diff --git a/lib/bcoin/chain.js b/lib/bcoin/chain.js
index f79eb917..d3a0fb95 100644
--- a/lib/bcoin/chain.js
+++ b/lib/bcoin/chain.js
@@ -629,7 +629,7 @@ Chain.prototype._checkInputs = function _checkInputs(block, prev, flags, peer, c
       else
         sigops += tx.getSigops();
 
-      if (sigops > constants.script.maxBlockSigops) {
+      if (sigops > constants.block.maxSigops) {
         utils.debug('Block has too many sigops: %s', block.rhash);
         self.emit('verify-error',
           block, 'invalid', 'bad-blk-sigops', 100, peer);
diff --git a/lib/bcoin/mempool.js b/lib/bcoin/mempool.js
index 9a5d9692..5ca8c14e 100644
--- a/lib/bcoin/mempool.js
+++ b/lib/bcoin/mempool.js
@@ -40,6 +40,7 @@ function Mempool(node, options) {
   this.db = null;
   this.tx = null;
   this.size = 0;
+  this.orphans = 0;
 
   this.freeCount = 0;
   this.lastTime = 0;
@@ -63,6 +64,7 @@ Mempool.mandatory = constants.flags.MANDATORY_VERIFY_FLAGS;
 Mempool.ANCESTOR_LIMIT = 25;
 Mempool.MAX_MEMPOOL_SIZE = 300 << 20;
 Mempool.MEMPOOL_EXPIRY = 72 * 60 * 60;
+Mempool.MAX_ORPHAN_TX = 100;
 
 Mempool.prototype._lock = function _lock(func, args, force) {
   return this.locker.lock(func, args, force);
@@ -225,6 +227,7 @@ Mempool.prototype.purgeOrphans = function purgeOrphans(callback) {
           return callback(err);
 
         self.size = size;
+        self.orphans = 0;
 
         return callback();
       });
@@ -448,7 +451,7 @@ Mempool.prototype.verify = function verify(tx, callback) {
         0));
     }
 
-    if (tx.getSigops(true) > constants.script.maxSigops) {
+    if (tx.getSigops(true) > constants.tx.maxSigops) {
       return callback(new VerifyError(
         'nonstandard',
         'bad-txns-too-many-sigops',
@@ -670,7 +673,18 @@ Mempool.prototype.storeOrphan = function storeOrphan(tx, callback, force) {
     if (err)
       return callback(err);
 
+    self.orphans++;
+
     batch.put('m/D/' + hash, tx.toExtended(true));
+
+    if (self.orphans > Mempool.MAX_ORPHAN_TX) {
+      return self.purgeOrphans(function(err) {
+        if (err)
+          return callback(err);
+        batch.write(callback);
+      });
+    }
+
     batch.write(callback);
   });
 };
@@ -731,6 +745,7 @@ Mempool.prototype.resolveOrphans = function resolveOrphans(tx, callback, force)
         });
 
         if (orphan.hasCoins()) {
+          self.orphans--;
           batch.del('m/D/' + orphanHash);
           return self.verify(orphan, function(err) {
             if (err) {
diff --git a/lib/bcoin/protocol/constants.js b/lib/bcoin/protocol/constants.js
index 37f2a876..2869ca6b 100644
--- a/lib/bcoin/protocol/constants.js
+++ b/lib/bcoin/protocol/constants.js
@@ -206,30 +206,25 @@ exports.hashTypeByVal = Object.keys(exports.hashType).reduce(function(out, type)
 
 exports.block = {
   maxSize: 1000000,
-  maxCost: 4000000,
   maxSigops: 1000000 / 50,
-  maxSigopsCost: 4000000 / 50,
   maxOrphanTx: 1000000 / 100,
   medianTimespan: 11,
-  bip16time: 1333238400
+  bip16time: 1333238400,
+  sighashLimit: 1300000000
 };
 
 exports.tx = {
   version: 1,
   maxSize: 100000,
-  maxCost: 400000,
   minFee: 10000,
   bareMultisig: true,
   freeThreshold: exports.coin.muln(144).divn(250),
   maxFreeSize: 1000,
+  maxSigops: exports.block.maxSigops / 5,
   coinbaseMaturity: 100
 };
 
-exports.tx.dustThreshold = new bn(182)
-  .muln(exports.tx.minFee)
-  .divn(1000)
-  .muln(3)
-  .toNumber();
+exports.tx.dustThreshold = 182 * exports.tx.minFee / 1000 * 3;
 
 exports.script = {
   maxSize: 10000,
@@ -237,9 +232,7 @@ exports.script = {
   maxPush: 520,
   maxOps: 201,
   maxPubkeysPerMultisig: 20,
-  maxBlockSigops: exports.block.maxSize / 50,
   maxScripthashSigops: 15,
-  maxTxSigops: exports.block.maxSize / 50 / 5,
   maxOpReturnBytes: 83,
   maxOpReturn: 80
 };
diff --git a/lib/bcoin/protocol/network.js b/lib/bcoin/protocol/network.js
index d93ba49f..7aca7c7b 100644
--- a/lib/bcoin/protocol/network.js
+++ b/lib/bcoin/protocol/network.js
@@ -151,6 +151,11 @@ main.deployments = {
     startTime: 1459468800, // April 1st, 2016
     timeout: 1491004800 // April 1st, 2017
   }
+  // bip109: {
+  //   bit: 28,
+  //   startTime: 1453939200, // Jan 28th, 2016
+  //   timeout: 1514764800 // Jan 1st, 2018
+  // }
 };
 
 main.height = -1;