high compression 3400 build

[stewartfn18]

so,for those who dont know this isnt my first rodeo. my mods list includes:
old 1393(stage 2) cam
3500 heads
comp 986's
ls lifter springs
s&s
cai
65mm tb
2.5 custom header back
comp ported manifolds
tune
28 lb injectors
tce afpr

to add to the madness ive ordered:
dohc pistons
head studs
stock conrods
cometic 3400 head gaskets, compressed thickness of .075 to yield 11.6:1. more parts are to be ordered.
probably p series rod bearing
pre 00 timing set.
new crank cuz the snout on mine is stripped
maybe arp rod bolts
maybe arp main studs

i need advice on the last two.

[SappySE107]

Don't need the main studs, but I would use the rod bolts.

[stewartfn18]

ordered my gaskets last night. i read that itll take 2 weeks to be shipped. do they get shipped to me from cometic or do they get shipped to you and then you ship them out

[3400-95-Modified]

Hello high octane fuel... LOL good luck with the build.

[SappySE107]

The cometic gaskets get shipped to me first though I could see if they will drop ship without an extra fee. Other than the cam, the compression does work with 93 octane.

[stewartfn18]

parts came in

and what do you mean "other than the cam"

[SappySE107]

260 adv duration is not much for 11.6:1.

[stewartfn18]

what will not having enough duration do? noob question

[Blacktree]

With high static compression, and a camshaft with short duration & low overlap, your engine will be like a diesel... lots of low-end torque, but won't like to rev. Plus, the mild cam will yield a higher dynamic compression ratio than a more aggressive cam, which will put more stress on the rod&main bearings. Plus, it'll probably ping... even on 93 octane.

A more aggressive camshaft will reduce dynamic compression, which will reduce the tendency to ping, and allow the engine to rev higher (i.e. more power). For ~11:1 compression ratio, you should be looking for around 225-240 degrees duration @ 0.050" lift. (I used duration @ 0.050" lift, because advertised duration can vary from one mfgr to the next)

[SappySE107]

The tune will have to be perfect and even that might still have an issue with detonation. The cam is meant to trap as much as possible, with -18.9 overlap at .050 and 42.6 seat to seat. With higher compression you want to bleed off some of the charge at lower RPM to keep the same power or increase it slightly, while enjoying the full benefit at higher RPMs that the lower compression wouldn't allow to carry so well without costing a huge hit to bottom end power.

[stewartfn18]

question then, can you grind a cam with the same lift but a longer duration so that i can keep my pushrods and not have to get new ones?

[stewartfn18]

i mean really the duration is not THAT far off

[trotterlg]

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

[SappySE107]

Cam selection isn't black magic. Your cam is no where close to hot enough for your compression. Are you running it right now?

[Blacktree]

Yeah, those cam specs are pretty mild. At least, the lift and duration are pretty mild. But what's up with the LSA? It looks like that camshaft was designed to maximize cylinder pressure (i.e. for an engine with a low compression ratio). With a 12.4:1 SCR and that camshaft, your rod bearings are going to take a beating. The engine will also be prone to detonation.