SBC lacking power

2486 Views 37 Replies 18 Participants Last post by Moosecountry, 3 mo ago

SWV

Discussion Starter · 4 mo ago

Hi,

I am hoping someone can help shed some light on my current set-up. I know this has been raised a lot on here before but I couldn’t find anything that really gave me an answer.

I have only just got my 66 C10 with a 350 on the road and it feels like a bit of a slug/like it is still a stock motor (before all the upgrades happended). I have measured the 0-100 and its around 10 seconds (shifting manually on the TH350) which is slower than my 1.2 litre Volkswagen Polo and from a rough calculation would equal around 150 hp at best. The engine is as follows:

Stock bottom end – standard bore and compression test is all within 4% of each other
New alloy heads with 195cc runners, 64cc chambers 2.02 intake and 1.60 exhaust which are a little big but looking to go a 383 in the future. Flow numbers are:
Lift Intake Exhaust
200 145 106
300 192 135
400 232 160
450 242 168
500 242 178
XE262h cam – Was a comp cams kit with timing chain, lifters and springs
Edelbrockperformer RPM intake
Brawler 650 carb (brand new) vac secondaries
Flowtechheaders – 1 ½ primary, 3 in collector but runs a duel 2 ¼ in exhaust to Flowmasterstraight through mufflers
MSD StreetfireHEI distributer – new MSD leads and spark plugs
Initial timing is set at 14 degrees and total 34 degrees (all in by 2800 rpm)
Stock TH350
Stock Converter
Rear gear ratio 3.73
Rear tire height is 28 inches

The car starts, idles and cruises perfectly and sounds strong but just doesn’t seem to have much go at all. The plugs are not fouling or over rich or lean. My question is whether I am just expecting tomuch out of the engine (although looking at the dyno sheets from comp cams for the cam I am not) or whether it sounds like something is a misssomewhere? While I feel like it would benefit from a looser converter I don’t feel like this would change the accelationthat much.

I have ordered a cam degree kit to check whether it has been installed retarded and is the correct cam. No loose lifter and pushrods spin when cranking so don’t think I have wiped a lobe.

Hopefully I have provided enough info for someone who knows more then me.

Thanks,

Jamie

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Rustbucket366

· #11 · 4 mo ago

Weird. My 78 C20 350 with a Crane version of the l82 cam (difference is its a 106 lsa), 882 heads, and the most basic Chinese dual plane will ignite the tires until I have no tires left if I want. You definitely should be making more power.

Are you 100 percent positive your ignition timing is correct?

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Rustbucket366

· #13 · 4 mo ago

I'd check for a semi accurate timing reading. Most issues are caused by timing. However, it seems like you know how to check that and adjust it. The reason I asked if you were positive on the timing isn't because I was doubting you as much as we all often overlook things regarding the ignition. Perfect example of my own. Could not figure out why a 383 wouldn't run right and the balancer mark was jumping around. It was dumping fuel through the secondaries at idle and fouling plugs. Same exact thing happened to me when I magically had a rock (or something) holding the secondary needle open and fouling plugs not even a month later. Weird.

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Rustbucket366

· #15 · 4 mo ago (Edited)

That will work although not totally necessary. What is important is a steady mark through the rpm range of the mechanical advance. As in it should increase with engine rpm up to the point the mechanical advance is at its peak, and then decrease. The mark should not wave or flicker around under throttle at the rpm where the mechanical advance is at its highest.

Once you have determined the ignition system to be operational, then you can move to carb tuning and hopefully not a rebuild due to flat lobes or whatever the current thing is.

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Rustbucket366

· #18 · 4 mo ago

Moosecountry said:
what you can do is advance timing until you get ping at higher rpm under power. Then back off timing slightly until it no longer pings at higher rpm. This is not accurate but close enough to see if you find power. If you find a bunch of power then go to the trouble to verify timing marks. If no substantial increase in power we have other issues to chase. If A/f is way off then dial that in next. 12.5-13:1 at wfo is a good place to start. I run my engine at 12.2:1 at WFO for the type of power I want with my parts. Also check carb linkage that gas peddle to the floor is actual w/o at the carb. Then we tune secondary opening rate (make sure it is opening)

I do actually agree. It makes no difference if the timing marks are accurate as far as reading them. Adjusting it to what it likes best has always worked for me. Can I say for a fact my GMC C25 likes 38 degrees? No. I don't bother with piston stops or any of the over analytical stuff. I'll just say that I do know what timing it likes based on tuning and it runs very strong.

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Rustbucket366

· #19 · 4 mo ago (Edited)

Good point about the secondary opening rate (if it's a vacuum secondary). Either way, if it has secondaries it may not be opening them properly. Personally, I haven't experienced this but it is something to take into consideration. Only issue I've had with secondaries was WAY too much fuel. This goes for all 4 barrels, holley (4150 and 4160), edelbrock, quadrajet. Hell I even rebuilt an autolite 2 barrel and it sucked. Seriously. It sucked a lot more fuel than a 2 barrel should. I should say the autolite suckage was pre rebuild. It was fine after.

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Rustbucket366

· #21 · 4 mo ago

Whatever you do. Don't throw money at it. That's guaranteed to make things way worse. Unless you're like me and hoping for an excuse to spend 3 or 4 grand on an aftermarket big block block. In that case. Yes. Throw the money.

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Rustbucket366

· #31 · 4 mo ago

You don't need an AFR gauge, although it is helpful. You don't need a different engine. It will make the power just fine if you tune it right. It doesn't even have to be "right" as long as its working

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Rustbucket366

· #36 · 3 mo ago

Eduramac said:
Bogie nailed it as usual.

Not sure what that means.

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