Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Steve on May 03, 2005, 09:24:48 PM
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Advise welcome and needed please!
I instructed guy building my bottom end to get dished pistons. When I went to pick up my block it had flat top pistons(by probe). This makes the compression w/ the dart heads at 11.7 to 1.
According to my buddy who will be helping me put my motor together, he said that compression is too high to run pump gas; that the engine will ping like mad.
In order to reduce compression and get my motor back(the guy has had it WAY too long) my friend said we should go to a 72 cc combustion chamber pair of heads instead of the 64 cc heads we had originally ordered.
I trust this guy but I would welcome other opinions. Will the flat top pistons w/ the 72cc heads be comparable to what my initial setup was to be?
Any input welcome and appreciated. thank you!
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Compression ratio is actually the volume (or volumetric) ratio. By increasing the clyinder head volume when using a flat piston you should get a similar volume ratio with the dished piston and standard heads. I say similar because I don't know all the details regarding your 'dished' pistons and original heads.
Yes, an 11.7:1 compression ratio is too high for 93 octane pump fuel. However, you might get by with an octane booster and retarding (delaying) the ignition timing if you want more horsepower. The solution your buddy suggests sounds pretty reasonable if you don't want a high compression engine.
Regards,
Malta
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Well Steve, that 200 shot is deffinately out of the question now, might as well just box it up and send it my way :). Are you able to just send back your new Darts for 72cc set? Otherwise it would seem more reasonable to just have the guy swap out the slugs... If you ordered it right and he built it wrong its his problem not yours, I understand the frustration and wanting to get it done though.
Geary
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many questions.
are the heads on your block?
if he built the botton end why did he put the heads on?
are you really sure they are flat top?
how much trouble would it be to pull a head and see what pistons are in there?
did he give you a parts receipt, (check part numbers)
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Geary, why is the 200 shot out? This is major.I am meeting him tomorrow at 9:30 AM>
The heads are not on the motor, but my friend has seen it and it is definitely flat top.
He bought the heads bare and assembled them, but they are not yet on the block. He says the assembled heads sometimes have valveguides that are too tight, causing the valve to hang up, then slapping the piston.
All the receipt says is "optional probe forged pistons"
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what you need is one of those how to build my engine books at the autoshop.
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Comment on the 200 shot was with regards to the 11.7:1 compression ratio. High comp. + N2o = BOOM! If you get it back down to a reasonable level im sure it will be fine, but as previously stated i think 200 shot pushing it with that block. A lot of guys run a lot of spray through L98's and all is good, but most of them are 100 or 150 shots, and probably not on top of a setup thats already makin 450-75. Btw, what tranny are u running? Thanx for the tip on the pre-assembled heads, had not heard that before.
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Gocha Geary. Ya, we are going to go to a bigger combustion chamber , 72 instead of 64. to pull the compression down to 9.5-10.
The 200 shot is a dual stage so I'm hoping it will be ok. If I get info that 200 is a bit much I'll get smaller jets. The tranny is the stock AT for now, until I blow it up I suppose. I'd like to get a nice 4 or 5 gear auto w/ an overdrive... I'm told I'm dreaming.
Same thing w/ the rear end.. dana 35. Will wreck it and get the 44. I don't really plan on racing it more than a handful of times just to see what it will do. I put less than 2000 miles on it in the year prior to tearing it down so I'm hoping tranny and rear end will hold up.
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steve... that sounds wrong. It is hard to get allmost 12 to 1 compression with flat tops and 64 cc chambers. if you had pistons that did that then they would have to have huge valve relief's in em and.. I can't belive that going to 72 cc chambers would lower from 12to1 down to 9.5 to one. You might get on compression point for the difference in heads... say, from 10.5 down to 9.5.
lazs
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Thanks lazs, I'm leaving to go to the shop and get this straightened out. I want this car to run on pump gas, so I have to make sure he gets this comp thing right.
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My Triumph runs 12.0 to 1!
So would I be better running 97 oct super or standard (over here ) 95 oct?
Just wondering.
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As long as it's tuned properly it can run 11.0 : 1 on pump gas.
I'm looking to build a 1.8L built to 2.0L (bored to 1995cc) with carrillo H beam rods, wiseco pistons and a few other goodies.. And it will be a 12.0:1 compression motor. :D
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Originally posted by Skydancer
My Triumph runs 12.0 to 1!
