Just attended the Eve of Destruction at my local race track...I say boost! LOL
BEST ANSWER EVER!
Am I an idiot for wanting to boost a high compression 318?
- Thread starter dusterbuster5621
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BEST ANSWER EVER!
Hi All, I have a 318 in a 1975 Duster with the following specs: 10.3:1 static compression, 4 barrel dual plane air gap intake, Clevite hydraulic flat cam w/226 duration and 0.453 valve lift, headers, edelbrock carb, stock bottom end, some head work I did on my own, and at 5200 ft in elevation. I estimate I have around 320 hp at the crank based on those fun online engine hp calculators. Here's what I want: I want the engine to be more reliable (I have been getting vapor lock in the summer) and I want 400 hp at the wheels and I want to do it in the easiest way possible (not the cheapest) and I do not want to run NOS. I have been looking at Holley's Sniper EFI system along with their hyper spark set-up to increase the reliability. For those extra horses I am considering a Paxton super charger. Again, not cheap (around $10K in total for both EFI and charger) but easier than rebuilding an engine or so I think ha. A few questions I have below:
I'll pay to have the car dynoed and tuned by someone with more experience than me after I get everything installed.
- Is this really stupid? I was thinking I could keep the boost pretty low maybe less than 4 PSI if I opt for a bigger pulley on the charger?
- If I was running 4 PSI of max boost, what octane level would I need for this set-up? I am okay with using 91 and then mixing in something like torco to increase the octane level.
- The Paxton kit requires a hole be made in the oil pan. Does anyone have experience doing this? Curious to hear how you did it? Did it with the oil pan still on the car? Remove the oil pan and drill it?
This engine is not the end goal for the car. I want to build a 360 set up to take on boost in the future (650 hp) but this is maybe 5 years down the line. I am hoping that the supercharger and holley EFI system will be transferable to that new engine. For now I just want the car to be more fun and not worry about breaking down. Not going to be a drag car. Just want to feel some punch driving it around
Read up:
Supercharging Basics – Engine Preparation.
Detonation on a stock or worn engine can cause piston damage or burned valves. Most late model "smog" engines work well with a supercharger, due to their lower compression ratios and smaller cam profiles.
Guidelines
If using a stock engine, follow these guidelines for optimization.
- 7.0:1 to 9.0:1 compression ratio. The optimum compression ratio is 8.0:1.
- Higher than 8.0:1 is not necessary or recommended. Fuel, ignition timing, and total boost could become critical factors.
- 4 - 7 psi boost level. This range has proven to be the best compromise for power and reliability.
- 4,500 - 5,000 engine rpm. When using stock cast pistons, the engine should be limited to a maximum of 4,500-5,000 rpm.
- Exceeding this limit may over-stress the cast pistons and cause failure.
- Properly blueprinting an engine will allow higher rpm reliability. It will also maximize a supercharged engine's potential.
- Eliminate detonation (pinging). Detonation is the single most destructive force in a supercharged engine.
- This may include lowering boost level, retarding timing, installing a boost timing master, increasing fuel flow to prevent leanout, and/or using a fuel additive to raise octane level.
- The cooling system should also be in good condition to prevent overheating, which could lead to detonation.
At that altitude, it’s probably somewhat doable with water/meth injection and boost timing retard. I know of a 318 stroker that was over 9.5:1 with ported Edelbrock heads and cometic head gaskets with head studs. He was pushing 7 pounds at 2,000 feet of altitude, but it was also set up to swill washer fluid at breakneck pace at the first hint of boost.
About 8.5/1 with alloy heads.
1971 360 block. Hughes Engines main girdle, bushed lifter bores, bored .030”. Forged K1 crank and forged rods. 228/224 @.050 cam with 114 LSA. Custom forged Diamond Racing pistons. 8.5:1 compression. Hydraulic roller lifters and roller rockers. Hughes ported Edelbrock heads, super Victor intake. 750 Holley blow through carb. 1-7/8” headers, …
Beautiful street manners and it goes like hell.
650hp / 600lbft
My problem was not having the boost referenced timing retard and the water/meth system not being reliable. Right now it is sitting (7-8 years) and needs to be freshened. I have a new Snow water/methanol kit and an MSD 6 Programmable box with MAF sensor to sense boost. New game plan for ignition and boost cooling.
My suggestion to you is to buy the fuel system and set it up and tune it to your current engine. Next, find a new block and start collecting parts for a new short block . You will need a forged rotating assembly, use your heads, use a single plane. Get everything switched over and tune the ECU for boost. Also, if you can fit it use an intercooler. I would but I don’t have room on the front of my E-body ‘cuda.
