Inliners International Forums General Discussion Hi Performance high compression street engine

I just bought a 250 engine out of a late model dirt track car. I know I have to run premium fuel. My question is would a 12:1 compression motor be able to be street driven for any length of time? And as a side note I need advice on a header which one flows best. Thank you in advance for your input I figured I would ask the experts!

The only way it would really be able to take anything but the highest octane is to run a huge cam. But that will also make it not streetable.
Find out what it has for pistons, maybe they can be cut down to lower the comp.
Maybe the head could be swapped to also lower the compression.

Another idea is to use a copper head gasket with a standard head gasket, this will also lower the comp. Flatout gaskets are good to use here. They have a rubber coating and are made to run with a oringed head gasket. Tom

If you have 12:1 compression in that motor, it will NOT, repeat, NOT run on any gasoline currently available without preigniting like crazy, even if you run premium gas. You have 2 choices here. You can either lower the compression ratio like Tom said, or add a water injection system, but even with water injection you would probably have to use premium gas to keep the knock under control. You can check out water/alcohol injection systems at http://www.coolingmist.com. I used one on a street motor that had 11:1 compression and it eliminated the preignition (knock) really well, but I still had to run 92 octane to keep the engine happy.

If you have 12:1 compression in that motor, it will NOT, repeat, NOT run on any gasoline currently available without preigniting like crazy, even if you run premium gas. You have 2 choices here. You can either lower the compression ratio like Tom said, or add a water injection system, but even with water injection you would probably have to use premium gas to keep the knock under control. You can check out water/alcohol injection systems at http://www.coolingmist.com. I used one on a street motor that had 11:1 compression and it eliminated the preignition (knock) really well, but I still had to run 92 octane to keep the engine happy.

Is there a cheaper water/alcohol inj kit for nonboosted motors all the ones I see say they are boost referenced.

Aquamist and snow performance both used to market Naturally Aspirated kits.

You could check Ebay for one of the older Edelbrock kits.


As I understand it though the newer higher pressure kits work better due to finer atomization of the water.

Yes, the newer systems have up to 250 psi,the old Edelbrocks are just basically a windshield wiper pump,low pressure.

The newer systems are much better.

http://www.alcohol-injection.com/water-injection-kits-1/chevy-20/camaro-97/

MBHD

I put a 12:1 engine in a street rod and hated it. Blew two head gaskets. I took the pistons out and milled the domes to about 10.5 I still have to mix in a gallon of 110 race fuel with every tank of pump premium. Bummer.

I think a street six runs best in the 9.0 - 9.2 range, and even at that you will probably need premium fuel to optimize the camshaft and ignition timing.
Good luck.

Everyone has there own Idea as to what is streetable and what isn't. Yes a 12-1 is not streetable to everyone. My and I say MY
250 was pushing over 12-1 as a daily driver 583/607 lift cam. It ran on 87 L cheap O gas it ran upper(high) 14s LOW 15s with 3:08 gears and 16mpg city. It would start with a Bump of the key. ANd NO this motor did not ping a lick.BUT it would not shut down with out loading the clutch OR useing 112 in it.But anyway I ran That motor for over 17 plus yr. And Reused the same Pistons in a new Build.

But anyway bottom line is either Pay the fuel bill Or drop the compression.

Thanks guys I'm really looking forward to driving this new motor and I will let you know how it goes. Thanks for all the advice. And larry thanks for answering my questions on every forum.

Got to agree with twisted on Compression, Static and dynamic compression are 2 very differnet things, you can have a high static cr but if the dynamic cr is to high it will require race fuel, the camshaft will dictate what your DCR is. I ran 12.5's in 283 daily driver and even drove the truck fully loaded pulling a fulley loaded trailer from Texas to NH on pump gas and never had an issue. Even an engine with only 10.1cr and aluminum heads can require race gas if you have to small of a cam installed to blead of compression. As far the 12cr in that 6 chances are that the previous owners have the head shaved to the max along with pistons, a stock 250/292 head with out shaving it would probally drop you a full point minumum maybe even as much 1.5 points. Most of these guys will shave these heads .120 possibly putting you down to 58cc chambers vs stock 72-76cc chambers.

Not practical and a lot of work to put a race engine on the street,you might find someone wanting a race engine and find a stock 250 to build for the street.that much compression with a big cam will load up on the street,and race gas is a must,trying to tune a race engine for the street isnt worth the drivability problems.If that engine has good parts you could trade or sell it for enough to build a nice streetable one.just my opinion.

