Looking for more pep off the line
- Thread starter Alecb
- Start date
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Dale Davies
Well-Known Member
Just my $0.02 on the tire size. The front tires appear to be close to original size. Effect on gearing, speed and acceleration, absolutely zip. It appears the OP has installed taller and wider rear tires for the rake they provide. Yes the tires change the effective final drive ratio, but are not the big issue. If the shift linkage and kickdown cable are not adjusted properly the transmission could start in 2nd gear. Yup, that is not aiding getting the car rolling. If the throttle linkage is not pulling the carb to WOT, it is not performing the way it should. If the ignition is not set to function with the rest of the parts, it will not perform.
Now y'all can pick on the 3.23 gears, but it could be 2.75 or 2.56 like emissions GM and Ford. For racing the torque converter is not in the range needed, but for street and the gearing it is not bad. Without a lockup feature the converter will still be slipping a bit which is not efficient.
I do believe the cam selection was not the best, but considering that is what is installed I would recommend verifying all adjustments and the tune is correct.
These days with the cost of fuel switching to lower gears is likely going to hurt fuel economy which can be a big hit in the wallet, unless an OD trans is also installed. Does a trans shop offer a kit using the GM 700R4/4L60/65e transmissions for installation behind the SBM engines? The 3.07 first aids acceleration and the .7 OD lets you run down the freeway at low RPM sipping gas. Yah, I know, a transvestite. But sometimes you have to go with what works. I have no knowledge what ratios might be in Mopar OD automatics.
Now y'all can pick on the 3.23 gears, but it could be 2.75 or 2.56 like emissions GM and Ford. For racing the torque converter is not in the range needed, but for street and the gearing it is not bad. Without a lockup feature the converter will still be slipping a bit which is not efficient.
I do believe the cam selection was not the best, but considering that is what is installed I would recommend verifying all adjustments and the tune is correct.
These days with the cost of fuel switching to lower gears is likely going to hurt fuel economy which can be a big hit in the wallet, unless an OD trans is also installed. Does a trans shop offer a kit using the GM 700R4/4L60/65e transmissions for installation behind the SBM engines? The 3.07 first aids acceleration and the .7 OD lets you run down the freeway at low RPM sipping gas. Yah, I know, a transvestite. But sometimes you have to go with what works. I have no knowledge what ratios might be in Mopar OD automatics.
Alecb
Well-Known Member
Alright this took a minute but I did some work on the car. I bought the FBO plate and set it at 16 with initial at 18 for a total of 34, I put in heavier springs to hold the timing back, it came in way too early. I can’t run the vacuum advance because it sends my timing thru the roof and it stumbles and pops out the exhaust.
I ran a compression check and all cylinders except 7 look good. Spark plugs look like they’re ok too. The car does not have a steady idle nor a steady low rpm, at higher rpm it evens out.
I’m currently rebuilding an 850 Thermoquad so I can ditch the 600 cfm Holley.
Alecb
Well-Known Member
Quick update on #7, I poured a lil ATF in the cylinder and it brought my compression up to 160. So there is a good chance my rings are worn.
Alecb
Well-Known Member
Another update on Cylinder 7, I let the cylinder soak with Marvel Mystery Oil for a few days then gave it an Italian Tune-up and the compression came back in that cylinder. I checked the compression again and it was up to 130. So that's one problem solved.
Alecb
Well-Known Member
Welp, my lack of power is not an issue anymore. The intake valve on cylinder 7 got stuck halfway down, the piston hit the valve and bent it. So the engine is going to come apart so I can make sure everything inside is alright. My plans for the engine are a full tear down, install a Comp XE268H cam, port the heads and install 2.02 valves, headers and 850 TQ.
PRH
Well-Known Member
Uuuuuhhh, the rocker shaft is installed upside down.
Woodys_Cuda
Ontario, Canada
At this point Alec might want to check the whole engine build. I give him credit for being hands on but there are too many issues so far. Looks like he needs expert help there.
