Engine performance problems

[Tepot]

Hi guys,

I really need you help on this one.

Last year I've got my car on the dyno and got 225 Hp at the wheels. This year I've installed brand new Patriots cylinder head part # 2181 64 cc aluminium.

Then Put the car on the dyno, what do I get? 225 HP at the wheels. What the f***k just happened? I had the smallest cylinder heads a L-48 engine could come with. There is no way I shouldn't gain a good 40 HP at the wheels.

I know at the dyno, we could see blue smoke coming out of the exaust at High RPM's. We got a full dyno tune up on my car and could only come up with 235 HP at the wheels. the guy at the dyno told me that the engine was probably warn because this engine should be pusshing 300 Hp at the wheels.

Here's my setup

350 L-48 chevy engine
Comp cam 268 Xtreme Energy Hydrolic flat tappet
Edelbrock performer EPS intake
Holley 770 cfm street avenger carburetor
Patriot performance cylinder 64 compression chamber part # 2181
running on headers and chambered exaust. true dual exaust

Now one thing I should mention, since I've put these heads on. I'm getting backfires coming throught the carburetor.

Is this a distibutor problem? I had the car timed correctly, changed vaccum advanced canister, timing cap, wires etc... I have an electronic pertronic conversion in the distributor as well. The car works really good when I drive besides those backfires once in a while through the carburetor. But the power is just not there. I should have more condisering the parts combination on this engine.

And by the way, I've checked compression in my cylinders and I have 150 psi in each cylinder. Should i have more? Is my engine really warned out?

Please help

Thanks

 

[Vettehead Mikey]

Backfire through the carb-

weak/erratic ignition (get rid of the pertronix POS)
carb/intake vacuum leaks
intake valve adjustment too tight

 

[Tepot]

Backfire through the carb-

weak/erratic ignition (get rid of the pertronix POS)
carb/intake vacuum leaks
intake valve adjustment too tight

Forgot to mention, carb/intake vacuum if fine. tested ok
Intake valve adjustment as been set. Should be ok.

Is it possible that an old distributor would be responsible for a 40 HP @ rear wheels lost?

 

[Hib Halverson]

First, you're not going to get 40 horsepower just from those heads.

Second, do you have any air/fuel ratio info from a chassis dyno run.

Third, if the engine is popping back through the carb, are you sure:
1) the carb is calibarated right, especially the accel. pump circuit
2) there are no ign problems
3) the camshaft is degreed properly.
4) "blue smoke" out the exhaust...not good.

 

[Tepot]

First, you're not going to get 40 horsepower just from those heads.

Second, do you have any air/fuel ratio info from a chassis dyno run.

Third, if the engine is popping back through the carb, are you sure:
1) the carb is calibarated right, especially the accel. pump circuit
2) there are no ign problems
3) the camshaft is degreed properly.
4) "blue smoke" out the exhaust...not good.

Carb as been tuned up right. don't have the fuel/air ratio but dyno guy told me they were at best.

camshaft is degreed properly.

bluesmoke is only a bit at high RPM's. and compression in cylinders are 150 each. all equal.

Now question is,

1. if I have 150 compression in all cylinders but have a bit of blue smoke coming out the exaust. is this enouph to not see any gain in HP?

2. If compression in all cylinders is @ 150 psi. Would it be possible to loose HP if engine is old and smoking a bit?

3. Should the compression in cylinders be higher than 150 psi with this setup?

4. Could ignition/distibutor cause all that HP lost?

Boy this is complicated. but thanks , this is alot of education. keep posting idea's boys

 

[Rodney Gold]

Im running a similar config , but getting a LOT more hp more than you are (335 at the flywheel)
L48 + Edelbrock 64cc performer heads , Comp cams 270h cam , 770 street avenger ,Edelbrock performer intake , MSD dizzy + msd 6al
I run 36-38 degrees total advance. Headers , dual exhaust. Carb jetting straight out the box , but bigger shooters (I run a 2500 stall)

I'll tell you what I think has happened , and it happened to me , is that you have perhaps lost your cam ....

 

[baxsom]

is that enough engine to be able to take that large of a carb?
was there any rejetting done after changing heads?

 

[Vettehead Mikey]

is that enough engine to be able to take that large of a carb?

It's overkill and no advantage over the stock 750cfm Qjet, but until the OP does some more investigation (see to-do lists above) we'll just have to wait and see.

 

[Tepot]

Im running a similar config , but getting a LOT more hp more than you are (335 at the flywheel)
L48 + Edelbrock 64cc performer heads , Comp cams 270h cam , 770 street avenger ,Edelbrock performer intake , MSD dizzy + msd 6al
I run 36-38 degrees total advance. Headers , dual exhaust. Carb jetting straight out the box , but bigger shooters (I run a 2500 stall)

I'll tell you what I think has happened , and it happened to me , is that you have perhaps lost your cam ....

Hi, thanks for the reply, you know what, I hope that you are wrong but I was affraid that it could be the cam, I've put this new cam 2 years ago but my local engine shop told me that unless you put motor oil that contains Zink in it. It could damage my performance cam. And to tell you the truth, I've been running this cam with regular oil and adding GM OES additive because it contains a bit of zink but probably not enouph. I guess I'll probably have to check my cam, if I need a new one, I'll start using Joe Gibbs Hot Rod motor oil. It's full of zink to protect your cam shaft.

Can you tell me, your cam is bigger than mine, do you have any problem with Vaccum? brakes, lights etc.. ???

 

[Tepot]

It's overkill and no advantage over the stock 750cfm Qjet, but until the OP does some more investigation (see to-do lists above) we'll just have to wait and see.

