Hello !

Can I run 9.5 :1 Dynamic Compression Ratio on 98 RON ( I believe this is 94 USA AKI )? Highest Octane easily available fuel Here.

It would be possible to add 10% ethanol using E85 to get about 100RON with a trip about an hour away and a few 20L jerry cans. Would need to do this once every few months with a few 20 L drums . But would be only if I really had to.

Planning on 11:1 SCR and a similar cam to RV10 with Intake closing 55* ABDC .

AP5 Valiant 2800lbs with 3:23 Diff, 904. No towing and rarely will have more than 2 people aboard.

I am trying to find 68 onwards head. Have a 5 hole block. May have to use pre 68 head and grind the dime off.

Thinking forged pistons might be a good idea. Long term project (about a year)to help spread these type of costs.

Weekend driver ,street only . Want to maximise torque between 1500RPM and 4500RPM ..5000RPM Redline.

Hobby car so can spend time on tuning . If I dont run right today ,play again next Sunday..........and repeat.

Planning on mild port work . Cleaning up and getting the short side radius to open up the back of intake valve.

Bigger valves will depend on availability. If not easily available, stock valves with 3 angle seats.

Yay or Nay to 9.5:1 DCR ?

Thanks

Brendan

_________________
1963 AP5 Valiant 225 PB 904 Stock except extractors & 2 1/4 inch exhaust.


1962 S series valiant 225 PB auto. factory every thing. Full restoration job.
Currently on hold till AP5 is on the road.

Why are you planning on such high compression and such a small cam? (If memory serves me correctly)

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

First, I don't know. What did you base your volumetric efficiency at to come up with your DCR? The slant head isn't very good in that arena. You may not have a true 9.5 DCR. The 225 tends to have a horrid V.E. Even with big valves and port jobs. If you were using a number in the 80's, it'll be a bit less optimistic.

I can share that I was unable to run US pump premium based on an 11:1 build, but that was a special case. Late Drool-tube head, but a long-rod with a lot of dwell. Once I bled off some of that compression with a follow-up valve job, getting closer to 10.5:1, I could carry quite a bit of cam, but only running 97 octane race gas. (Strip only) On the road, burning pump premium, as long as I keep my foot out of it, I can run without issue. If I stand on it, with around 28-32 degrees of timing (all-in at 1500 hop-out), it'll still go into detonation, but if I back it off, my ET tanks. I do not have vacuum advance, which can caus issues in transition as the throttle rolls on prior to kick-down. I haven't run Vacuum advance since modding the valve body, governor weight and cranking the TV to come in for early kick-down, so could be all wet as far as your build goes. My WOT shifts up at 5k rpm, breakaway-2, 2-3. Anything less than 5,000 rpm, it kicks down if I stuff it. I have a solid accumulator, over-clutch and run Type-F, so the shifts are extremely fast, so a good fit for a racing transmission. It's a pretty hard up-shift.

If you suffer from high humidity, I wouldn't run E-85. It'll grow an eco-system in your tank and carb in no time. Up here, those that run E-85 dump all the fuel from the tank and filter following the race weekend. Your results may vary.

Hope that helps!

CJ

PS: Yes, the RV10 is equivalent to the Late 244 cam. The RV15 RDP I had would detonate on pump gas with a SCR of 11:1, but cleared up on 97. Went to a rather wild cam for a bit, then backed off to an Erson 280 for better mid-range. Even with Ford 300 valves, and oversized seats, my DCR was pretty pitiful.

_________________
Part of Tyrde-Browne Racing

I am trying to work out the highest compression that I can run on pump gas ,with a "street " cam . Got any cam suggestions? I want reasonable gas mileage and am interested in 1500 - 4500RPM torque increase. I want to work out DCR, SCR so I can work back from 54cc combustion chamber. On 98 RON Premium. Wanting to get some feedback from those that may have gone too far . So I dont do the same.

_________________
1963 AP5 Valiant 225 PB 904 Stock except extractors & 2 1/4 inch exhaust.


1962 S series valiant 225 PB auto. factory every thing. Full restoration job.
Currently on hold till AP5 is on the road.

Thanks for the detailed reply CJ
VE was not included. the calc I used does not have it. Will be using a better calc with more detail as ideas progress. Any suggestions? I have not done anything like this in about 10 years and need to re-learn. Good calcs help.

I have read on this forum ,suggested max DCR of 9:1 on Premium pump gas. Including the warning that much tuning will probably be required. I am willing to try water injection if Tuning cannot quite get there.

I am also thinking of building to 52 cc Chambers.(got some here,just need valves) If I cant beat the detonation with those heads and tuning then change the head to 54CC ( or whatever the math works out before I build, after cc ing heads in stock) .. I have a few heads here.

