cranking compression on alcohol motor, cam advance question

[seefour]

I have a alcohol motor and the cam is in on 107 c/l , 108 sep
775-757 266-273 @.050
the cam is supose to be in at 104 int ex 112
now its 107 int 109 ex
my cranking compression is 240- 245 lbs, I was wanting to put it back on 104 c/l like its supose to be. when does cranking compression become to much and the motor fights itself? being a alcohol motor would it like it better with more cylinder pressure?

[Ron C.]

Probably not.
You didn't ask but I will make a suggestion anyway. You've got way to much cam overlap for a alcohol engine. Your power (heat) is all going out the exhaust.

That's my experience anyway.........blessings.........Ron.

[UDHarold]

You didn't say what this cam was for, but I have had some experience with alcohol-injected sprint cars, and too high of a compression, and not enough 'juice' in the spark, that around peak torque(peak cylinder pressure), the spark couldn't fully ignite the charge.
If the engine seems to come alive about 5500-6000, you may have too much cylinder pressure around peak torque.
Let us know more about your combination, and type of racing.

UDHarold

[seefour]

The car runs 6.0 in the 1/8 at 113.95 mph, leaving off idle it runs 1.35 60 ft on leafsprings and 10 inch M?T slicks, I am shifting at 6500 rpm. the motor will physically turn more rpm 7400-7500 but does not pull any higher than 6500 rpm . I have a sheetmetal intake , two rons toilets 1435 cfm each, msd 7al2 ignition, hvacII coil , plugs gapped at .025
the cam is stated above 4.0 stroke 6.0 rod 4800 stall 4,30 gears 1 7/8 headers 3.5 collector
its 410 inches , I run the CHI 3v head 218 cc runner the heads flow 340/240
the car is 3050 with me in it
I run a 0 1/2 pump 35 nozzel 82 return, Ive been told to drop back to 33 nozzel and 68-72 return pill.
Timming is run at 26-27 degrees due to the combustion chamber design, lost power on chassis dyno at 28 degrees.
Im wanting to make the car run harder in the 1/8 mile since i mostly run nothing but 1/8 mile, looking for more et drop

the cam overlap is 53.5 degrees wich I fell is short
i have a transbrake but never used it, I leave off idle
1.3523 60 ft;s

Mike

[Strange Magic]

I was wanting to put it back on 104 c/l like its supose to be.

I would recommend to put it on ebay. Your cylinder pressures are severe for alky and severe dynamic pressures will leed to disasterous results. You run the risk on wrist pin failure, bearing failure and wall distortion. I would recommend to have a cam ground more suitable for your application.

Timming is run at 26-27 degrees due to the combustion chamber design, lost power on chassis dyno at 28 degrees.

This is not due to any design other than excessive dynamic pressures from an incorrect camshaft. Unusually reduced timing for an engine that is not supportive of it, is also an indication of high dynamic pressures.

[Ed-vancedEngines]

Look at what Harold wrote.

The 7AL2 is killing you.

A Digital 7 is much better but if you are having a lot of cylinder pressures running alcohol, I suggest instead to do either a MDS 8 or an MSD 10. Next step up from that would be a Mag44. In my opinion for what you are doing a Digital 7 would be the minimum. Alcohol does not burn like gasolene. It explodes after being ignited while under high pressure. That is considered to be a hostile ignition environment requiring more initial spark.

You already have far too much cranking compression. If you advance the cam more like you are talking about doing the cranking compression will go outta sight. If at all possible you do need a different cam that is better suited for what the rest of your engine combination is.

Not sure, but i don't think you told us measured static compression ratio? We can already see that your dynamic compression is leaning toward the danger side.

Ed

[Strange Magic]

A Digital 7 is much better but if you are having a lot of cylinder pressures running alcohol, I suggest instead to do either a MDS 8 or an MSD 10. Next step up from that would be a Mag44.

This is a normally aspirated engine on alky, not a blown fuel digger or flopper making north of 6000HP.

Personally I think the 7Al is one of MSD's best boxes ever made. I like the digital 7 boxes but only slight positive results will come from it . When certain functions are used in an effort to harness the engines power so the ride is more manageable through the first 15 feet of the race track, big et gains can be found.

[seefour]

13.8

52.5 cc head
4.04 bore
4.0 stroke
6.0 rod
.041 head gasket
-3.5 cc for valve relief

[Ed-vancedEngines]

Personally I think the 7Al is one of MSD's best boxes ever made

I too feel they were. I used them for years and liked them. The MSD 7AL 2 does not have near the energy that the Digital 6 Plus box does and is far below the MSD 7AL3 box in potential. The Digital 7 pt# 7520 blows all the mentioned away though. I mentioned that one because it is easily adjusted by hand and needs no lap top or PDA. It is the simpliest of the bunch.

There are still plenty of racers still using the older MSD AL stuff like the 6AL and 7AL but all of those are now outdated technology. Yes they are still for sale and they still work as good as they ever did.

It is like the Holley Blue Fuel Pumps. For years even the Pro Stocks were using Two Holley Blues. It was all we had. Now we know better and many have realised better rusults by going for the better later technologies.

Fuel PUmps and Ignition Systems do not make any additional power. But if you are lacking in those areas when you make positive upgrades you allow the engine to make more of what it's potential is.

Ed

[Ron Golden]

seefour,

I agree with Ed on the ignition. I recently had a 15:1 alcohol engine on the dyno with the engine owners MSD 7AL box. The engine sounded ragged and was laboring and the TQ curve wasn't smooth. We switched to a MSD 10+ and it was as different as day & night. The engine also made 70 more HP.

Ron

[seefour]

What was the cranking compression on that 15.1 motor?

seefour

[Ed-vancedEngines]

I should be putting an alcohol 14.50 -1 engine on the dyno toward the end of the week or next week that should be cranking at less than 200 psi, I hope. It is a 708 cu in engine. The dyno has a 7AL 2 on it, so we are bringing the MDS 10 from the car and coil EFI box etc, to hook it all up. I will know what cranking is after we run it a bit.

Ed

[Ron Golden]

I didn't do a cranking compression test on that engine. If I was guessing, I think it was pretty high.

Ron

[CamKing]

Probably not.
You didn't ask but I will make a suggestion anyway. You've got way to much cam overlap for a alcohol engine. Your power (heat) is all going out the exhaust.

???
On the 410 sprint car engines we run 264/272@.050" on a 108-LSA all the time. 15:1 on Alcohol with mechanical fuel injection. Why would this be any different?

[Ron C.]

Probably not.
You didn't ask but I will make a suggestion anyway. You've got way to much cam overlap for a alcohol engine. Your power (heat) is all going out the exhaust.

???
On the 410 sprint car engines we run 264/272@.050" on a 108-LSA all the time. 15:1 on Alcohol with mechanical fuel injection. Why would this be any different?

I think he's using it as a drag race motor, not a sprint car motor. Personally if it was my drag race motor.....I'd change the cam.

On MSD ignitions.....jumping from a 7AL2 to a 10Plus is a big increase in millijoules to the plug. Like 105-115mj's to 700mj's.
The increase from 7AL2 to a 7digital is 105-115mj's to 190mj's. Not that great of an increase but the Digital7 does have multi sparks below 3000 RPM which makes it sound a lot cleaner. But it can make a difference.

Blessings........Ron.