Which block/crank combo for roadracing?
Thread Starter
Staging Lane
Joined: Jan 2013
Posts: 52
Likes: 0
Hi DK,
Thats a 'half way house' engine to my own 3.625" short stroke engine, as it keeps the standard 4.125 bore which saves a bunch of money, so I understand the reasoning behind that build decision.
What I also don't understand [like yourself] is why use 1.7 expensive Jesel Mohawk rockers, instead of 1.8's, that's leaving very cheap BHP on the table.
The rod ratio could be improved further by using a 6.200" rod but then again that's more money, so staying with common components such as the 6.125" rod saves money, but it does mean the piston will be heavier that ideal because of the compression height needed unless they have decked the block.
In my opinion there is no point in upping the compression ratio, because that is going to increase the torque potential of the engine.
Its interesting that the engine also use the Dailey Engineering V8ST spec pump and pan that Bill Dailey and I designed, and I also use in my Mosler's present engine.
I dont see a price on that engine build but I think it will be mid $20's if not higher.
Cheers,
Mark.
Thats a 'half way house' engine to my own 3.625" short stroke engine, as it keeps the standard 4.125 bore which saves a bunch of money, so I understand the reasoning behind that build decision.
What I also don't understand [like yourself] is why use 1.7 expensive Jesel Mohawk rockers, instead of 1.8's, that's leaving very cheap BHP on the table.
The rod ratio could be improved further by using a 6.200" rod but then again that's more money, so staying with common components such as the 6.125" rod saves money, but it does mean the piston will be heavier that ideal because of the compression height needed unless they have decked the block.
In my opinion there is no point in upping the compression ratio, because that is going to increase the torque potential of the engine.
Its interesting that the engine also use the Dailey Engineering V8ST spec pump and pan that Bill Dailey and I designed, and I also use in my Mosler's present engine.
I dont see a price on that engine build but I think it will be mid $20's if not higher.
Cheers,
Mark.
Actually, with a 3.625 (or is it a 3.622??) stroke, you can use a 6.325 rod (Callies for example) which would leave you .0375 on the table if you were using off the shelf 1.065 pin height pistons such as JE.
I might be in over my head here but if tmy math is correct, this would yeld a great rod ratio which is way better than the Thompson build with a 6.125 rod (and a low pin height).
Given that, 7500 seems like a piece of cake, specially using a LLSR cam.
In a 2600~ob car, this, in my mind would be: goodbye you Mitsubishi fart bomb.
Last edited by DK; Jul 11, 2015 at 10:31 AM.
Actually, wouldn't a more mild rocker arm ratio provide better high rpm stability? Same thing for milder cam lobe profiles. I have always heard it's best to let the cam do the work, not the rockers. If you want more lift, get a cam with more lift, don't compensate with wild rocker ratios.
Just my two cents, but I will be the first to tell you that I don't know ****.
Just my two cents, but I will be the first to tell you that I don't know ****.
Thread Starter
Staging Lane
Joined: Jan 2013
Posts: 52
Likes: 0
Good info.
But would you start with a 1.8:1?
But would you start with a 1.8:1?
It depends on the entire system. NASCAR used rockers with 2:1 ratio and higher, but that's because they were limited to flat tappets which limited the lobe lift. With a stock diameter .842" lifter, despite being roller lifters, there will be a point when it's better to increase rocker ratio rather than lobe lift.
Launching!
Joined: Jan 2011
Posts: 274
Likes: 1
From: Collierville, TN
4.125 Bore x 3.27 Stroke
.... runs 9.03 in a 2800 pound LX Mustang using 488 gears.
COPO 350
.... GM COPO version but well below your HP goal normally aspirated..... but with lower compression and a turbo..... maybe.
Just thinking out loud with these posts.....
.... runs 9.03 in a 2800 pound LX Mustang using 488 gears.
COPO 350
.... GM COPO version but well below your HP goal normally aspirated..... but with lower compression and a turbo..... maybe.
Just thinking out loud with these posts.....