Changed enough heads/Head gaskets ,in my 51years ,that the head change in car is a minor issue.
In other words I am not afraid to go a little to high in compression as I have the heads /experience to rectify with larger chambers.


Another issue is ,I checked and I only have pre 68 heads. Post 68 heads are a bit more difficult to find here. This is due to the valiants here going to the Aussie "hemi 6" in 1970 I believe. That only leaves 2 year models with the better heads. The VE and VF Valiants. I got a 5 hole block (free)from a VE but It did not come with a head.



So Im thinking Of a few things to help with detonation with these heads. At least with the smaller 52cc head I have.
Here are some things I was thinking about while at work today.

Clean up chambers. Try to eliminate or smooth those "nooks and crannies" where fuel hides from flame front.
Bigger exhaust valves. This may help with scavenging . It may be possible to have a lower overlap "street cam" but get the intake charge initial "help" of a longer overlap.

Another possible advantage of a larger exhaust valve is the larger valve takes longer to heat up . And the larger seat area should take more heat from the valve head.

One more advantage of a bigger ex valve MAY be, the valve head is closer to the "vertical wall " that the spark plug comes through. Not to the point of shrouding ,but helping the intake charge direct into the ex valve. ie a wider track of intake charge ,that gets thrown around as ex v closes.

Possible lower pump out loss?

Rounding off of valve head sharp corners,for less chance of hot spots.

Rounding but not eliminating ridge between seats. Need the bump to launch as much fuel/air as possible over exhaust valve edge, while it is closing.

Just some ideas. I see much head work and iron dust in my future!

Brendan

_________________
1963 AP5 Valiant 225 PB 904 Stock except extractors & 2 1/4 inch exhaust.


1962 S series valiant 225 PB auto. factory every thing. Full restoration job.
Currently on hold till AP5 is on the road.

Don't take this wrong, but it sure seems like you are doing a lot of work to run a higher compression. If I was willing to do all the things you say, then why not just drop the compression a point or 1/2? You are not gaining much with that little extra compression. As for the valves; The intake side is much more in need of help than the exhaust on our engines. I'd install bigger intake valves before exhaust any day.

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Same. Too little cam with that much SCR. I would run the high SCR and run a bigger cam, AND/OR drop the SCR 1/2 -1 point. That should get you very good MPG, tolerate pump premium, and get you more power than a tiny cam. I have found this works well from personal experience. It sucks to drive a car that is right on the edge of detonation all the time. Water or water/meth injection is a good way to run the high DCR too, but I do not have personal experience with that. Will you run EFI, or suffer through the crappy tuning of a carburetor. I have found that most of the time EFI gets you about 10% in MPG if you tune it right, even with a "well tuned" carb. If you don't have a stick trans with OD, then get that too. That's worth 10-25% depending on what you have now.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Wallace calculators used to have a DCR calculator that had guidelines for octane requirements. Just a note, especially in an engine that has no quench in its chamber, detonation is a big enemy you will be fighting. The difference between one compression point will hardly be noticeable on a dyno, and can even harm performance if you don't have the correct gas to support it....

_________________
There's no such thing as too much cam....only not enough engine!

OK. Seems the answer to my question is no. At least not on 98 RON Fuel.



Thanks for the advice everybody.


Brendan

_________________
1963 AP5 Valiant 225 PB 904 Stock except extractors & 2 1/4 inch exhaust.


1962 S series valiant 225 PB auto. factory every thing. Full restoration job.
Currently on hold till AP5 is on the road.

I'd like to have quench pads welded to a slant six head. I'm a big fan of the Suzuki G10 in the Geo Metro - two valve wedge with quench pad and factory 9.5 cr. Some export G10 were 10.0 cr.

9.5 cr falls into the "can't hurt" category as I'm willing to use water injection or have the pistons dished a little.

On the leading edge of gasoline development is propane injection, nothing I'm aware of in the aftermarket. A little brief on-demand propane will enable increased cr - maybe someday.

I'm pretty sure I can build a Geo Metro to 70 mpg, higher compression helps. Safer than a motorcycle. This is off topic but check out the Casey Putsch "Omega" car that uses a 2000 model VW ALH diesel - does zero to 60 in 4.6 and 104 mpg.

EDIT: A 9.5 static CR quench chamber might be easier on a 170 than a 225. Zero deck on a 225 is probably greater than 10:1 w/o the quench pad , adding the quench pad requires a proper sized piston dish. Is there a calculator to help design the dish? I could make a piston from wood on a lathe and test the CR.

Tim