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Anemic HP from a C3

80Vette

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1980 pearl white vette
Hey all, our corvette group had a Dyno-Day and I was the only C3 representing.

I have a 350, brand spankin new Edelbrock Performer intake & carb, an aftermarket slightly beefier cam & shorty headers to a 3" Y pipe which is married to a free flow 3" cat, from the cat back it's true 3" exhaust to the magnaflow 40's.

I was thinking that the car would at LEAST get 230HP.
toetap05.gif

But, on the MustangDyno I only pulled a 181. Three times in a row.
ack2.gif


I mean, my wifes saturn has a Yamaha DOCH V6 which will pull a 210hp on the dyno.


What I want to know is, how can I get my 350 to perform better?
It shouldn't be THAT hard to get 250hp out of a SB chevy, right?



Andy
 
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Denver, CO
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'72 Targa Blue Coupe
One quick input-you need more compression. 8.5:1 is pretty anemic. You didn't say what cam, or how it was installed (straight up, +4 or -4). Some distributor advance work may be in order, also-are the mechanical and vacuum coming in/working correctly?

More compression can be had pretty easily with the Edelbrock Performer heads with 64cc chambers. Make sure the rest of the engine is solid, though. Boosting compression on old rings doesn't work out too well.

Maybe a new ZZ383...? ;)

Rick
:gap
 

srs244

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the deep south
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1978 pace car, 04 CE convert
it would really all depend on exactly how much $$$ you want to invest to get the extra HP. when it is all said and done (unless you are doing all the work yourself), you might want to explore pulling the original engine and going with a crate replacement. if that doesn't appeal to you, the best way to get what you want is to get the specs and build a 383 stroker. that way (assuming the block is strong) you have replaced all the components that wouldn't hold together with a simple head changeout to increase the compression..
 

80Vette

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1980 pearl white vette
The Engine is new (professionally rebuilt) with only 6,000 miles on it. could a new performance distributor advance (Accell) help with advance ignition timing,couple to a new set of heads give it the "big-push"???/


Hmmmmmm.....
 
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Messages
485
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'72 Targa Blue Coupe
Check your distributor. My suggestion, before you go out and drop hundreds of dollars on ignition upgrades-is to troubleshoot what you DO have. Make sure it is working correctly. There are several threads and papers in this Forum that will get you started. A timing light, tach/dwell meter and vacuum pump (Mity-Vac) are very handy and inexpensive tools.

If you are not so mechanically inclined (not everyone is), then find a shop that can do it. 1 hour's labor can be very enlightening.

What is the current compression ratio? What pistons? What combustion chamber size on the heads? Still need cam info, too. Not that I am an expert, but I have played enough to know that some combinations do not play well together. There are some experts here-perhaps they can chime in.

Rick
:gap
 

L48

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Wadsworth OH
You have not provided enough information to be able to completely assess the issue. But I'll take a shot anyway.

I am making the following assumptions:
1) Flooring the gas pedal opens the carb all the way, and there are no restrictions on the secondaries (opening too slow due to adjustments, springs, whatever), and the carb is not too small
2) Your timing is reasonable, about 12 degrees initial on the crank and a total of 36-38 at maximum advance, and it does advance properly on acceleration
3) Whoever rebuilt the engine put flat top pistons (stock) and 76 CC chamber heads (stock 8.5:1 compression)
4) There are no partial restrictions to airflow on the intake side, or on the exhaust side
5) You are not losing compression through scored cylinder walls, bad rings, valves

If all these things are correct (a big IF), then your problem is the heads. Gasket match the intake side, put a 3 angle (or more) grind on the intake valves, and open up the intake ports (or buy better flowing heads). There is a spot near the pushrod where the port gets narrow.

I would also like specifics on cam grind, as this can have a large effect on the performance. Stock Chevy heads on these vehicles do not like single pattern cams. The exhaust needs to be lifted a little higher and open a little longer than the intake.

