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Old 04-19-2013, 07:39 AM
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355 first timer

I recently built my first motor. With the help of an experienced friend. Of course I made a few bad choices 2 years ago when I began it on a budget but I'm just now cranking it up. It's a 355 with dish pistons(unsure on compression) h beam rods and eagle steel crank on bottom. The problem is mainly in the top. First big mistake and most crucial was pro comp heads. Advertised to have already ironed out its old problems. No trick flo or afr heads but should at least be better than stock right??? They're 210 cc intake, 325lbs spring pressure 1.225 open and 140lbs at 1.8 closed and 600 max lift. The cam is a hydraulic flat tappet 214 intake and 224 exhaust at 050. List is 444. My pushrods are 100 longer than stock and have 1.6 ratio roller rocker arms. Summit street and strip carb and stage 2 intake. Somewhere here I made a bad mistake. This bored and cammed 350 is making less power than my old l65 weak 350 bottom end and heads. I am not sure if the double springs are way too much for these summit hydraulic lifters or if these heads are so big i can't make power with these mid range power cam and lifters. Can't afford another set of heads and only have my old heads to put back on. Should I try and go balls to the wall cam and stall (if this will even fix it) or put my old heads on and settle with a bored and cammed decent 350?

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Old 04-19-2013, 08:17 AM
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Originally Posted by Rickyellison View Post
I recently built my first motor. With the help of an experienced friend. Of course I made a few bad choices 2 years ago when I began it on a budget but I'm just now cranking it up. It's a 355 with dish pistons(unsure on compression) h beam rods and eagle steel crank on bottom. The problem is mainly in the top. First big mistake and most crucial was pro comp heads. Advertised to have already ironed out its old problems. No trick flo or afr heads but should at least be better than stock right??? They're 210 cc intake, 325lbs spring pressure 1.225 open and 140lbs at 1.8 closed and 600 max lift. The cam is a hydraulic flat tappet 214 intake and 224 exhaust at 050. List is 444. My pushrods are 100 longer than stock and have 1.6 ratio roller rocker arms. Summit street and strip carb and stage 2 intake. Somewhere here I made a bad mistake. This bored and cammed 350 is making less power than my old l65 weak 350 bottom end and heads. I am not sure if the double springs are way too much for these summit hydraulic lifters or if these heads are so big i can't make power with these mid range power cam and lifters. Can't afford another set of heads and only have my old heads to put back on. Should I try and go balls to the wall cam and stall (if this will even fix it) or put my old heads on and settle with a bored and cammed decent 350?
Problem may be on top, but I guarentee its because of the bottom....dish piston, likely 0.025 in the hole, low low comp, way too big head, I bet your right and your stock motor was stronger.....you need to find out what machine work was done ie: was it zero decked, find a pn# for your pistons, what's the chamber size on your procomps, they were available in 58cc so maybe its not that bad....but you need to know all of these things before you can go any further.....without knowing, you need to tear it down and start from the bottom up. Your pro comps aernt that bad, and with lots more cam, lots more compression and a willingness to turn the thing hard they will make decent power....but you need to know what you have before you go any further.
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Old 04-19-2013, 10:41 AM
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Sorry if your thread is going to be the example.


A bunch of guys on here almost daily post about how do-overs cost twice as much.How matched parts builds are the only way to go even at the lowest budget build.Those heads are huge for anything mid range,low compression.I'm going to make this real simple for you.Most of what you want to know is in the Wiki link(s) at the top of the forum.Read it.Then ask questions for what you don't understand.
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Old 04-19-2013, 10:55 AM
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Sorry if your thread is going to be the example.


A bunch of guys on here almost daily post about how do-overs cost twice as much.How matched parts builds are the only way to go even at the lowest budget build.Those heads are huge for anything mid range,low compression.I'm going to make this real simple for you.Most of what you want to know is in the Wiki link(s) at the top of the forum.Read it.Then ask questions for what you don't understand.
It really should be stickied as a "what not to do" but hey, we have all been there and done that, and the stubborn ones more then once (i fit that category). Hopefully he can find some paperwork on his parts and maybe it won't be as bad as it sounds.....
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Old 04-19-2013, 11:11 AM
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Originally Posted by Rickyellison View Post
I recently built my first motor. With the help of an experienced friend. Of course I made a few bad choices 2 years ago when I began it on a budget but I'm just now cranking it up. It's a 355 with dish pistons(unsure on compression) h beam rods and eagle steel crank on bottom. The problem is mainly in the top. First big mistake and most crucial was pro comp heads. Advertised to have already ironed out its old problems. No trick flo or afr heads but should at least be better than stock right??? They're 210 cc intake, 325lbs spring pressure 1.225 open and 140lbs at 1.8 closed and 600 max lift. The cam is a hydraulic flat tappet 214 intake and 224 exhaust at 050. List is 444. My pushrods are 100 longer than stock and have 1.6 ratio roller rocker arms. Summit street and strip carb and stage 2 intake. Somewhere here I made a bad mistake. This bored and cammed 350 is making less power than my old l65 weak 350 bottom end and heads. I am not sure if the double springs are way too much for these summit hydraulic lifters or if these heads are so big i can't make power with these mid range power cam and lifters. Can't afford another set of heads and only have my old heads to put back on. Should I try and go balls to the wall cam and stall (if this will even fix it) or put my old heads on and settle with a bored and cammed decent 350?

