[Nabush]

Basically if I lose torque below 3000rpm I don't care at all.
Low to mid to me is below 3400 rpm.
The cam makes good airmass from 2800-3400, very close to stock if not equal...basically looking again at my logs the 3400-4600 is weaker than it should. The other graphs I posted the loss is below 3500, everything comes right back at those rpm's.
I don't think this is an altitude related issue. I did a test yesterday night, climbing to 6000Ft and the issue remained EXACTLY the same, but with lower airmass all accross the board (81kpa baro).
This damn camshaft has an issue. If it was related to altitude I would have seen a change one way or another.

[oldman]

I do see the sag is a little higher up than expected. I thought with ported heads there would be some pickup as the stock heads stall over .550 lift and actually flow less.

[Nabush]

Originally Posted by oldman

I do see the sag is a little higher up than expected. I thought with ported heads there would be some pickup as the stock heads stall over .550 lift and actually flow less.

Yeah I don't see how air intake or headers could impact this much. I know that intake manifold or TB has no effect. AFE intake is commonly used and had no negative effect with stock cam. American racing headers 1"7/8 is a proven one. This little more restriction from catted X pipe could not do that. NPP in stealth or track no changes.

Definitely pointing to the cam.

I don't see a lifter or pushrod issue causing that ? I have 7.850 pushrods which is standard. I can check again how many turns of preload I have on the rocker bolt but it seemed good.

Moreover I would assume too long or pushrods would create even more issues in high rpm's than mid rpms ? Especially not create a dip...oil pressure is very consistent on those engines so I don't think of something weird going on with the lifters...

Really to the point of buying a new cam...

[Nabush]

GPI cams seem to be good...

https://gwatneyperformance.com/product/lt1-cam/


Full SS3 setup does 555WHP on E70

226/246 112LSA +2

SS4 and Track attack are perhaps a little too extreme... (233/257 112LSA +3 and 237/255 +3.5)

[Nabush]

Guys,

Some (bad) news...

I bought the GPI Stage 3 cam, did a complete engine rebuild with new oil pump, crankshaft bearings, rod bearings etc...

I have exactly the same issue with the GPI Stage 3 cam, perhaps even worse.

I tried a stock ported IM manifold (weapon X) with no changes.

I started to run E85 today, my tune is far from being finished but I see the same behavior.

Like I said before I would assume a cam retarted a lot would mean the engine would be a dog below 3000 rpm...Which is not the case...

2 different cams, dot to dot like OEM, I don't see how 2 different cams from 2 different manufacturers could have the same issue.

Also, yes it did not degree the cam, but even if did and found it off by 4deg : 1- Jumping a teeth is 8deg 2- 4deg of retard would not create a dip from 3500-4500 right ? It would be all accross the range...

The only stuff I did not try is the exhaust. But a lot of people are running ARH without this kind of issue

Here is pic of my first E85 run this afternoon



Seriously this is getting old...

[6spdhyperblue]

Pray cam and tune and be Done.

[oldman]

you might want to invest in some sort of desktop dyno software instead of just trying cams. I'd make sure the software can take altitude adjustments:
https://www.enginelabs.com/engine-te...t-to-the-test/

https://www.motionsoftware.com/Dynomation6.htm

It is NOT unusual for large cams to have flow drops or sags in the mid range. Probably more pronounced because altitude is effectively making the engine 10% smaller and the port size significantly bigger. Also sure 112 LSA and large exhaust duration offer "free" midrange power by trading idle quality for a large tug of exhaust velocity on overlap. But this is at standard pressure, you are getting far less air into the cylinder and thus the exit velocity of the gas is low, the extra exhaust duration combined with the 112 LSA is going to cause exhaust reversion (can prove that via software). Close to single pattern cam could have been tried with a 112 LSA. 226 / 230. Basically you have too little air velocity in the mid range and FAR too little exhaust velocity and what in theory should be giving you a strong mid range (112 LSA and an extended exhaust duration), is giving you the exact opposite, too little exhaust tug (the negative pressure area of the exhaust column of burned gas that is going out the exhaust at the same time the intake is open, aka overlap) combined with too little intake velocity. IMO and I probably let you down, I would caution any use of extended exhaust duration and this GPI it is HUGE on an engine at altitude unless sims were run on cam software. For example the GPI cam has 8 degrees more exhaust duration compared to a nearly identical Cam Motion cam. IMO even at sea level the CM cam makes more sense. At elevation I'd whack another 4 to 8 degrees off the CM design.
https://cammotion.com/gen-5-lt-camsh...226-238-113-3/


your original TSP cam:
Cam Specs: 235/239, .645"/.635", 116 LSA

Just an eyeball look tells me the GW cam opens the exhaust far earlier that the TSP cam. This is only going to sag the midrange flow. The suggesting was to hack 10 degrees off intake and exhaust. Not hack 10 degrees off the intake and add it to the exhaust on an engine that is already intake flow limited (due to altitude). TSP cam 3.5 degrees before TDC... GW cam 11 degrees before TDC.

