Porting and Polishing

[sdg3205]

Does anyone by any chance know what the measurable difference is between stock and port and polished heads with aggressive cams? Are we talking 3 hp? 5 hp? 10 hp........ 0.5 hp?!

Before I go spending the money i like to know its worth it, but i want this to be the first and last time the heads ever come off 3205 so i figure do it once and do it right or don't do it at all.

[louielouie2000]

From what I’ve seen, most stock manual transmission DeLoreans make roughly 100hp at the wheels. Most Stage II cars seem to make about 140hp at the wheels. So a 40% bump in power for well under $10k while keeping the car mostly stock looking seems like a pretty decent proposition to me.

[opethmike]

Most of that can be attributed to the cams and the exhaust. On a small displacement motor like this, and without the valve sizes getting modified, porting and polishing isn't going to make a huge difference.

[David T]

The heads on the PRV are already pretty good. Not rough iron castings like most American muscle that responds well to porting and polishing. While it can't hurt to port, polish, and gasket match. I don't think it is going to make a noticeable difference. The PRV does respond well to opening up the induction, and exhaust systems. The stock ones are VERY restrictive. More aggressive cams will then make a big difference.

[MPPDMC]

from experience you gain 20-60 hp. blending the seats into the ports helps and opening the ports out to the gasket helps. the big question is how much to do this? You can do it yourself like I do and after porting get a valve job. then adding a performance cam will really wake it up. look on you tube for porting videos ,good luck

[opethmike]

20 - 60? Sure, on an SBC or an LS, but certainly NOT a PRV.

[Christian Dietrich]

My engine in 11035 has the Spec 1 exhaust/no cats mod, larger air box with a K&N filter and CAI tube and a throttle body spacer. Stock heads and cams......... for now and i will say from a seat of your pants feeling, it is definitely a night and day difference over a stock DeLorean and it is much more responsive and the throttle is much more snappier and I have no problem hitting 60mph off the line. I'd say with the mods, that im probably pushing a 25hp gain? It feels it. A good porting and polishing will probably free up between 5 to 7 horsepower it's like Mike said and you polish the seeding real well. I dunno, mabye another 30 hp with cams. I will be really interested to see someone go from a stock engine and have it dynoed then slowly do mods to it from simple bolt ons to full cams and head work to see the gains. Simply getting rid of this cars induction system and exhaust system really does make the PRV engine way better then in stock form. I know I'm loving how my setup is and I have no problem revving my car to redline at times and she pulls very nice. 200hp (engine, not wheels) can be easily done with the right tricks.https://uploads.tapatalk-cdn.com/20171104/fce4981b22a67d4ff7c4b0a7ad76bace.jpg

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[Josh]

200hp (engine, not wheels) can be easily done with the right tricks.


200hp out of a 2.8L odd fire PRV with Kjet is not an easy task. Even at the crank.

You need to consider forced induction. Or get very aggressive with the heads, cams, rebuilding the bottom end for more compression (rods, pistons).

[Christian Dietrich]

200hp out of a 2.8L odd fire PRV with Kjet is not an easy task. Even at the crank.

You need to consider forced induction. Or get very aggressive with the heads, cams, rebuilding the bottom end for more compression (rods, pistons).Yeah if you go a little deeper you can but I don't think it's going to be as bad as some think it is and the prv actually responds well to modifications but maybe not as simple as a small block Chevy engine. You might have to get a little bit more aggressive with the heads and maybe even slightly larger valves. I have never really dug too deep in a prv engine but I would love to find one so I can see what I can do with it

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[Christian Dietrich]

Yeah if you go a little deeper you can but I don't think it's going to be as bad as some think it is and the prv actually responds well to modifications but maybe not as simple as a small block Chevy engine. You might have to get a little bit more aggressive with the heads and maybe even slightly larger valves. I have never really dug too deep in a prv engine but I would love to find one so I can see what I can do with it

Sent from my SM-N920P using TapatalkNaturally aspirated I mean

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[opethmike]

My block is rotting, so it wouldn't be a usable engine, but you're welcome to it (sans heads) for a reasonable price if you'd like to come to Rochester to get it.

Or with the heads for a slightly less reasonable price, lol.

[Christian Dietrich]

My block is rotting, so it wouldn't be a usable engine, but you're welcome to it (sans heads) for a reasonable price if you'd like to come to Rochester to get it.

Or with the heads for a slightly less reasonable price, lol.You mean you will give me head..... for a price.....? Hmmm that definitely might be worth the trip! How bad is the block rot? Well I already talk to you about wanting to buy the heads from you here eventually

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[opethmike]

You mean you will give me head..... for a price.....? Hmmm that definitely might be worth the trip! How bad is the block rot? Well I already talk to you about wanting to buy the heads from you here eventually

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It isn't terrible; it's just the start of it. Shoot me a PM on Facebook and we can talk details.

