Okay; I've been posting on the TPI section but now I think the problem warrants general engine tech help. For those of you who don't know, I built a 355 using the complete Edlebrock TPI package (58mm TB; “Hi-Flo” baseplate; Hi-Flo runners; Performer Aluminum Heads; Tubular exhaust), I added a relatively mild Crower cam (213/222 @.050" with .506/.525 of gross lift and 114* lobe sep – part no 00482LM) and Diamond ultra-light forged flat top pistons. The rest of the reciprocating assembly is comprised of forged Crower I-beam rods and Scat crank. I also have Crower roller lifters, runners and hardened push rods.

Anyway, with the 60cc combustion chamber on the heads and the flat top pistons, the engine's compression ratio is estimated to be around 10.83:1. The plenum is ported to the 58mm TB, but not the Hi-Flo runners. SO, when the engine was being dyno tuned it made 343 lb/ft of rear wheel torque at 3500 RPM and only 243 peak rwhp at 4000 RPM.

Originally, we thought it was valve float, but it wasn't; we also thought the failure to port the plenum to the runners was the problem, but that wouldn't cause such a dramatic drop either; we even thought that the TPI setup itself was to blame, prompting me to start looking into buying AFR heads, an HSR and a new cam.

However, the shop thought maybe the cam wasn't degreed right by the builder, so they did a quick compression test today and found that it was off the chart! Cam was probably installed too far advanced - and that cam comes with 4* of advance built into it to begin with.

But here's my question: the reason my power is dropping off is probably because the compression ratio is too high and the cam is too short, thereby compounding the problem - causing a significant increase in cylinder pressure and leading to the risk of detonation which in turn causes the computer to pull way back on the timing. So if I buy a bigger cam - 222/234ish @.050 - port the plenum to match a pair of new AS&M runners, but keep my Edlebrock baseplate and heads, will I still run into the same problems because of the LTR TPI? Can a good flowing TPI work with such a high compression ratio? Would it matter if I also buy new heads (the Edlebrocks flow 232/175 at .600" lift and 229/166 at .500" lift)?

I really would prefer not to buy an HSR, I'm not going to drag race the car and I'm worried it's just going to be a whole new can of worms. Ideally, I'd like to keep the TPI and my Edlebrock heads since they're already there. What do you guys think, bearing in mind that I WILL NOT BE TAKING THE CAR TO THE DRAG TRACK???

 

A stock engine has 220 psi cranking compression. You didn't say what off the charts was for yours.

You said you dyno'd but didn't mention anything about your AFR.

Your cam is not too short.
Put a degree wheel on it and check it. If it was installed out of time you will be lucky to not have bent valves or worse.

What are you using to tune with? If it's a stock TPI tune, then I'm not surprised at your results.

 

They didn't say what the pressure was - I just got an email from them saying that it was really high - I'll find out exactly tomorrow. The reason they haven't put a degree wheel on it yet is to save the extra expense if it wasn't the cam.

As for the AFR - I assume you mean at WOT - it was 13:1. The shop is saying that for the compression ratio I have (13.8:1) the cam is too short - you don't think that's correct?

As far as the valves being damaged - there doesn't appear to be any indication of that.

As for the tune, they were custom dyno tuning it when this problem (peak rwhp of 243) reared it's ugly little head - the car hadn't been tuned since the engine was built in 2003 and it just sat in the garage with fuel stabalizer until I finally found someone to do it here in LA.

Do you think that with that cam, and the high compression ratio that I have, it'll still get me in the 343 rwhp range if it's correctly installed? To Degree the cam it's going to cost me $1100 so I figure I might as well install a new one since the labor will be the same.

 

Cam timing does change where power happens. My cam was installed a tooth off one time, basically retarded 18 degrees from the recommended spec. It made crazy power from 4000-8000rpm, but couldn't get out of its own way under that range. Moving the cam to 4 degrees advanced dropped this powerband to 3000-7000, and I noticed less mph in the 1/4 but faster e.t. from properly spooling the turbo.

You'll notice a difference retarding the cam 4 or 8 degrees in a raising of the powerband up in the rpms. Your cam is smaller than I'd like, but either the one you have or the one you pointed out would be fine for the streets. The head flow isn't very impressive, but I have seen those heads make good power for what they flow. You could make a good bit more power from better heads, like AFR's that can flow in the 300cfm area, but I'm not sure the price would be worth it for a street car.

If you really have a true 10.8:1 compression, you definitely have room for more cam duration to bleed off some pressure.

 

thanks - my hesitation about the AFRs is that I'll spend the money and only get minimal returns since I'm not going to be reving it to 7K or racing the car down a strip.

