high compression 3400 build

[trotterlg]

I hope I didn't mess up this thread, I was posting about cam numbers and what I was doing with a high compression 3.1, when I first posted these numbers this is the response I got, them plus that it may not be able to idle below 2,000. So, from the info I got here it is either way too mild or way too wild! Larry

Running those numbers shows an overlap of 71* at a checking point on .006 which is the norm for hydraulic cam. That is endurance racing territory. Did you ask for this?

I can also see they have a very tight LSA of 99. 45 which is very odd. If your running a 3.4 L with 1.72 intake valve then lobe separation should be 108* to 110*. So I really do no know why they decided to make the cam this way.

If you wanted a street cam the overlap should be much less (around 30* to 50*) which means you could keep the same duration but widen the LSA to a more optimal 109* but that would not be possible if the original cam you ground it from was made with a tight LSA.

Now if I just knew who was/is right. I guess I should compare these numbers with the numbers on the cam being used for the 3.4 high compression build and see what that shows.

[stewartfn18]

i would trust what ben says. ill just put it like this. i would trust ben to build me an engine and no one does work on my car except me.

[trotterlg]

I tend to agree with you, but it just shows what kind of advice you can get on the internet. I hope this doesn't affect the origional poster or his questions, his cam may be just fine for his application, I did not intend to steal his thread. Larry

[Blacktree]

Yeah, sorry for the thread-jack. That said, the specs on that camshaft are confusing. The lift and duration remind me of a mild performance cam. But the LSA and timing retard are pretty extreme. That's an odd combination.

Edit to add: That could also be why you're getting the conflicting opinions.

[Joseph Upson]

It will be interesting to see how these things run. Below are the cam specs on the cam I have in my 3.1 12.4 to one build, and I am told it may be too hot. Guess this is all black magic, or that cam selection is not a very understood process. Larry

I kind of feel like throwing a couple of rocks at Scott the camshaft operator at Delta. I asked their advice on a recommended camshaft regrind and I can't say that I ever received the kind of certainty I realize should have been present in their recommendation. First of all as of last year at least through a call to them after the fact, they have no simulation software from which to retrieve a recommended camshaft based on application, they just make a suggestion based on what you tell them so you're better off researching it yourself or going with a service that can actually simulate the cam specs.

For some reason attachment upload has stopped working for me so I can't post my cam card for you to view eventhough it's posted somewhere else on the forum.

To the point:

3900 V6,
stroked to 3.555" ~4.2L,
LS1 pistons, this is a big problem area now because the engine is damaged & it may have to do with my forgetting to address proper clearance for forged pistons as they are in a stock bore that is probably on the tight side since the stock top ring was gapped to .006.
Compression at least 11.5:1+
Camshaft regrind to 216.6/213 duration, 114 LSA, -13.2 overlap, 1deg adv, Cline 112/114
5.7" H-beam rods using chevy V8 bearings
Turbocharged
Methanol injection

RESULTS:
Absolute rocket off the line, no lag, no delay it just goes.
Removed the turbo for an assumed needed repair due to smoke, closed off the turbine housing and ran it naturally aspirated to find there was NO TOP END as has been alluded to by Ben. Any race beyond about 100yds and I'd be in big trouble without the turbo, a Ford Ranger showed me that. I have a good understanding of cam dynamics but hadn't considered my cam duration might be way low for the compression, it had also been ground before the planned engine upgrade.
I had to pull a good bit of timing from the wideopen throttle area to the tune of single digits, partly due to the 3 mistakes I made that damaged the motor which now experiences oil contamination and detonation on any attempt at an all out acceleration now. I should have it tore down in a week to survey the damage.

High compression is a novel idea but at this point especially given how much fuel was used trying to tune the motor. 93 octane = no fun at the moment. I have it timed on the weak side now to run 89 and am looking forward to getting the stock motor installed so I can at least enjoy boosted performance. I'll be using a mildly upgraded cam above stock until the Forged motor is repaired.

Get the cam specs right or this will be a big headache for you. I'd say my engine falls off at about 3500 rpm, it could be the cam, it could be the pistons swelling in the bore as sometimes it would run as if it had some guts up top without the turbo but only when it was cold.

http://www.carcraft.com/techarticles/ctrp_1106_turbo_camshaft_guide/index.html

[stewartfn18]

so in other words, with the cam that i have its a good thing that i put a halt to this build until i can get a cam that works well with high compression. good info to know. thanks!

[SappySE107]

Larry, your lobes are small but the timing is very very narrow for overlap, which helps but its just not enough duration. You will see the same cylinder pressure at 12.4 that the OP would see at 11.6 if the same motor was used.