Who tuned it? What carb, what ignition? What headers? What exhaust? Even with that poorly chosen cam and pistons you should be over 350hp.

The PC heads are NOT the problem. Going "balls to the wall" on the cam will make a bad problem MUCH worse.

PM me and I'll try to walk you through the basics.
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Old 04-19-2013, 12:37 PM
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You know Ricky, I read this kind of stuff all the time and it just makes me want to sit down and cry. AP72 has offered to try and help, through the Private Message system on this forum. He may or may not be able to help you, but it's worth a try.

I would tell you to unbolt everything and start over, but that's just the way I am. You have no idea what's inside the motor or anything about it and that tells me that you will not know which way to go to fix the problem.

I suspect that this is the cam you used, but you and your experienced friend didn't understand that the static compression ratio has to be matched to the cam timing in order to make a good combination. Immediate problem is......you don't know the static compression ratio of the motor.......
http://www.summitracing.com/parts/su...make/chevrolet
I would disagree with AP72 though. I think the heads are the biggest problem right now. That cam is pretty mild and would work with a lower static compression ratio that you probably have in the motor, but the heads would work way better on a small block 427. A good runner size for a 355 street motor would be in the 180cc range.

There are many good minds on this forum and most all of them are willing to donate their time to help you if you'll hang in there and answer all the questions put to you and your experienced friend.
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Old 04-19-2013, 12:40 PM
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You know Ricky, I read this kind of stuff all the time and it just makes me want to sit down and cry. AP72 has offered to try and help, through the Private Message system on this forum. He may or may not be able to help you, but it's worth a try.

I would tell you to unbolt everything and start over, but that's just the way I am. You have no idea what's inside the motor or anything about it and that tells me that you will not know which way to go to fix the problem.

I suspect that this is the cam you used, but you and your experienced friend didn't understand that the static compression ratio has to be matched to the cam timing in order to make a good combination. Immediate problem is......you don't know the static compression ratio of the motor.......
http://www.summitracing.com/parts/su...make/chevrolet

There are many good minds on this forum and most all of them are willing to donate their time to help you if you'll hang in there and answer all the questions put to you and your experienced friend.
It could be a poor cam choice, but its a basic RV cam, with dished pistons and 64cc heads, that's not too unusual of a cam. If it runs without any weird noises or smoke I'm guessing it just needs to be tuned. We all know the tune can make a really good engine run like ****.
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Old 04-19-2013, 12:45 PM
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Yeah, I added some other thoughts to my post as edits. Please go back and re-read it. Thanks.
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Old 04-19-2013, 12:57 PM
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Been said many times before the tune begins with the build......................
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Old 04-19-2013, 01:32 PM
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The compression ratio is low. Further the valve job probabily sucks on these PC heads.
Leaky valves... Start by doing a compression test.

Ya it a lame build but you can fix it.
You don;t say what you were actually trying to achieve.
If you want real power plan on reworking the WHOLE THING.

The PC 210 heads will need a lot of work to get them where they need to be for real power.
Do no assume they are 64cc. Do not assume the valves seal.
They will need full porting.
Post information on the car and power level desired and car purpose details.
You tried the cheap route buying all the discount parts, now you can $FIX IT$$$

If you wanted big torque the heads are wrong and the cr is too low.

Start by doing a compression test. Plan on replacing the pistons.
Or supercharge it.

Just curious: What are your old cylinder heads? casting number?

