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Wed Oct 29, 2014 11:53 am

I have a low time engine, 2000 miles, 1915 with stock crank, 1.1 rockers on solid shafts, Mofoco 042 heads (42x35.5) and an Engle 110 cam. Right now my deck height sets about .110. I want to stroke this engine, and fix that big deck, but my heads only have 48cc combustion chambers. I have a set of 40 HPMX carbs on the shelf for the upgrade. What will be the issues IF I choose to use the same cam and lifters, the Engle 110, with this much compression. It is in my fiberglass street buggy, so I am not hindered by engine compartment heat.

Wed Oct 29, 2014 12:18 pm

2176 78.4x94. .070 dh , 10 cr. Choices get limited with low head cc and decent deck. Same cam, lifters, clearance case and all new bearings. Balance internals and a 12-13 flywheel. Id get a dpr crank. I like how the crank throws are thinner.

Wed Oct 29, 2014 12:28 pm

It sounds like your case wasn't decked correctly for 94's. The right thing to do is have the case machined and re measure your deck. Aim for .040"-.060". Then see if you can unshroud the valves in the chambers for more CC (do not hemi cut). Around 9:1 compression is what you want. Dish the pistons if necessary.

Wed Oct 29, 2014 12:42 pm

I realize one normally should shoot for the 9:1 with this cam, but the question is " what are the consequences?" Why is running 10:1 a problem with good octane and good parts? Just looking for someone to explain the issues......

Wed Oct 29, 2014 12:46 pm

David Wayne wrote: I have a low time engine, 2000 miles, 1915 with stock crank, 1.1 rockers on solid shafts, Mofoco 042 heads (42x35.5) and an Engle 110 cam. Right now my deck height sets about .110. I want to stroke this engine, and fix that big deck, but my heads only have 48cc combustion chambers. I have a set of 40 HPMX carbs on the shelf for the upgrade. What will be the issues IF I choose to use the same cam and lifters, the Engle 110, with this much compression. It is in my fiberglass street buggy, so I am not hindered by engine compartment heat.

did you machine the step off the heads?

Wed Oct 29, 2014 12:53 pm

Yes Roy, I had the step machined out when I had them cut for 94's, leaving a 48CC chamber, I thing I could machine out a couple CC's, but I want to reuse the cam and lifters if possible. Would there be an issue running that CR ratio with your heads?

Wed Oct 29, 2014 1:08 pm

If you can drop the deck to .070" it's 8.9:1, which is still going to be ok. Borderline, but ok. Better than the deck you have now!

But if you also stroke it, you'll need to re-work the chambers to get more chamber volume to keep the CR under 9:1.

Wed Oct 29, 2014 1:10 pm

David,
Sorry I have to recant what I suggested earlier. Your dcr will be too high. In the 8 point range.
You have a few choices, change cam and lifters to find a cam that has a later ( higher number) closing point or open your head cc's to at least 52 and run a deck of .080. This will leave you with a 7.4 DCR and 9.2 CR. I wouldnt go higher than that. If you can get 54 even better. A third option is to dish the new pistons you will be buying to gain the target total CCs. I think that would be cheapest if you want to keep the cam.
I suggest working with a engine dcr calculator to find your happy zone.

Wed Oct 29, 2014 1:15 pm

I would like to add one thing. IF you added a stroker crank, simply do a cam change to a W120, which you can run 10:1 with. This is the simplest solution to your situation. Even though you have a bigger cam, you will not lose any low end at all because of the bigger crank.

Wed Oct 29, 2014 1:25 pm

jfats808, it took me forever to figure out what your avatar was. I JUST figured it out. I have two myself. They will rule the world someday. :lol:

I have a turbo, and run 7:1 CR. Lots of deck, and a small cam. It runs great even off boost. But a turbo engine is a different animal.

Wed Oct 29, 2014 1:28 pm

I appreciate all the suggestions, especially from some big names, and especially John who offers B piston without cylinders and has the Scat rods I want at a decent price. I understand if I ran a 78 crank, 5.5 rods, and dished the pistons I could get along with this low mileage cam and lifter combo. But still no one has answered WHY can't I run that compression ratio. I know how to get it lower, I just want to know WHY 10:1 is bad!!!

Wed Oct 29, 2014 1:35 pm

Because it will ping and destroy your engine.

Wed Oct 29, 2014 1:38 pm

Thank's John! Ok, but can't detonation be addressed with the higher 93 octane, or is that just not enough?

Wed Oct 29, 2014 1:42 pm

David, in short there is no reason or bad side to running 10cr. But in running 10 to 1 with your current cam and combo without some component and build adjustments will result in too high of DCR. There are tons of guys running 10 to 1 or higher on their rides., street and sand. Engine build particulars become highly important.

Bah John said it simpler. :)

Wed Oct 29, 2014 1:56 pm

10:1 is too high for pump gas with a W110 cam.

Wed Oct 29, 2014 2:07 pm

David,

Whats your altitude in your part of Indiana?

Jeff

Wed Oct 29, 2014 3:33 pm

We are between 900 and 1000 above sea level.

Wed Oct 29, 2014 3:35 pm

I run 10.4 with those heads ,street daily. you should be fine around 9.5

Wed Oct 29, 2014 4:40 pm

David,

10 to 1 is in the realm where you can still manage it. If you keep your initial timing at 10 or less, and your total at 30 or less, premium gas, I bet it works.
The point at which it "doesnt work" is when you go higher then 10 to 1. The reason it wont work(higher then 10-1) is even with premium pump gas it pings and detonates no matter where your timing is set. Then parts start breaking.

Jeff

David Wayne wrote: We are between 900 and 1000 above sea level.

Wed Oct 29, 2014 4:53 pm

Well, it looks like my options are to go to a cam with a longer duration, dish the pistons, or change heads. Cam is the simplest..... I suppose I must change out the lifters, even though they are short time also? Besides the W120, should I look at other cams for a light street fiberglass buggy?