High RPM valvetrain

[Dave]

What will I need to run up to 6,500-7,000 RPM's? I'm getting a big intake built and I should be able to pull to atleast 6,500 with that and a ported head.

Thanks,
-Bryan

[glhs875]

What will I need to run up to 6,500-7,000 RPM's? I'm getting a big intake built and I should be able to pull to atleast 6,500 with that and a ported head.

Thanks,
-Bryan

I was using MP 061 spings, everything else stock. I was having valve float problems above 7K. Was fine at 6500rpm. I'm upgrading to Steve M spec Comp springs with titanium retainers and matching keepers. I've done some rocker arm lightening as well. I've yet to see how all the upgrades are gonna work. I'm shooting for 7500 to 7600 rpm.

[Frank]

On the 2.5L? You still wont go past 6k... especially in a heavy car because the weight will use up way more available power.

[ShelGame]

You should check out Esslinger Engineering. They build a 2.5L USAC Midget engine (based on the Ford 2.3) and they spin it to 10K. They have a lot of valvetrain parts, and the head design is fairly similar to the Dodge (it's a splay-valve, cross-flow head, but the valvetrain geometry is very similar). I wouldn't be surprised to find that the springs, valves, retainers, lash adjusters, etc. would work in our head with little modification.

[contraption22]

What will I need to run up to 6,500-7,000 RPM's? I'm getting a big intake built and I should be able to pull to atleast 6,500 with that and a ported head.

Thanks,
-Bryan

Hmm to take a 2.5 up that high... I would say you need a broom and some oil dry.

[turbovanman²]

^^^^^^Yep, its not the valve train you need to worry about but the pistons coming apart. The rod ratio sucks and the only way around that is custom rods and pistons.

[glhs875]

^^^^^^Yep, its not the valve train you need to worry about but the pistons coming apart. The rod ratio sucks and the only way around that is custom rods and pistons.

The rod ratio is bad I agree. But the engine could still spin high revs if things were set up right. Needs a ton more flow then even the way most 8V heads are ported to achieve. A better rod ratio would help in the durabilty dept. for sure. But even the 2.5 is not that far off the the rod ratios that Honda engines have and look how some of them rev. Our 2.4 engines have only a slighlty better rod ratio than a 2.5, and alot of people get 8K + revs out of them. If you revs out of a 2.5, get as much flow as you can even with a 16V head, and look at what cross sectional area the ports have. A too small area of a port even if it flows well, will run out of steam way eariler in the R's than a larger area port will. In the search for high revs, I have found that the rod ratio, undersquare (bore smaller than stroke) and even the stock cam are not the major limiting factors.

[turbovanman²]

^^I am no expert on rod ratio's but from reading and researching, the 2.5 has high side loads, high rpm can cause well, you know. I don't really know anyone revving a 2.5? I guess we will find out when my 2.5 TIII is done, although I was told to keep it around 6500 max rpm, even though my head will flow like gang busters and have ligher rods and hopefully lighter pistons.

[glhs875]

^^I am no expert on rod ratio's but from reading and researching, the 2.5 has high side loads, high rpm can cause well, you know. I don't really know anyone revving a 2.5? I guess we will find out when my 2.5 TIII is done, although I was told to keep it around 6500 max rpm, even though my head will flow like gang busters and have ligher rods and hopefully lighter pistons.

rod ratios

2.5 = 1.454
2.4 = 1.525
2.2 = 1.643
Honda engines are in the 1.5's also spinning to 9k+

Yes, a shorter rod puts more side loading on the piston/cylinder wall, but it doesn't necessarily keep the engine from revving. It may rev higher with a better rod ratio, especially with using the same head. Because longer rods tends to work a little better with a smaller cross section port size vs. a shorter rod, which needs larger ports to rev high. And the engine would most likely last longer with a longer rod due to less piston/ring and cylinder wear. And it could probably make more peak HP but might be a little more saggy in the lower revs. A shorter rod usually makes better low rpm torque.

You shouldn't have a problem spinning to 6500rpm with a 16V head on a 2.5. The reduced weight of the parts will help. It just depends on what your after. A low rpm engine will last longer and be less likely to scatter than a high rpm one. Personally, I like the rush of a high rpm engine, even if I'm gritting my teeth waiting for rods to exit the block while turning it up.

[turbovanman²]

rod ratios

2.5 = 1.454
2.4 = 1.525
2.2 = 1.643
Honda engines are in the 1.5's also spinning to 9k+

Yes, a shorter rod puts more side loading on the piston/cylinder wall, but it doesn't necessarily keep the engine from revving. It may rev higher with a better rod ratio, especially with using the same head. Because longer rods tends to work a little better with a smaller cross section port size vs. a shorter rod, which needs larger ports to rev high. And the engine would most likely last longer with a longer rod due to less piston/ring and cylinder wear. And it could probably make more peak HP but might be a little more saggy in the lower revs. A shorter rod usually makes better low rpm torque.

You shouldn't have a problem spinning to 6500rpm with a 16V head on a 2.5. The reduced weight of the parts will help. It just depends on what your after. A low rpm engine will last longer and be less likely to scatter than a high rpm one. Personally, I like the rush of a high rpm engine, even if I'm gritting my teeth waiting for rods to exit the block while turning it up.