Beautiful street manners and it goes like hell.
650hp / 600lbft
My problem was not having the boost referenced timing retard and the water/meth system not being reliable. Right now it is sitting (7-8 years) and needs to be freshened. I have a new Snow water/methanol kit and an MSD 6 Programmable box with MAF sensor to sense boost. New game plan for ignition and boost cooling.
My suggestion to you is to buy the fuel system and set it up and tune it to your current engine. Next, find a new block and start collecting parts for a new short block . You will need a forged rotating assembly, use your heads, use a single plane. Get everything switched over and tune the ECU for boost. Also, if you can fit it use an intercooler. I would but I don’t have room on the front of my E-body ‘cuda.
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Impressive numbers. Hey "8.5/1 compression"
@dusterbuster5621
Oh yeah, use a Procharger. Self contained gear oil, not dirty motor oil. Change every two motor oil changes.
Oh yeah, use a Procharger. Self contained gear oil, not dirty motor oil. Change every two motor oil changes.
And it doesn’t stress the block like making 650hp by natural aspiration. Very smooth and progressive power delivery.
TT5.9mag
Two atmospheres are better than one
I bet no one on this thread has ever built a high compression boosted engine. If you have please chime in. I’ll wait.
It’s 100% doable and I’ve done it. And I am currently doing it. Two things have to happen. You have to have a fuel with enough octane. PERIOD. I recommend e85. And you have to have your tune up spot on. At 5000 ft elevation there will be a little larger tuning window. 8.5:1 and 20 psi is no different than 10.5:1 and 5psi. Cylinder pressure is cylinder pressure I don’t care how you get there. As you go up in compression the tuning window gets tighter and tighter and the engine becomes more rowdy. If the ring gaps are tight now don’t even think about boost. 4psi at 10.3:1 will make enough heat (especially with a supercharger) to stick a ring and break the ring land. One more thing, intercooling is not an option it’s a necessity. Good luck.
It’s 100% doable and I’ve done it. And I am currently doing it. Two things have to happen. You have to have a fuel with enough octane. PERIOD. I recommend e85. And you have to have your tune up spot on. At 5000 ft elevation there will be a little larger tuning window. 8.5:1 and 20 psi is no different than 10.5:1 and 5psi. Cylinder pressure is cylinder pressure I don’t care how you get there. As you go up in compression the tuning window gets tighter and tighter and the engine becomes more rowdy. If the ring gaps are tight now don’t even think about boost. 4psi at 10.3:1 will make enough heat (especially with a supercharger) to stick a ring and break the ring land. One more thing, intercooling is not an option it’s a necessity. Good luck.
TT5.9mag
Two atmospheres are better than one
that car is bad ***.
64mopar
Well-Known Member
No.
Just take the necessary precautions.
I boosted my 318 with around 9.2 to1 with about 8 psi max.
Just take the necessary precautions.
I boosted my 318 with around 9.2 to1 with about 8 psi max.
Before you jump through hoops about vapor lock. Run your tank down to 1/8 tank.
Go to Pure-gas.org - ethanol-free gasoline in the U.S. and Canada
Find a station near you that has alcohol free gas. Do it a second time and then see if your vapor lock issues are gone.
Go to Pure-gas.org - ethanol-free gasoline in the U.S. and Canada
Find a station near you that has alcohol free gas. Do it a second time and then see if your vapor lock issues are gone.
TT5.9mag
Two atmospheres are better than one
That list is a joke. How can they make such general assumptions and publish it. The only thing I agree with is the part about making sure it doesn’t detonate. The rest is bogus. Example, “8.0:1 is the optimal compression ratio”. Even on methanol? Come on. Another example, “maximum rpm 4500-5000”. The highest load the piston sees is at the torque peak. That’s when cylinder pressure is highest. I don’t know who wrote that but damn.
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You need to contact Summit and set them straight. They apparently are idiots.
mopardude318
Well-Known Member
I was going to suggest to switch to e85. Then you can run all the boost you want.
Agreed that e85 is great, but you'll want to use one of the online calculators for displacement, boost, and power goal to size your fuel system if you go with EFI. It takes significantly more fuel system from the pump to the injectors to keep up with a given horsepower output with e85 than straight race gas.
