v8vette84

Ok, so I have been talking with Solomon of LT1pcmtuning.com trying to figure out the possibility for my high rpm power loss. I sent him a datalogg where I ran the car up to about 6k (as the power starts to drop off around 5800) and he said that I need bigger injectors. Looking at my Datamaster log when I'm at 5925rpms my duty cycle is 90%. The other thing he mentioned was a possible half assed tune but seeing is it's a madtuner tune he didn't seem to think that's really the problem as he knows ion did good work when he was tuning LT1's. I ordered a set of 42lb injectors as solomon recommended I should get at least 36lbers. Could this have been an overlooked problem from the get go? The fuel pump is a Walbro 255 so fuel pressure isn't the issue.

Also at 4750rpms my MAP reading reaches 100.4 then it drops until I stop the pull at 5925rpms in which the MAP reading is 93. Does that signify a restriction with the intake?

**Oh also I'm running 30lb Red tops currently along with a stock b-body intake elbow that runs right to the MAF then to a K&N cone filter.

Fishing for opinions.

v8vette84

Cam specs: 232/240 .578/.574 110 LSA (1.6 RRs)

Head flow specs:
Lift: = Int/Exh:
.200 = 134/104
.300 = 190/144
.400 = 235/172
.500 = 257/191
.550 = 265/195
.600 = 265/200

Not sure if that helps but solomon said it could also be a "healthy" heads/cam setup that is flowing more than expected. Not sure as these numbers don't seem super amazing, more like just ordinary for ported heads. Even though I never had the heads flowed on a bench, I only used the numbers I was given by the prior owner.

SS RRR

iTrader: (2)

What do you mean by losing power? Does it start missing up top or do you have some dyno graph which proves your loss? 30lb injectors should be just fine for what you have. How do you know fuel pressure is not an issue? Have you checked to see what your fuel pressure is at higher rpm? How are your spring pressures?

v8vette84

Seat of the pants power loss, like it pulls really well and once it hits 5500-5800rpms its starts to feel like its loosing power and the pull stops. It feels like you have to force the engine past 6k. It feels like you are overrevving a stock engine almost. It's making noise but it's not "pulling". I have plans to hit a dyno this spring. I have tested fuel pressure driving and sitting and it was fine. Springs pressures are fine according to Lloyd Elliot (the one I got the cam from) I had a machine shop check 2 springs and I got 146 lbs and 142lbs at 1.760". I also swapped locators and that brought the installed height to 1.740" which lloyd elliot said should be around 150-155lbs on the seat. I'm running 26918 beehive springs.

v8vette84

This cam should run to 6500rpms according to lloyd elliot but it stops at 5800rpms. That to me means there is something wrong. Also I set valve lash at 1/8 turn past zero lash per LE's recommendation.

v8vette84

Last time I went to the track I ran a few MPH slower with 3.73's than with the factory 3.07's. My time got slower too. I can only attest that to being in the high rpm more with the 3.73's and the engine not making the correct power up top to run a better time/mph. 3.07's to 3.73's and I loose MPH and time? Something is wrong.

SS RRR

iTrader: (2)

That doesn't say a whole lot of anything. You need to test all springs and you need to test their rates for whatever lift your cam is. The power curve on a dyno graph should also tell you if you are experiencing valve float.

v8vette84

Honestly I have been considering just getting a good set of double springs. I like the extra security of not dropping a valve or at least having another line of defense even if the 2nd spring isn't designed to control the valve. According to LE beehives have been known to loose pressure a lot faster than a good double spring. Dyno is on the schedule for this spring once I get the car out.

BALLSS

what you describe sounds like your valve springs are done. If you have 15-20k miles on those 918's, they likely are done.

I got a set of Lunati springs from Lloyd. I believe he will not use/install the Comp 918's anymore

or your cam was installed wrong

I also agree your 30# injectors are good.

On your FP check....did you put a gauge on and go for a SUSTAINED WOT run and watch to see if FP starts to drop at high RPM's?

v8vette84

I'll bet those are the same springs he told me he could sell me. He didn't seem too fond of the beehives in the emails. The springs could very well be shot. I got them used from a buddy of mine, and I have put probably 12k on them myself. No idea how many miles he put on them.

I would have run the car to 6k testing the fuel pressure.

v8vette84

Also if 30lb injectors are fine then why am I at such a high DC? I can't imagine my tune is hacked as many have had good luck with madtuner.

steveo_

you have no idea what your duty cycle really is with an LT1 - the your ecm doesn't output injector duty cycle in the datastream.

datamaster EE makes that **** up just based on injector pulsewidth, and does a poor job of it.

SS RRR

iTrader: (2)

Even at 90% you'll be fine. Stock 24lb injectors can support upwards of 370+rwhp. 30's will be fine for what you're doing.

hrcslam

I agree with most everyone else here. You need to put it on a dyno to see what's going on. Sounds like valve float though. The Lunati Dual springs will get you where you want to be with your cam. The kit (73925K2) is like $240 or so at Summit IIRC. Your build is similar to mine (not sure on the work to the bottom half of your engine though, I'm 355 with forged slugs and rods and machine work and 36# injectors) and last time my engine would feel like it hit a speed limiter at about 6K RPM it was the valve springs.

v8vette84

I have the stock pistons, Scat forged rods as far as the bottom end goes. Well I will be retuned to the #42 injectors regardless as I have them now. (I wouldn't think there is a major problem running #42 injectors on my setup?) I was thinking the valve springs myself for a long time. I was just never able to positively convince myself it was valve float and I just don't want to change parts like crazy. That's what a bad mechanic does. Either way that's a good price on the valve spring kit and I will end up getting a dual spring setup anyways because I want the added safety.

How can you determine the car is getting valve float on the dyno? A sharp drop in power at high rpm?

hrcslam

I determined valve float by the speed limiter feel I got at 6k. Not really a drop in power, it just kinda stopped pulling. If you Google image search valve float dyno graph you'll see what it looks like.

Fly on the wall

Another here for valve float. Friend of mine had the same exact problem. Swapped out the old springs for Lunati doubles and problem disappeared.

v8vette84

The feeling is not like a jerky speed limiter is hitting its just like the power falls off. You can push the car past 6k but it just feels like you are overrevving the engine. I just was never sure as everything I had read about valve float seemed to be the power drops off really abrubtly then the engine sounds like it's missing.

It is good to see it's more common than I thought. Vavle float is starting to sound more likely the culprit.

hrcslam

Yeah, mine would feel like a speed limiter, but it would pull past it. But, the acceleration was notably worse. If you have that many miles and you bought them used, they are likely not doing so well. My Howards cam 98215 springs only lasted about 16K (first set) and 10K (2nd set) before I went with the Lunati 73925 set. Lloyd said the Lunatis should go 30-50K on my cam and set up. IMO, especially on cammed up engines, never install used Valve Springs unless they are the ones you pulled of your engine and have known low mileage.

Kevin97ss

I had a similar issue, stopped pulling @ 6k. Thinking it was spring related, it was not. Turned out to be lifters, old retainer style comp R's, the supposed good ones. They would bleed down. It felt just like weak springs and floating valves. Replaced with a set of stockers and now pulls hard and clean to 6600 limiter.

This is just FYI, not saying this is your issue.