So do you think that the AS&M runners - ported to the plenum - and a bigger cam will get me in or above the 343rwhp range?

 

I haven't really studied up stuff with the 3rd gen fuel injection intakes, but I'd do like you're thinking. I do know that a buddy of mine makes something like 325rwhp and runs 12.2-12.4s with a carbed vortec 350 with hardly more than a cam in the 225 degree duration and supporting mods like headers and a dyno tune.

 

GOD; if I can solve this problem, I'll be so happy! This project's been a nightmare since its beginning - IN 2001!

 

I'd think about degreeing the cam myself. You can buy the tools to do it, I think like $120 at summit, and the only other special tools you need would be a puller/installer for the balancer, can be rented for free at most parts places, and a puller/installer to get the gear on/off the crank. I guess this granted I have done this myself, but the degreeing tools come with directions.

 

At a WOT AFR of 13:1 you are right at the AFR point that tends to create detonation from a over heated combustion chamber, especially if there is a hot spot in the cylinder to light off and or the compression ratio is just too high.

Retune the WOT AFR so its bit richer say 12.5:1 maybe a bit richer.
A 13:1 ratio at WOT should be avoided. Its too close to the edge even if it makes the most power. The combustion chamber just runs too hot at 13:1 @WOT.

You do not need a new cam.
Degree the cam to verify its real specs and open close events. Move the camshaft you have so that when measured at .050" the intake close event occurs at 42ATDC.
When you are done doing this: The cam will be 1.5 deg retarded from true "straight up". Don't guess, assume or estimate, degree it accurately and move it to this specific .050" intake closing point 42°ATDC


The peak cylinder pressure point @WOT will be tamed and the rpm range will be extended. The upper rpm horsepower will improve And it won't knock. The over all torque/power band will be improved and not so spikey.

While you are degreeing the cam and correcting its timing events to suit your LTR TPI motor,, correct the timing tab/balancer TDC mark.

i guarantee its out of wack.

Put some decent fuel in the gas tank. Crap fuel just ain;t going to cut it.
High compression ratio motors need good gas.

Reduce the spark advance, an efficient motor that really packs the air in the combustion chamber, requires and wants less than typical spark advance for best power. Try 31-32deg ish at WOT.
Use cooler heat range non projected type spark plugs.
Stock plugs are too hot for a high perf/high compression ratio motor. Extended tip plugs run hotter. you want cooler.
A performance motor wants a cooler plug.

Be sure no plug body threads or other sharp edges are exposed in the combustion chamber that will cause preignition/auto ignition.
If the block was "0decked" you can swap to a thicker .051" head gasket and still have effective quench yet dial the cr back a bit. While you got the heads off consider taking a few CC out of the combustion chamber and remove all sharp edges. Thats a win win as you will enhance detonation/preignition resistance and tame the cr at the same time.

These heads are as cast production heads. Edelbrock leaves it up to you to port them and finish the job. These heads improve a lot lot with some porting. They will flow all the air you want need with a bit of hand work.
All you need to do is get the cr back down under the detonation threshold and get control of the AFR and timing.

Inspect all injectors for proper flow. The AFR guage only reads the average of the 8 cylinders. If 1 cylinder is leaner than the others it will tend to knock.

"To Degree the cam it's going to cost me $1100"

You need to get a reality check. The last cam I degreed in cost me $0. 'cause I did it my self. You can too.

If you have to pay someone else to do everything for you, why not just hire someone to drive the car too?

 

Wait a minute. Who figured you have 13.8:1 compression ratio? How are you getting that?

Maybe it was the same person who figured $1100 to check a cam with a degree wheel.

wtf?

I think it's time for you to get a handle on the facts, and probably find another mechanic before you make a big mistake.

You need to be armed with ALL of the facts before deciding on another course of action.

What tuning software was being used for your tune? and what have they changed so far? What does the timing curve look like?

 

I'm pretty certain the cr is right - I knew what the variables were and did the math - although I don't have it with me now.

As far as the cost - this thing is WAY out of control. I've had to re-do so many things it's been crazy. I just want it done. The shop where it's at is good and I trust them - it's just that they're not really familiar with this type of setup, but then again, out in Los Angeles, NO ONE IS! That's the problem.

For the tune, I got the full Moates emulator/burner, etc. and I think they're using TunerCat. The guy doing the tune is VERY knowledgeable, the shop is dedicated to Vipers and they also do alot of high performance European cars too. That's why I took it to them since they've always done right by me with my Viper. To degree the cam they have to pull the entire front of the motor off and that's what costs so much.

