First this is not a TPI engine.

Im running a modded HSR, 200cc alum. Toplines, and a XR282HR-110 Comp hyd. roller with R lifters (1/4 turn past zero lash) and 987 Comp springs. KB lightweight pistons, Scat rods, nodular crank, assy. balanced professionally. SLP 1 3/4" headers, 3in. exhaust. Stock distributor, MSD coil, module, etc. Stock fuel pump.

The problem is that the engine completely runs out of power at 5800rpm...no valve float or gradual loss of power...just no more go. As expected, it really begins to pull at 3500-4000, but it pulls very strong only to 5800, then stops. The fuel pressure does not drop when this happens. I am aware of the high-rpm shortcomings of hyd. cams, but Im not positive that this is the problem. Could the stock distributor be losing spark and hurting power? Is a 2 1/2" y-pipe too small and strangling the engine? Any ideas would be appreciated.

 

just to get this started...

how long has it been since you did a tune-up? Looks like you have a fairly beefy setup there, but if you're still getting bad connection from the rotor to the terminals (or points or whatever they are in the dizzy cap) then you still wont be getting very good power output at higher RPM even with the other beefy components

Now I am craving beef

 

The engine (including everything on it except the distributor itself) has less than 1500 miles on it. The plugs all look good, the fuel filter is new

 

I am not familiar with the details of the manifold. What rpm should it pull to?

 

An HSR? Should be good well beyond 6,000rpm on a 350.

You said you have a stock coil, is it a possibility that it just can't keep up at those revs? I noticed a small improvement at higher rpm's when I put a MSD coil on my car. Granted, I don't have the ignition box, but the coil did help a bit on the top end.

 

Is the tach accurate? If it is the factory tach it could be way off. If the car has cats they could contribute to that problem.

 

Coil is MSD. Aftermarket (Sportcomp) tach. No cats.

 

my bad, when I went through it i somehow mistook MSD coil, and Stock dizzy.

Wish I could tell you.

 

An MSD 6A/6AL or Crane Hi6 will work wonders for that setup. The dizzy *should* be okay, but an MSD unit obviously would be a nice upgrade.

 

a stock HEI with MSD module and good coil will certainly hold it's own against one with an MSD box. sounds like you either have an advance problem in the distributor, a cam timing issue, or fuel issue. i'd check the a/f ratio on a wide band and check total timing with an advance light.

 

Do you mean the timing with the computer-control wire plugged in? The base (unplugged) timing is around 8* advanced. The cam was degreed (well, checked) when the engine was assembled. Oh yeah, Im also running LS1 (25lb?) injectors, and PCMforless programming.

Interesting. Do you think its a tuning issue? Possibly an issue with the programming?

 

Stock fuel pump would be my target.

I had similar problem on my old L98, HOT cam, GMPP 'Vette heads after switching to an HSR. The Delco fuel pump had done well w/ the TPI and only revving to ~5600rpm, but it just couldn't keep up with the HSR and higher revving.

I diagnosed it by disconnecting and capping the fuel pressure regulator vacuum reference, connecting my fuel pressure gauge, taping the gauge face to my windshield, and going for a spin.

Sure enough at around 5000rpm WOT the fuel pressure would start dropping...the longer I held the gas open, the further it fell. Soon as I lifted, the gauge snapped right back.

I swapped in a Walbro GSS-340 high volume/high pressure in-tank pump and have had no further issues with fueling.

 

I agree, take a fuel pressure gauge and tape it to your windshield and go for a drive and nail into it somewhere and see if it drops at WOT. If so, time to change the pump. Its probably starving the motor at those high rpms.

 

I still think an MSD/Crane box will help in the upper RPMs. It made a huge difference on my last car. I'm going to buy an MSD 6A one of these days again..

I had thought he said FP was okay, but then again, it may have just been a driveway test and not under load.

 

He needs to check FP under WOT. I had the same problem my stock pump could not keep up with the LT1. Put in a Walbro 255 ltr/hr and hah, it can take anything I can throw at it now. I also suggest a accell or msd coil. Im running an accell and its great, it idles a lot smoother and it pulls strong at 5600 rpm.

 

i had a similar problem with my car that it wouldnt rev past 5500 rpms.I installed a bigger fuel pump ...didnt fix it.So next i threw out the hei distributor and went msd everything....problem fixed.Now i can rev it to 7000 rpms no problem.

 

The ignition is all aftermarket except the distributor itself.