TT5.9mag
Two atmospheres are better than one
Hi All, I have a 318 in a 1975 Duster with the following specs: 10.3:1 static compression, 4 barrel dual plane air gap intake, Clevite hydraulic flat cam w/226 duration and 0.453 valve lift, headers, edelbrock carb, stock bottom end, some head work I did on my own, and at 5200 ft in elevation. I estimate I have around 320 hp at the crank based on those fun online engine hp calculators. Here's what I want: I want the engine to be more reliable (I have been getting vapor lock in the summer) and I want 400 hp at the wheels and I want to do it in the easiest way possible (not the cheapest) and I do not want to run NOS. I have been looking at Holley's Sniper EFI system along with their hyper spark set-up to increase the reliability. For those extra horses I am considering a Paxton super charger. Again, not cheap (around $10K in total for both EFI and charger) but easier than rebuilding an engine or so I think ha. A few questions I have below:
I'll pay to have the car dynoed and tuned by someone with more experience than me after I get everything installed.
- Is this really stupid? I was thinking I could keep the boost pretty low maybe less than 4 PSI if I opt for a bigger pulley on the charger?
- If I was running 4 PSI of max boost, what octane level would I need for this set-up? I am okay with using 91 and then mixing in something like torco to increase the octane level.
- The Paxton kit requires a hole be made in the oil pan. Does anyone have experience doing this? Curious to hear how you did it? Did it with the oil pan still on the car? Remove the oil pan and drill it?
This engine is not the end goal for the car. I want to build a 360 set up to take on boost in the future (650 hp) but this is maybe 5 years down the line. I am hoping that the supercharger and holley EFI system will be transferable to that new engine. For now I just want the car to be more fun and not worry about breaking down. Not going to be a drag car. Just want to feel some punch driving it around
No, just uneducated.
- Look up Rusty Rat Rod's guide to hot rod bliss.
- Look up the requirements to run forced induction, you don't want to start with a high compression engine.
- Get a bunch of books on small block mopars, put them in the bathroom and read them every time you are on the throne.
- There are easier options than $10k to supercharge a 318. Look up blueprint engines, they have an ad here, and a dedicated forum here.
- For that kind of money you could easily drop a third generation hemi in your car. 392 Crate HEMI Engine
- For that kind of money, you could drop a b or rb in as well.
- Check out the 10, 11 and 12 second combos. That will serve you better than building for a horsepower number, there you will learn about gearing, suspension and torque converters as well.
- Work on your suspension and braking capacity before you worry about going fast. Being unable to stop or turn to avoid some kid on a bike will kill your soul as you sit in prison and all that power under your right foot is no consolation. Don't race on the streets.
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Are you running domed pistons in your 318 to get the compression up to 10.3:1 with a 65cc head?
My 318 (+0.060") works out to 9.8:1 with a 63cc chamber and flat top pistons 0.013" above the deck. If your compression ratio is a bit optimistic it will make things easier for you.
Either way you will need to open the motor up to enlarge the ring gaps, so good to verify what your starting with and you can adjust your final compression ratio by cleaning up/enlarging the combustion chambers and/or head gasket selection. My daily driver has 10.5:1 static and is fed a max of 14psi from 2 snails but that's new tech (alloy motor, direct injection, VCT ect ect with a million sensors to pull things up when something is not happy). Not sure I would try doing that with a old 318 without a LOT of previous experience building & tuning boosted motors. 8-8.5:1 and 5-7psi is probably a good place to start.
Having said that the easy button for a reliable 400hp would be a 408 crate motor - might even cost less
dusterbuster5621
Member
I have pretty much zero experience tuning outside of playing with timing a little bit. I would take the car to dyno and to someone with more experience to help out. I was eyeing this company in Denver: Finish Line Automotive & Performance
Dan the man
Well-Known Member
I might be mistaken here, but I think it would be a good idea to fix the vapor lock issue before introducing more heat into the engine.
TT5.9mag
Two atmospheres are better than one
He is. He will be switching to a high pressure fuel system if he goes to sniper or fitech.
Dan the man
Well-Known Member
I'm not familiar with the FI system's, will this take care of the problem then? Is the fitech system about the easiest one to install and program?
TT5.9mag
Two atmospheres are better than one
I have not installed either, but I have tuned both. My opinion of throttle body efi systems is not what most people like to hear so I’ll stay quiet on the subject. Fuel under vacuum on the inlet side of any pump will vapor lock easily. It is very important to limit restriction on the inlet side. Most quality EFI systems use an in-tank pump that does this very well, and uses a return style regulator which also helps with fuel temperature. Another benefit of an in-tank pump is the fuel is now pressurized for the run between the tank and engine which raises the boiling point of the liquid (think radiator) and helps with vaporization. So yes it solves the problem.
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