Coolingmist also has a setup for normally aspirated engines. You just have to dig around a little on their website to find it, but it's there, and the price last year was about $300. Haven't checked it lately, though, so it might have gone up a bit by now.

Greetings . . .

My experience is similar to Twisted and Bowtie's. I had 12:1 pistons in a 327 v-thingie. Cranking pressure was north of 200 psi on all cylinders. It ran fine on regular.

But I was running a stock cam and a stock jetted Rochester 4 barrel. So I think decreasing V.E. as RPM rose kept dynamic CR down to the point that it didn't ping.

Only problem I had with the setup was hot starting. The engine needed to cool down before the starter could cope with hot cranking pressures. With initial timing set to maximize vacuum it was impossible to start hot. Even with timing set slightly retarded from stock it was hard to start hot.

regards,
stock49

What doesn't ping in Reno may self destruct in Oakland. Yes, streetable is not a scientific term neither is daily driver. I know a guy who claims his 1200hp blown BB is a driver. He hauls two barrels of 110 to Hot August Nights and can burn it all in two nights of short cruses. Like Bill Clinton said, " It depends on what yes means." I had a couple of cars that I had to park on hills because the starter wouldn't turn them over when warm. I wouldn't want to put up with the added hassle and expense for a few extra HP, But then I'm not the one doing it. Best of luck to you and let us know how it works. You can always drop the CR with new head or gaskets as suggested. Beater

When I mean daily driver,,,,That was my only car & only transportation I had for years,,,,averaging 10,000,12,500 miles a year daily driver. Had to go to work everyday,do errands, etc.

Any thing confuseing in my statement?

On my 250 6 inline,,,there are only 6 cylinders,starter does not get hot & I ran a high torque factory GM starter,not the standard shorter low torque 6 cyl one.

Only time I ever blew ( a few BTW ) a cyl head gasket was when I used to run Nitrous & had detonated. <BUT,,,I did not run nitrous w/12:1

MBHD

In the late 70's, Bruce Crower developed a 14-1 compression 350 Chevy engine that ran on pump gas. It was featured in either Car craft or Hot Rod. His company, Crower, manufactured a special camshaft to offset the high compression to be able to run the lower grade pump gas instead of racing fuel. The cam had a 114° LSA to be able to do this. The power results were about the same as if it were a true pump gas engine with 9-1 compression with the same cam with a tighter LSA, not much difference HP wise. So, in a nutshell, if you build a purpose built high compression engine to yield maximum output, you will need racing fuel, because all your components will be tailored for that purpose. Having a high compression engine that will allow you to truly run pump gas, should suggest that your parts selection isn't matched or optimized significantly enough for the engine to recognize there is a need for the better fuel, and you wont be getting any real added benefits by using high compression to start with. If your engine was purpose built as a dirt track racing engine as you suggested,its likely, its built for nothing else but racing, and will more than likely not be suited for pump gas.

"Any thing confuseing in my statement?"
Nope, and there's not much confusing about your attitude either. I never meant to infer that YOU didn't drive Your car just that what is a driver to some is not a driver to all and that the term is not exact. Some need heated seats and AC. Don't get your skivvies in a wad every time some one posts something near what you have posted. I'm sure your opinion here packs more weight than mine because there are some things I don't know. Beater

My comment was not directed torwards you in particular,,
I do realize people say they have a daily driver car that runs on race gas & high boost 565 CI BBC runs 9's & say they get 25 MPG.

I do not see I have an attitude,,just shows how people take offense on the internet so easily,I guess like my comment ""Any thing confuseing in my statement?" It was not capitolized letters AKA yelling"

My comment was just to make sure when I say my car was a daily driver it really was & no sand bagging to go along with it.

Like I hear other people running 30 psi of boost pressure 10:1 compression on 87 octane, w/no meth injection & 36 degrees total timing,,,,,,,I think it's funny to think some people fall for that.

So,, no harm ,no attitude as you think I do,& I am learning as you are also,peaceout!


MBHD

Hank, No problem here. It is hard sometimes to look at words and not be able to hear the tone that goes with them. I my have read more into it than was meant. If so I apologize. Sorry to bring you skivvies into the discussion too. I hope we all learn on this board there is so much information and some of it is true.:D There is not a better place for us to talk. Thanks, Beater