Last edited by FLYZNTN; Jul 11, 2015 at 01:58 PM.
Thread Starter
Staging Lane
Joined: Jan 2013
Posts: 52
Likes: 0
Yep
Its looking more and more likely I will be doing a similar configuration.
LS7 block, Dragonslayer 3.625, 6.35 rods, 0.0125 taller JE's
- or something like this anyway.
That should get me pretty close to 8K anyways.
Its looking more and more likely I will be doing a similar configuration.
LS7 block, Dragonslayer 3.625, 6.35 rods, 0.0125 taller JE's
- or something like this anyway.
That should get me pretty close to 8K anyways.
4.125 Bore x 3.27 Stroke
.... runs 9.03 in a 2800 pound LX Mustang using 488 gears.
COPO 350
.... GM COPO version but well below your HP goal normally aspirated..... but with lower compression and a turbo..... maybe.
Just thinking out loud with these posts.....
.... runs 9.03 in a 2800 pound LX Mustang using 488 gears.
COPO 350
.... GM COPO version but well below your HP goal normally aspirated..... but with lower compression and a turbo..... maybe.
Just thinking out loud with these posts.....
Launching!
Joined: Jan 2011
Posts: 274
Likes: 1
From: Collierville, TN
I actually have that exact crank. Overkill for my needs but when my builder was looking for cranks that was all he could find.
Good luck with your build.
Your car will be an absolute blast to drive.
Good luck with your build.
Your car will be an absolute blast to drive.
Last edited by FLYZNTN; Jul 11, 2015 at 04:12 PM.
Launching!
Joined: Dec 2014
Posts: 215
Likes: 1
It may not be worth the cost of shipping it back to the USA, but I do have a brand new LS7 engine block still sitting in its crate, if your interested PM me and we could work out a price if your ready to buy.
Cheers,
Mark.
Thread Starter
Staging Lane
Joined: Jan 2013
Posts: 52
Likes: 0
Everybody.
There is a lot of knowledge on this site.
I will be following and reading about a lot of projects and dont be surprised if I pop up somewhere
David
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TECH Addict
Joined: Jul 2013
Posts: 2,189
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From: Portland, Oregon
@ KCS, I fully understand that there is a point of diminishing returns with lifter diameter. However, for those of us mere mortals that live on earth, usually 8k rpms seems to be relatively sufficient.
If you need more than that, please talk to your local NASCAR sponsor.
If you need more than that, please talk to your local NASCAR sponsor.
Yeah probably. I'm considering using a mild lobe in my engine like an HUC, and amplifying it with a 1.8 rocker. As far as the lifter is concerned, you have a very slow and stable lobe that will probably never beat up or wear the roller. The valve on the other hand sees stable but slightly quicker motion thanks to the rocker ratio.
If you're using an LS7, then you're starting with a 1.8:1 rocker anyways since it comes that way stock.
If you're using an LS7, then you're starting with a 1.8:1 rocker anyways since it comes that way stock.
@ KCS, I fully understand that there is a point of diminishing returns with lifter diameter. However, for those of us mere mortals that live on earth, usually 8k rpms seems to be relatively sufficient.
If you need more than that, please talk to your local NASCAR sponsor.
If you need more than that, please talk to your local NASCAR sponsor.
TECH Addict
Joined: Jul 2013
Posts: 2,189
Likes: 123
From: Portland, Oregon
Ok, I absolutely understand how general head flow numbers have changed, well, everything. No, we shouldn't UN-evolve back to the old 1.5 rockers...
1.7 cobra rockers are a standard sbf upgrade. It makes sense to upgrade one point from 1.7 ls6 rockers, to 1.8 (ls7-ish) or 1.85 (slp) rockers.
But for OPTIMUM high rpm stability, lower ratio rockers will absolutely prove best. As will less aggressive lobe profiles.
1.7 cobra rockers are a standard sbf upgrade. It makes sense to upgrade one point from 1.7 ls6 rockers, to 1.8 (ls7-ish) or 1.85 (slp) rockers.
