86LG4Bird

iTrader: (1)

It doesn't work that way. The earlier IVC will trap more cylinder pressure, not less, during cranking. Also, overlap won't reduce cylinder pressure during cranking. It could care less whether it's drawing from other cylinders through the manifold or entirely fresh air through the intake; it's all the same during cranking. In fact, one could argue that since it has more paths to draw from, you could get slightly HIGHER cranking pressure.
In practice, you'll always see higher cranking pressure from these types of cams versus wider separation lower overlap cams with the same lobes (with typical ground-in/installed advance on each).


I'm betting it will be close to your 230 psi number.


This cam was originally installed "straight up" as ground (3 deg advance = 105 ICL). I advanced it 2 degrees further since I was spending more time below power peak than above it during a 1/4 mile run. Power peak is at 6400, I have to shift at the ~7050 rpm PCM cutoff, and it was dropping to 5400 rpm even with the 8" 4200 stall converter. That picked up the ET by .05 to .1 sec, mph didn't change. Interestingly enough, I put it on the dyno again after changing headers from 1-5/8 Tri-Y's to 1-3/4 LT's, and the peak was still at 6400 rpm, but the curve was higher by about 15 hp.

86LG4Bird

iTrader: (1)

haha....I don't care about the numbers. I DO care about my fingers freezing and falling off in an unheated garage as I do this! :wink:

skinny z

I stand corrected. Advanced intake closing will increase cylinder pressure. I was thinking intake opening (for what reasons I can't say). Yes, that will raise cylinder pressure as you state. I'll agree on the overlap too having had a second to think about it.
So much for my engine theory "expertise".
At any rate, I'll be interested to see your test results.
I apologize for the confusion and feel completely the fool.

I've edited my post to reflect my stupidity.

86LG4Bird

iTrader: (1)

Not stupid, skinny. We all have those occasional lapses!
I realize that you ARE one of those on here with an analytical mind and good understanding in general, and was considering just asking you to re-think what you typed, but went ahead anyway for the benefit of others reading the thread. BTW, I've noticed many supposedly knowledgeable members here and elsewhere argue till the cows come home how overlap "bleeds off pressure". I usually don't take the time to try to explain, but wth, it's just another crappy day outside

skinny z

I also run some cam timing software through one of my engine simulation programs and am always noodling around with effects of timing events and how they play out.
If I could, I'd spend days on an engine dyno swapping out cams and playing with advance/retards settings, LSAs and ICLs. I know that's all been done before but the engine theory part of it is all part and parcel of the hobby.
If I could only get it right...
I'm really looking forward to this season. I've mentioned it before elsewhere that I've moved to within 20 miles of the local (IHRA) dragstrip (and roadcourse too for that matter). I hope to spend every Friday night at the track trying to get faster. It should be interesting. That is if I can keep my junk together.

2005Impalla

Ya the cylinder starts making pressure after the intake valve closes. The sooner it closes the sooner it starts making pressure. This is how you band aid a low compression motor if you cant afford pistons or new heads and are still trying to make power, sooner ICL.

skinny z

Same here but crappy outside AND inside....

skinny z

Absolutely. One of the fixes for a cam too large for an application is to install it an advanced position. This helps to recover some of the cylinder pressure and will aid in the production of low engine speed torque. There are trade offs of course.

89newfun

iTrader: (3)

I've realized I know nothing about the nitty gritty of engine specs. Lol

89newfun

iTrader: (3)

Here is my sad results from dyno. Another reason I'm sad. Heh. There isn't any rpm numbers and seems like all power torque is in way early then falls on face. Any comments on it are welcome.

skinny z

It would have been nice if they had overlayed the HP curve onto the TQ curve. At least then we could get an approximation of the rpms involved.
At best you can guess at the rpms based on the speed. I had to do the same as the rpms weren't on one of my graphs either. I had to use my final drive ratio and rear gear plus tire diameter and work the probable engine rpms in do a reverse calculation. At the same time trying to estimate how much torque converter slippage there might be. What a pain in the *** that was. And nothing conclusive either.

86LG4Bird

iTrader: (1)

It looks like the curves cross about 108 mph.
Wild guess says they started the pull about 3000 rpm, so power peaking at ~4500'ish ? Something is choking that engine badly!
I don't see much converter flash on the hit, so I doubt it has any more than an S-10 type converter.

skinny z

That should explain a few things. Add a guesstamated SCR that could be as low as 8:1 and a DCR of 6.5:1 and you can see what's going on.
Keep in mind that's based on few assumptions like piston to deck height (.025") and piston dish volume (12cc) and a .040" head gasket.