 

305sbc - where did you get the info on the cranking compression? I called the shop and they said that the cylinder pressure on mine was 220 pounds - but that's what you said is normal. I asked and he said that a stock 350 with 9.1:1 or 9.5:1 cr wouldn't be at 220 psi - where can I confirm this, do you know?

 

As per his first post.
The 13.8 is a typo based on his AFR I believe.


A stock, short cam 350 engine should have a cranking pressure of around 220psi (pounds- for short). If you cam it, or have a lot of wear and tear, etc etc you can be in the 180psi range. That's normal for an engine with 100,000 miles, or with an aggressive cam. A very aggressive cam might be in the 170 range. The actual number isn't important, it's more important that all cylinders are the same across the range.

10.8:1 is quite high, but depending on other factors, you might be able to get away with it. Running out of steam at 4000 RPM screams a few different problems. Valve springs could be one, cam installed wrong *could* be one, but I doubt it. The TPI setup is another, but it seems like it's been upgraded. I don't have the knowledge to confirm or deny that, as TPI is not my strong suit.

You definitely need to get doing this yourself. Do you have a garage to work in? Never trust someone else to learn and do it on your car, that gets very expensive...

 

at this point - I'm passed the point of "expense". The money I've spent far exceeds the value of the car and I'm willing to spend a little more just to finish it so that I can then, PERSONALLY, push it off a cliff! The valve float issue was already investigated and turned out to be okay. So we're thinking it's the install on the cam. Edlebrock sells its TPI package all day long and it supposedly makes pretty good power - but I think it's being installed on a stock compression motor and with a stock cam. The problem here is that I have a 213/222 cam with high lift - while not too aggressive, it's still alot more than the stock cam - and high compression flat top pistons with just 2 eye brow reliefs. So there's some detonation issues.

When the guys was tuning it, he said that he had to take a bunch of timing out of it - which makes sense if the cam is installed wrong particularly since that cam has 4 degrees of advance ground into it.

So, I guess, my question at the end of all this is whether I can still make good power if I trade the Edlebrock runners for AS&M runners and get an even more aggressive cam - but keep the Edlebrock heads and 10.8:1 compression ratio as is?

 

Hold on - what engine is this anyway? I'm trying to determine how 60cc chamber heads can make 10.8:1 ratio? I'm at 64 cc heads, zero decked, and i'm at 10.3:1. I didn't think 4 cc would give you half a point. Engine specs perhaps?

He'll have to take timing out of a 10.8:1 engine running on 93 octane - that's pretty normal. You need less static compression.

You could try different runners, and a more aggressive cam - But i'd personally recommend trading in the heads for something with like 68cc chambers (or porting your existing ones to open up the chambers) and keep the runners and cam. That's a good cam, great for street use, you just need a bit less compression.

Make sure you check the cam timing and spark plugs and other little things first though.

 

Just do a compression test on a stock engine. You'll see 220 psi or thereabouts depending on it's condition.

10.8:1 compression is nothing with aluminum heads.
Get a degree wheel and check your cam install. It's not that big of a deal of a job to do yourself. While you're at it, verify your timing mark on your damper. Also, go back over the preload adjustment on your lifters to make sure it's right.

I'm assuming you've already verified your knock sensor is indicating real knock, and that you've verified your throttle is opening all the way, with no blockage.

Too small of a camshaft is definately NOT your problem.

You're not running a stock CAT on the exhaust are you?

 

I don't have the numbers in front of me now - but I used the info provided with the forged diamond flat tops that I have - plus, if I remember correctly, it wasn't zero decked either; but I did the math 10 times and it kept coming up the same.

No - its not a stock cat and they tested the back pressure and it was within normal limits - I actually confirmed that it was normal with I believe Jim from AS&M.

 

Well you had to use your actual measured deck height and compressed gasket thickness to do it correctly. Consistent doesn't mean correct. I don't know as not having done your measuring, but I also doubt your static ratio is even as high as 10.8:1
Even so, that's nothing for aluminum heads and points to another problem.

Personally I wouldn't run less than 11.0:1 with aluminum heads, and I always use camshafts slightly smaller than yours. The facts don't add up unless there was a problem with the cam install.

Theorizing about other people's cam/compression combos to make more power isn't a solution to your problem. I'm not trying to tell you that this part is better than that, or that so and so parts make so much power. I'm just trying to steer you to do the proper troubleshooting to get closer to solving your problem.