Dale Davies
Well-Known Member
Glad you found the issue. What caused the valve to stick? Was there an oiling issue due to the rocker shaft upside down or was the valve to guide clearance tight. Tight guide clearance generally shows its ugly head soon on a new rebuild.
David Vizard for the mission impossible engine was looking to install Chev 2.00/1.55 LS valves. Magnum valves could work also with 5/16" bronze guides. The small diameter stems are much lighter.
If purchasing a new XE268H cam I would spec it with a 106° or 107° LSA.
I would watch some of David Vizard's porting videos. Yes many are pertaining to Chev or Ford heads, but the information can pertain to Mopar also. Listen to his nogo area and undercutting to unshroud the intake. I would purchase a sonic thickness tester to ensure you leave enough metal there and not make a water gyser.
With stepping up to 2.02 intake valves, degreeing the cam and checking valve to piston clearance is mandatory.
When porting his 289 Ford heads he shows cutting the scavenge plateau, to aid the exhaust getting pushed out the port rather than skipping over the valve head. Some minor appearing features that could be a great aid to inexpensive power.
Alecb
Well-Known Member
I'm going to go through the whole engine just to make sure everything else is ok. I am very hands on with my build, I've done probably 95% of the work by myself. Unfortunately, I don't really have access to an expert outside of the internet or the books/magazines/videos I see. The internet and published media have a plethora of knowledge, but it's a great asset having an expert with you to check your work.
I'm not sure yet what caused the valve to stick, as soon as I have a chance I'm going to tear into it. The engine ran just fine for the ~600 miles I had driven it before it decided to stop running. Oil pressure and water temp were excellent at all times. Why the 106/107 LSA? The grind I was looking at has 110 LSA. I am going to call Comp Cams to get their recommendation for my application.
Paint your damn upper control arms already lol
Dale Davies
Well-Known Member
Look into David Vizard's 128 formula for determining LSA. SBF use 127. These apply to parrallel valve engines.
128 - (1 cylinder displacement ÷ (intake valve diameter × .91)).
110° LSA was the norm chosen for a wide range of displacements and valve sizes for an engine series. Look in the cam catalogues and you have cams listed for SBC from 262 cubes to 400 cubes with an RPM range and idle quality. A cam that will give a 262 a fair idle will be quite smooth in a 400. Going the other way, a cam in a 400 giving a fair idle will likely idle a bit rough in the 262.
The valve size relates to air flow prior to .25D of the intake valve. At .25 × the intake valve head diameter lift, the valve curtain area is equal to the valve head diameter. In the .350" to .400" lift and less the valve and seat are the limiting factor to flow. At higher lifts the port becomes the limiting factor. So David uses the displacement of one cylinder and valve size to determine the best LSA for overall performance. Idle quality is then a function of duration which affects overlap. According to David, get the LSA correct and you may use a shorter duration cam or single pattern and get the same performance. Other contributing factors can be compression ratio and whether the cam and valve train provides quick off the seat or not. Best to search the video to get the rest or whole story from DV.
David Vizard theory is people generally run too much duration so cam companies run a wider Lsa to compensate, so basically you figure out needed lsa with 128 - (cid/8/valve size x .91) and the overlap you require and the duration sorts itself out, the formula is for I think a 10.5:1 cr probably need to go around 1 degree tighter lsa for 8.5:1 cr I forget exactly.
A 1.88 360 = 106 maybe 105 with 8.5 cr, if you ran the overlap of the xe268h you need probably 5-10 less duration so something like 115/120 on 105 lsa.
Bigger valves like 2.02 would be wider like a 107 lsa and maybe 118/124
you have to calculate I'm guesstimating.
Dale Davies
Well-Known Member
Alecb
Well-Known Member
Alecb
Well-Known Member
Boy, I feel silly now, my current cam has an LSA or 114. No wonder it's such a dog!
I wouldn't go that crazy, Richard Holdener did 108 vs 112 vs 120 couldn't get a 116 on time.