But for OPTIMUM high rpm stability, lower ratio rockers will absolutely prove best. As will less aggressive lobe profiles.
Thread Starter
Staging Lane
Joined: Jan 2013
Posts: 52
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If GM decided to build a 100000 mile 427 that revved to 7K and they used a 1:8, then I sure as hell want to follow their methology.
Im sure by the proof of concept stage they had tried all iterations not available to lowlives like us
So me taking some stroke away, is only going to emphesize that more.
I might even end up with 1.85
Who knows?
3-7000 is what Im looking for.
With all my gearing calculations, I dont think Ill ever see anything below 3600 ish. And thats gonna be at 1.1x lateral G, so I dont mind giving up torque there at all!
D
Last edited by DK; Jul 12, 2015 at 01:43 AM.
Thread Starter
Staging Lane
Joined: Jan 2013
Posts: 52
Likes: 0
It would do everything I want and more.
Thats a little over 4k of useable powerband and nice over rev for carrying a gear.
Plus, I want this to be a little more than some guy just sticking a 100k mile LS1 in a car and going drifting.
I want a proper roadrace engine.
The LS7 and it's 100k mile warranty is on a VERY stable/mild lobe profile.
I may or may not be partial to the RX-7 but dry sump is a lot of weight and complexity for an engine bay with not a lot of room to spare. The improved racing baffle in the f-body pan and an accusump and proved 1.4g continuous capable time and time again.
An LS7 with stock dry sump won't fit(rx7) due to the front of the pan being deeper than the f-body pan.
600whp will be too much(imo) in such a light car unless you are on a HUGE track. You WILL need at least 315 tires(read wide flares). Head over to norotors and check out gnx7's car. Another issue, many folks feel the staggered setup kills the balance of the car. Most with flares will run 315 all round on the rx7.
For the motor. I'd go with a sleeved LS anything block(gen IV ideally not LS7) and go 4.125" bore on a 3.622" stroke. Maybe go to an aftermarket block for better main oiling. The RPM/power you want does not require short stroking or crazy expensive cranks. Good call on the longer rod. The valve train should be 90% of your focus. The lightest valves you can get. A very stable lobe profile(LSL or HUC) and Jesel rockers. Then get the spring with the proper seat pressure. <600lb most likely. And the stiffest pushrod that will fit in your heads. 11/32" .120" for most heads.
Another option is low lash solid lifter setup. Sure it requires adjustment but would be well placed in a track car. ITB's would make for another awesome addition.
You'll want to swap out the rear diff for a ford explorer 8.8. Ronin makes a kit for it.
I may or may not be partial to the RX-7 but dry sump is a lot of weight and complexity for an engine bay with not a lot of room to spare. The improved racing baffle in the f-body pan and an accusump and proved 1.4g continuous capable time and time again.
An LS7 with stock dry sump won't fit(rx7) due to the front of the pan being deeper than the f-body pan.
600whp will be too much(imo) in such a light car unless you are on a HUGE track. You WILL need at least 315 tires(read wide flares). Head over to norotors and check out gnx7's car. Another issue, many folks feel the staggered setup kills the balance of the car. Most with flares will run 315 all round on the rx7.
For the motor. I'd go with a sleeved LS anything block(gen IV ideally not LS7) and go 4.125" bore on a 3.622" stroke. Maybe go to an aftermarket block for better main oiling. The RPM/power you want does not require short stroking or crazy expensive cranks. Good call on the longer rod. The valve train should be 90% of your focus. The lightest valves you can get. A very stable lobe profile(LSL or HUC) and Jesel rockers. Then get the spring with the proper seat pressure. <600lb most likely. And the stiffest pushrod that will fit in your heads. 11/32" .120" for most heads.
Another option is low lash solid lifter setup. Sure it requires adjustment but would be well placed in a track car. ITB's would make for another awesome addition.
You'll want to swap out the rear diff for a ford explorer 8.8. Ronin makes a kit for it.