So would I be better running 97 oct super or standard (over here ) 95 oct?
Just wondering.
I'd use 97 if that's the highest you got. And make sure it's not knocking. That's pretty damn high comp ratio, is it a bike?
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Yeah Its a 1200 daytona and thats how they build em probly why I'm getting 147 at the rear wheel. :D
Thanks for the tip been using 95 but will try 97
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modern engine control systems allow for higher compression because the control not onlyu fuel mixture but advance curve. With a carb and mechanical/vacuum advance you need to run less lead.
A cam with a lot of overlap will negate some of the bad affects tho because it has lower compression at low RPM... aluminum heads cool better so can take a half to one point more than iron heads. sooooo... it all depends.
skyprancer... I believe your octane is rated differently than ours but I would go with the manufacturers recomendations... I also believe that the daytona is rated at 147 HP at the flywheel not the rear wheel.
lazs
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My mistake your correct, 147 at the crank. I just dug out the Dyno chart I had done. 130 at the rear which seems right allowing for about 10% loss or thereabouts through transmission.
Cheers:aok
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I'm looking to build a 1.8L built to 2.0L (bored to 1995cc)
Is that for a motorcycle? VW?
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Originally posted by Skydancer
Yeah Its a 1200 daytona and thats how they build em probly why I'm getting 147 at the rear wheel. :D
Thanks for the tip been using 95 but will try 97
OK, If it's stock do as Lazs said.
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Lazs, you were right. The guy had the figures wrong. My friend has some software that actually computes the compression for you. It requires you to have a lot of info besides piston and combustion chamber info. Things like deck height, gasket thickness etc. Fortunately we had all that info. The engine will have around 10.4, making it quite driveable.
Nuch I defer to you on compression knowledge.. I don't know that much about it but I have been told by several people that if I was running high compression and added NOS that I'd end up w/ a blown motor.
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skyprancer... 10% loss at the rear wheel is a little low even with a belt drive. My buddies Harley loses about 20% from 171 hp at the flywheel to 140 hp at the rear wheel... cars can lose a lot more.
since you had nothing to do with the building of your bike (picking out the color doesn't count) then you should do as the people who did recomend..
lazs
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Nope I didn't build this one. I did rebuild the other 1200 Triumph I owned before ( just sold that )
The one I rebuilt I put a thicker head gasket in and trophy pistons which lowered compression. I guess I'll give Triumph a ring see what they recomend. Good thing about buying a home product you can ring the factory tech dept and get an answer.
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well... we have lots of factory reps for all sorts of products here. If you lower the compression on a computer controled vehicle then you need to remap it.
as for triumph...
In the old days we used to see T shirts that said "triumph... if they built an airplane would you fly in it?"
lazs
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Theres not realy any comparison between the old and the new. I know I got both. A 1960 Tiger 100 and a 1995 Daytona 1200. Chalk and cheese. The new stuff is better put together than a lot of the Jap stuff. At least experience of riding through the kind of sh*tty conditions that leave Jap bikes looking years older than they are whilst my trumpet shines up like a new pin tells me so.
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Originally posted by Steve
Is that for a motorcycle? VW?
Steve,
Its for my '94 Mazda Miata, I've built a dedicated track/autocross car. The current motor has 150,000 miles. It's dynoed at 115rwhp which isn't too bad considering the mileage on it. It's a good block. This motor has hydraulic lifters which after long runs at high RPM she starts ticking as the oil get too thin. I'm picking up a '00 solid lifter motor with 60K on it for the new motor work which that new motor will get a complete teardown. It should be a 200rwhp motor..atleast I'm hoping.
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well... triumphs may be better these days but we will never know over here since it is rare that we see one... too many people got burned by brit products and too few years have passed since we have..
Ford did make jag into a car that people expect to start most of the time now tho.
lazs
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Odd Lazs as the Triumph Riders site I frequent appears to have quite a few US members and the US is Triumph's biggest export market! Still maybe they are still comparatively rare over there. But definately better made and one of the few Brit owned Brit built vehicles left so i'll stick by the home product.
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The U.S. has allways been the british bike and autos biggest market. We had more Healeys here than you ever had over there. You even put the steering wheel on the correct side when you made em. We simply don't see many of the new triumphs... I see a group of two or three on the retro twins from time to time but nothing like any other brand.
lazs