I have checked the FP under load, the reading (~40-45psi) does not drop when the power cuts out. This is what lead me to believe it was a problem with the distributor itself or possibly restrictive exhaust, or even just a drawback of a hydraulic valvetrain. Thanks for the ideas guys.

 

I have a real fear of aftermarket ignition components, except for plugs and wires. Accel caps/rotors, aftermarket ignition modules, and MSD coils especially.

If you can, I'd reinstall the stock stuff one component at a time and re-test each time.

 

Have you checked your valves? They may be a bit tight. Other than that, im baffled as to what it could be with out any other intermittent problems occuring.

 

if you're running a pcm for less tune, why do you have the timing so far advanced? i'd look for K/R and yes, i'd check the a/f ratio. there could be a problem with going lean at that rpm. are you still running a maf?

 

Maybe the people who did the memcal put a rev limiter in the prom. It wouldn't be the first time I've seen that. Have your memcal scanned by someone and check that out.

 

The Topline guides were shot out of the box. The new guides are about perfect.

The car seemed to run best at around 8 deg. The power loss seems to be present no matter what the timing is set at, though.

Yep.

Interesting. But if that were the case, would the engine attain the higher rpm at all? The engine will go to 7K+, it just makes zero power after ~5800.

 

That usually indicates poor tuning. Possibly your knock sensor is pulling a lot of timing out. I have done some tuning on engines with the HSR and top end power has never been a problem.

You need to get a scan of the engine done while it is reving out. Wideband O2 reading would also be good.

With EFI engines, you need the right tools (scan tool & Wide band) to properly analyzing these engines. Everything else is just "a guessing game".

 

aside from having a good possibility of KR*, you may be maxing out the maf readings which will just lead to a lean condition up high.

 

Yup, that (maxxing the MAF and running lean) would be the other most likely culprit. Again, that is where a scan tool and WB can give you the definitive answer (and proper fix).

If you lack a WB sensor (and don't wish to buy one), consider having a chassis dyno done as the majority of the good dynos take WB readings.

 

Im not familiar with that term...what does KR* mean?

Thanks for the responses guys, if I ever get the money Ill look into getting it on a dyno and getting some WB readings.

 

I'm assuming that KR is Knock Retard.

 

Yes, KR means Knock Retard.

As for money, I don't think you really have an option if you want your car to perform to it's potential. Also, if the MAF is indeed maxing and you are running lean, then you are seriously risking your engine. As the saying goes "You can pay a little now, or a LOT later...your choice".

 

I know when I datalog my MAF has the gm/sec listing. I'll have to look over an older log to see how much its pulling. You can do the same if you can get access to a laptop, and the cable.

 

Of course, even if the MAF is not maxing out, doesn't mean he has the AF Ratio right, which will seriously affect power also.

But you are very correct; the scan tool will indicate whether or not you are maxxing the MAF. (Though on certain bins, the max reading MAY only be 230-245. On some MAF bins, the eprom may limit the max gm/sec permitted at certain rpms and this usually needs to be tweaked in the eprom to hit 255). I am just mentioning this to make people aware that you MIGHT be maxing the MAF and it won't say "255".

This is why I also recommend this be done inconjunction with a WB reading...it's the only way to know for sure.

Aren't EFI cars fun?

 

I have had problems with high RPM power when I advance timing over 5 degrees.

 

Sounds like the Knock Retard Sensor is biting you in the butt. On some engines, I have found the KRS to be the biggest problem in making power. It tends to pull a lot of timing out even before you even hear detonation while it seems to go deaf when it occurs.

Sometimes, the best fix (other than a tear-down) seems to be to limit the amount of retard the knock sensor can permit when in WOT and use your ears instead.

 

Yeah I figured as much. Unfortunately all cash goes to college...anyone wanna buy a car?

What is your opinion on using a resistor in the knock sensor circuit to desensitize it? It sounds tacky, but its difficult to come up with cash to get another PROM burned.

Do you think that the programmer (PCMforless) would have considered that the MAF may max out?

 

I have not idea about PCMforLess, but my initial thoughts are "doubt it". Most of the things we are mentioning are NOT done by your typical eprom writer. Only guys who are deeply into eprom writing look at these things.

My thought would be to "hang around" the TGO Regional Board for your area and try and tag up with one of the local members that has all the proper equipment to scan your engine and tweak your eprom. LOTS of guys now can burn eproms. Burning eproms "via mail" just doesn't work well. You need someone to do it "hands on".

Once you have completed school, then you can consider getting into eprom burning yourself. The cost of the equipment is not expensive, it's more the "initial learning curve".

 

Thanks for all the help, glenn.

Ok, either that or DFI I suppose.