Drag ported 4 mil cylinders

[J-Madd]

I've got a set of ported cylinders that were allegedly ported for 4 mil longrod motor with a spacer plate. If I put a motor together and use cut domes, the port timings would be off, ........right? How can I tell if it was ported for the plate or not? I don't trust the person that these cylinders came from.

 

 

Thanks.

[blowit]

I've got a set of ported cylinders that were allegedly ported for 4 mil longrod motor with a spacer plate. If I put a motor together and use cut domes, the port timings would be off, ........right? How can I tell if it was ported for the plate or not? I don't trust the person that these cylinders came from.

Thanks.

 

 

Post your port heights and I will tell you what will work best for a 4mm crank.

 

 

Brandon

[J-Madd]

How do I measure the port heights? Do I measure from the the top of the cylinder to the top of the port? Please elaborate :thumbsup: . I can fix anything on these things, but I don't have a clue about that :shoothead: .

 

Thanks.

[odaen]

How do I measure the port heights? Do I measure from the the top of the cylinder to the top of the port? Please elaborate :thumbsup: . I can fix anything on these things, but I don't have a clue about that :shoothead: .

 

Thanks.

 

yeah, meaure from the top of the cylinder to the top of the exhaust port, and your transfers.

[RadarRacing]

yeah, meaure from the top of the cylinder to the top of the exhaust port, and your transfers.

I dont think it would be different from a non plate to spacer motor if measuring from the top of the cyl down to the ports. Measure the gasket to gasket distance as well....Head gasket to base gasket distance.

[blowit]

I dont think it would be different from a non plate to spacer motor if measuring from the top of the cyl down to the ports. Measure the gasket to gasket distance as well....Head gasket to base gasket distance.

 

 

So you are wanting the barrel length? Curious why you want that? The ports should be different if used with a spacer or not.

 

 

 

 

Brandon

[RZBansheeMan]

I am not 100% positive on this but I think when they are ported for the spacer plate that the bottom of the ports - exhaust and transfers are lowered more-so and the tops not raised so much.

 

When ported for standard base gasket and cut domes the ports are lowered and raised both. and the domes are cut with a 2mm recess to allow clearance for the pistons.

 

The thicker base gasket or spacer plate is the cheaper way to go, mostly for people that want to stuff 4mil cranks in without the porting.

 

The standard base gasket and custom cut domes is a litlle bit more expensive route, but will keep the stealth factor and is the preffered way to go.

 

As for measuring your ports you should measure from the head mounting surface to the tops of your exhaust and transfers and then measure again from the head mounting surface to the bottom of your exhaust and transfers.

 

Experienced people will be able to tell you if it was ported for a spacer or domes.

 

Hope this helps

 

Mike.

[J-Madd]

The stealth factor is out the window, unfortunately........the cylinders are polished.

 

I measured from the head mounting surface of the cylinder to the top of the exhaust port and transfers and they measured about 34 mm and 44 mm, respectively. I don't have better measurements b/c the battery is dead in my digital caliper, only I can only measure 1 mm increments without the display. If more precise measurements are needed, I'll get them this evening.

 

thanks!!

[odaen]

The stealth factor is out the window, unfortunately........the cylinders are polished.

 

I measured from the head mounting surface of the cylinder to the top of the exhaust port and transfers and they measured about 34 mm and 44 mm, respectively. I don't have better measurements b/c the battery is dead in my digital caliper, only I can only measure 1 mm increments without the display. If more precise measurements are needed, I'll get them this evening.

 

thanks!!

 

I think there's something wrong with your exhaust measurement for sure, since stock is about 30mm. But it would seem that if your transfer measurement is correct, it's setup to run the spacer plate, because it's sitting at the stock height, which will give you a transfer duration of around 131 or 132'ish. Without your spacer plate, the durations would be in the low 120's, which doesn't seem to jive with the typical drag porting numbers I've seen.

 

But, you may want to measure both again to be sure since the exhaust is for sure fubar.

[J-Madd]

I think there's something wrong with your exhaust measurement for sure, since stock is about 30mm. But it would seem that if your transfer measurement is correct, it's setup to run the spacer plate, because it's sitting at the stock height, which will give you a transfer duration of around 131 or 132'ish. Without your spacer plate, the durations would be in the low 120's, which doesn't seem to jive with the typical drag porting numbers I've seen.

 

But, you may want to measure both again to be sure since the exhaust is for sure fubar.

 

 

I had to put caliper in the exhaust port for it to fit inside the cylinder........and its tapered, so I probably didn't get the reading that I was looking for.

[RadarRacing]

Measure everything. Gasket distances,ports etc.

[odaen]

I dont think it would be different from a non plate to spacer motor if measuring from the top of the cyl down to the ports. Measure the gasket to gasket distance as well....Head gasket to base gasket distance.

 

Yeah, it's different. A non plate motor basically has a negative deck height around 2mm to make up for the longer stroke (ie pistons coming out the top of the cylinders 2mm). So, the ports would need to be 2mm higher to keep the same duration as a motor that is setup for around a zero deck heigh (spacer plate motor).

 

The overall cylinder height doesn't matter. What matters is the deck height, stroke, rod length, and distance the port opens with regard to the deck.

[blowit]

So, the ports would need to be 2mm higher to keep the same duration as a motor that is setup for around a zero deck heigh

 

 

Not quite accurate. Stroking and port duration are not related in a linear manor. There is around 10-15 degrees difference between the stock setup and the one you describe.

 

 

 

Brandon

[odaen]

Not quite accurate. Stroking and port duration are not related in a linear manor. There is around 10-15 degrees difference between the stock setup and the one you describe.

Brandon

 

I'm not sure what you're trying to say. What I'm saying, is that given a motor with the same stroke and rod length, you can move the deck height up or down, and the port openings will have to move the same distance to yield the same durations.

[blowit]

I'm not sure what you're trying to say. What I'm saying, is that given a motor with the same stroke and rod length, you can move the deck height up or down, and the port openings will have to move the same distance to yield the same durations.

 

 

Maybe I just do not understand what you are saying but moving the cylinder up or down will not have a linear change in duration. I thought you were referring to a stroker in which you would just adjust the ports up 2mm to "match" the -2mm deck. That would not yield the same durations as a stock motor. That is about all I was saying.

 

 

 

Brandon