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Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
What would be the go to CR when building a dedicated E85 Group N engine with the 33mmrestrictor in place ?
currently at 9/1CR pushing 329flywheel hp
Currently has absolutely no knock veriefied while tuning wth knock ears and on the road in 6th WOT for minutes
its on E85 race fuel , not the smelly french E85 from the pump
First thing would be to check the rule book to check what is, and isn't, allowed.
Second thing is N/A or 'boosted', and if so by how much?
There is no limit on engine build as the group N thing isnt really a thing anymore here , just some rules like the 33mm intake restrictor need to be in place
its boosted 1.5 bar dropping to 0 after 5.5k rpm as the restrictor prevents it from getting enough air
You might want to read this article
Interesting article, but there some contentious parts, such as the claims around "volumetric efficiency" and "unswept volume".
From the claim of zero 'boost' at 5.5k, with a 33mm restrictor that should support around 320hp, or more, which is a lot more than the engine can produce with those figures, I'd suggest having a careful review of the engine, turbo's cold air path, charge cooler, and exhaust plumbing before worrying too much about the compression ratio.
A big part is the design of the restriction*, as that can have a huge affect on the airflow, and correctly sizing the turbo' to the actual power of the engine with the restriction.
Anyway, back on topic, as a general rule, the higher the better, as long as it doesn't compromise timing for best torque, and that shouldn't be an issue with the relatively low boost, or the burning of the flame front. Even if there is a slight compromise around peak torque, the higher compression may make a noticeable difference below and above that, more so if the breathing is actually restricted.
*Further reading? - https://www.raetech.com/Restrictors/Restrictor_GT.php
What do you mean with"which is a lot more than the engine can produce with those figures"
all the cars here in the shop make that power level with that setup somewhere from 310-325 flywheel hp on a superflow dyno
the boost isnt actual zero at 5.5k rpm but its drops steep and keeps on dropping the higher you rev
thats why i was interested to hear other experiences with CR relevance to power when it starts dropping boost
- shiftpoint is at 5.5K but in top gear it revs till 7.4K so it does need some power up top
about the intake: its the longest legal intake restrictor straight in an air box , car has a front mount intercooler, intake temps are at 70-80 degree C when the water injection is off
its not having a happy life at all
Kenny, with the "zero" manifold boost initially posted, and the rpm cited. You confirmed this may not have been accurate, thank you.
As I thought I said, the higher CR will improve efficiency, especially below and above the 'boost' region where torque was reduced by poor cylinder filling.
If you have a spare/development engine the simplest thing would be to build one with, say, 10:1 and try it - it improves the overall output, without hurting peak, try with a bit more on the next build. That way you'll have confirmed test data for your specific vehicle packages and there's no variables others may have with their setups.
In short, the good/bad thing about the restrictor is it limits the airflow, and hence potential power AFTER the pumping, frictional, and other parasitic losses - this means that for the same pressure drop across it you'll have the same airflow regardless of the rpm. In practice, this means a fairly flat power band with a drop-off being normal at higher rpm, as you've found.
If you haven't done so, logging the absolute pressure before, and after, the restriction and comparing that to manifold and rpm may be informative.
This may be TLDR, and you may already be looking at all of them, but if not, your competition will be doing at least some of them, and there may be something that gives you an idea.
There really isn't much you can do about it except extract as much useable energy from the fuel with an optimum CR; minimise the pressure drops in the plumbing; possibly rework the heads for the rpm range that would normally be 'peak 'torque rather than 'power'; minimise parasitic loads like water pumps (larger pulley on it and/or smaller crank, if applicable to the design) with possible use of an electric one; look at the engine's operating temperature - the higher you can safely run it, the lower the energy loss to the cooling system - and potentially lower drag if less intake opening is needed; alternator(if used) cut-out and or large pulley if required; avoiding excessively high oil pressure as that can take significant power; look at the engine and transmission lubricants - you may be able to drop the viscosities a little to reduce drag while maintaining protection - running them at little higher, safe temperature will reduce drag.
Then there's the other stuff, look for the lightest practical (budget and strength) wheels, look at general weight saving if there's something you missed - you know the story. Can you use a lighter/smaller brake package if you improve ducting and/or select better pads?
We did use 9,5:1 CP pistons and modified heads. Cut some squish areas out. With G25-550 and 34 mm restrictor it did 225 Wheel kw and 563 Nm. Equal lenght manifold and top mount intercooler.
That was, indeed, a very good article. I'd draw the OP's attention to the part where there was a comment on restricting boost - as the restrictor you have to use is doing - and offseting this with more compression to broaden the power curve off boost, as I was suggesting may be an option.