Thanks for the info. I would probably only spray from 3500 or 4k up and there is a very slim chance of puddling with my 5" PSR intake anyways. I am running a ford GT pump right now, will have to see how my duty cycle looks before spray to see if thats sufficient. Any chance you could give me a full list of parts I would need to spray safely? I know this has been answered on this forum before but I am having trouble finding a list.
Highest compression for boost?
- Thread starter trxcobra
- Start date
Thanks for the info. I would probably only spray from 3500 or 4k up and there is a very slim chance of puddling with my 5" PSR intake anyways. I am running a ford GT pump right now, will have to see how my duty cycle looks before spray to see if thats sufficient. Any chance you could give me a full list of parts I would need to spray safely? I know this has been answered on this forum before but I am having trouble finding a list.
You want a blow down tube, wot switch, window switch, nitrous gauge, purge, and a bottle heater.
Thanks buddy! Probably won't jump the gun until summer time but I think it will make for a little more fun!
Yes it's a rush lol
I am literally giving you word for word from his "how to build a high performance modular engine" book.
This is not just for race car engines, but he also from testing tons of street cars. He said out of the many engines he has built and tested flat top pistons work best with centrifugal superchargers and typically have a ratio of 10.2:1
I read the same book. Keep in mind the line between "race car" and "street car" can get blurred especially with professional engine builders are concerned. As stated high compression is used to compensate for the lack of low end on a centrifugal blower at the cost of limiting boost before detonation sets in. :idea: The solution: "race gas" (see what I mean). Centriffy's make mad hp but there are issues.
The difference between 10.2:1 and 11.5:1 is about 100+ psi in cylinder pressure and a 70 degree increase in cylinder temp at then end of the compression, and now you think you can boost that on pump?:dw: That's pretty significant when talking about running on pump gas. That's a similar to change to a 10:1 engine running around 10 psi of boost...even though the increase in cylinder pressure and temp would be somewhat lower. Take Sean Hylands word if you wan't, I'm sure he has a whole line of parts to sell you when you break taking his advice....marketing.
i never said anything about boosting 11.5:1 on pump, I'm not trying to be a know-it-all either, I'm just trying to gather some facts and reason along the with the original poster of this thread because I have a some what similar setup as him and and also curious about going centri-charged.
But if you want to make assumptions and be a smart ass about it, MORE POWER TO YOU!:thumbsup:
I wouldnt run 10.5:1 on stock internals and pump...
im running 10.4:1 with forged internals,e85 and meth and 18psi
thats in my stroked ls3 417ci though
Not being a smart ass...That's just how I talk. Straight forward and non sugar coated.
10.2:1 isn't high for engines with efficient combustions chambers. Also, high compression is not a band-aid, it's necessary and adds power. No street driven mod motor should run low compression (8.5:1) when boosted, it flat kills power and off boost driveability. I've seen people go with low compression and lose 50hp/50tq by doing so. Going with flat tops is just plain smart.
Obviously, because to get 10.5:1 you would have to replace the stock pistons. Why would the pump have to be replaced?
I would trust the recommendation of a racer over the suggestions from a non-racer.
Hyland as well as Mihovetz recommend higher compression on boosted engines. Both have also built and tuned more street engines than most anyone else. With a good tune a flat top pistoned engine will survive and make a lotta power. With a good tune and 8.5:1 compression, an engine will survive and make a lot less power.
I recommend flat tops because they increase off-boost power substantially and when driving around with FI friendly gears the added compression helps greatly.
Last edited:
I wish there was a rule of thumb instead of "a lot." Nobody seems to risk running high compression and boost so there's no anecdotal evidence as to what the max compression is for a centri setup at x psi/y hp.
I would like to make ~600rwhp on boost only, but the "safe" bet is to just build a 8.5:1 motor and run 19+ psi vs building a 10:1 motor and hoping it doesn't detonate before I hit my power goal (thus forcing another rebuild).
I would like to make ~600rwhp on boost only, but the "safe" bet is to just build a 8.5:1 motor and run 19+ psi vs building a 10:1 motor and hoping it doesn't detonate before I hit my power goal (thus forcing another rebuild).
There is no rule of thumb because every combination is different, i.e., cam duration, cam lobe centers, intake manifold, heads, etc. 10:1 is not high for a mod motor, not even close.
Building a 300hp/300tq base motor and throwing 17psi at it is much better than a 270/270 starting point with over 20psi. Making boost cost hp, the higher the boost the more it cost in terms of hp loss and stress (heat, fatigue) to the engine.
Here's an example of what a low compression engine will do for power. The strting point was as stock Mach engine and it made 465rw with a P1SC. With the new engine, an 8.5:1 stroker and the same boost level the power was down 30hp/30tq depsite the larger cubes.
I meant pump gas, there are also other ways of getting to a desired CR within reason than changing pistons.
Last edited:
like how? shaving the heads for more compression or thicker head gaskets for less, but either way your not going to gain or lose a lot without messing with the pistons. id listen to na svt and slow2v they seem to know what their talking about.
Last edited:
The CR can be changed by a max of .5 with milling.
^ this! that is the answer i was hoping for to back up my previous post.
Users who are viewing this thread