Last edited by Exidous; Jul 15, 2015 at 03:31 AM.
It's a balancing act. If you have the cam do all the work, as you said earlier, you're going to reduce the base circle of the cam and reduce its stiffness and put more side load on the lifter. Conversely, as you increase rocker ratio, you put more load on the lifter and quicken the valve motion. My whole point is that it's not ideal to do only one or the other. If you do just enough of each within the geometric constraints of the engine, then you get your ideal results.
TECH Addict
Joined: Jul 2013
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From: Portland, Oregon
If dry sump oiling is out of the question, then isn't 8000rpms also out of the question? It doesn't take too much effort to build a valvetrain that's 7k capable. But you started exceeding the stock oiling system with any sustained amount of time spent over 7000rpms.
A baffled f-body pan and an accu-sump may handle the G forces of road racing, but can they keep up with your intended rpm goals?
And individual throttle bodies would be awesome! Don't see nearly enough ITB builds.
A baffled f-body pan and an accu-sump may handle the G forces of road racing, but can they keep up with your intended rpm goals?
And individual throttle bodies would be awesome! Don't see nearly enough ITB builds.
The factory LS7 oiling system is complete crap. The remedy is a different pan and external pump in conjunction with the dual gerotor oil pump. That's a $2-3K fix.
You can run a factory dry sump pan in an FD RX-7 as I did for years. You just need to modify the crossmember and bumpsteer correction. I sold my LS7 simply to do the fact that the oiling system for racing is subpar.
My next motor is going to be a 4.190" bore/4" stroke 441 with Daily billet dry sump and Callies Magnum crank/billet H beam rods. I plan to spin it to 7-7500rpm and to avoid up shifting 8K if needed. AllPro heads/intake/Cammotion solid roller. I bought most of the parts used to save money. I'm still going to be into it for $15K easy.
You need to determine your budget for the engine.... definitely run a REAL dry sump system and go from there. ARE/Dailey etc make nice stuff.
Also a polymer FAST/MSD intake above 6800rpm pretty much flat lines as they reach their airflow max no matter how good of heads. So spinning to 7500-8000rpm is a waste of time.
I built a 460rwhp LS2 stock bottom end aside from ARP rod bolts with LS3 top end/intake with baby 230 duration cam.... kept the rev limiter at 6600rpm and ran an ARE dry sump in a track FD I sold.... he campaigned it for 2 years beating the living crap out of it.... and it hasn't had issues yet in SCCA racing. Perfect example of a budget reliable track motor.
Look up vids for Cameron Rogers RX-7. Set a couple track records with it also for his class... car was 2550lbs wet.
You can run a factory dry sump pan in an FD RX-7 as I did for years. You just need to modify the crossmember and bumpsteer correction. I sold my LS7 simply to do the fact that the oiling system for racing is subpar.
My next motor is going to be a 4.190" bore/4" stroke 441 with Daily billet dry sump and Callies Magnum crank/billet H beam rods. I plan to spin it to 7-7500rpm and to avoid up shifting 8K if needed. AllPro heads/intake/Cammotion solid roller. I bought most of the parts used to save money. I'm still going to be into it for $15K easy.
You need to determine your budget for the engine.... definitely run a REAL dry sump system and go from there. ARE/Dailey etc make nice stuff.
Also a polymer FAST/MSD intake above 6800rpm pretty much flat lines as they reach their airflow max no matter how good of heads. So spinning to 7500-8000rpm is a waste of time.
I built a 460rwhp LS2 stock bottom end aside from ARP rod bolts with LS3 top end/intake with baby 230 duration cam.... kept the rev limiter at 6600rpm and ran an ARE dry sump in a track FD I sold.... he campaigned it for 2 years beating the living crap out of it.... and it hasn't had issues yet in SCCA racing. Perfect example of a budget reliable track motor.
Look up vids for Cameron Rogers RX-7. Set a couple track records with it also for his class... car was 2550lbs wet.