TSP stage one is 227/231 on 116 LSA so GW cam is just way out there on the exhaust duration.

[Nabush]

Originally Posted by oldman

you might want to invest in some sort of desktop dyno software instead of just trying cams. I'd make sure the software can take altitude adjustments:
https://www.enginelabs.com/engine-te...t-to-the-test/

https://www.motionsoftware.com/Dynomation6.htm

It is NOT unusual for large cams to have flow drops or sags in the mid range. Probably more pronounced because altitude is effectively making the engine 10% smaller and the port size significantly bigger. Also sure 112 LSA and large exhaust duration offer "free" midrange power by trading idle quality of a large tug of exhaust velocity on overlap. But this is at standard pressure, you are getting far less air into the cylinder and thus the exit velocity of the gas is low, the extra exhaust duration combined with the 112 LSA is going to cause exhaust reversion (can prove that via software). Close to single pattern cam could have been tried with a 112 LSA. 226 / 230. Basically you have too little air velocity in the mid range and FAR too little exhaust velocity and what in theory should be giving you a strong mid range (112 LSA and an extended exhaust duration), is giving you the exact opposite, too little exhaust tug (the negative pressure area of the exhaust column of burned gas that is going out the exhaust at the same time the intake is open, aka overlap) combined with too little intake velocity. IMO and I probably let you down, I would caution any use of extended exhaust duration and this GPI it is HUGE on an engine at altitude unless sims were run on cam software. For example the GPI cam has 8 degrees more exhaust duration compared to a nearly identical Cam Motion cam. IMO even at sea level the CM cam makes more sense. At elevation I'd whack another 4 to 8 degrees off the CM design.
https://cammotion.com/gen-5-lt-camsh...226-238-113-3/


your original TSP cam:
Cam Specs: 235/239, .645"/.635", 116 LSA

Just an eyeball look tells me the GW cam opens the exhaust far earlier that the TSP cam. This is only going to sag the midrange flow. The suggesting was to hack 10 degrees off intake and exhaust. Not hack 10 degrees off the intake and add it to the exhaust on an engine that is already intake flow limited (due to altitude). TSP cam 3.5 degrees before TDC... GW cam 11 degrees before TDC.

TSP stage one is 227/231 on 116 LSA so GW cam is just way out there on the exhaust duration.

You may be right, though I have a hard time believing being 2700FT elevation could change this much engine behavior... We are not talking about 10% more like 7%...

This is clearly not what we can call high elevation by any means...

This whole stutt pisses me off so big that I'm considering buying an LT4

[6spdhyperblue]

Just wondering why you went stage 3...both times if your worried about mid range torque.
Get a proven cam/tune combo with the curve you want.

[oldman]

I actually looked at a LT4 retrofit, they look great, have a OEM stock appeal and build quality and can be found heck of cheap. Also the LT5 cam is basically the LT1 manual cam (not made as GM just made all engines DoD). For altitude this is going to give you the bang for the buck period. I do the smallest CM blower cam with a custom .596 lift, if you don't want to go back to DoD or you don't want to by the LT5 cam. The CM will give you the big fuel lobe (you want that).
https://cammotion.com/gen5-lt-camsha...220-236-118-4/

[oldman]

16 degrees of exhaust duration is a HUGE amount. The exhaust stroke is only 180 decrees. This cam has 66 degrees total on both sides of the stoke that the valve has reached flow .050. Actually off the seat maybe 90 or more. That not only means overlap reversion potential, but it means that there is much less working time for the power stroke to work on crank. Heck the piston is just passing 60% down the bore on the power stroke when the exhaust valve cracks open.

Yes 7% less intake means 7% less exhaust as proportion. The cam should have been close to or an actual single pattern cam.

[KingLT1]

I still think the OP should have a competent tuner look over the tune but that is jm2c. I know Pray has been able to get much better mid range results with similar size cams on his NA builds.

[Dads1le]

Here’s my pray performance ported heads and ported msd package with a ported stock 89 tb. 17/8 arh headers. Cam is 223/231. 111+3. Has very good low and midrange. Have since this dyno installed a ported 95 and picked up 5-10 midrange hp /tq with no top end increase

[Dads1le]

Also forgot to note the heads were milled .025 to bump compression and runs much better on e85