89newfun

iTrader: (3)

So what do you think is choking it up? Heads and low compression? Or the intake or... could it be bad wires and plugs contributing? This is why I was bummed at what I've got. I wanna say they ran it to 5500..iirc

86LG4Bird

iTrader: (1)

Thanks for the summary, skinny. I was too lazy to sift through the 3 pages to look for it
The low compression would explain a weak torque peak and lack of low rpm horsepower, but not the lack of power toward the top.
The curve doesn't look ratty like it would with ignition breakup or valve float, so I'd have to say it's simply lack of flow. Heads, exhaust, or intake. Maybe those heads are worse than I'm imagining? I've never messed with them. A 600 cfm carb should feed it well above where the pull ended.
AFR looks decent.

skinny z

I would think that it could be any or all of the above.
Common knowledge says that cam would "like" a compression ratio of 9.5:1 or so. I've speculated that you're less then 8.5:1. (This where a compression test would give us a hint as to what's going. As it is, running what might be your specs through any one of the compression ratio calculators gives us a clue). A move to 64 cc heads would be a step in that direction not to mention your "stock 76cc" (and I assume OEM stock), aren't doing anything to help. I think it's been widely suggested that some aftermarket heads would be a big improvement.
If my cam makes peak power in or around 5600-5700 rpm, and it's 274 adv intake duration, then it's safe to assume that's yours should be close. Most likely higher if it's matched with a proper intake, heads and exhaust system. I don't think I saw what intake you have. Just an RPM range. Not sure about your exhaust either.
As for the plugs and wires, there's no substitue for a stout ignition system. An HEI with a quality module and coil will go a long ways in that regard. Of course a decent set of wires is important. If any of the ignition system is suspect, then any results you get, dyno or otherwise, aren't going to tell you much.

89newfun

iTrader: (3)

Ok, I will prob do wire and plugs anyways since they were off the old worn 305. That intake is a performer. The exhaust at dyno time was a dynomax short headers with a custom ypipe that I made, pretty crappy one for sure. The rear end is out of car now so I'm doing to full slp catback with a actual exhaust shop made 3" ypipe. Maybe my exhaust was messing with it. I had a 24 inch glass pack on it. I've noticed the car gets quieter as the car warms up. So I know this new exhaust will help for sure. Intake wise I have a rpm air gap sitting here, , but that was suggested to not put it on yet. I know these heads sucks, but they said there was work done on them, another mystery part. Yeah.

skinny z

The exhaust on a 3rd gen is difficult at best. Not a lot of room for a true dual setup and in my opinion, that's the way to go for a performance orientated engine. That said, I know there are a lot of guys with very healthy packages that have a single exhaust. It's just that the facts point towards that being a compromise so, as 3rd genners, we kind of have to live with it. Your glass pack on the end of short headers isn't far off a decent arrangement in terms of outright flow and reduced back pressure. Zero back pressure is the ultimate objective. (Let's not get into collector length tuning as that's another thread for another day) I've often thought of a couple of well positioned mufflers on the ends of my headers as a "race only" option but with my car lowered by about 2" all around, there's not enough room.

In case you're interested in my own setup, I have mid-length headers to a 3" y-pipe and then to a single 3" muffler in the stock location. The muffler doesn't flow any CFM and tests at the dragstrip, with the muffler by-pass cut-out open, I gain several tenths and a few MPH in 1/8th mile testing. That should tell you something.

There's nothing wrong with your performer intake although it's RPM range is just slightly below the cam you have. A 1" spacer may help. NightRider has some experience in that regard. There's nothing at all wrong with the RPM Air Gap. It's very versatile and in your case, your heads notwithsatnding, well suited.
Plugs and wires for sure. That's a given.
PS. Upgrade your "mystery heads". If nothing else, the lack of compression is compromisng the rest of a not bad package.

89newfun

iTrader: (3)

So it would be worth putting the air gap onto my current setup? Sorry if I'm acting dumb just wanted to be crystal clear. Just at least until it can change my mystery heads.

Buddy didn't bring the compression tester so it'll be done at a later date.

89newfun

iTrader: (3)

I reverse calc the rpms at cross and it's 4700 to 4900 give or take. Now with that said is that where I should be shifting or pull past that?

skinny z

I'd say that's a pretty accurate assessment.