Last edited by F-BIRD'88; 04-19-2013 at 01:41 PM.
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Old 04-19-2013, 03:44 PM
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Originally Posted by Rickyellison View Post
I recently built my first motor. With the help of an experienced friend. Of course I made a few bad choices 2 years ago when I began it on a budget but I'm just now cranking it up. It's a 355 with dish pistons(unsure on compression) h beam rods and eagle steel crank on bottom. The problem is mainly in the top. First big mistake and most crucial was pro comp heads. Advertised to have already ironed out its old problems. No trick flo or afr heads but should at least be better than stock right??? They're 210 cc intake, 325lbs spring pressure 1.225 open and 140lbs at 1.8 closed and 600 max lift. The cam is a hydraulic flat tappet 214 intake and 224 exhaust at 050. List is 444. My pushrods are 100 longer than stock and have 1.6 ratio roller rocker arms. Summit street and strip carb and stage 2 intake. Somewhere here I made a bad mistake. This bored and cammed 350 is making less power than my old l65 weak 350 bottom end and heads. I am not sure if the double springs are way too much for these summit hydraulic lifters or if these heads are so big i can't make power with these mid range power cam and lifters. Can't afford another set of heads and only have my old heads to put back on. Should I try and go balls to the wall cam and stall (if this will even fix it) or put my old heads on and settle with a bored and cammed decent 350?
The problem most likely isn't the heads, we’ve used them on a number of budget builds and have no issues with them other than the port are rather large for their flow compared to pricier heads.

The problem is most likely with compression combined with the cam combined with the selection of a 210 cc port head. Starting with the latter a 355 expected to operate no higher than 6000 RPM, a 210 cc port is too big which kills off the mixture velocity needed to overcome the reversion forces of the piston pumping mixture back into the intake when the cam is late to close the intake valve. The smaller port 195 cc head would have been a better choice as it speeds the mixture up at a lower RPM which overcomes the reversion forces sooner thus bringing the power band lower into the RPM range.

To a big extent the cam is one of those old grinds that are so cheap guys on a budget can't resist. They do have an advantage of using a lot of duration for their lift which is certainly easier on the lobes and lifters. The down side is that these cams have very long ramps where the valves, intake in particular, are held slightly off the seat for a long time. Your choice of 1.6 rockers only exacerbates this problem. The very long ramp hangs the valve almost but not quite closed exposing the inducted mixture to the force of the rising piston which blows it back through the intake valve into the ports and manifolding, finally out the carburetor, hence the term reversion. As I said in the previous paragraph, the only cure is more RPM to get the mixture velocity up high enough to overcome the reversion force. The better option here is a more modern lobe design like the Comp Extreme Energy or the Lunati VooDoo. These cams use a much more aggressive lift rate with much shorter ramps so the valves aren't hanging almost but not quite closed for long periods of time. The down side is they are hard on wear between lobe and lifter when not properly broken in and high levels of ZDDP additive are not kept up with in the oil. ZDDP is a consumable it is not wise to stretch oil changes. The longer the oil is in use the lower becomes the ZDDP percentage from where it started in the fresh oil change.

The third major contributor to the problem is compression and the relative of squish and quench. Piston selection can kill the motor if you didn't pay careful attention to what you ordered. Circular dish pistons simply kill squish and quench which are needed for successful ignition and complete combustion as well as their mechanical octane contribution to the fuel offering as much as 4 to 5 octane’s worth of performance above the fuel's octane rating. Flat tops are the best choice piston with a small chambered head for best performance, period! The next best option is the so called D dish, D cup, or step dish pistons, These put a flat surface close to the squish/quench step of the head (you want as close to .040 inch as you can get, a couple thou over or under will work) while using a D or step depression under the head's valve pocket to dial in the compression for the fuel you with to use. Many aluminum headed engines have been built with your heads running 10 to 1 compression while running just fine on 87 to 89 octanes unleaded. You gotta be careful with this design I don't recommend it for the casual engine builder, but it can be done.
The other huge issue for pistons that traps the unsuspecting builder is the presence of what's called rebuilder pistons. These pistons measure 1.54 inch between the pin center and the crown edge, however, the stock replacement 350 piston measures 1.56 inch. The rebuilder piston is made for the mass rebuilders that zero deck all blocks they run through their shop; they restore the original .020-.025 inch crown to deck clearance in the decked block. If these pistons are accidently used in a block that wasn't zero decked (it happens a lot) there is a significant loss of compression. When a late closing cam is used in an engine it results in high reversion. To recover the power lost to the lower density mixture left in the cylinder it is a requirement to greatly add to the compression ratio as a means of restoring the bottom end power lost to reversion. This in large measure is the reason competition engines use such seemingly extraordinarily high compression ratios. There is a thing called the Dynamic Compression Ratio (DCR) which adjusts the Static Compression Ratio (SCR) (SCR being the measure of all the cylinder's volumes divided by the volumes above and including the piston crown when it is at TDC) for the loss of cylinder volume resulting from the rising position of the piston when the intake valve closes in crankshaft degrees. The later the valve closes to larger is the loss of effective stroke. A good calculator for this is at this link <<< United Engine & Machine Co. Incorporated >>>.