 

I appreciate it thanks - I do have the gasket thickness and the deck height, but that's all at home now. I'm getting SO many mixed suggestions - cam is too small; cam is just right; LTR TPI sucks; LTR TPI is great... you know what I mean? I just want to be done with this - it's not a hobby if it's keeping me up at night wondering what I need to do.

 

You must live in a different "Los Angeles" than me. I guess "The OC" must be a long ways away from being considered "Los Angeles"?

I think you're barking up the wrong tree/s. Not to mention a whole bunch of other things.

My .02:

Your heads suck. Nothing that Edelbrock makes, out of the box, does well. Ever. I have yet to see it. With awful flow #'s those have and a whole 165cc on the intake I'd be surprised to see any real HP from these.
Your intake is apparently not ported. You may as well have left the stock base on it.
I'm not familiar with their runners, but I have little faith.
You have a fairly mild cam.
Your injectors are likely a very questionable brand (Accel), not to mention they are way more than your needs. A 24# injector would do you fine, a 30# is just overkill... esp with only 243 RWHP.
I'm no fan of your exhaust either.
I dont think there is any problem with your valve springs. 110seat/300 open sounds ok to me. Not ideal, but that is not the problem.

Just for giggles, I threw your numbers into Desktop Dyno. I know its just a computer simulation program, but its kind of funny. You know what I got? If I take your numbers, figure a 20% drivetrain loss, I get:
304HP@4000
429TQ@3500

On DD I get:
344HP@4500
467TQ@2000 (the TQ peak may be lower) At 3500 it is 454TQ

So... not really all THAT far off.

No offense, but that combo is the picture perfect build of what NOT to do. Almost like that "Magnum TPI" or whichever magazine combo it was that failed miserably.

I'm curious about a few things, like... what your timing curve is. How your BLM's and AFR look. Is this a MAF or SD car?
If I was to do anything to your car at this point to get more power, probably the first thing I would do is get rid of those heads. Sorry. Can probably work with the cam, and the intake could be ported to get some more power and put on a better flowing exhaust to pick up a little (I'm talking 10-20HP each or so), but those heads are doing you no favors whatsoever. They're not much better than stock. Bolt on a miniram, and things are just going to get worse. I'd stop going around in circles trying to figure out what to do and what to replace and who to believe, start with the heads and go from there. If you are looking to avoid that at all costs, then port your intake and get some better headers but I dont think either of those will put you where you want to be. As far as the whole LTR thing goes, unless you start doing some serious work to it, its going to peak at 4500-5000RPM on a good day. Bolting on parts, aside of maybe the ASM runners helping a little, isnt going to do anything. That base needs to be ported out, and you need the right engine under all of that or some siamesed runners to get the peak HP RPM number up higher.

 

Thanks for that. But honestly, tell me what you really think. I know; I learned the HARD way. I wil NEVER buy anything Edlebrock again. They're okay if you want to add oomph to an otherwise stock setup, but for my short block - all forged reciprocating assembly and high compression ratio - they SUCK! Although I shouldn't talk too much **** about them since I'll be selling the heads and the runner - along with that cam. Also, I had no real way of getting the car to the OC and even if I did - I didn't know where to take it. The place that built it in Burbank screwed it up to begin with and they were a well reputed "hot rod" shop.

However, you have to admit, 343 rw torque is pretty good and I'm sure it would've made more rwhp if the cam was degreed in right and the plenum was ported to the runners. But that's neither here nor there.

At this point, it looks like I'll be getting the AFR 195cc heads (part # 1040) and a more aggressive cam too (222/234ish). I'll also get the AS&M runners and this time I'll make sure that the plenum is ported properly to them. With that, I assume I'll be okay. I don't want to go to an HSR or stealth ram; just too much hassle and not really necessary since this will only be a street car.

And to answer your questions: I don't have the timing curve here - but my AFR was 13:1 at WOT; and the car is a MAF.

I've spoken to AS&M quit a bit and they tell me that the baseplate is fine - although there is a place out in your neck of the woods that can port the hell out of it, getting it to flow 300cfm - will cost me $620 though. And that's where the delema lies - if I'm paying $450 for the AS&M runners and then $620 for the porting of the baseplate - I might as well get a stealth ram, BUT I DON'T WANT TO! See how circular this is????

Whatever; I'm just hoping that with the AFR heads, a bigger cam, the AS&M runners and the plenum ported, I'll be able to get it to rev into the 5000 rpm range (GOD willing 5500)which will undoubtedly make alot of rwhp judging from the 343 rw torque at 3500 rpm. However, we'll have to see.