86LG4Bird

iTrader: (1)

The crossover will be at 5250...always. With converter slippage, you can't directly correlate rpm to mph.
My best recommendation from looking at that power curve would be to shift about 5500 rpm. The power doesn't tail off badly above its peak, and you want to make sure you don't fall too far back on the power curve in the next gear. Your rpm will drop at least 2000 on the gear change with that stockish-stall converter.

89newfun

iTrader: (3)

Ok, I agree. Just looking for glimmer of hope. Hah. Thanks though skinnyz

89newfun

iTrader: (3)

ok I'll shift 5500, I believe that's where I was doing it just as seat of pants feel. Thanks for sure!

89newfun

iTrader: (3)

I'll post compression results once I get the tools. Any updates to motor I'll post as they come.

Overall, I got ripped off or didnt. Just like to try to pick head up a little for money spent.

FRMULA88

IMHO I think you got what your budget at the time allowed you to build.

Understand we all have to start somewhere, it took me 20 years to build mine to current state it is in.

As a reference point my heads ( fully assembled ) cost more than what some people paid for their entire 3rd gen.

86LG4Bird

iTrader: (1)

I have to agree. Despite all the discussion and suggestions, it IS a helluva lot more than the car had stock And it's a fresh build to work from.

89newfun

iTrader: (3)

Ok, I can swallow that pill. Thanks again guys for all help and support. Again I'll post new updates and followup and look forward to your posts.

89newfun

iTrader: (3)

One question. What about nitrous? Can I apply 100 shot until I get a set of more performance heads?

86LG4Bird

iTrader: (1)

NOW you're talkin'
That will certainly get you some impressive time slips with some slicks or DR's. Any SBC in decent shape will swallow a 100 shot with no issue, as long as you have adequate fuel supply, pull back the timing 4 degrees from optimum NA, and run at least one heat range colder plugs - NO platinum tipped plugs, just plain copper. With a tight converter, I'd recommend a window switch to be safe, although we ran a 100 shot many times on the LG4 with an S-10 TC and no window switch. Definitely a WOT switch.

Nbrooks1841

I have a 89 camaro I did a motor swap from 305 to 350 every since then it runs hot at idle

89newfun

iTrader: (3)

My only worry was those pistons material. I was told that those pistons would not hold up, true or false? I'd love a little spray for when I'd need it . Would I be ok also with my current ignition. The stocking hei and all?

86LG4Bird

iTrader: (1)

Even cheap cast pistons will withstand the relatively low cylinder pressure you now have combined with the added pressure of the 100 shot, as long as you get the fuel and timing right!.
Always start with baby jets, no more than 50 hp, make a run, pull a couple of plugs. If all looks good, step up to 75 and repeat the same steps. If good, on to 100....and check again.
In my LT1 with hypereutectic cast pistons, I've sprayed a 100 shot to a total of 660 hp at the crank, almost 600 ft lbs torque. If I didn't have the fuel and timing right, it would definitely go kaboom!


A stock HEI in good condition will handle it.


It will barely hurt your power, and maybe not even at all, to pull 6 degrees timing from the best NA setting. I'd start with that.


You should brush up on plug reading with nitrous. Probably somewhere on this forum, or Google it.

FRMULA88

I sprayed a 125 shot thru a stock 305 with over 100,000 miles for years. LOL

held me over until I built my 383.

Since the 305 has a mild 8.5:1 compression I figured out that retarding the timing was not needed. I just ran premium fuel ( 93 ) instead of 87 and I used the same spark plugs. sometimes I spiked my fuel with some 100 octane unleaded, but probably was a waste of money.

Guidelines are just that, they are starting point to keep your engine safe.

I was cautious because the 305 TBI engine did not come with a knock sensor because it was meant to run on 87 octane.

If I had a tuned port car I would have let it eat with no worries and just did a dry system spraying right into the MAF. with a mild 125 shot The ECM would add fuel and retard timing as needed.

With a carb setup you can't be so liberal.. there is no computer to make real time adjustments.

FRMULA88

I would add a small fuel cell up front (1-2 gallons) for your nitrous enrichment fuel.
a small inline pump and regulator.

Use 100 octane unleaded to be safe.

The spare tire well makes a great place to mount and vent a 10# bottle.
The ashtray makes a great spot to mount the arming switch.

a basic kit will come with a throttle switch, the N20 will only come on at WOT and when the system is armed.

a purge valve is nice, but not needed with a small kit like this.
a bottle heater is nice if you plan to run in cold weather as it will keep the bottle pressure consistent.