The bottom end should be good for 300 HP easy, and should not need replaced unless you have dish pistions. If you want a beefier one that is up to you, but my 2-bolt main stock crank, rods, pistons 350 runs 12.60's in the 1/4 mile on 87 octane (8.5:1 compression) in my 76 TA.
 

80Vette

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1980 pearl white vette
Thanks L48.

In regards to the Dyno:
It showed that the primaries are running a little too lean, the secondaries are opening late & when they do kick on, they're one size too rich.

It has a brand new performer 600cfm carb & performer EPS intake manifold.

I wish I know what the cam rating was. I've sent a call into the shop that rebuilt the engine...Still waiting...

But, here's the crappy part, the gentleman I bought the car from (I am the 3rd owner & the car was very well pampered its whole life) but the guy I bought it from (actually his wife) is suffering from early on-set advanced Alzheimers disease. So, he doesn't even know he ever had a Corvette and it's sad So, I have given up trying to find info on that route.

I agree with you, something isn't exactly right with the engine, it does idle well & always fires right up but under acceleration there is seemingly a bit of "static."
 

Evolution1980

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ZZ4, 700R4, Steeroids rack & pinion, VB&P Brakes
Hey all, our corvette group had a Dyno-Day and I was the only C3 representing.

I have a 350, brand spankin new Edelbrock Performer intake & carb, an aftermarket slightly beefier cam & shorty headers to a 3" Y pipe which is married to a free flow 3" cat, from the cat back it's true 3" exhaust to the magnaflow 40's.
I was thinking that the car would at LEAST get 230HP.
toetap05.gif

But, on the MustangDyno I only pulled a 181. Three times in a row.
ack2.gif


I mean, my wifes saturn has a Yamaha DOCH V6 which will pull a 210hp on the dyno.

What I want to know is, how can I get my 350 to perform better?
It shouldn't be THAT hard to get 250hp out of a SB chevy, right?
I thought I'd add a couple things here too.
1) I've heard Mustang dyno's tend to Dyno on the high side. That being said...

2) My ZZ4 (355HP / 405tq) only dynos around 280HP (or less) I believe. I can't full recall now. But figure around 25% loss if you are running an automatic trans. About 20% if it's a manual.

3) The wifey's Saturn pulling 210hp??? What Saturn has a 6 cylinder? And what 6-cylinder does it have that's rated in the 250+ (crank) HP range???

4) As stated above in other replies, there's not enough info to know what your engine 'should' be doing. And way too many variables on top of that. An important factor here is your torque rating. I put more emphasis on torque anyways. Torque is what you feel. Torque is what moves the car. Build torque and the HP will follow. What were your torque numbers? With such large exhaust, you'll likely lose torque but gain some high-end HP. (although it doesn't seem to be helping in this case.)
I can say from my collected "knowledge" over the years that if you only need a 600cfm carb to feed your engine, then 3" exhaust is probably too big. With that in mind...

5) Depending on the specs of your engine (unknown?) it's possible your carb is too small.

6) What engine did you start with? Not that it matters too too much, but was it an L82 or an L48? I would assume the engine builders weren't using "ricer math" and just threw things in/on the engine and figured a HP/Tq rating based on what the mfg's claim was. Pieces parts needs to be matched up to obtain optimal results.

7) Also note that L48's response above about "300HP easy" is relative to crank HP, not 'rear wheel' HP. Or at least I would think that's what he meant.

8) Before you drop (any more?) amounts of money in to the engine, be sure to define what you really want in the end and if the cost of rebuilding an old engine is worth what you'd get from simply buying a new, warrantied , tried & true crate engine (and having a spare to sell or save).
There are / used to be tons of threads in the C3 forums here about "rebuild old engine -vs- crate engine".
 

80Vette

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1980 pearl white vette
I3) The wifey's Saturn pulling 210hp??? What Saturn has a 6 cylinder? And what 6-cylinder does it have that's rated in the 250+ (crank) HP range???

:)
Hi Evolution1980,
The Saturn is a 2001 LW300 series, Yamaha DOHC. Seriosuly, the thing is a butt-ugly, sleeper rocket.