The DCR minimally needs to be 8 to 1. This would sustain regular fuel in and engine with iron heads and ordinary (smog era) combustion chamber. For a Vortec head this could be pushed to 8.2 or 8.3. You could go further but that would step the fuel grade up to 89-92/93. For an aluminum head like the L98 chamber this can be pushed to 8.5 on regular to 8.7 on premium. A better aluminum head that mimics the Vortec combustion chamber which your Pro Comps do can be pushed to 8.7 on regular and 9.0 on premium.

So unfortunately you have gotten yourself into a position of not knowing what the all important compression ratios (SCR and DCR) are for your engine nor probably whether you have a rebuilder piston in there or one with the OEM pin to crown height. Without that knowledge you really don't know where to turn. First thing is to get the heads off and identify what the volumes of the parts are that establish the SCR. From there you can use the linked DCR calculator to figure the DCR. You will also need to know the connecting rod length, standard SBC is 5.7 inches for the 350's 3.48 inch stroke. IT looks like you have the cam timing, The problem with the DCR calculator is the assumption of 15 degrees added to the .050 inch closing point, but for these older design cams the degrees between .050 measures and .006 (considered by the SAE as valve closed timing) can easily be 5 to 10 more degrees than KB's average of 15, this makes a huge difference. Keep in mind how serious this is compare a 28 inches of water depression on a flow bench is only 1 PSI while the rising piston is at this point producing from 20 to 50 PSI, so the backward force on the flow past the valve in CFM is a lot more than would be registered at that same low lift on a flow bench. In terms of bottom end power loss this results a huge number.

So the combination of large ports with a long duration cam having 1.6 rockers and most likely low compression is really crippling this motor. I'd recommend starting with getting control of the compression as you just can't get performance with out it. If you get that correct, even the 210 cc ports and long cam can be sorted out with tuning to a very good degree.

Bogie
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Old 04-22-2013, 06:07 PM
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Well the heads are traded. I now have the vortec heads with 510lift on comp springs and are polished. Stick rockers. Now what kind of pushrods do I need and will the hydraulic flat tappet cam I have in there work with these heads or do I need to change my standard timing chain and cam?
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Old 04-22-2013, 06:35 PM
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Well the heads are traded. I now have the vortec heads with 510lift on comp springs and are polished. Stick rockers. Now what kind of pushrods do I need and will the hydraulic flat tappet cam I have in there work with these heads or do I need to change my standard timing chain and cam?
Given there are so many variables you need to use an adjustable push rod with a light spring on the valve to make a witness mark on the valve stem. Follow the link this is one of several ways to do this, it is reasonable.

COMP Cams® - Sorry...

This points out the variables that cause this to be more complicated than just throwing some OEM parts into it and calling it good. A big issue will be how uniform the valve stem height is above the spring pocket. The process of renewing the valve seats of the head and of the valves themselves causes the valves to sink into the seat. This raises the stem in relation to the spring pocket. A good valve job would include the time to equalize the height for all the valves to some uniform dimension. Often this isn't the case, so the first thing is to do the installet height measurement to determine if they are close enough that one valve's measure will be suitable for all others.

Further the selection of push rods needs to be the hardended type or not. The Vortec head is designed to use a self-guiding rocker, if you are using these then you don't need a hardened push rod nor push rod guide plates, unlike older heads the latter guide was in the head casting itself. The Vortec has no such feature, so if the rockers are not self-guiding then sheetmetal guides have to be added or the rocker type changed. Sheetmetal guides also require that screw in studs with a hex be used which requires machining the rocker stud down and tapping the remaining stud hole.

Bogie
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Old 04-25-2013, 05:47 PM
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No need to tear the engine apart to see if you have rebuilder pistons. An easy way to measure the squish on an assembled engine is to stick a length of 1/8" dia solder into the combustion chamber thru the spark plug hole, up into the squish area. Rotate the engine, pull the solder, measure it's thickness.

If it's got a ton of squish, you could just make the best of it. I've got a 355 that i put together on purpose w/ .094" squish. Flat tops, ported -10 Brodix heads, around .650" solid roller w/ 114 LCA. It only cranks 90psi, but it gets 20mpg on 87 octane. Not much power NA, but i built it to spray on regular gas. Runs pretty damn good, 5's in the 1/8th.
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