FRMULA88

probably 800-1,000 $ for a basic setup ( no purge valve or bottle heater) if you do all the work yourself.

89newfun

iTrader: (3)

I will certainly look into that before I spend money on a system

I've seen kits out the door for 450 ish, that's a basic kit. I've got friends that run nitrous religiously, multi kits. Mine would be a simple kit. The use of a secondary pump, is that so the nitrous system doesn't rely on the stock pump. My setup still has the tbi pump in it. Couldn't I t into the fuel before the regulator to ensure it gets more psi to the fuel jets than the 6 psi the carb gets?

86LG4Bird

iTrader: (1)

Yup, pretty similar to what I've done. Even with the 9.4'ish CR, the same technique worked just fine: timed for 87 octane NA; 100 shot with 93 worked just fine at the same timing. I'd agree you shouldn't need any better fuel in that case. The stock spark plugs on that 86 LG4 are already on the cold side, so I didn't change them either.
I'm just cautious with application-specific info, especially to a newb at this business, because they may not understand how their motor and mine are not apples to apples

FRMULA88

lots of way to do it..

A separate fuel cell means you can have just 1-2 gallons of 100 octane unleaded for the enrichment fuel to keep you safe when you spray. You would not have to blend it with the 87 octane fuel in your main tank. Even on the street it will take a long time to burn thru that supplemental fuel.

When spraying the enrichment fuel would spike the octane to 93.5

A 10# bottle is good for 3, maybe 4 1/4 mile passes.

This is also a setup you can "grow into" if you build an engine with higher compression or want to spray more.

tee off the main fuel line is OK for low power levels.. certainly not the best solution since you will have to upgrade later on and higher power levels will have fuel starvation issues..

89newfun

iTrader: (3)

Ok so if I do the extra tank, then that would be the sole supply for the nitrous? Also where would I even think of mounting a spare tank as to not be hideous.

FRMULA88

lots of places to mount it:

it you relocated the battery to the truck or deleted the charcoal canister you have room in the front corners.

otherwise there is room in front of the radiator.

but these are just suggestions. if I did N2O all over again I would do it this way because it simplifies the install, less wiring, &is easily removed if you get rid of the car.

89newfun

iTrader: (3)

Ok thank you. My charcoal canister is already gone. So I'll look into that. Run just a simple inline pump I take it? I'll google .

FRMULA88

1 or 2 gallon cell -6 fuel line with an small
inline fuel pump connected to a regulator then to the fuel solenoid on the nitrous system.

all sort of room on the fender to mount the relays for the nitrous system and fuel pump.

No need to google if you search on this site you will find all the info. you need.

89newfun

iTrader: (3)

Perfect. One question, would the fuel system have air gap inline if the system isn't always running, how to prevent that, or that's isn't even a problem

FRMULA88

when you arm the system the inline pump will push the fuel to the solenoid.
if you are worried about air or dead heading the fuel you can install a regulator with a bypass and run a return line back to the fuel cell. but IMHO at this power lever it's not a big deal.. besides when the solenoid is closed it acts like a check valve and should keep fuel from draining back to the cell..

think about a straw you put in a cup of fluid cover the end of with your finger and take the straw out of the fluid, the fluid stays in the straw until you remove your thumb.



you arm the system typically after your burn out while staging. this will give the pump ample time to build up fuel pressure before you go WOT besides with the cell up front this is very short trip to the solenoid...

89newfun

iTrader: (3)

Ok, that makes sense. Thank you

sabien

Do a compression test. Will approximate compression ratio.

FRMULA88

common sense; if you are running pump gas and not knocking using plain old 87 unleaded your static CR probably no more than 9:1 and possibly a bit lower if using stock rebuilder pistons and factory heads.

safe to guess it is anywhere between 8.5 & 9 : 1

actually this is great for a nitrous engine it gives you a huge margin for error.

skinny z

safe to guess it is anywhere between 8.5 & 9 : 1

actually this is great for a nitrous engine it gives you a huge margin for error.[/QUOTE]

Based on the parts listed I'd think 8.5:1 is optimistic. 76 cc heads, 12 cc piston dish and what's probably an undecked block doesn't make for much compression. Then again, who knows at this point.
That said, as it's been, mentioned, it would be a prime candidate to make power on NO2.

89newfun

iTrader: (3)

Ok cool, that's what I kinda wanted to hear. I may give that a whirl if I can get into a system reasonable. Thanks guys.

And again I will do a comp test when I get tools from buddy.