Other than bore, does the 3.1 share everything of the 2.8....?

3.1 = 191 CID, 3.50" Bore x 3.31" Stroke

2.8 = 173 CID, 3.50" Bore x 3.00" Stroke

Compression ratio (2.8) = 8.9:1

Compression ratio (3.1) = ????

Intake / Exhaust Valves (2.8) = 1.725" / 1.425"

Intake / Exhaust Valves (3.1) = ????? ?????

Thanks....

-Rob

 

intake an ex valve sizes/heads are the same on all fuelinjected 2.8/3.1/3.4 engines
cr of the 3.1 is also 8.9:1

 

The only difference is the crank.

 

on a side note u can swap in either 1.94 intake valves or 1.600 ex valvesbut not both into the iron heads
there are other combinations of valves that can be droped in together though

 

Thanks guys for the responses. I needed to clarify a few things, as some of the information floating around the board is very questionable. On the '92 LHO 3.1 history page of ThirdGen.org, it states that the 3.1 came with 8.5:1...

Now, it's critical that I know the precise compression ratio(s) prior to ordering the boosted camshaft for my project. So just to confirm this, the compression ratio is in fact 8.9:1, and not 8.5:1.....?

-Rob

Click here to see why I need confirmation....

 

what gm specs read and what they actually are are 2 diff things.my 3.1 came out to 8.8:1 with the factory pistons,the only way to know for sure is to take it apart measure everything and calcualte it urself.

btw ive seen specs on the 3.1 from 8.5-9.1:1

 

.4 of a point is not going to make that much of a difference.

Any camshaft ordered will work in a range of SCR.

Then wrap your head around this one, once you go boosted, SCR means ****, since the effective compression ratio changes drastically with boost, then to add to the confusion dynamic (or cranking) compression ratio is different than SCR, that can also be effected by camshaft selection (overlap) and effciancies of the intake and exhaust systems.

 

The difference of .4 SCR is huge in boosted applications. Why, because of fuel. Unless you want to run C16 on it on regular basis. Yes, the cylinder pressures are stratospheric and that .4 is a huge element in multiplying that equation. Basically, it will knock if octane requirement is not met, timing is pulled, power is lost. So yeah, SCR is in fact important....

Regarding DCR, yes it is constant in a motor and cam specs at .006 lift determine its value. It is less important in boosted motors to get the optimized DCR than in NA, just as long as you do not go over 8.5....

-Gaspar

Dave, can you touch a little more on why .500" lift is pretty much max on the iron headed 3.1's. Need to clarify a few things with someone. Thanks Bro....

-Rob

 

well if u take a iron head and try to go over .500 lift the valve reatiner will crash into the stemseal/valve guide.now u can go over .500 but u have to machine the valve guides down for the clearance,and or get a longer valve/custom pushrod

 

^

 

im suspecting a pretty mean sounding v6 here...

 

This is if Delta can grind me the camshaft that I'm after. It's lift will really be pushing the engine's limits, but duration and overlap will be very key though. I might be able to have Thunder Racing grind me up one, and if they can pull it off, heh, watch out.

Dave and Rob both have something up their sleeves, as I believe Dave just talked my cousin into something last night. So if your reading this Dave, it's definitely a go....

-Gaspar

 

hehe i guess u or rob can let the cat out of the bag then so to speak

 

gasper btw can u pm me the specs or post the specs on the cam u are thinking about, it will help me out when i do the heads.
id also like to point out that from .450 - .550 + u might only pick up 2-5 cfm or so.High lift on these heads isnt as important as getting the valve open fast.
with the ex housing(s) size and the header design we should be able to maintian that a 1-1 to 2-1 ratio of preasure ex vs intake side
the ex side(s) have p-trim wheels stuffed into t3 housings

 

I'm just waiting for Thunder to give me the nod, then I'll shoot you over the specs. Lift is important with these specific cam lobes that I have in mind, as it will allow him to run greater duration, without effecting the car's drivability. If Thunder can't swing it, then lift will definitely be moderate, as I don't believe Delta has access to such lobes. But if Thunder can grind one for me, then lift will be very key with optimizing curve power....

Cat(s) have just been let out of the bag....

-G

 

You guys are actually sharing a screen name?

 

???????????????

 

Been that way for quite awhile. I stopped posting entirely a couple of years ago when I got my hands on my first LS1. Joined the LS1 boards, w/my cousin still occassionally visiting this forum under my User ID. There was no need for him to create his own. I chose "street lethal" specifically because of him, it was to honor him, and his sick sick SICK Third Generation Camaro....

Click here, and enjoy....

 

As you can imagine, I disagree, why? Because in my experiance and from watching what other people do, that .4 means squat, people will say it makes a big difference, when I see similar engines running vast differences in SCR, and run just FINE. The reason I mentioned DCR is because it is more important IMO than SCR, due to the fact that DCR is what makes the engine run, Static is all based on static (not running) mesurments and calculations, last time I checked my engines moved or rather had parts move while they ran. DCR can be calculated and to a point measured, but I only use these compression calculators to get n a ball park, and then let the engine know what it wants from there.

I also subscribe to the idea that higher SCR and lower or equal boost will be a much more drivable combination, and enjoyable, based on my experiance and others.

 

naw cat(s) havent been let out yet

 

Can I guess, can I guess?!?!?

Two V6 3rd gens, one turbo and the other supercharged???

 

lol not even close lol