[Alex Brooks]

My engine in 11035 has the Spec 1 exhaust/no cats mod, larger air box with a K&N filter and CAI tube and a throttle body spacer. Stock heads and cams......... for now and i will say from a seat of your pants feeling, it is definitely a night and day difference over a stock DeLorean and it is much more responsive and the throttle is much more snappier and I have no problem hitting 60mph off the line. I'd say with the mods, that im probably pushing a 25hp gain? It feels it. A good porting and polishing will probably free up between 5 to 7 horsepower it's like Mike said and you polish the seeding real well. I dunno, mabye another 30 hp with cams. I will be really interested to see someone go from a stock engine and have it dynoed then slowly do mods to it from simple bolt ons to full cams and head work to see the gains. Simply getting rid of this cars induction system and exhaust system really does make the PRV engine way better then in stock form. I know I'm loving how my setup is and I have no problem revving my car to redline at times and she pulls very nice. 200hp (engine, not wheels) can be easily done with the right tricks.https://uploads.tapatalk-cdn.com/20171104/fce4981b22a67d4ff7c4b0a7ad76bace.jpg

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Christian,
Where did you get that air box ? I would love to add it my car. Thank you Alex

[Christian Dietrich]

Christian,
Where did you get that air box ? I would love to add it my car. Thank you AlexDeLoreanAutoParts.com Glad you like it. I believe its adds a bit of performance due to the larger opening.

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[sdg3205]

DeLoreanAutoParts.com Glad you like it. I believe its adds a bit of performance due to the larger opening.

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And with the plexiglass on the top you actually see the ponies just flying into the engine!

[Christian Dietrich]

And with the plexiglass on the top you actually see the ponies just flying into the engine!It would be ponies and not horses lol!

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[dn010]

When I had a stock engine I cut around the base of my air box (the part the filter sits in) so that there was no longer anything below the filter, no more hose, no housing, etc. and I didn't notice any difference in performance. I did have to clean the K&N filter more often though. Run it with no filter box at all and there's not a difference. The NA engine can only consume so much air, if you're looking for performance you need to start doing more expensive, involved work to the PRVs.

[FABombjoy]

I logged MAP at the throttle edge vacuum fitting on my turbo car. At full load / WOT the I saw up to a .8bar pressure drop. So while it's possible there is some restriction in the intake it might take a draw-thru turbo to find it. Naturally aspirated I doubt you'd really find much gain on a dyno outside of the realm of measurement error.

That aftermarket airbox deletes the PCV tube which will expose more of the air filter element to the engine, but at the expense of increased crankcase pressure at higher load. In trying to find free HP the meter flap probably is the greater enemy.

[Grover]

I'll throw in my .02 since I have port and polished heads.

I have a thread in the Mod section about my engine build, but long story short, with high compression pistons, port and polished heads, a 1mm shave on the heads and aggressive camshafts, my car dyno'd 147whp.

Now, if the statement is that a Stage II is 140whp (I don't know since I haven't seen an actual stage II dyno'd), that leaves 7 extra horsepower. But, is that from the port and polish or the high compression pistons and compression raise from shaving the heads?

I will say this, looking at my dyno graph I have a big drop in power between 3500 and 4500 RPM. The graph shows that the car leans out in that range, raising to a perfect full fuel enrichment ratio after 4500rpm. So, the engine has more air than fuel available to pump (I have raised the fuel pressure as well and the full enrichment switch is working). Because of the lean condition I had to reduce my engine timing to 15 degrees, thus losing more power.

Because of this I plan to look into modifying the fuel system some, but that is a different topic.

Back on topic, I know Josh at DPI has told me that they stopped port and polish when they did offer that service, saying he found it was actually worse. I have no proof to back this up. I can say that one the two cars I drove that are setup the same except for the pistons and port and polish, they have a smoother power band whereas when my fuel enrichment catches up it has a VERY noticeable kick up in torque/power (http://dmctalk.org/showthread.php?5097-Custom-Engine-Upgrade/page5 - Post #42).

[dn010]

My heads have been done as well but I am using B280F with heads that were very restrictive in the exhaust ports. On those heads there is a large chunk of aluminum partially blocking the port which can be safely ground away. One day I'll dyno my B280F/efi setup just for kicks.

[delornut]

Does anyone by any chance know what the measurable difference is between stock and port and polished heads with aggressive cams? Are we talking 3 hp? 5 hp? 10 hp........ 0.5 hp?!

Before I go spending the money i like to know its worth it, but i want this to be the first and last time the heads ever come off 3205 so i figure do it once and do it right or don't do it at all.

Velocity is a major part of head design. Porting should stop short of upsetting air flow velocity. Without a flow bench and the experience to back it up you could do more harm than good. One of the last years I worked for Ford I went to a two day class with a NASCAR engine builder and a major drag racing engine builder. We bench flowed a 351 Cleveland head and it was quite obvious when things had gone too far and velocity started to drop off.

Bruce