noticeably warmer then the right side of the motor under load.

I hope this helps, and anything that you can help with would be greatly appereciated. Thank you Don for getting this ball rolling.
Thank you all in advance for any help.

**mardonzi** · 04-20-2009, 01:37 PM

Good Luck Dave,, and welcome to the boards..

**Beer:30** · 04-20-2009, 05:50 PM

What do all 8 plugs look like? Black? White? Brown?

I would hang a fuel pressure gauge on it and see what the PSI stays at (or doesn't) at WOT and when the power stops. Maybe as simple as fuel supply not keeping up with the 625 EDELBROCK that I agree should be adequate.

The other thing to look at is what the cam specs are and how it was broke in. You are probably still flat-tappet and could have a flat cam if not properly lubed and/or broke in.

Is your throttle cable adjusted so that you get full-throttle? Sometimes it is the simple basics.

You might also check and make sure the intake doesn't have something binding the secondaries. If it is a mis-matched intake setup, the secondaries could be hitting some casting material and not opening enough or at all.

**Boat Tech** · 04-20-2009, 07:47 PM

Are you sure they degreed the cam in the right way? Also I believe you should have a little black ground wire that hooks up to the bottom side of the "distributor" ignition sensor by the white/green and white/red wires.You should see or feel a longer bolt sticking thru the distributor bottom holding the sensor down. Also their should be a black wire with I believe clear plastic heat shirnk cover layin next to the white/red / green wires. Try rehooking that wire back up tight. I say that becouse i had too engines not go over 3800 rpms and those wires where unhook. Did you ever find and fix the ingition problem you said you had that made you half to rebuild the engine? Also do you see a pink wire layin on top of the intake, If so you should be grounding that wire out to put it in base timing to set you timing at 750 rpms. Also are you triming the drive up while running the last trip out? Just some ideas for you. Good luck

**bigdave196** · 04-20-2009, 07:55 PM

Ok today I pulled my starbord side exaust manifold off to look for the missing exaust flapper that I did not see when I was removing the motor. Sure enough it was at the bottom of the Y pipe and that solved the Hot Exaust Elbow issue and helped with a 7 mph gain but same RPM celing. I hit 42 today, lol. Still about 15 mph shy of what the old motor turned out. I played with the timing a little and advanced it to about 12*BTDC and actually lost speed and about 200 rpm so I turned it back to 8*BTDC. I am not sure what the total timing was at 3000 rpm but it was about 3-4 times the distance from TDC to 8*, from the 8* mark to where it was advancing to. If that makes any since to any of you. ( I wish I had a Dwell Timing Light,

)

How would I go about making a fuel pressure gage that doesnt involve cutting the bent fuel lines from the pump to the carb?

To be totally honest I have no idea what cam or the name of the kit that was used.

WOT on the helm matches WOT on the carb. I will pull the plugs tonite and give a solid update.

From what I understood everything in the motor was "NEW" and not reman parts.

Today we attempted to pull my friend up on 2 skis, hes about 6'5 and 220. The boat struggled with him on 2 skis. It acted like there was 2 of us on 1 ski out there. The motor just doesnt want to perform under a load.

I am off to pull the plugs, so talk to all of you in a few.

**scarabrick** · 04-20-2009, 08:05 PM

You Need Tp Get A Total Timing Light And Check All Teh Wires As Posted Before

**OCMerrill** · 04-20-2009, 09:27 PM

Originally Posted by Beer:30

What do all 8 plugs look like? Black? White? Brown?

With todays fuels it is EXTREMELY difficult to read a plug unless your melting one or puking black smoke.

**Beer:30** · 04-20-2009, 09:30 PM

Originally Posted by OCMerrill

With todays fuels it is EXTREMELY difficult to read a plug unless your melting one or puking black smoke.

True enough. Also the fact that alot of people like to add 104+ or similar additives, which turn the plugs a rusty-brown color. Regardless of the mix!

Thread:
SBC upgrade issues.

LinkBack

Thread Tools

Display