Datsun Roadster Forum-311s.org

Sr20 ka24

We had Charley Slover do extensive flow testing and porting on our 1977 BRT 1600 including porting a cast iron 1500 head. The 1500 CI head was clearly inferior. Charley did many of the Penske Trans Am car heads. We gave him a new head and a set of competition valves (1.69" int, 1.38" exh) He cut the Exh valves down to stock size and ported the head. Experience at work. We protested and he put in full size comp exh valves. My thinking was that while the peak flow might not increase (I was correct) that the flow at lower lifts would (also correct as tested) What was unexpected was that the flow decreased at lifts above about .400" lift. Charley fixed this to the point that the flow did not decrease above .4 nor increase above .4. I do not know what he did. He did get a slight increase in flow by cutting the exh guide even with the top of the port. I would not suggest this for a street car. As for the intakes the porting was pretty straight forward but the valve prep and the valve job are key. Do not go too narrow on the intake valve seats as they will pound out the stock head. We ran about .080" wide on both intake and exhaust. Of the 2 engines that came with Pat Daly's BRT roadster neither had the block relieved at the intake valves. I would take the bare block, put bluing (magic marker will do) on top where the head gasket moves away from the cylinder bore.(under the Intake Valves) Then put the head on (no gasket) with a few head bolt. Reach thru the bore and you will feel a large ledge where the head overlaps the block under the intakes. Take a curved scribe (a sharpened bent piece of 1/16 welding rod will do) and hook it over the ledge and scribe the top of the block. Remove head and with a grinder, grind the block at an angle from the scribe line to a little above where the top ring has left its mark. Don't try to get too close here. The ring area needs to be perfect to seal.
I keep reading about computed HP. 100 HP/liter was always our goal. We exceeded that with the U20, L18 and the L20B but never came close with the R1600. And yet with our 141 HP We were by far the fastest G car at the 1977 Nationals.

I’m not familiar with Charley Slover, is he related to Micheal “Mike” Slover, who owns Slover Porting Services in the San Fernando Valley? I used to see Mike from time to time back in the late seventies and early eighties. We had a few friends in common back then, I haven’t seen him since the late nineties but he’s an incredible porting guy, he worked magic on Nissan heads back in the day.
Dave

I don't know on that but I do know Charley's son was taking over the shop about the time we left Datsunville, about 1977. If he was 25 then he'd be about 71 now. I never met him.

Sounds like that’s about right, I know that his father used to port heads, was charley in the San Fernando Valley?

Interesting discussion about modifying combustion chamber on the BLOCK side. I've never seen this before or ever brought up in previous discussions here.
Thanks for posting your experience @cascadeclovis

"I keep reading about computed HP. 100 HP/liter was always our goal. We exceeded that with the U20, L18 and the L20B but never came close with the R1600. And yet with our 141 HP We were by far the fastest G car at the 1977 Nationals."
Computed HP? New term for me...is this just referring to HP as calculated by a dyno program?
I keep reading how racers are getting 2 hp/ci on MG's, Triumphs, Volvos, and other 2 valve pushrod engines similar to the R16 and wondering why the Datsun just can't seem to get there, and I don't think(?) it has to do with the engine itself, possibly the supporting parts and prep?
Rebello seems to be getting 180+ hp from the strokers, if they can get the airflow for that, it should translate to the same for 1600cc's, just at a higher rpm....??

"Interesting discussion about modifying combustion chamber on the BLOCK side."
I think this is pretty common on 2 valve heads with a very oversize intake valve. Stock possibly on the U20?
Hard to see, but, looks to be done on this U20 block, halfway down the article...
https://www.enginebuildermag.com/2019/0 ... 20-engine/

Stock on a U20. Mine had to be clearanced more for the larger valves and .531 lift.

neato. Always learning!

Happened to have a block with the head off....
From casadeclovis....
"the block relieved at the intake valves. I would take the bare block, put bluing (magic marker will do) on top where the head gasket moves away from the cylinder bore.(under the Intake Valves) Then put the head on (no gasket) with a few head bolt. Reach thru the bore and you will feel a large ledge where the head overlaps the block under the intakes. Take a curved scribe (a sharpened bent piece of 1/16 welding rod will do) and hook it over the ledge and scribe the top of the block. Remove head and with a grinder, grind the block at an angle from the scribe line to a little above where the top ring has left its mark. Don't try to get too close here. The ring area needs to be perfect to seal."

This is the bit that casadeclovis was mentioning....Likely worth a few cfm/horsepower (maybe more?), particularly on a stroker and with oversize valves. Looks to be about a 4mm overlap. This relieving is not uncommon, it is also being done on Chrysler hemi sixes in Oz. Other british engines as well.

Anyone able to get the dimensions of the cut on the U20 block? Width and depth? Close up picture would be appreciated....
Thanks

I'll post pics of mine, but they are made even larger and deeper with the larger intake and exhaust valves and the cam lift. And yes, I have trashed a block by going below the ring line and had to get another block. I don't recall which one this is, but I was looking for valve strikes. I have more recent pics, some with clay showing where the valve extended to, but they're on my phone. I could probably email those to you.

Thanks Greg,
Those reliefs must make it interesting to calculate the compression ratio......How have you calculated/measured that extra volume?

If possible, I would like to get the dimensions for the stock U20 block reliefs? Anybody?

Well, the reliefs were there when Steve the machinist measured everything and came up with 11.7 to 1 (and why I know it was that exact number). However since then the block has been changed, the pistons have been machined down some more to reduce compression, the reliefs were redone and a bit more material was removed after that by me so now it's a guess... something like 11 to 1? I did a compression test the other day, 950 miles on it, and cold compression is 210-220... pretty much what it's been for several years. And why I must have ignition and fuel control! You know!

Gregs672000 wrote: ↑Sat Mar 30, 2024 12:16 am I'll post pics of mine, but they are made even larger and deeper with the larger intake and exhaust valves and the cam lift. And yes, I have trashed a block by going below the ring line and had to get another block. I don't recall which one this is, but I was looking for valve strikes. I have more recent pics, some with clay showing where the valve extended to, but they're on my phone. I could probably email those to you.

In the first picture with the two pistons, the one on the right, is that the piston ring gap on the bottom side?