It's overkill but with the proper jets. It will do a fine job

 

[Rodney Gold]

I have no vacuum problems at all.
Thing is , if the new heads came with higher rated valve springs , even if the cam was run in , you could have hurt it - your HP figures are very low for your combo and that , along with your carb backfire (which could also be a lean condition , vaccum leak or severly retarded timing) could point to lobe damage.
I would also try advancing timing till you ping under load and retard 2 degrees from then.
With my 2500 stall and 3.55 rear gears i do Mid 12's with that combo - on stock tyres.
The Holley st avenger series is a very good replacement carb for a performance 350 , 770 is just dandy..- far better than the stock 750 Holley.
It's infinately more tuneable than anything else out there. I even use the same carb on a 390kw/700nm 454.
I use the comp cams cam additive stuff at every oil change..havent lost a cam since starting that and following their break in proceedure posted on their website.

 

[Tepot]

I have no vacuum problems at all.

I would also try advancing timing till you ping under load and retard 2 degrees from then.
QUOTE]


well. that's what I did at start, no pring, lots of power and no backfires through the carb. But I had that white smoke coming out of the exaust as soon as I was over 3000 RPM.

then got the car on the timing light and it was way to high, Then engine shop said they where surprised I didn't blow up a piston. So they've put a total of timing of 34. White smoke stopped, but then backfires started and incredible lost of power.

I've called the engine shop today, They said that my cam can't be bad, if it was, valve would've became loose and knocking.

So I'm wondering now, Is my problem timing??? distributor gone bad?

 

[Rodney Gold]

Hmmm
The cam can be bad without a "valve coming loose and knocking"...your machine shop is wrong there, it's a lobe that will wear...not the base circle of the cam. Generally if a cam has gone very bad , a lot of the metal will be in the oil , take some white paper and drip oil from the dipstick onto it and look at it in the sun , any glints = bad. Also connect a vac guage to the engine - any "flickering" of the gauge can indicate a valve problem. If , and touch wood it isnt the case , the cam is gone , then you might as well pull the motor and refresh it as there would be metal in the oil which wont do your bearings any good - then you know you starting with a clean slate anyway.

As to timing , Depends on how they set the timing and of course whether the timing mark on the damper is accurate.
Set timig with vac adance to the distributor disconnected ...use a dial back light and set to 36 degrees at 3000 rpm. Reconnect vac. Dont worry bout where it lands up at idle

At any rate I have found with ally heads that the timing can be advanced quite a bit ...
You say you never heard pinging and your advance settings cured the problem but you had white smoke? how much white smoke , clouds or just a bit , blueiush smoke is normally oil burning , white smoke is never oil burning , it is something else like antifreeze or atf burning , could be the heads were not installed correctly and you getting water in the combustion chamber or have a bad head gasket or the like , you might not see water in the oil or the traditional oil that turns into mayonaise in that case ... That would also contribute to a power loss...

 

[Tepot]

Thanks for the response, you know what, there is so much possibilities and I've put so much money into it without being able to resolve this issue. I've decided that I had enouph.

I've called the engine shop. They've found a 400 small block, they will build me a 406 ci and they will use re-use my Cylinder Heads, intake, carb and cam if it's good, if not I'll buy a new one. they will use my old stuff and buy new pistons etc..

This should be the end of all my problems and will give me over 400 HP for sure. there problem fixed. Go Big or Go home !!!

I will probably save money going that route instead of paying everytime for trouble shooting. It is an old engine and I'm not gonna play with it anymore.

thanks for all your responses. I'll repost when I have all that work done and give an update.

 

[JohnZ]

They've found a 400 small block, they will build me a 406 ci and they will use re-use my Cylinder Heads

Make sure they know to drill the added holes in the deck surface of your heads to match the steam holes in the 400 block deck.

 

[Vettehead Mikey]

Thanks for the response, you know what, there is so much possibilities and I've put so much money into it without being able to resolve this issue. I've decided that I had enouph.

I've called the engine shop. They've found a 400 small block, they will build me a 406 ci and they will use re-use my Cylinder Heads, intake, carb and cam if it's good, if not I'll buy a new one. they will use my old stuff and buy new pistons etc..

This should be the end of all my problems and will give me over 400 HP for sure. there problem fixed. Go Big or Go home !!!

I will probably save money going that route instead of paying everytime for trouble shooting. It is an old engine and I'm not gonna play with it anymore.

thanks for all your responses. I'll repost when I have all that work done and give an update.

Sounds like an extreme solution for what could be a minor problem. Did you look at your ignition? The first generation Pertronix pos are famous for erratic ignition (right before they die and leave you stranded)

 

[Evolution1980]

Sounds like an extreme solution for what could be a minor problem. Did you look at your ignition?

I'm with you on this one.
As well, based on what Tepot has said, I'm somewhat questioning the technical expertise of his dyno shop. Wondering if they aren't more versed in digital tuning as opposed "old technology" tuning.
On the other hand, he may not be relating every thing they've been telling him.

 

[Crimson Thunder]

Back to the first post. Did you use the same dyno for the before and after dyno runs? Different brand dynos can have very different results.

 

[Rodney Gold]

He's not just having dyno porblerms , there are other issues ...
I think the 400 block is a fine solution - apart from the go fast bolt on stuff - he has 50+ cubes extra and will get a lot more low end grunt...
My advice is to use a new cam and lifters in that set up , 400 hp and a huge bump in torque is easy...

 

[Tepot]

Back to the first post. Did you use the same dyno for the before and after dyno runs? Different brand dynos can have very different results.

Same dyno yes. It's not like you have much choice here in New-Brunswick , Canada. there is only 1 dyno around.