Good info. Not really after a revver, don't really need it or want if for a DD but its nice to have in reserve if needed.

Yeah, nothing like a good revving engine, my old 78 Civic that was warmed over would easily pull to 7500 rpm, I loved it and had that same, when will it let go fear, lol!

[TonaChris]

rod ratios2.5 = 1.454
2.4 = 1.525
2.2 = 1.643
.

I am not very knowledgable on the subject. Doesnt 0.1 make quite a bit of difference?

[8valves]

rod ratios

2.5 = 1.454
2.4 = 1.525
2.2 = 1.643
Honda engines are in the 1.5's also spinning to 9k+

Good point! There is a significant difference here though.

A B18C engine has a 5.429" rod. Not only is that around a .500" shorter than a stock rod for us... have you picked up a Honda rod before? There SO light! They have very little material to them. Even when going to the built rod market of Manley's or Crower's like a lot of them get, they're still above and beyond lighter than our stuff. Forged piston weight's are right around the 300 gram mark, over a 100 grams from us!

Granted, we have a lot of strength in our stock bottom ends, but they're rpm advantage is in more than just R/S ratio and they're head.

[Dave]

What is a rod ratio?

[86Shelby]

It's the length of the rod center to center; divided by the stroke.

[turbovanman²]

Good point! There is a significant difference here though.

A B18C engine has a 5.429" rod. Not only is that around a .500" shorter than a stock rod for us... have you picked up a Honda rod before? There SO light! They have very little material to them. Even when going to the built rod market of Manley's or Crower's like a lot of them get, they're still above and beyond lighter than our stuff. Forged piston weight's are right around the 300 gram mark, over a 100 grams from us!

Granted, we have a lot of strength in our stock bottom ends, but they're rpm advantage is in more than just R/S ratio and they're head.

Thats why I am using Eagle rods, 130 grams lighter per rod,

[glhs875]

Good point! There is a significant difference here though.

A B18C engine has a 5.429" rod. Not only is that around a .500" shorter than a stock rod for us... have you picked up a Honda rod before? There SO light! They have very little material to them. Even when going to the built rod market of Manley's or Crower's like a lot of them get, they're still above and beyond lighter than our stuff. Forged piston weight's are right around the 300 gram mark, over a 100 grams from us!

Granted, we have a lot of strength in our stock bottom ends, but they're rpm advantage is in more than just R/S ratio and they're head.

Lighter weights definitely can help with revs. But there's also durabilty to think about. So there should be a little compromise in that dept. Yes, there's not much to stock Honda rods. Leaner than our LW rods! And I don't think they will take much beyond stock power levels for very long. I wouldn't want to try it anyway. But I have seen 8V TD engines with ported heads (large valves) with upgraded valve springs and Aluminum rods and still not rev alot better than stock. Maybe make power to 6500rpm. I feel the main parts to acheiving extended power in the higher revs is in the head and intake. Of course everything else needs to be matched up as well. I was making power to 7K + with a stock cam and T1 2.5 rods (right at 700 grams each after balancing) on my 8V this last time. Should make even more power up there this next time. I found a pretty large port restriction in my lower runners when compared to the head I'm using. Should breathe alot better! We'll see. Now if I can only find the time to put it all back together to try it out!

[glhs875]

I am not very knowledgable on the subject. Doesnt 0.1 make quite a bit of difference?

Not really. The average piston speed will be a little less but not by much. Changing rod ratios only changes piston speeds at certain points during crankshaft rotatation. The piston cannot move slower than the crankshaft for ever. It has to catch up to speed with the crankshaft no matter what length rod is used. When changing rod lengths, the speed of the piston is changed around TDC and BDC only and the difference is measured in crankshaft degrees with opposite effects. In other words, put in a longer rod to slow down the speed at TDC, and the speed will be raised at BDC, and vice versa. Now how much HP can be had by playing around with rod lengths? I don't know, and I don't think anyone else does either. Each way has it's own wants and needs, and would take a ton of time and money to figure out. But I do feel longer rod engines tend to work better with smaller ports and smaller cam (s) (duration). And short rod engines needs a larger port area and larger cam (s) to work really well.

[WickedShelby88]

I'm building a 2.2 simply because it will inherently rev higher with less issues. I've seen a 2.5 with T2 rods break long before a beat on 2.2 with light rods did. That rod ratio also plays a big role in how long the bearings can withstand the constant load. The bearings go first from what I've seen. I'm going to check out that midget engine head though. Something that will rev along with a turbo is an amazing powerplant. I used to own an RX7 and I loved the way that thing could rev to the moon and not hurt itself.

[turbovanman²]

I'm building a 2.2 simply because it will inherently rev higher with less issues. I've seen a 2.5 with T2 rods break long before a beat on 2.2 with light rods did. That rod ratio also plays a big role in how long the bearings can withstand the constant load. The bearings go first from what I've seen. I'm going to check out that midget engine head though. Something that will rev along with a turbo is an amazing powerplant. I used to own an RX7 and I loved the way that thing could rev to the moon and not hurt itself.

Rotaries are fun but as we know, totally different engine,