What type of porting is this?

[Ryan_G]

I was concerned about my compression on my SJ. An even 155psi with an ADA head w/ 33 cc domes. I was hoping for somewhere around 175/180psi.

So I pulled my cylinder today to take a look at the pistons and rings.

Can someone please tell me a little about my porting?

Does this porting justify 155psi w/33cc domes?

Where do I go from here?

 

[Kennay]

definitely some scoring to the left of the exhaust port on the cylinder and the piston

 

[Kennay]

Someone who knows what they are talking about (Not me ) is about to come in a few minutes and tell you to measure from the top of the cylinder to the top of the exhaust port in MM and repeat measuring to the bottom of the exhaust port

 

[#ZERO]

It looks like very mild freestyle porting.

The exhaust has been widened a bit and the transfer walls were ported with a small Dremel tool giving that rough appearance.

 

[Matt_E]

transfer walls were ported with a small Dremel tool giving that rough appearance.

It wasn't me!

Seriously, it looks very decently done if it was done with a Dremel. Corners look good.

You'll have to measure from deck to exhaust port roof, but I am guessing that they have been raised a bit.

 

[Ryan_G]

Someone who knows what they are talking about (Not me ) is about to come in a few minutes and tell you to measure from the top of the cylinder to the top of the exhaust port in MM and repeat measuring to the bottom of the exhaust port

Top of exhaust port to top of cylinder - 37mm
Bottom of exhaust port to bottom of cylinder - 71.5mm
(My caliper is not perfect so it might be off by a half a mm or so)

 

[Matt_E]

See, it's been raised.
If I am not mistaken, stock distance is 39.xx mm.
There's why you got lower compression.

Note: I could be completely wrong. I am a hack and a poser.
Top poser on this site, actually.

 

[Ryan_G]

So should I be ok putting it back together with a new base gasket, and 31cc domes? Will that bring me up to 175psi? Will I still be safe with pump gas? Or do I need new rings and a hone?

 

[Matt_E]

I would not lower dome size without talking to someone that knows what they're talking about (Not me!), like a pro-builder.
Your cranking compression may be low, but I'll bet your dynamic - running - compression is quite high.

 

[Ryan_G]

I would not lower dome size without talking to someone that knows what they're talking about (Not me!), like a pro-builder.
Your cranking compression may be low, but I'll bet your dynamic - running - compression is quite high.

Thanks Matt, Ill have to make some calls.

 

[SUPERTUNE]

IMO, I would say a bit over ported for freestyle. The other issue you have is the one piston pictured in this post is junk and needs replacing as it has had a fairly heavy seizure and now has what I call black death imbedded into the piston skirts and will just continue to have more seizures. This may be caused from being too lean, too much timing and also not enough piston clearance for a modified high compression engine, add dual cooling and you really aggravate the problem.
If you need any ADA domes that need to be smaller than 33's to pump 175 lbs on a 701 cc cylinder would be very borderline pump gas engine, a very good ignition system like MSD Pro Digital TL would get you there possibly depending on the rest of the setup on the engine.
Boring the cylinder and using bigger pistons like 82mm or 82.5mm will also help raising compression ratio.
Not many options when cylinder is overported for freestyle/rec ride.
One way to help would machine base gasket surface then re-machine custom domes, careful of the squish clearances and ratio's.
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Clearwater, Fl. 33765
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[superramjet]

add dual cooling and you really aggravate the problem.

chuckie,

is dual cooling bad for motors? Tom

 

[SUPERTUNE]

NO Tom. Seizures are more likely when engines are modified...and dual cooling added.

 

[kevbo]

That porting may be fine depending on how much you jocky the throttle. You will need low pump loading regardless. Hone the cylinder and rejet.

 

[Ryan_G]

That porting may be fine depending on how much you jocky the throttle. You will need low pump loading regardless. Hone the cylinder and rejet.

What do you mean by low pump loading?

 

[Matt_E]

Impeller pitch

 

[Ryan_G]

Thanks Matt
I was running a scat swirl 12/17 cut back 3mm. Will that work?

 

[thegoldenboy]

No, you should sell it to me.

 

[loictahiti]

See, it's been raised.
If I am not mistaken, stock distance is 39.xx mm.
There's why you got lower compression.

Note: I could be completely wrong. I am a hack and a poser.
Top poser on this site, actually.

+1
and bore your cylinder with 0,50 new pistons and rings, afterthat you'll win some lbs
I have one cylinder (650) with the same porting (specialy for race) and I have low compression, I need put 27 cc to upgrade the compression to 180 psi, so finaly with hight compression with this porting you cannot have freestyle engine, bad low end, but very good top end.
today this cylinder is stored on a shelve.....

sorry about my bad technical english, I hope you understand what I mean

 

[SUPERTUNE]

Matt's got it right, 38.7-38.9 mm's is a stock 61x cylinder.
so 37mm is pretty close to 2mm higher...somewhere around 192-194 degrees of exhaust duration, good race spec's, not too friendly for freestyle porting without lots of compression, race gas and some healthy ignition timing w/ very light flywheel. (MSD-TL)
You possibly might be able to glass bead (must remove the black death on piston) and mic the piston skirt and see if you killed it or not, depending if the piston skirt is collapsed. Hone cylinder, Check piston clearance and use new rings if the piston is savable.