 

Why keep paying other people to get you nowhere fast besides a lighter wallet? Port the base yourself. Find some SLP runners, and port those. Both will save you a lot of money, and it will flow a lot better. If you just want to pay people to do all the work for you, you'd be better off spending that money on your ZO6.

I figured it was MAF, just knew it. Just another hurdle to have to overcome, most people know nothing about how to make it work and work well.

 

I would, but I don't have the time or the energy. It's just easier to pay to have it done. When I was in college, I converted the car from an automatic to a manual and I did it alone - figured out how to rebuild the gearbox by myself as well. But those days are LONG over. And YES, that's one of the biggest issues - I COULD BE SPENDING THE MONEY ON THE Z06 or even the VIPER! That's what makes this "project" so hard to swallow.

 

I paid $125 to have my base ported, but I went to it with a grinder afterwards anyway. If you are going to spend $600 that is just WAY too much. You could have it extrude honed for that much.

Find some different places to do the work.

Given how much time you want to spend doing your own work, I'd suggest converting to SD as well unless you find a tuner that knows TPI MAF.

 

the tuner knows MAF - all vipers are MAF and he's very good with it. he Place that I called is out by you - I believe its Dr. Js. They'll "raise the ceiling, weld it and the port them to flow about 300cfm." So I figured to leave it alone - but if you're saying that I can get close to that without that price tag, I'm ALL EARS! Where do I call?

 

Just because he knows how to tune a car with a MAF does not mean he knows the limitations of the one in your car, in fact I will bet he does not.

 

I know my last settup wasnt fully dailed in, ( AFR in the 15-1 range on the dyno) but with that said, your current settup should be putting down more than it is.
Just for reference, with a Crane Cam HR 276-2S-12 IG, .488I, .509E, 214 and 222, old school Trick Flow Twisted Wedge heads ( crap valve springs ) 9.2ish-1 compression ratio and ZZ4 shortblock it put down 300rwhp and 360ish rwt.

Didnt see this asked, but what exactly are you expecting out of this engine?

 

I'd like to see 350rwhp. I think because the cr is so high, the computer is pulling way back when it gets up there; according to some guys here, the 13:1 AFR is right where knock occurs and so because my cam might be improperly degreed, I'm having this problem. I have a feeling that if I had 9.5:1 compression, I'd be getting more out of it.

 

Your combination is not that bad it should run good but it will never make 350 RWHP. Your combination is designed as a low RPM torque set-up. The intake runner length plenium to valve is 23" and that length is designed to operate from 2500 to 4500 RPM. To make 350 RWHP you will need to make max power around 5500 RPM or higher in a 355 and the combination of parts will not allow this to happen. Changing the runners will not help because the length of the system will remain the same. What you need is a higher RPM set-up like the Superram plenium and runners bolted to your existing manifold and heads. That may have the ability to break 300 RWHP but it still will not hit 350 RWHP.

If you decide to keep your current combination of parts I believe you could get around 275 RWHP and 350 RWTQ with tuning and verification of the correct cam installation.

The MAS system is fine you do not need a speed density system, just make sure you have a good tuner.

I have played with my car for years and I progressively built it up over the years and one of my first combinations was a 355 long tube runners engine with similar parts to yours. It made 276 RWHP and then I swapped to a superram plenium and runners, that single change was worth an additional 33 RWHP and additional RWTQ over the long tube runner design.

Look at my sig, the combination I have now has somewhat better heads, bigger cam and the supperram plenium when compared to yours but other then that it is very similar. If you are planning to change your heads and cam I would definately switch the intake to a supperram design. Easily one of the best modifications I ever did. (I also like the HSR)

 

Get the HSR and afr 195's. Should do it with mild high lift cam.

Your combo doesnt seem that bad right now for what its making. 4000 rpm peak does seem a bit short of what normally would happen, i would have expected peak closer to 4400-4500 but fall off quickly after that. Considering unported base and runners and those not really any better than stock heads, 243whp isnt all that bad. I would think 250's maybe 260 is doable on that setup. Maybe the cam is not in right, but i dont see much more than 10whp gain with cam in perfect.

My HSR swapped L98 with 1.6 rockers, full exhaust and a very lean tune made 254whp/315wtq. I think the stock TPI setup was 230whp or so. So you should see more than 243hp from your setup. Thats why I was thinking closer to 260.

Nothing wrong with MAF, I find it very easy to tune. Easier than SD. stock MAF was more than enough to make 400whp on my 383 so it should handle a mild cam head L98.

IF you have good gas in the car, richen it up to 12.5 because 13.0 is lean, especially on the dyno. Find out what timing you are running. It should not need more than 35 degrees