I appreciate your input. The block is a standard, run of the mill chevy 350. I do want a dependable, solid powerplant. I don't neccesarily want to get the engine too hot (meaning: radiator/cooling upgrades, tranny upgrade, rear end upgrades etc). I just am certain that the engine should pull better #'s on the dyno than 180hp. But, you are correct, the owner of the dyno-shop said that the Mustang Dyno will whack 20% off the top due to the autotranny. So, it's probably safe to say the engine is rated around 220hp at the crank. I am going to re-adjust & tweek it again tonight. The owner of the dyno did say that it would be a easy adjustment to dial it in to around 200 rwhp. (meaning 240 at the crank, right?)

Thanks for the input. I'll re-evaluate my expectations of the powerplant. :)


AP
 

Evolution1980

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I mean, my wifes saturn has a Yamaha DOCH V6 which will pull a 210hp on the dyno.
Sorry to linger on this and get off topic somewhat, but if that Saturn was dynoed on the same dyno as your vette, then you need to go elsewhere. Preferrably where they use a DynoJet and know how to use it properly.

Here's the spec from an '02 Saturn LS3000
  • Engine... 3.0 liter DOHC V6
  • Drivetrain...four-speed automatic, front-wheel drive
  • Horsepower...182 bhp @ 5600 rpm
  • Torque...190 lb-ft @ 3600 rpm
Now how did her car make MORE HP at the wheels than what's available at the crank??? I think you meant either 110 or 120 HP. :)

And to give you an idea of what my ZZ4 pulls on a DynoJet brand dyno...
Crank HP: 355.... At the wheels: 253 (give or take)
Crank Torque: 405.... At the wheels: 316 (give or take)

Like you said...evaluate what you really want in the end. Are you striving for quarter-mile times? Dyno numbers? Top speed? Just plain ol' fun? There's various way to accomplish those things and each has different ways of getting there. Obviously, engine is always a good palce to start. But you can also simply change rear-end gearing to accomplish certain tasks as well! And blah blah blah blah blah :D
 

L48

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Wadsworth OH
I would double check the distributor advance and get a 650 cfm carb at least. Stock q-jet flows 750 IIRC.

Also - I suggest putting it on the 1/4 mile and get some ET's so we can end the debate about the dyno HP. My 75 L48 is stock except for the hollow cat and 40 series flowmasters and I have run 15.72.

7) Also note that L48's response above about "300HP easy" is relative to crank HP, not 'rear wheel' HP. Or at least I would think that's what he meant.
Actually I was referring to rear wheel HP. I am thinking my TA must be right close to 300 rwhp - though I have not had it on a dyno yet.

I bought the cheapest rebuild kit I could from NAPA to build a "mule" engine until I could build a real racing engine. I never figured it could make the 12's in the 1/4 - especially in the TA which probably weighs in around 3400 pounds. I race probably 8-10 times a year (except the Vette ate up all my free time this year) and the only bottom end item that is better than stock is the oil pump - though it is only a step above stock and runs the 5 quart pan.

My experience it the stock Chevy bottom end from the 70's can handle 300 rwhp (casting 3970010). Maybe the late 70's block was different?
 

Evolution1980

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I would double check the distributor advance and get a 650 cfm carb at least. Stock q-jet flows 750 IIRC.

Also - I suggest putting it on the 1/4 mile and get some ET's so we can end the debate about the dyno HP. My 75 L48 is stock except for the hollow cat and 40 series flowmasters and I have run 15.72.
  • Yep, the stock QJet is a 750cfm.
  • 15.72 seconds in the 1/4 miles sounds about right for a stock L48.
My best is a 13.3x with the ZZ4. I need to get my trans dialed in to squeak off another 10th or so...
 

Crimson Thunder

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Orange Park FL USA
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1970 Marboro Maroon Convertible
The problem may be your cam.Although you don't know the specs,more duration and low compession leads to unsatisfactory power.I agree with the previous post that the Edelbrock heads with the small chambers would help.
 

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