OK Let me start by saying I know this is not exactly the right section for this, so if the mods feel the need to move it then so be it. I just thought it would get the most exposure from the best engine builders in drag racing in this section, so I figured it would be the best place...

So heres my issue. I recently completed my build for my True Street car and took the car to the dyno. After only making 525whp at approx. 30psi boost on a Precision PT67, we were scratching our heads. A full check up was performed including boost leak check, timing, valve lash, compression, leakdown, and all was good, but compression only yielded 120-125psi across the board. The engine is an 84mm Darton sleeved B16 (stock stroke), with Wiseco K545M84 pistons, and built 2001 ITR head with ITR cams. Heres the thing, the block was decked (unknown amt) by the previous owner, so upon assembly we found that the pistons were sitting slightly above deck height at tdc. Due to this my engine builder reccomended running a Cometic .075" MLS headgasket to avoid the pistons contacting the head.

So here are my questions...

1)Does it sound right for this combo to only yield 120-125psi compression?

2)Would having the combustion chambers cut to 84mm to match the bore allow me to run a stock .030" headgasket without the pistons contacting the head?

3)Should I just put higher comp. pistons in it and call it a day?

4)Should I just scrap this block and start fresh for 2011???

5)Does anyone else have any other suggestions or things I should check???

Im on a bit of a budget here since I already spent a TON of money to get this car done for 2010, so I was looking for the most economical way to get some numbers out of this thing until I complete my monster build....

For more info on the build, refer to this thread https://honda-tech.com/forums/drag-racing-36/my-2010-67mm-true-street-build-2740629/ , or just ask...

Thanks in advance for your help H-T!!!
-Chris

 

that's way low for compression. you asked if you should get higher comp pistons, what are they now? you should measure the height that the piston is protruding the deck. then get a shop to bore the combustion chamber to match and try to use a honda head gasket. it sounds like rings are installed wrong, have a big gap, or valves are bent. did you check the valves?

 

The pistons are advertised at 8.4-9.0:1 compression depending on block/head combo... Rings are fine, as are the valves... Leakdown test was good...

 

what were the leakdown numbers?

how about cam timing? is it spot on? your severe lack of compression is your problem and it isn't due to your piston selection.

another ninja edit: was the engine at or near operating temp when you did compression test?

 

I dont remember the numbers for leakdown as I didnt personally do it... My engine builder did... And before it is mentioned, Collin Etienne, owner of Racing Integration / R.I. Automotive is my engine builder. He is hands down the best in my area, so he knows what he is doing... Cam timing was at 1*adv intake and 0 exhaust when it made the most power...

 

Sorry I made a mistake... Advertised CR for these pistons is 8.4-8.8:1, but that is on a B20 block/B16 head... I am running a B16 block / ITR head so compression will be lower off the bat...

 

You aren't going to be making a ton of power with that little motor and no compression. What does the rest of the motor consist of?

 

Darton MID sleeved 84mm B16 block, Wiseco K545M84 pistons with coated skirts and upgraded wrist pins, Eagle ESP HBeam rods, Calico coated ACL bearings (mains, rods, and thrust), OEM B16 crank balanced and micropolished, OEM ITR water and oil pumps, OEM girdle, ARP main studs and head studs, ITR head with full Ferrea valvetrain, ITR cams, Victor X intake, OmniPower 70mm throttle body, etc..
Turbo setup is Jay Thornton ramhorn manifold, Precision ball bearing PT67 with "H" compressor cover, PTE 46mm wastegate, PTE intercooler core (24"x12"x3.5"), 3" aluminum IC piping, custom 3"->4" downpipe, 4" aluminum exhaust w/ Burns stainless race muffler etc. etc....

 

I would get new pistons. That combo might only have around a 7ish-1 compression ratio. I bet that is what your issue is. Get something built that keeps the pistons at deck level. Sounds like a flat top at deck leve would get you around 9-1.

 

That was another option I had considered... Custom pistons would probably solve the issue, but thats probably a bit more than I would like to spend right now... If I were going to do that though, I would like to get the compression up to about 10:1-10.5:1

Any way you could PM me more details on how to go about doing this??? I've never done anything with custom pistons before... All my builds have been shelf stock parts lol

 

Its not hard, you can call myself or any other builder that has the know how. Even some piston mfg that will deal direct will be able to help. You just need to know the deck height and the rest is pretty easy. Just know to get that high of a comp you will have a dome on your piston.

 

just keep turning the boost up

 

but i also think that the timing is off slightly. i know u said that the guy that built ur motor knows what he is doing but everyone makes mistakes. have someone else look at ur motor and see what they say.

 

I am by no means an engine builder but my old setup was a 8.2:1 1.8L 87mm stroke and I made 500whp at 20psi and 585 at 23psi also with a PT67 so I don't think his comp is hurting him that much unless its on the low low side of 7:1 if not less... How loose is the P/W clearance?

 

Gotcha... Thanks man.. I will most likely end up going that route. I will get the numbers together and get in touch with you....

 

LOL and make the same power at 45psi that the car SHOULD made at 30, and cut the life of my turbo in half... Nah Im good haha...

Timing was checked, double checked, and triple checked.. Its spot on... Myself, my tuner, and my engine builder all checked it...

With 120-125psi cranking pressure, I really doubt this thing is even making 8.2:1 compression... According to the math it should be around 8:1, but F&%@ the math, from experience and comparing it to other setups, Im thinking this thing is in the mid to low 7s... Not sure of p/w clearance.. I will have to get a copy of the spec sheet from my engine builder... I know its on the loose side because the motor was build with the intent to run some serious boost and make big power... But again, if it were too loose, that would show in the results of the leakdown...

 

Did a car a few years ago with the same CR but 81.5mm bore (stock sleeves) car made mid 400whp on pump and high 500whp on race gas. Car went low 10's.....

 

are you refering to the advertised ratio of the pistons (8.4-9.0:1), or the 7ish:1 compression it actually has???

 

Did you degree this motor?

 

Sorry if i missed it but what brand dyno.

 

All I am saying is I ran the same Wiseco Low Comp Piston with a Cometic .065" gasket with my head milled .010 (my pistons were out of the deck +.016) which IMO still puts me and you in the same ballpark as far as compression goes and I had no issue making power... although I had a GSR block/stroke/head so I am not sure how that affects the final CR without doing the math

 

Turn up the boost.

 

Was the .075" gasket the lowest you could run? Did the builder measure the piston to head clearance/clay the motor?

1) yes, I think 120 psi is kinda low...I just did a 98 ford ranger and it was 200 across the board.

2)Possibly. The engine needs to be clayed to verify actual clearances. I think anyway you can get the plug tip closer to the piston w/o touching is good.

3) no

4)no

5) I think you need to get some of your compression back. How experienced is the tuner?

 

The tuner is very experienced

 

No this engine was not degree'd... Didnt think it would be neccesary with these cams....

DynoJet

That setup would yield a higher CR than mine of course...



1) don't mean to sound rude, but I dont know what a Ford Ranger has to do with any of this.

2) I agree, but thats not much of an option right now... If I am going to rip this engine apart, I am probably just going to start over with one of the LS blocks in my parts shed...

3) what is your reasoning for your answer??

4)again, your reason? I am looking for informed technical input not just yes or no answers

5)I agree that I need to get some compression back, that was basically what I was trying to accomplish... The whole point of this thread... And I don't know what my tuner has to do with my compression, but Alpha (my tuner) is very good, and has plenty of experience...