Questions about this 360LA combo?

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FlDart360

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Would it be possible to get a ballpark on my compression ratio based on the following that I have been able to identify off my 360 block and heads. Also are these decent heads to work with if I would consider a cam change down the road. What I would like to end up with is a street car that would be a solid 13sec car if it went to the track. It already runs really good now and honestly may not be far from that number. Here is what I do know. The piston picture I copied from a post on this site. When I stuck a camera in my spark plug hole that’s what my pistons look like. Is that what a stock piston looks like? What is that style commonly called?

1. 4027596 – 360 LA-series small-block, 1.88/160 valves, 66cc-72.5cc

2. Block 4006830-3602 S/N

3. 670 CFM Street Avenger 4150

4. Edelbrock RPM Air Gap

5. 8.25 rear with 3.55 gears

6. 727 trans unknown stall

7. Unknown cam but has slight choppy idle.

Runs off 87 octane with no problem.
Piston.PNG
 
Would it be possible to get a ballpark on my compression ratio based on the following that I have been able to identify off my 360 block and heads. Also are these decent heads to work with if I would consider a cam change down the road. What I would like to end up with is a street car that would be a solid 13sec car if it went to the track. It already runs really good now and honestly may not be far from that number. Here is what I do know. The piston picture I copied from a post on this site. When I stuck a camera in my spark plug hole that’s what my pistons look like. Is that what a stock piston looks like? What is that style commonly called?

1. 4027596 – 360 LA-series small-block, 1.88/160 valves, 66cc-72.5cc

2. Block 4006830-3602 S/N

3. 670 CFM Street Avenger 4150

4. Edelbrock RPM Air Gap

5. 8.25 rear with 3.55 gears

6. 727 trans unknown stall

7. Unknown cam but has slight choppy idle.

Runs off 87 octane with no problem.
View attachment 1715354170
Gonna need to know how far down in the hole piston is, and if it has valve reliefs. Gasket thickness, and head cc's. 66 to 72 is a pretty big swing in head cc's.
 
I believe those pistons in pic are the standard 360 LA smog pistons. They are just like the ones I removed from my 1975 360 LA block. They are called "Dished" pistons. Mine were roughly .100 in down from the deck. I'm installing some Keith Black valve notched domed pistons in mine, when I get the block back from sleeving #3, and boreing.
Dave
 
It's usually always a lot lower than what you are hoping for with a stock type bottom end. Looks like the stock 7cc dish type piston, probably about .050 below deck on average on a good day, sometimes .080 (or farther!) under deck, and the chambers are usually the maximum volume as minimum and usually even larger... For example, I'm going to assume stock head gaskets with pistons and a .043 head gasket, 75 cc chambers, and pistons .040 under deck, we come up with a booming 8.4 to C.R., which will coincide pretty well with your usage 87 octane fuel. Probably accurate to 1/2 a point. If you haven't already, run a compression test and at least get a map of your cylinder pressures. Probably the quickest way to a lower ET is headers with low restriction exhaust (if you don't already have them) and deeper gears, if you can live with them on the street. Be sure to baseline your car before doing anything, though.
 
It's usually always a lot lower than what you are hoping for with a stock type bottom end. Looks like the stock 7cc dish type piston, probably about .050 below deck on average on a good day, sometimes .080 (or farther!) under deck, and the chambers are usually the maximum volume as minimum and usually even larger... For example, I'm going to assume stock head gaskets with pistons and a .043 head gasket, 75 cc chambers, and pistons .040 under deck, we come up with a booming 8.4 to C.R., which will coincide pretty well with your usage 87 octane fuel. Probably accurate to 1/2 a point. If you haven't already, run a compression test and at least get a map of your cylinder pressures. Probably the quickest way to a lower ET is headers with low restriction exhaust (if you don't already have them) and deeper gears, if you can live with them on the street. Be sure to baseline your car before doing anything, though.

Thanks… yes I forgot to mention I have headers with exhaust that dumps at the rear axle. I have only tuned the carb and played with the timing for now. At some point I will turn my attention and money to the motor. For now it is burning no oil and the plugs look all the same. I have no reason to believe that there is much deviation from stock. I might add that when I removed the valve covers everything is very clean.
 
Assuming a good uniform compression test on all cylinders could you gain anything from a cam change if your compression is that low? I guess what I’m asking is could I get more out of this combo without a top to bottom rebuild. I really like the drivability of the 3:55 gears.
 
Probably, but you'll need to baseline run the car, figure out what camshaft you have, and have your average cranking pressure to proceed. Depending on the combination weight, thirteens aren't unreasonable to expect. But, if it were me, I would just ran the car to see what it doing. If it feels like it is needing more bottom end torque, I'd run a Lunati Voodoo 262/268 with required springs, but if it felt like it needed more mid range torque, I'd go for this grind, installed 4 degrees advanced to keep a little low end.
Howards Cams Hydraulic Flat Tappet Camshafts 710991-08
When the static compression is this low, it's real easy to step too far forward with the cam if you don't have the compression to match.
 