108 vs 112 was fairly close.
Dale Davies
Well-Known Member
Another thought DV states is that if you are going to err on LSA, go a degree tighter. When doing the calculation do not forget to multiply the valve diameter by .91. The valve seat is generally in a little from the outside diameter. So a 2.02 valve × .91= 1.838. 45.875/1.838 = 24.959. Rounding it to 25 is OK. 128 - 25 = 103°. Doubtful you will get anyone to grind a cam that tight. You may be able to get 105° but 106° may be easier.
In Billy Godbold's High-Performance Cams and Valvetrains book, he speaks in selecting EVO and IVC points and then IVO and EVC points. He also goes into these as they are related to NA, supercharged, turbocharged and nitrous.
EVO starts cylinder blowdown and the pressure wave tuning.
IVC is when piston compression starts.
Ivo and EVC are the overlap figures.
A different method of going about selecting the timing events and to use this you better have intimate knowledge of camshaft design.
DV essentially simplifies this by determining the LSA. You then can use acceptable overlap to determine duration. More duration equals more overlap and more misfires delivering the loppy idle, but more power at higher RPM.
When you talk to the tech at comp he will want to convince you toward the 110° to protect themselves if the idle is too choppy. That could be once you get to the 280° to 290° cams, but the XE268H is not much more than an "RV" cam. At 110° they are fairly docile.
I installed an Engle [email protected], 210@ .050 cam.in a 351W. This cam was ground on a 109° LSA and has .472 lift. It is a hyd flat tappet cam. Very docile with smooth idle but a bit more torque and fuel economy. That same cam will go in my 0.030 over 289 with 1.9/1.55 LS valves. The LSA by formula should be 107°, but I will be shooting for 11 to 11.5:1 compression. Intake rockers will be Scorpion 1.72:1, so the intakes will be quick off the seat. Best LSA would likely be 108° but considering I have the cam I may as well use it.
That 351W got rebuilt even though it ran great. It has the 1.78 intake valves and the 268H cam. The truck has not been completed yet, but I think my 289 may be a stronger runner.
Right after I get my garage up, you bet!
Next week the 6 inch foundation should be poured.
(Key word - “Should.”)
It’s not the end all. Keep poking around the engine elsewhere. Initial, total and timing of the ignition curve, converter, gears and tires. It’s all in the combination. Keep hammering away at it.
@Dale Davies I don’t know why a cam company would have a problem grinding a cam to your spec. Though I agree they would think you’re crazy for wording your own stuff, a thing I have ran into before…. Sigh…… but insist on it and you’ll get it.
I
Sweet
Dale Davies
Well-Known Member
The 114° LSA does not make the engine a dog, but does tend to lower the torque peak and flatten the curve, as in not as peaky. Depends on the engine build. A supercharger may require the wider LSA when carburreted while an injected engine could delay the injection to reduce fuel wasted out the exhaust. The extra airflow can increase the airflow into the cylinder.
Bullshit.
Thanks proving me right. (Amazing! Do you even realize what you’re writing?!?!)
Wait a minute! Hold on… something ain’t right!
You just broadened the spectrum of the discussion in an attempt to justify yourself and prove me wrong in addition to showing yourself as a hypocrite, or know, nothing above.
Does the engine at hand use a super charger?
If not, the rest of your reply need not apply or be read.
IF the engine in question is supercharged, there’s still a lot of room to wriggle around on this.
And there is the key word.
So is the engine being discussed garbed or fuel injected?
If a carb is in use, the rest of your argument is moot.
IF it is fuel injected, there’s another can of worms, 3rd one, outside of what’s normally done.
Since 3 point of your retort are opening up the spectrum of what’s being discussed into a realm of what is not being used, why bring it up and use it as a argumentative point of discussion and what seems like your trying to school me and/or prove me wrong on a topic not in the OP’s builds parameters?
OH, I will add that I’m sure there’s more to this issue than a cam on a 114 LSA.
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