to get into the 13s with a streeter takes a W/P (weight to power ratio) of about .075 to .084, so
@3400# raceweight
With a low-compression engine I'd target 3400x .084=286hp
With a high compression engine.. maybe 3400 x .075=255hp
Easy 360 targets.
That's 30hp difference and about 2 cam sizes right there.
On paper it looks like no big deal right?
In reality, when you put that big cam into your ~8/1 engine the pressure plummets, and below 3000rpm or so she turns into a marshmallow.
Here are some examples
First a plane-Jane stock 360, then up-cammed by 2wo sizes,ok
Scr 8.0/ Ica 56*/ Dcr 6.8/ psi132/ VP 118
Scr 8.0/ Ica 61*/ Dcr 6.5/ psi124/ VP 105
Check out the VPs;
these are less than a stock 5.2Magnum(~124to 128), so you can expect the 360 to have less than 5.2 performance below 3000
Ok now lets pump the Compression up and still using the same two cams.
Scr 9.4/ Ica 56*/ Dcr 7.97/ psi163/ VP146
Scr 9.4/ Ica 61*/ Dcr 7.71/ psi156/ VP134
So lets analyze this;

On the street a VP of 134 is good; of 146 well that's where the fun starts

3.55s and the stock TC will get you 3000rpm @~26mph, in first gear (2.45ratio) and with 26.5 tires ... the more VP you have, the easier it is to initiate tirespin, and the easier it is to keep them spinning for longer. If you spend some money on your suspension to help it hook, the sooner you will be going faster.
Now consider how often, as a streeter, you will be at below 3000 rpm. 32mph is about 3700in low,2200 in second,1510 in Drive. 64 would be double.
So, imagine; here you are, idling along in traffic, 1500 in drive, and you want/need to accelerate briskly . With a VP of 105 and a stock TC, you got nothing, well maybe bit better than slanty-power. So you are gonna want to downshift, hit 2200 in second, and now you have sucked out Teener power, OK so you gotta mash it into first, and now at 3700 you got about stock 360 power.I guarantee you a VP of 105 with 3.55s sucks. Guaranteed.
Ok next, Mr Ellison recommended a 262 cam.. just right to get that 56* Ica, if speced out right. So you then have a choice of; stock 8/1 for a VP of 118, or 146 with 9.4Scr; or some in-between VP number with some lesser Scr.... Whadareyagonnadu?
The money you are gonna need to spend on bigger rear gears and a high stall, as you can see, is far, far better spent on pistons, and has a far far better return in the long run. IMO; I see zero benefit to an 8/1 360 streeter and up-camming; it just makes a bad situation worse.

Big VP
is not necessary for to get into the 13s,
in fact it is easy to get too much VP, and overpower the tires in the 60ft; but VP of146 is not too much,lol. 175 is waaaaaaay too much. 165 is too much, 155 is about right with slicks.145 is about just right with street tires. I'm kindof guessing, seeing as how my car is rated around 165 at sealevel and just kills the tires, including 325/50-15 BFG-DRs, with street suspension. Yes with 3.55s, but with a manual trans.
read about VP here V/P Index Calculation
Happy HotRodding
 
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Blend the bowls on the heads a little..or not...mill them .020.. and then get a nice .470 lift 270 duration hyd cam with matching springs. Jmo.
 
Agreed, the dynamic C.R. is going to go away too far to make a camshaft worthwhile without getting some compression first. The best solution, IMHO, is tune and use what you have to get the rest of the car tuned. In the future, either plan on rebuilding what you have with more compression. If you want to do it quick and dirty, 93 octane in the tank and a 50 hp plate system after getting the combo tuned in will make it a completely different animal on the track. Just don't get too happy with spray on a dead stock bottom though.
 
Agree with AJ and most others
with stock bottom end and stock heads 256 degrees .006 cam like the Lunati 001 for a 360 (less for a 318)
mill the heads (a bunch) and you can go 260 with 360 or 256 with 318
anything else is going to take pistons and I recommend the KB dome quench pistons for stock heads
do the bowl thing yourself as you are going to be changing springs
but first
step back and baseline as others have suggested
post a compression test
270 cam- or the 340 cam dog below 3000 with stock converter and gears and compression
you will feel flat then the motor will "come up on the cam" ok for a stick light or sports car- not so fun after awhile in traffic
 
Agreed, the dynamic C.R. is going to go away too far to make a camshaft worthwhile without getting some compression first. The best solution, IMHO, is tune and use what you have to get the rest of the car tuned. In the future, either plan on rebuilding what you have with more compression. If you want to do it quick and dirty, 93 octane in the tank and a 50 hp plate system after getting the combo tuned in will make it a completely different animal on the track. Just don't get too happy with spray on a dead stock bottom though.


I really appreciate the effort to explain this I am sure this topic has surfaced a number of times for you Mopar veterans out there. I will do a compression test next and see what kind of numbers this motor puts on the board.
 
IMO the scale is too small and too condensed, and considering a MacTools is like $200C, Ima thinking you'll get what you pay for. My Mac has got to be over 3 maybe 4 decades old and still reads pretty accurate. I know what's inside that HF pressure gauge; don't drop it.
 
I know the value of buying quality tools because most of what i have was passed down from my dad back before the introduction of Chinese tools to the American market. Unfortunately most of what is easily available to me today is just the opposite. Harbor Freight tools do work ok in many insistence they just might not last long enough to pass down to the grand kids.
 
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